Recent developments in sensor technology have made it possible to develop simpler automatic turn detection methodologies, however they are not feasible for regular use. The aim of this study was to develop a sensor set up and an algorithm to precisely detect turns during alpine ski, which is feasible for a daily use. An IMU was attached to the posterior upper cuff of each ski boot. Turn movements were reproduced on a ski-ergometer at different turn durations and slopes. Algorithms were developed to analyze vertical, medio-lateral, anterior-posterior axes, and resultant accelerometer and gyroscope signals. Raw signals, and signals filtered with 3, 6, 9, and 12 Hz cut-offs were used to identify turn switch points. Video recordings were assessed to establish a reference turn-switch and precision . Precision was adjusted based on reference and the best signals were selected. The  The qualitative assessment of alpine skiing is necessary at both the recreational and elite levels. A deeper understanding of the different features related to skiing would allow for improved injury prevention or coaching efficiency. Between elite alpine skiers, the differences in performance are very small, frequently only hundredths of a second . To asseThere have been different approaches to determine ski turns. Supej et al.  were theThe development of smaller, long-lasting, wireless technology has made it possible to implement different sensors into the structure of sports equipment, making the collection of data much easier. Furthermore, as the athlete does not feel the sensors, possible alterations in the data collected based on discomfort and/or related technique modifications are avoided. This development has encouraged several attempts to simplify the application of the aforementioned turn detection methods using systems such as instrumented binding (force platforms/bindings) ,10, videThe movement of skiing has been often modeled as an inverted pendulum ,14,15. TIn an attempt to fill the gap between easy to use and reliable methodologies, we aimed to develop a sensor set-up using IMUs and the necessary algorithms to detect turns precisely. The objective of the system is to be simple, comfortable and feasible to use on a daily basis. We hypothesized that the local extrema of angular velocity signal would correspond with the edge changing and thus, with the beginning of the turn.To identify the most precise automatic methodology to detect turns in alpine skiing, an experiment was designed where an IMU was attached to the upper posterior cuff of each ski boot. The protocol was performed on a ski-ergometer based on a commercially available simulator . Before the measurement, he was informed in detail about the testing procedures, as well as possible benefits and risks of the investigation prior signing the consent form approved by the local Ethics Committee (EK-GZ: 11/2018). The experiment was conducted in accordance with the Declaration of Helsinki.An IMU  was placed in the back of the upper cuff of each boot . The X axis of the IMU was aligned with the vertical axis of the boot pointing superiorly, the Y with the lateral axis pointing to the left, and the Z with the roll axis pointing posteriorly. 3D Angular velocity and acceleration signals were recorded at 833 Hz, after an analog low-pass filter and a digital low-pass filter after the ADC, the raw data extracted from the sensor had a rate of 64 Hz. The sensor data was transmitted via Bluetooth and collected by an in-house smartphone application . For precise determination of the true turn switches (gold standard) a camera  sampling at 50 Hz, was placed perpendicular to the frontal plane of the ski-ergometer. The IMU data was resampled to 50 Hz using a shape-preserving spline interpolation algorithm in order to match the sampling rate of the camera. Three different slope conditions were recreated using different ski-ergometer positions. In the first position the ski-ergometer was placed flat on the floor of the laboratory. In the second position, the ergometer was leaned forward at an inclination of 6.3°. In the third position, the ergometer was leaned to the left at an inclination of 5.7°. Based on the average duration of GS and SL turns , two difThe instant of turn switch for each turn was assessed by three experts  using the video recordings. One way repeated measures ANOVA  with Bonferroni post-hoc tests were conducted to test for differences between raters. The maximum level of precision and evaluation of bias were calculated using the limits of agreement (LoA) as proposed by Bland and Altman  . Thresholds for prominence, separation, and distance were adapted for each signal. The semi-automatic algorithms developed for the signals with best precision were further developed into automatic algorithms  were visually inspected. The signals were synchronized with the reference turn-switch points identified in the video analysis. Features and patterns were identified from the synchronized data to develop turn detection algorithms. The development process consisted of various steps and was individual to each signal, or group of signals with similar characteristics. First, semi-automatic algorithms were developed in order to find the landmarks for every signal and filter cut-off option. The semi-automatic algorithms consisted of a strong low pass filter (0.5 or 1 Hz) to determine the turn switch window. Afterwards, each signal was filtered using a fourth-order zero-lag low-pass Butterworth filter with cut-off frequencies of 3, 6, 9 and 12 Hz. The implementation of different filter options increased the number of variables to 120: two sensors (accelerometer and gyroscope), four axes , three signals  and five filtering options . Local maxima, corresponding to the turn switch point, were identified within the windows defined by the strong low-pass filter using the The results for the three different slope conditions and turn lengths were pooled to reproduce true skiing conditions where changes in slope gradient, inclination and turn duration occur. This procedure increased the potential robustness of the turn detection methodology by replicating in-field conditions during the development process. Mean bias between each variable and the reference value, and 95% LoA  in ms weThe precision of a measurement system cannot be higher than its reference system or gold standard. To express the precision of the measurement in terms of the reference precision, the measured LoA were adjusted to the reference system precision. The LoA of the reference were defined as the highest upper limit and the lowest lower limit between the three raters. The measured precision was adjusted as follows: if the absolute values of the upper and lower measured LoA were higher than the absolute values of the reference LoA, the upper and lower reference LoA were subtracted from the upper and lower measured LoA see a. If the1)The variables where the bias was outside the reference LoA were excluded.2)The variables with an adjusted precision higher than 20 ms were excluded.3)The lowest adjusted precision was select as the best methodology.The selection process to determine the best automatic turn-switch detection system consisted of three steps:p = 0.015) and 5.2 ms (p < 0.001) was found. The maximum precision of our reference system was set as the difference between the highest upper limit, in this case 30.0 ms and the lowest lower limit, –21.4 ms. Consequently, the maximum precision of the reference system is 51.4 ms.The results of the bias and 95% LoA between raters are reported in z-axis (z-axis 12 Hz right boot and the resultant of the left boot with no filter). While the resultant acceleration in the right boot showed adjusted precision values lower than 1, both the left and average showed greater values. Consequently, the acceleration signals were not chosen as a reliable method to assess turn switches.The steps of the method selection process along with its results are presented in z-axis  of the gz-axis and the resultant had the best measured precision. The best values were average z-axis (6.6 ms), left boot z-axis (6.2 ms) and average resultant (11.6 ms).Within the gyroscope data, the filter option that showed the best measured precision was the 3 Hz filter. The gyroscope data in the z-axis and gyroscope resultant, see The proposed algorithms for the best signals .Step 5:Find the local maxima in the signal from step 4 between the local minima from step 3.Step 6:Find the local minima values in the signal from step 4 between the local maxima from step 3.Step 7:Organize values from steps 5 and 6 in ascending order to represent proper turn switch points.Algorithm for gyroscope z-axisStep 1:Calculate the resultant of the 3 axes  for one or both boots .Step 2:If the desired signal is the average between both boots, calculate the mean of the resultant from both boots. If using the signal from one boot, proceed to step 3. Step 3:Filter the signal using a fourth-order zero-lag low-pass Butterworth filter with cut-off frequency of 1 Hz. Step 4:Find local minima in the filtered signal.Step 5:Filter the signal from step 2 using a fourth-order zero-lag low-pass Butterworth filter with the desired cut-off (3 Hz recommended).Step 6:Find local maxima in the signal from step 5 between the local minima from step 4.Step 7:The local maxima values represent the turn switch points. Algorithm for gyroscope resultantz-axis algorithm and Step 4 in the resultant algorithm) is to determine the individual windows where to look for the turn switch points. The second process  was developed to find the actual turn switch points.It should be noted that there are two different filtering processes. The first process goal  and the resultant acceleration for the right boot also presented high adjusted precision. It is important to note that the data collection was performed in a highly controlled lab environment, where the movement was limited to one plane. With this particular arrangement, it is evident that the resultant values were predominantly determined by the axis in the plane where the movement was allowed. In the field, where motion is not restricted to a single plane, the resultant may be more affected than other axes. The freedom of movement, the vibrations associated with skiing, and the conditions of snow and slope could introduce noise, affecting the resultant to a greater extent than the g skiing ,14,15, tz-axis). In consequence, we suggest that a single IMU placed in the back of the upper cuff of one ski boot is the simplest method for turn switch detection. Nonetheless, depending on the desired future measures, it might be relevant to use IMUs on both boots. This could potentially measure and compare performance metrics such as edge angle, symmetry, G-forces, etc.The results showed similar precision levels between a single boot signal and the average between boots . Based on these results, more research is needed, where more participants are involved in an ecologically valid environment to enhance the external validity of this concept. While on-snow skiing, the plane of movement and the skiing technique are not limited, as it is the case on the ski-ergometer. In further field based studies, a broad variety of external conditions , skiing styles, and skill levels will introduce adequate and relatable variability to the signals allowing further development and scientific proof of the algorithm. z-axis of the gyroscope) were very similar. However, further research needs to be done in order to assess the validity and robustness of the system during on-snow skiing with different skiers, slope and snow conditions and skiing styles.A pilot test was performed on snow to have the first insight to the system’s performance during in-field alpine skiing. An expert skier performed a complete downhill run (of carved turns) and the turns counted by the system were compared to the turns counted using a wearable kinematic global navigation satellite system  measuring at 10 Hz. With both systems the same number of turns (N = 28) were counted and the characteristics for the selected signals (e.g. To our knowledge, there was only one previous study reporting precision of turn detection methodologies. Fasel et al.  assessedThe calculations used to assess the system’s precision in this study are different than the calculations used by Fasel et al. . We baseIn conclusion, the algorithm and sensor set-up proposed in this study is a precise and simple system to automatically detect turn switches during alpine skiing. Moreover, this methodology is non-obtrusive, wireless, and could be implemented in a smartphone application, providing semi-instantaneous feedback. Further research is necessary to implement this algorithm in the field and evaluate its validity with respect to different skier abilities, slope conditions and turn styles. It also represents a first step in order to develop new measurements to better understand skiing technique and performance.


The HOPG graphene concentrations were found to be 0.260–0.385 mg/mL in methanolic graphene dispersions stabilized with 10 wt % (relative to HOPG) PTFEMA-b-PVP block copolymers after one week. Raman and atomic force microscopy (AFM) analyses revealed that HOPG could not be completely exfoliated during the sonication. However, on-line turbidity results confirmed that the dispersion stability of HOPG in the presence of the block copolymer lasted for one week and that longer PTFEMA and PVP blocks led to better graphene dispersibility. Force–distance (F–d) analyses of AFM showed that PVP block is a good graphene-philic block while PTFEMA is methanol-philic.Despite the superior properties of graphene, the strong π–π interactions among pristine graphenes yielding massive aggregation impede industrial applications. For non-covalent functionalization of highly-ordered pyrolytic graphite (HOPG), poly- This unique structure gives superior properties, such as light transparency [i.e., carboxylic acid, hydroxyl, and carbonyl groups or holes) of graphite structure [Graphene, a two-dimensional structured material, is a type of carbon allotrope exhibiting a hexagonal structure with sparency , mechanisparency ,4, and esparency , amongstsparency , solar csparency ,8, inkjesparency ,10, toucsparency , flexiblsparency . Neverthsparency , mechanisparency ,14, molesparency ,16, epitsparency , and liqsparency ,19. Amonsparency . Both cotructure ,21,22. Ttructure ,24,25.block-poly(4-vinyl pyridine) (PTFEMA-b-PVP) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization while molecular weights, dispersity (ĐM), and compositions of the block copolymers were finely controlled. Graphene dispersions were then prepared from highly-ordered pyrolytic graphite (HOPG) in methanol with four different types of PTFEMA-b-PVP block copolymers, and the characteristics of their dispersion states were investigated.In order to prepare stable graphene dispersions with minimal aggregation, various types of solvents  and surfactants  have been exploited ,27,28,292,2,2-Trifluoroethyl methacrylate  and 4-vinyl pyridine  were used after purification by an inhibitor remover column . 4-Cyano-4-(phenylcarbonothioylthio)pentanoic acid , 1,4-dioxane , hexane , tetrahydrofuran , toluene , chloroform , methanol , and hydrofluoric acid  were used as received without further purification. 2,2′-Azobisisobutyronitrile  was used after recrystallization in methanol. HOPG  was used as a source of graphene nanoplatelets. Ultra-pure water  was used throughout the experiments.2 gas, the flask was sealed. The reaction mixture was then immersed in a preheated oil bath at 70 °C and stirred for 24 h. The product was purified by precipitation in hexanes three times. The resulting polymer was characterized by Fourier transform infra-red (FT-IR) spectroscopy, nuclear magnetic resonance (1H-NMR), and size exclusion chromatography (SEC).RAFT polymerization was carried out to prepare the PTFEMA macro-RAFT agent. The reaction scheme is shown in b-PVP block copolymers were prepared by RAFT polymerization using PTFEMA macro-RAFT agent. The reaction scheme is shown in 2 gas purge. The mixture was then immersed in a preheated oil bath at 70 °C and stirred for 24 h. The resulting PTFEMA-b-PVP block copolymer was purified by precipitation in hexane three times. Following the synthesis procedure outlined above, four different types of block copolymers were obtained as shown in 1H-NMR.PTFEMA-For industrial purposes, such as conductive ink or barrier coating, it is important to prepare a stable and highly concentrated graphene dispersion. To study the dispersion stability of graphene nanoplatelets, HOPG was dispersed in methanol with PTFEMA-b-PVP block copolymer as a dispersant. For the dispersion, 90.9 mg of HOPG, 9.1 mg of the block copolymer, and 20 mL of methanol were added to a vial. The concentrations of all block copolymers were fixed at 10 wt % of HOPG (0.058 wt % of methanol). The vial was then sonicated in a 40 kHz bath-type sonicator  for 2 h.2 gas, and then immersed into a 50 mL round-bottom flask containing a monomer solution  at 110 °C. The monomer solution was kept for 2 h, and then the cantilever was rinsed with chloroform. Then, the cantilever was dried with N2 gas. To prepare the graphene sample, an M-25 powder sample was pelletized by using evacuable pellet dies. F–d curves were taken from 16 points on a graphene surface for one set, with 20 total sets collected. Finally, the average values of adhesion forces were calculated from the measured F–d curves.Adhesion forces between the block (PTFEMA block or PVP block) and graphene surface were investigated by measuring Force–distance (F–d) curves obtained with an atomic force microscope  with modified cantilevers. To modify the cantilevers for the measurements, a cantilever  was etched by 2% hydrofluoric acid solution for 1 min to remove the oxide layer on the silicon surface, rinsed by ultra-pure water, dried by an air gun with gentle flowing of N1H-NMR) spectra of PTFEMA macro-RAFT agents and PTFEMA-b-PVP block copolymers were obtained using a 500 MHz NMR spectrometer  in chloroform-d . Fourier transform infra-red (FT-IR) spectra were obtained using an FT-IR spectrometer  using an ATR attachment (MIRacleA (ZnSe), Shimadzu). The polymers were dissolved in chloroform for the FT-IR measurements.To characterize the block copolymers, molecular weights of PTFEMA macro-RAFT agents were measured by SEC . SEC analysis was performed with a refractive index (RI) detector and three different columns  in series. Tetrahydrofuran  was used as an eluent . Polystyrene narrow standards  were used for the calibration. Proton nuclear magnetic resonance  and photographic images were taken for a week. After the turbidity analyses, the supernatant graphene solution was isolated for further analyses. The graphene concentration of the supernatant solutions was measured by the gravimetric method with a microbalance . For Raman spectroscopy and AFM topography, the isolated supernatant solution was spin coated on a silicon wafer under inert conditions with a spin speed of 700 rpm. In the case of pristine (without block copolymer) HOPG dispersion, there was no graphene in the supernatant solution due to the rapid sedimentation, thus the bottom precipitates were taken for analyses. Raman spectra  at 532 nm wavelength and AFM images were obtained for the precipitate sample. The AFM images were collected using an AFM  with a PPP-NCHR (Park system) cantilever in non-contact mode.Mn) were 11,092 g/mol (ĐM = 1.160) and 22,870 g/mol (ĐM = 1.102), while the degrees of polymerization were calculated as 66 and 136, respectively . Thus, the molecular weights of the block copolymers were estimated from the proton peak integration of 1H-NMR spectra.In this work, four different block copolymers listed in refer to . The age1H-NMR peak integrals for PTFEMA-b-PVP block copolymers. As shown in 2CF3 protons in PTFEMA block. From the degree of polymerization for PTFEMA from SEC with the ratios of peak area a, b, and c, the length of PVP block could be calculated. The molecular weights of four PTFEMA-b-PVP block copolymers are listed in 3 from PTFEMA block at δ 1.10 and 0.94 ppm are also observed since the protons are hindered.The degrees of polymerization of PVP block were obtained from the SEC results for PTFEMA macro-RAFT agents and 66-CTP homopolymer and PTFEMA66-b-PVP41 block copolymer. As shown in the FT-IR spectra, a sp3 –C–H stretching at 3000–2940 cm−1, C=O stretching at 1743 cm−1, C–F stretching at 1278 cm−1, and C–O stretching for ester at 1159 and 1127 cm−1 were observed for the TFEMA unit. On the other hand, sp2 –C–H stretching at 3080–3000 cm−1 and aromatic C=C peak at 1598 cm−1, which correspond to the pyridine units of PVP block, are only observed in b-PVP for the surface of HOPG graphene, F–d curves were recorded using the monomer-modified AFM cantilevers. The adhesion forces were found to be 2.2 ± 0.7 nN for TFEMA and 9.3 ± 0.9 nN for VP, respectively. From the adhesion forces, one can see that VP has 4.2 times greater adhesion force than TFEMA. This suggests that PVP block is more graphene-philic than PTFEMA, despite the greater methanol solubility of PVP relative to PTFEMA. As previously determined, the lone pair electron on the nitrogen atom has an attractive interaction with pi orbitals in a graphene sheet [In order to measure the affinity of each block in PTFEMA-ne sheet . Due to i(h) is ith turbiscan intensity at height h. Based on the TSI value, aggregation, precipitation, or creaming of the dispersion can be evaluated. As the dispersion becomes less stable, the TSI value increases [raw) surges for the first few hours. Comparably, the TSI curves for the samples designated as 1, 2, 3, and 4 show insignificant change with time—less than one-tenth of the variation seen in sample raw—indicating that the block copolymers stabilize graphene in methanol media effectively.ncreases . As showraw settled down within 4 h. On the other hand, samples 1, 2, 3, and 4 were stable even for one week. These results confirm that PTFEMA-b-PVP block copolymers are suitable for methanolic HOPG graphene dispersions.3 and 4 show little TSI value increases as compared to 1 and 2  shows better stability relative to the copolymer with a shorter PVP block length (1). However, for the samples with the longer PTFEMA block length , there was no significant difference in TSI for samples 3 and 4, despite differences in their PVP block lengths.Further, block copolymers b-PVP copolymers can retard the aggregation of graphene nanoplatelets by steric hindrance among adsorbed block copolymers. PTFEMA-b-PVP copolymers are anchored at the basal plane of graphene by the adsorption of graphene-philic PVP blocks, while lyophilic PTFEMA blocks are stretched into methanol medium. As shown here, both PTFEMA and PVP block lengths are critical for minimizing the destabilization of graphene.It has been known that the destabilization of graphene nanoplatelets in a solution is attributed to strong π–π interactions among graphene surfaces. Aggregation among the graphene nanoplatelets is thermodynamically favorable but the aggregation can be kinetically retarded by using either a stabilizer or a surfactant. PTFEMA-1 < 3 < 2 < 4. These results suggest that PVP block length is critical for maintaining stability and preventing graphene nanoplatelets from aggregation. For the preparation of a stable graphene dispersion, both longer lyophilic and graphene-philic blocks are favorable.The graphene concentrations of supernatant solutions were measured from the HOPG dispersions by gravimetry one week after the sonication. As shown in −1. When the hexagonal structure of graphene is disturbed, the intensity of the D band increases. Defectless or perfect graphene usually has an ID/IG value of zero, while graphene oxide has an ID/IG value of >0.9 [−1, respectively. The thickness of graphene can be estimated from the I2D/IG value, where the I2D/IG value for monolayer graphene is >2.0, and the I2D/IG value for pristine graphite is <0.4 [I2D/IG value for pristine graphite  is 0.4281. Compared to this, the I2D/IG values for samples 1, 2, 3, and 4 are slightly increased with the range from 0.4692 to 0.6125. On the other hand, the ID/IG value of sample raw is 0.14735, but the ID/IG values for 1, 2, 3, and 4 are in the range from 0.17071 to 0.26248. The increases of the ID/IG for graphene dispersions with block copolymers are due to the increased number of edges in graphene nanoplatelets. Since Raman spectra for 1, 2, 3, and 4 were taken from the supernatant solution of HOPG dispersions, the graphene size would be smaller than in sample raw. This small size of graphene has more edge sides working as defects.In order to study the graphene structure after sonication, Raman and AFM analyses were carried out. In the Raman spectra shown in  of >0.9 . In addi is <0.4 ,37,38. F4 shows the largest block copolymer aggregates due to the largest molecular weight relative to the other samples.b-PVP block copolymers were prepared by using stepwise RAFT polymerization. The molecular weights of PTFEMA-CTP homopolymers were measured by SEC, and the molecular weights of PTFEMA-b-PVP block copolymers were calculated by SEC and 1H-NMR. Pristine HOPG was dispersed in methanol by using the block copolymers, and the dispersion stability of the resulting graphene dispersions were evaluated using the Turbiscan stability index. Dispersion stability of HOPG in the presence of PTFEMA-b-PVP lasted one week and the graphene concentrations of the supernatant solutions ranged from 0.260 to 0.385 mg/mL. Time-dependent backscattering intensity confirmed that TFEMA-b-PVP copolymers could substantially retard the aggregation of graphene nanoplatelets. It can be suggested from the F–d curve results that PVP blocks would adsorb at the basal plane of graphene while PTFEMA blocks are soluble in methanol. Therefore, both PVP and PTFEMA block lengths are critical in determining both graphene concentration and dispersion stability.Four different types of PTFEMA-


We numerically demonstrate a broadband terahertz (THz) absorber that is based on a hybrid-patterned graphene metasurface with excellent properties of polarization insensitivity, wide-angle, and active tunability. Our design is made up of a single-layer graphene with periodically arranged hybrid square/disk/loop patterns on a multilayer structure. We find that broadband absorption with 90% terahertz absorbance and the fractional bandwidth of 84.5% from 1.38 THz to 3.4 THz can be achieved. Because of the axisymmetric configuration, the absorber demonstrates absolute polarization independence for both transverse electric (TE) and transverse magnetic (TM) polarized terahertz waves under normal incidence. We also show that a bandwidth of 60% absorbance still remains 2.7 THz, ranging from 1.3 THz to 4 THz, for a wide incident angle ranging from 0° to 60°. Finally, we find that by changing the graphene Fermi energy from 0.7 eV to 0 eV, the absorbance of the absorbers can be easily tuned from more than 90% to lower than 20%. The proposed absorber may have promising applications in terahertz sensing, detecting, imaging, and cloaking. With the rapid development of terahertz technology, terahertz absorbers have attracted increasing attention in recent years . TeraherSurface plasmons are the electromagnetic waves coupled to collective excitations that usually exist at the metal/dielectric interface, which have extensive promising applications in optics, microscopy, biosensing, etc. . GraphenIn this study, we propose a novel absorber that is made up of a single-layer periodically hybrid-patterned graphene on a multilayer structure for wide-angle and polarization-insensitive broadband terahertz absorption with flexibly active tunability. The patterned graphene is an electric continuously net-shaped structure with periodically arranged hybrid squares and disks that are connected by graphene loops, which enables the broadband terahertz absorption and the possibility of absorption tuning using a simple gating layer structure. We first demonstrate the structure design of the proposed tunable polarization-insensitive terahertz absorber. Then, we investigate the broadband terahertz absorption properties of the absorber under normal and oblique incidence for both TE and TM polarizations, as well as compare the absorption spectra and electric field distributions among the absorbers with different graphene patterns. To better understand the mechanism of the broadband absorption properties, we further analyze the field distributions of two graphene in-plane resonant mode peaks at 1.6 THz and 3.2 THz and the influence of the geometric parameters on the absorption spectra. The analysis reveals that 90% terahertz absolute  absorbance bandwidths of 1.41 THz (64%) and 0.72 THz (30%) can be obtained for the absorbers with only the square-patterned and only the disk-patterned graphene layer, respectively. However, the bandwidth can be significantly increased to 2.02 THz (84.5%) for the proposed absorber with a hybrid square/disk/loop patterned graphene. Because of the axisymmetric configuration, the absorber also has excellent properties of absolute polarization insensitivity for both TE and TM polarized terahertz waves under normal incidence. Its bandwidth of 60% terahertz absorbance still remains 2.7 THz, ranging from 1.3 THz to 4 THz for a wide incident angle ranging from 0° to 60° for both polarizations. Finally, the active tunability of broadband terahertz absorption is studied. By controlling the graphene Fermi energy from 0.7 eV to 0 eV, the absorbance of the absorbers can be easily tuned from higher than 90% to lower than 20%. The proposed absorber may have promising applications in terahertz sensing, detecting, imaging, and cloaking.gσ = intraσ + interσ (Unit: S) with the intraband and interband contributions [ω is the radian frequency, cμ is the chemical potential or Fermi level, T is the temperature, Γ is the phenomenological scattering rate, and Γ = 2τ−1, τ is the relaxation time, e is the charge of an electron, ξ is energy, ћ is the reduced Plank’s constant, and Bk is the Boltzmann’s constant. The dielectric spacer layers are assumed to be a lossless polyethylene cyclic olefin copolymer (Topas) with a permittivity of dε = 2.35 [pt = 20 nm thick lossless polysilicon layer with a permittivity of gε = 3 [gV. The bottom layer is a silver plate, which is regarded as a dispersive medium according to the Drude model [ε(ω) = ∞ε − pω2/(ω2 + γi·ω), where the high-frequency dielectric constant ∞ε, the plasma frequency pω, and the collision frequency γ are 1, 7.25 × 104 cm−1 and 1.45 × 102 cm−1, respectively. The top view of the absorber unit cell is shown in p is the period of the unit cell, a is the side length of the central square, r is the radius of the disk, and b is the width of the outer square loop of the patterned graphene sheet. The thickness of the graphene sheet, upper Topas dielectric spacer 1, polysilicon gating layer, lower Topas dielectric spacer 2, and silver plate are gt, tt1, pt, tt2, and st, respectively. In this design, we set the dimension parameters as: p = 40 μm, a = 20r = 11 μm, b = 250 nm, gt = 0 nm, tt1 = 20 nm, pt = 20 nm, tt2 = 20.96 μm, and st = 500 nm. In the finite element method based numerical simulations, the graphene sheet is modeled as an infinite-thin layer with 2D surface impedance gZ = 1/gσ [x- and y-directions, and Floquet ports in the z-direction are assigned to the unit cell. The absorbance of this variety of absorbers can be calculated by the formula of A (ω) = 1 − T(ω) − R(ω), where transmission T(ω) = |S21|2 and reflectance R(ω) = |S11|2 [The proposed electrically tunable broadband terahertz absorber using a hybrid-patterned graphene metasurface and its unit cell are schematically depicted in ibutions ,34,35, of the absorber can be retrieved from the complex frequency dependent reflection and transmission coefficients, as shown in Z) and the imaginary part Im (Z) of the effective impedance Z, respectively. The results reveal that Re(Z) is close to 1 and Im (Z) is close to 0 between 1.38 THz and 3.4 THz, implying that Z nearly matches the impedance of free space. Therefore, a broadband absorption with high absorbance is achieved owing to the small reflectance and complete lack of transmission of the absorber in that frequency range.First, we study the absorption properties of the proposed polarization insensitive broadband terahertz absorber with a hybrid square/disk/loop patterned graphene under normal incidence. The Fermi level and relaxation time of the graphene are initially assumed to be m theory . The effb, the surface plasmon resonance of the square-loop-resonator occurs at a frequency much higher than the concerned absorption frequency range, and consequently, the absorption of the absorber based on square-loop resonators below 5 THz (green dot) is very small. By introducing a hybrid square/disk/loop patterned graphene resonator, the 90% absorbance bandwidth  of the proposed absorbers can be significantly increased to 2.02 THz (84.5%), ranging from 1.38 THz to 3.4 THz; see the black solid curve as shown in E| distributions for TE polarization of the absorbers that are based on the only square, disk and hybrid patterned graphene, respectively, on the graphene plane at a center frequency of 2.37 THz. It is clearly observed that the terahertz surface plasmon resonances are strongly bounded to the graphene edges at the frequency of 2.37 THz for different resonators, resulting in high terahertz absorbance over 90%. In particular, the surface plasmon resonance appears in more areas, including the edges of the square, disks, and loop of the proposed absorber. E| distributions of the proposed absorber on the graphene plane at 4.5 THz. The normalized |E| distributions that are shown in To investigate the broadband terahertz absorption property, we simulate and compare the absorption spectra and electric field distributions of the absorbers with different graphene patterns. Here, we consider the absorbers based on a patterned graphene unit cell with only one square resonator in the center, four quarter-disk resonators in the corners, a square-loop resonator, and the proposed hybrid square/disk/loop resonator (regarded as a combination of the aforementioned three structures) with the same dimension parameters as those shown in E| and |H| field distributions of graphene in-plane resonant mode peaks at 1.6 THz and 3.2 THz, as shown in E| and |H| distributions of these modes are distributed at a different part of the hybrid patterned graphene area. The absorbance can be enhanced when the impedance is matched at the resonance frequency of these laterally-propagating modes, and its spectral bandwidth can be expanded using the two optimized modes. To demonstrate these characteristics, we simulate the absorption spectra as a function of the geometric parameters a, b, r, and t . In the calculations, the dimensions are fixed as p = 40 μm, a = 20r = 11 μm, b = 250 nm, gt = 0 nm, tt1 = 20 nm, pt = 20 nm, tt2 = 20.96 μm, and st = 500 nm, if not specifically indicated. fI of mode I while having little influence around the resonant frequency fII of mode II. Particularly, the higher fI and the lower absorbance A of mode I can be observed with a and b increasing, while, both fII and A of mode II decrease with r increasing. Furthermore, t decreases, the fI slightly increases and the fII greatly increases with the lowering Q factors. In this way, the bandwidth of the absorber can be significantly expanded by overlapping these two modes with relatively farther-apart resonant frequencies. In this study, we choose the geometric parameters with a = 20b = 250 nm, r = 11 μm, and t = 21 μm to obtain the optimum 90% absorbance bandwidth property of the absorber.To get more insight into the physical origin of broadband absorption, we plot the normalized |φ at normal incidence (θ = 0°). It is clear that the proposed broadband absorber has absolute polarization insensitivity for all polarizations with φ ranging from 0° to 360° for the terahertz waves at normal incidence. As we know, the omnidirectionality is another important property for an absorber. To examine this feature, the simulated absorbance of the absorber as functions of frequency and the oblique angle of incidence θ for both TE and TM polarized terahertz waves are depicted in θ ranging from 0° to 60° for both polarizations. This is because the absorption properties of the absorber are mainly related to the tightly confined surface plasmon resonances, and the bandwidth is mainly decided by the hybrid disk, square, and loop patterned graphene structure, while being less dependent on the angle of incidence. It is also observed that the peak absorbance decreases gradually as the incident angle increases for both polarizations, and the peak absorbance of TM polarization decreases even faster than that of the TE polarization. That is owing to fact that the orientation of the electric field for the electric dipole resonance in the patterned graphene changes for TM polarization, while that remains for TE polarization when the incident angle is varied. Moreover, owing to the parasitic resonances that occur at a large angle of the incidence, slightly blue-shifts of the absorption spectra can also be observed. Nevertheless, the broadband absorption effect is still very strong, even at a large oblique incident angle; when θ = 60°, the absorbance remains more than 60% with bandwidth 2.7 THz from 1.3 THz to 4 THz for both TE and TM polarizations.Then, we further investigate the terahertz absorption behavior dependence on the angle of the polarizations and the angle of incidence. To eliminate polarization sensitivity, the absorber is carefully designed by arranging the individual disk and square and loop resonators axisymmetrically into the hybrid patterned graphene. gV is applied to the graphene-Topas spacer-polysilicon parallel plate capacitor to control the conductivity of graphene via the electrostatic doping effect. The relationship between gV and Fermi level cμ, as well as E0 and cμ are given by the formula [cµ, E0 Curve and the cµ, Vg curve are plotted in 0E and gV for achieving the cµ of 0.7 eV are around 1.5 V/nm and 30 V, respectively, which are achievable in the experimental work. By taking advantage of the graphene conductivity tunability, the absorption tuning of the proposed absorber can be achieved. The absorption tunability as functions of frequency and the Fermi level ranging from 0 to 0.7 eV are depicted in Finally, the absorption tunability of the proposed absorber is also studied. As illustrated in  formula : Vg=E0⋅tIn this study, we have demonstrated an actively tunable polarization-insensitive broadband terahertz absorber based on a hybrid-patterned graphene metasurface. The single-layered graphene with periodically electric-connected hybrid-patterned square/disk/loop structures can effectively enhance the terahertz absorption bandwidth. The results show that the absorber has over 2 THz  for 90% absorbance and absolute polarization insensitivity under normal incidence. The absorber also demonstrates near omnidirectionality with 2.7 THz bandwidth for 60% terahertz absorbance for the wide incident angle, ranging from 0° to 60° for both TE and TM polarizations. By introducing a simple polysilicon gating layer beneath the graphene layer, the absorber absorbance can be flexibly tuned from more than 90% to lower than 20% by changing the Fermi level from 0.7 eV to 0 eV. Benefitting from these promising properties, the proposed absorber may have great potential applications in terahertz sensing, detecting, imaging, cloaking, and optoelectronic devices.


Steroids used to treat sarcoidosis may induce aPAP. The cooccurrence of sarcoidosis and autoimmune pulmonary alveolar proteinosis (aPAP) is rare. In this case, aPAP merged into sarcoidosis regardless of the disease state of sarcoidosis and improved naturally. When using steroids during sarcoidosis exacerbation, attention should be paid to aPAP relapse. Steroids used to treat sarcoidosis may induce aPAP. Here, we report a rare case of aPAP complicating sarcoidosis. When using steroids during sarcoidosis exacerbation, attention should be paid to aPAP relapse.Pulmonary alveolar proteinosis (PAP) is a disease in which eosinophilic granular proteinaceous substances abnormally accumulate in the alveolar space because surfactant production or degradation ability is impaired. Autoimmune PAP (aPAP) is the most common form of PAP. aPAP in patients with sarcoidosis has rarely been reported.2A 58‐year‐old woman who was diagnosed with sarcoidosis eleven years prior was referred for the exacerbation of mediastinal lymph node enlargement, consolidation and multiple nodules on high‐resolution computed tomography (HRCT) eight years ago Figure A. Pulmon3We found that aPAP merges into sarcoidosis regardless of the disease state of sarcoidosis and may improve naturally. Some cases of aPAP with sarcoidosis have been reported.Additionally, aPAP with sarcoidosis presents a crazy‐paving appearance in HRCT images. Johkoh et al reported three types of processes that resulted in crazy‐paving appearance, including an alveolar filling process, interstitial fibrotic process, and a combination of both.4Autoimmune pulmonary alveolar proteinosis (aPAP) merges into sarcoidosis regardless of the disease state of sarcoidosis and may improve naturally. A crazy‐paving appearance can be found for various reasons. In aPAP associated with sarcoidosis with multiple perilymphatic nodules, the crazy‐paving appearance is due to an alveolar filling process. When using steroids during sarcoidosis exacerbation, attention should be paid to aPAP relapse.I declare, on behalf of my coauthors and myself, that we do not have any conflicts of interest. Appropriate written informed consent was obtained for the publication of this case report and accompanying images.YT: took care the patient and wrote the manuscript as the primary author. TS: took care and followed up the patient and critically reviewed and supervised the manuscript. KA: participated in patient care. AM and MK: provided pathological diagnosis of the patient. TS: supervised the manuscript.


High refractive index (RI) thin films are capable of pulling waveguide mode profiles towards themselves. In this study, it is shown that by applying high RI coatings with specific thicknesses on the side of optical waveguides, significantly different mode profiles for orthogonal polarizations can be achieved. This phenomenon, that we call it polarization-selective mode shaping, can be extensively used in the enhancement of polarization-dependent integrated optical devices. As an illustrating application, a tri-layer structure consisting of poly(methyl methacrylate)/graphene/chalcogenide on a side-polished fiber is designed to realize an extremely high extinction ratio polarizer. This structure changes the mode profiles in a way that the attenuation of TE mode is maximized, while the power carried by the TM mode remains relatively constant. Simulations and experimental characterizations confirm that polarization-selective mode shaping coordinates four loss mechanisms to maximize the extinction ratio and minimize the insertion loss of the polarizer. The fabricated polarizer is examined in the O, C, and L telecommunication frequency bands. This configuration achieves the high extinction ratio of 51.3 dB and its maximum insertion loss in the tested wavelengths is 1.79 dB. The proposed polarizer has been compared with other state-of-the-art polarizers in the conclusion section which shows its superiority. Among these structures, plasmonic coatings are capable of inducing significant difference between orthogonal polarizations. However, these structures usually work in a narrow frequency band and possess small penetration depth5. As an alternative, dielectric coatings can change the mode profiles into different shapes for orthogonal polarizations, and can overcome both of these limitations. However, they have not been extensively used for polarization-selective mode shaping (PSMS) and their ultimate functionality has not been revealed yet. The development of such dielectric structures can lead to various functionalities in integrated optical devices that do not suffer from the ohmic loss of plasmonic structures.The interaction of light in waveguides with the surrounding media depends mainly on the penetration of the evanescent field in that media, which depends on the mode profile. There has been numerous researches on modifying waveguide structures to increase or decrease this interaction6. These properties has made chalcogenide a serious candidate for future integrated optical devices. In addition, chalcogenides can be easily coated on various substrates with different methods and low-cost equipments9. Considering these properties along with its high refractive index (RI), chalcogenide is an excellent choice to be used as the coating which induces PSMS.Chalcogenides, amorphous compounds containing sulfur, selenium, or tellurium, show interesting optical properties such as transparency in near- and mid-infrared, third-order nonlinearity, and waveguiding12, plasmonic structures15, tilted fiber Bragg gratings17, and microfiber couplers18 have been used to realize in-line polarizers. However, they are still far away from the specifications of state-of-the-art free-space polarizers.Controlling the polarization of light in integrated optical devices is an outstanding application that can illustrate the potential of PSMS. A usual component in integrated optics that can benefit from PSMS is light polarizer. This component plays a crucial role in optical systems, especially in communications, sensors, and the interaction of light with anisotropic media. Along with the development of optical fiber technology and integrated optics, the demand for in-line polarizers is increasing. Utilizing these polarizers in optical systems results in more compact, alignment-free, and fully integrated configurations. In recent years, modified photonic crystal fibers19. Soon after its introduction as a stable material, theoretical investigations have revealed its promising properties and a lot of devices have been made to harness its capabilities20. Graphene have been used for light modulation22, ultra-short pulse generation24, wavelength conversion26, and sensing31. Due to the 2D structure of graphene, this material exhibits some orientation-sensitive properties. One of these properties is the polarization-dependent absorption of light32, which makes graphene an ideal material to examine PSMS on it. This property was used by Bao et al.33 to realize a broadband fiber polarizer. After their work, a lot of papers were published reporting the utilization of graphene or graphene oxide in waveguide- or fiber-based polarizers41. To enhance the extinction ratio (ER) in some of these polarizers, graphene was used in conjunction with metal38 or dielectric coatings39. However, these efforts did not satisfy the demand for in-line polarizers, mostly due to their high insertion loss (IL) and low ER.Graphene, the two dimensional (2D) allotrope of carbon, has been the subject of numerous researches since its isolation as a single layer in 20042S3  tri-layer coating on the top of a side-polished fiber (SPF). This structure reduces the power carried by the TE mode more than that by the TM mode through four loss mechanisms. First of all, at low Fermi energy levels (<0.4 eV), the absorption of TE-polarization is intrinsically higher than TM-polarization in graphene41. The PMMA and As2S3 coatings also create PSMS so that the interaction of the TE mode with graphene is increased. In addition, the mode coupling loss of the TE-polarized light is higher than that of the TM-polarized light in the transitions at the beginning and end of the polished region. Finally, the TE mode experiences more scattering loss due to its propagation near the polished surface. All these four loss mechanisms reduce the transmitted power through the TE mode while imposing a minor reduction on the power carried by the TM mode. In the absence of PSMS, the last three mechanisms would not necessarily result in higher loss for TE mode. But, this coating which reshapes TE mode, makes sure that the loss induced by these mechanisms is coordinated with the intrinsic loss induced by graphene. Therefore, in the output of the fiber, the power of the TM polarization is much more than that of the TE polarization and the device works as a TM-pass polarizer. This device polarizes light with high ER and low IL in a wide range of frequencies in the telecommunication bands. Owing to the uniform optical response of graphene in a broad spectral range, this method can be used to realize polarizers for other wavelengths with appropriate fibers and coatings.In the current study, the capability of high RI thin films to induce contrast in orthogonal mode profiles is investigated numerically. To confirm these results experimentally and illustrate the potential applications of PSMS, a graphene-based in-line fiber polarizer (GILFP) is designed, fabricated, and characterized. This polarizer benefits from poly(methyl methacrylate) (PMMA)/graphene/AsIn what follows, in the first step, the variations of different polarizations in the response to changes in the coating structure are presented. Then, the influence of these variations on the attenuation of modes in the presence of graphene is studied. Afterwards, the coupling losses at the transition regions are calculated. In the next step, the experimental characterization of the fabricated polarizer including scanning electron microscopy (SEM), Raman spectroscopy, and optical performance investigations is presented. Optical performance of the SPF with different coating configurations is also investigated to validate the proposed loss theories. Finally, a comparison between the state of the art optical fiber polarizer and the polarizer fabricated with this method is presented. The simulation, fabrication, and characterization procedures are described in detail in the methods section.2S3 on a SPF revealed the best results  considering its transparency at telecommunication wavelengths. Besides, the low difference in the electronegativity of As and S results in a low polarization in the As2S3 structure. Therefore, it has a minor impact on the graphene conductivity, and as a consequence, the conductivity of graphene on an As2S3 substrate is higher than that on an SiO2 substrate43. PMMA is used as the cover layer since it is commonly used for transferring graphene and its thin thicknesses can be simply achieved by spin coating.The following reasons are also considered for the selection of coating materials. AsThree sets of simulations were conducted to verify the proposed reasons for TE mode attenuation. In the first set, the effects of different coating thicknesses on the mode profiles and on the interaction of light with graphene were studied. This simulation also confirms the concept of PSMS and illustrates the role of chalcogenide as a high RI material on this phenomenon. In the second simulation set, the attenuation of the modes for different coating thicknesses was numerically calculated. These simulations were performed by using the three dimensional (3D) beam envelope study of COMSOL MultiPhysics 5.2 software. In the third set, the losses at the transition regions were calculated using 2D finite difference time domain (2D-FDTD) solution of the Lumerical software. The parameters used in these simulations are presented in Table 2S3 and PMMA in Fig. 2S3 and PMMA thicknesses increase. However, the effective index increase for the TM mode is much slower. Due to the higher RI of As2S3, the impact of its thickness on the effective RI is significantly more than that of the PMMA.Mode profiles for various thicknesses of the coated layers are illustrated in Fig. I is the mode intensity in a plane perpendicular to the direction of propagation (z), and the integration is performed over this plane in the entire simulation domain. The second parameter is the ratio of mode intensity on the graphene layer (Ig) to its maximum (Imax) on a plane perpendicular to the propagation direction.To further investigate the effect of these coatings and optimize the thicknesses of the layers, two parameters are defined and calculated through the simulation. The first parameter is the y-coordinate of the center of intensity (COI) for each mode which is a measure of mode position. It can be calculated as:2S3 thicknesses. It is evident that for the TE mode, COI moves upward as the thicknesses of As2S3 and PMMA increase. Also, Ig/Imax approaches unity as these thicknesses increase. However, for TM mode, the change of these parameters is virtually zero. The attenuation coefficients due to the interaction of different polarizations with graphene in the SPF were also calculated through COMSOL simulations  of the 2D Raman band was monitored in a scan over the polished surface of the fiber which confirmed the presence of a single-layer graphene on the fiber 2 function versus angle for the tested wavelengths.Two different configurations were used to characterize the optical performance of the GILFP Fig.  see met measures2S3 coated SPF have a very low influence on the polarization. However, PMMA/As2S3 coated SPF shows about 17.4 dB power difference for perpendicular polarization angles which confirms the TE mode coupling loss in the transition regions and scattering loss in the polished region. As was expected, the highest ER is achieved when graphene is between PMMA and As2S3 layers.The first configuration was also used to investigate the effect of different coatings on the response of the polarizer. For this purpose SPFs with different coatings were placed in this setup and the transmitted power in various linear polarizations was measured Fig. . The resThe second setup Fig.  was usedThe IL of the polarizer is defined as the ratio of the transmitted TM mode power to the incident TM mode power of the GILFP. The IL measurements show that the IL of the fabricated polarizer is lower than 1.79 dB over the tested wavelengths Fig. .dB and >43.5 dB, respectively. This polarizer is also capable of polarizing light at 1310 nm wavelength with the ER of 39.3 dB. A comparison of the fabricated polarizer with other recent in-line polarizers is presented in Table In summary, we have proposed a dielectric coating which is capable of creating different mode profiles for TE and TM modes. This difference in mode profiles is so that the interaction of different polarizations with the surrounding media is significantly different for orthogonal polarizations. This method is examined on an in-line polarizer which benefit the most from the difference in mode profiles. This polarizer was created by a tri-layer coating on an SPF. The effect of these coatings on the increase in the TE mode loss due to the enhancement of light-graphene interaction, and mode coupling was described and validated experimentally. The fabricated polarizer achieves the maximum ER of 51.3 dB which, to the best of our knowledge, is the highest reported value for fiber polarizers. Also, the insertion loss is the least value among high ER fiber polarizers. This polarizer covers the entire C and L communication bands with the ER of >47.7 The parameters used in the simulation of the GILFP are presented in Table J = σE. This surface current density changes the boundary condition for the tangential magnetic field at the As2S3 and PMMA boundary to Hta − Htp = σEt, where, Hta and Htp are the tangential magnetic fields at the boundary just inside the As2S3 and PMMA layers, respectively, and Et is the tangential electric field at the boundary. Graphene’s conductivity (σ) is calculated by the Kubo formula45e is the charge of an electron, ω is the angular frequency of light, ℏ is the reduced Planck’s constant, τ is the electron relaxation time and μ is the chemical potential which is assumed to be 0.08 eV for graphene on the As2S3 substrate. The chemical potential is lower than the case when graphene is on an SiO2 substrate due to the lower doping introduced by As2S3 to the graphene.The graphene layer was modeled as a conductive boundary supporting the surface current density of P = P0eαz−), the total attenuation can be calculated as:lt, l0, and T0 are the total polished length, simulated length, and the transmission coefficient of the simulated length, respectively. Due to its long computation time, this simulation was performed for fewer points than mode simulations.The simulations were conducted by using 3D beam envelope study of wave optics module of COMSOL Multiphysics 5.2. To calculate the attenuation of the reshaped modes in the polished region, 1 mm length of the tri-layer structure on the SPF was simulated and the attenuation for the total length was calculated from the attenuation in this region. Assuming that attenuation per unit length is constant  water and blow-dried with nitrogen. A 30 nm thick As2S3 layer was coated on the polished surface of the SPF by radio-frequency sputtering. Single layer chemical vapor deposited (CVD) graphene on copper with 60 nm PMMA overlay (Purchased from Graphena) was cut to a 1 × 3 cm piece. Since graphene layers are coated on both sides of the copper foil, firstly, the bottom graphene layer was dissolved in nitric acid. Then, the copper foil was etched with 10% w/w iron(III) nitrate solution in DI for 35 min. Afterwards, it was transferred to another iron(III) nitrate solution with 1% concentration for 20 min, where the copper foil was fully dissolved. Then, a microscope slide which the SPF was fixed on it was placed in the middle of a crystallizing dish, and it was leveled as much as possible. The container was filled with DI water so that the water level was a few centimeters higher than the SPF. After that, the PMMA/graphene layer was place on the top of water in this container. Afterwards, the water was drained gently by opening a valve at the bottom of the container. During the water depletion, the PMMA/graphene layer was gently guided to the top of the SPF. If the slide is properly leveled, when the water surface reaches the slide, the PMMA/graphene layer remains at the SPF on the microscope slide and the water leaves the slide. After transferring the graphene to the SPF, the slide was placed in an oven at 60 C for three hours to vaporize the remaining water.Side polished fibers (SPFs) were bought from Phoenix photonics with a nominal distance between the polished surface and the fiber center (polished depth) of 5 ± 1 To investigate the performance of the polarizer, two different optical test configurations were used. In the first one Fig. , a polar2S3 coated SPF, and PMMA/30 nm As2S3 coated SPF were placed instead of GILFP in the setup and the transmitted power at 1550 nm for different angles was measured and compared with that of the GILFP (Fig. The configuration in Fig. LFP Fig. .For almost all the tested wavelengths, the minimum transmitted power from the GILFP which was achieved by adjusting PC2 and the FSP was so low that it could not be measured by the FSPM. Also, the nominal ER of the FSP used in the setup was 50 dB. Therefore, higher ER values could not be measured by using this setup and another configuration was designed to measure the ER more accurately.The more accurate ER measurement setup is shown in Fig. To measure the IL, a PC was placed between the source and the GILFP and the power was measured just after the GILFP and before any splices. By adjusting the PC, the transmitted power through the GILFP was maximized. When these conditions are met, the incident polarization to the GILFP is a linear polarization normal to the polished surface, i.e. TM polarization. This maximum power for various wavelengths was recorded as the transmitted TM power. Then, the fiber just before the GILFP and after all the splices was cleaved and the power for different wavelengths was measured. The ratio of the maximum transmitted power to the incident power is the IL of the device. In IL measurement test, FOT300 was used as the source for 1310 nm wavelength and mTLS-A1 was used for wavelengths in the range of 1520–1635 nm.2S3 coated SPF was scanned with the Raman microscope. Then the FWHM of the 2D peak of the spectrum in each scan point was measured and mapped to the position of the point and a color scale graph was produced. If the FWHM is lower than 40 cm−1 the graphene is single layer which is the case for almost all the points in Fig. 4b44.RAMAN measurements were conducted by utilizing a WiTec alpha300 RAS with excitation laser at 532 nm. To acquire Fig. The SEM analysis was conducted by a JEOL JSM-7900F SEM microscope.Supplementary informationSupplementary video


TH) in power dissipation was studied using a combination of electrical breakdown thermometry and infrared (IR) imaging. A simple lumped thermal model  graphene interconnects. The electrical performance of aerosol-jet printed (AJP) graphene was characterized using the Transmission Line Method (TLM). The electrical resistance decreased with increasing printing pass number (n); the lowest sheet resistance measured was 1.5 kΩ/sq. for n = 50. The role of thermal resistance (R Conventional fabrication processes such as vacuum deposition, photolithography, and epitaxial growth of electronic materials tend to be complex, expensive, and incompatible with rapid prototyping7. Additive manufacturing techniques, such as inkjet printing, aerosol jet printing (AJP), and extrusion printing, are being explored as alternative fabrication methods for such sensor systems12. Direct write techniques offer a low-cost fabrication alternative due to the reduced material consumption while allowing for rapid customization and prototyping14.Wearable technology is an emerging multi-billion-dollar industry that is made possible, in part, by advances in flexible and wearable electronic devices9. While conductive polymer inks provide low cost printing, their performance is limited by their low conductivities, and poor thermal and chemical stabilities. Carbon nanotubes (CNTs), have shown promise as an AJP compatible ink with significant mechanical flexibility and high mobility making them attractive for AJP applications16. Nevertheless, due to poor dispersion of CNTs in AJP compatible inks and the high cost of monodispersed solutions, the applications of CNTs remain limited for AJP printable devices18. One of the more promising nanomaterials for such applications is graphene, a two-dimensional (2D) hexagonal carbon structure with sp2 hybridized carbon atoms19. Due to its high specific surface area, high carrier mobility, and unique band structure, graphene has shown many promising properties and demonstrated breakthroughs in electronic related applications23. Graphene is also a promising sensor electrode material due to its flexibility and high electrochemical activity at defect sites26.Despite the rising popularity of printing techniques, there is a growing need for ink formulations and materials to meet the demand of the electronics industry. Printable, conductive metals like Ag and Cu have been widely studied, but their applications are restricted by their high cost and the rapid oxidation of Cu28, and several groups have demonstrated inkjet printed graphene chemical29 and biological30 sensors. Graphene inks are typically produced through liquid phase exfoliation of graphite or chemical and/or thermal reduction of graphene oxide32. These processes typically result in submicron graphene crystal domains, and give rise to numerous point defects within the lattice, and closed-contour defects around the flake’s edge33. Under applied electrical bias, these defects result in highly localized electric fields which can be modified by absorbed molecules/target analytes. Combined with the high electrical conductivity and specific surface area of graphene, these defects enable highly sensitive graphene based sensors able to detect target molecules with parts per billion sensitivity in controlled environments33. Furthermore, as inkjet is typically a drop-on-demand process, the microstructure of inkjet printed graphene typically results in a well layered structure with varying amounts of porosity, depending on annealing conditions, ink properties, and the number of print passes. In this regard, graphene’s compatibility with AJP is less understood34.Inkjet printing of graphene has been well established39. Substrate properties, microstructure, and thermal interfaces are likely to play a key role in limiting reliability and power dissipation in such applications. Previous studies have reported on power dissipation processes for mechanically exfoliated, chemical vapor deposition (CVD), and epitaxial grown graphene-based devices. However, power dissipation in printed graphene-based devices has yet to be explored45. This work, therefore, investigates the roles of microstructure and the substrate properties on power dissipation in AJP graphene interconnects. The information gained from this study is expected to provide new fundamental insights that will impact low-power and high-power applications of AJP graphene devices, as device models for both will require understanding the physical properties of such materials systems and printed devices.While additive manufacturing is rapidly advancing the low-power sensor applications of graphene, the high-power and high-temperature applications of additively manufactured graphene based devices have received less attention. Such applications include temperature sensors, resistive heaters, thermal heat spreaders, high-current carrying interconnects, and ordnance fuze technologyet al. and Secor et al.28. Bulk graphite powder was sonicated in ethanol and the stabilizing polymer ethyl cellulose to obtain suspended graphene flakes. The graphene flakes were then dispersed in a mixture of 92.5% cyclohexanone and 7.5% terpineol, which has been shown to be compatible with AJP  and characterized with both TEM and Raman spectroscopy. Raman spectroscopy revealed the characteristic D, G and 2D peaks for graphene at 1350 cm−1, 1580 cm−1 and 2700 cm−1, respectively. The ratio of the D/G peak intensities (ID/IG) determines the quality (defect/disorder) of the graphene flakes. The ID/IG peak ratio of 0.24 is lower than previously reported values (0.33–0.7), suggesting the exfoliated flakes are of higher quality with fewer defects46. TEM images show the graphene flakes vary in lateral size from ~50–200 nm. To correlate the TEM and Raman data, the ID/IG peak ratio and 532 nm excitation wavelength was used in Cancado’s general equation47 to extract the crystal size (La ≈ 80 nm) of the graphene flakes. AFM characterization of the flakes shows the thickness (tg) ranges from monolayer to flakes with an average thickness of tg = 16 nm +/− 15 nm  were printed with an Optomec AJ-300 aerosol jet printer using the UA-max ultrasonic atomizer. The graphene print passes were varied from n = 5 to n = 50 and were deposited on SiOcts Fig. 48. A rec2O3 substrates remains constant as the peak height increases with increasing pass number  as expected. Based on the TLM measurements the lowest sheet resistance was calculated as 1.5 kΩ/sq. for n = 50 at room temperature. Similar conductance profiles are seen for Kapton and Al2O3  and TLM technique was used. As seen in Fig. 50. To study this effect, a simple lumped model was developed that uses a combination of infrared (IR) thermal imaging and electrical breakdown thermometry supported by finite element modeling (FEM) using COMSOL multiphysics software53.The overall power dissipation of a graphene device is dependent on the effective thermal conductivity and total thermal resistance of the system. Substrate material, interface thermal resistances, graphene quality, and device structure are a few of the factors that directly impact the total device thermal resistance2 × REL is the dissipated power and RTH is the total thermal resistance of the device. Here ΔT is comparable to ΔV, P is comparable to I, and RTH = L/(κEFF × A) is the total thermal resistance and depends on the device dimensions and an effective thermal conductivity for the system (κEFF). We note, that REL is the inverse of the device conductance , the thermal interface resistance between graphene and the substrate (RINT = 1/(g × A)), and the thermal resistance of the substrate (RSub). For the SiO2/Si substrate RSub is the sum of the oxide thermal resistance (ROX = tOX/(κOX × A)) and the silicon thermal resistance (RSi = 1/(2 × κSi × A1/2). Here, tOX = 90 nm, κOX = 1.4 Wm−1 K−1, κSi = 100 Wm−1 K−1, g is the graphene – SiO2 boundary thermal boundary conductance taken as 108 Wm−2 K−1, and A is the area of the printed graphene interconnect (A = L × W)55. For samples printed on Kapton and Al2O3 the ROX term is negligible and the substrate thermal resistances are simply (RSub = 1/(2 × κSub × A1/2), where κSub is the substrate thermal conductivity taken as 0.12 Wm−1 K−1 and 32 Wm−1 K−1 for Kapton and Al2O3 (sapphire), respectively57. Based on this model, a combination of IR microscopy and electrical breakdown thermometry can be used to quantify the heat spreading and estimate the “missing” RGTOT associated with the printed graphene interconnects.Simple lumped model: Similar to Ohm’s law , the high temperature rise at low power for Kapton results in a total thermal resistance of 9285 K/W compared to 350 K/W for SiO2/Si and 185 K/W for Al2O3.IR Microscopy: The thermal profiles of the graphene devices were characterized under varying bias conditions. The background temperature Tton Fig.  measured mW Fig. , and the mW Fig. . These dGTOT contributions to RTH a combination of electrical breakdown thermometry and COMSOL Multiphysics was used. Figure o) of 85 °C exceeds the breakdown temperature (TBD), which is either the decomposition temperature of Kapton or the oxidation temperature of the graphene on SiO2/Si or Al2O3  in order to observe where the maximum power dissipation is taking place. The total thermal resistance of the interconnect on SiO2/Si was calculated to be 372 K/W, with the highest temperature value of 520 °C being reached within the graphene interconnect. From these calculations it can be concluded that the power dissipation is dominated by the graphene interconnect. The high thermal resistance of the graphene interconnects is likely due to several factors: the porosity of the printed interconnect, the high thermal resistance between graphene layers, and the general disorder of the constituent graphene nanoflakes that make up the interconnect58. Cross-sectional TEM imaging was used to quantify the porosity of the printed graphene interconnects on SiO2/Si and better understand the structure of AJP deposited graphene. Analysis of the TEM images seen in Fig. COMSOL multiphysics was used to further analyze the thermal spreading in these systems. Figure −1 K−1)59 and high charge carrier mobility 60, which makes it a desirable material for device applications. Nevertheless, the overall performance of graphene devices can be limited by power dissipation and the thermal resistance of the system40. Understanding the details of heat spreading (or Joule heating) in the system is important as it can limit the carrier mobility of graphene and the overall current density41. Effects of Joule heating are influenced by device structure, thermal transport across material interfaces, and the choice of substrate material41. While several studies have examined the impact of Joule heating in graphene devices fabricated using graphene obtained by various synthesis techniques such as mechanical exfoliation, epitaxial growth on SiC, and CVD growth on transition metal substrates, this is the first to do so for AJP printed graphene interconnects64. Our studies of power dissipation in AJP printed graphene interconnects indicate that power dissipation in AJP graphene is dominated by the graphene interconnect morphology for high thermal conductivity substrates, but can be limited by the substrate properties in the case of low thermal conductivity polymer substrates typically used for flexible and wearable electronics applications.Graphene is known to have extremely good thermal conductivity 2/Si used in this study. In both cases we find a breakdown pattern parallel to the direction of current flow. This type of breakdown pattern is likely due to the high porosity causing trapped gasses and solvents within the interconnect, as well as weak interlayer bonding of graphene flakes. As the device undergoes Joule heating, these trapped gases and fluids expand or vaporize, resulting in physical expansion and mechanical failure of the interconnect. This is particularly well captured in Fig. 2O3 was catastrophic with the substrate completely melting and destroying the graphene interconnect (for Kapton) and a complete oxidation and disintegration of the interconnect (Al2O3).  in ethanol using a Qsonica (Q125) probe tip sonicators for 90 min28. To remove the larger graphite flakes, the dispersion was centrifuged (Heraeus Megafuge 8 Centrifuge) at 4500 RPM for 30 min and the supernatant was collected immediately. In a 1:2 volume ratio, the collected supernatant and 0.04 g/ml aqueous solution of NaCl  was centrifuged for 15 min at 4500 RPM, to facilitate the flocculation of graphene flakes. The resulting graphene/EC dispersion was dried overnight on a PTFE plate. To tailor the concentration and viscosity of ink to the AJP, the dried graphene/EC paper was then dispersed by sonication for 30 min, in a mixture of 92.5% cyclohexanone and 7.5% terpineol solution, followed by centrifugation at 4500 rpm for 15 min. The resulting ink concentration, as seen in Fig. Similar to the processes described in Jabari The graphene interconnects were printed using an AJ-300 Aerosol Jet printer manufactured by Optomec. The atomizer utilized was the UA-Max ultrasonic atomizer. A recirculating bath temperature of 15 °C was used to help stabilize the ink temperature and prevent the output from being too solvent rich. The tool platen was heated to 65 °C to help ensure rapid drying of the ink once on the substrate. The printing nozzle was a 100 μm inner diameter ceramic and the mist tube material was polyethylene. The power applied to the atomizer was 48 W (48 volts at 1 amp). The sheath and atomizer flows were 50 and 20 sccm nitrogen respectively. The tool translation speed used was 1 mm/sec and the resulting single pass line width was measured to be ~50 μm. After printing any remaining solvent was driven out of the lines with a 100 °C bake for 10 min followed by a ramp to 200 °C bake under a nitrogen purge for 30 min to maximize conductivity of the printed features.2 Si/SiO2 wafers we used for AFM and Raman characterization. The TEM grid and SiO2/Si wafers were then annealed on a hotplate at 250 °C for 10 min, to remove the ethanol/EC residuals. AFM images were obtained using a Bruker Multimode 8 system. The images were collected with 1 µm × 1 µm scans, and particle characteristics were determined using Nanoscope Analysis software. TEM images were obtained using a JOEL JEM 2100 system, and the particles were characterized by ImageJ software. Lastly, the Raman peaks were obtained using Horiba LabRAM HR Evolution Raman microscope, with an excitation wavelength of λ = 532 nm. The spectrum was collected at a laser power of 25%, with magnification of 100x with 30 s exposure time, and between the range of 1000–3000 cm−1. Baseline subtraction was employed to clearly deduct the peak intensities. Cancado’s general equation47: a axis (La) of the graphene flake from the Raman spectrum.For AFM, TEM and Raman characterization, the formulated graphene dispersion in ethanol/EC was diluted 1:10 volume ratio graphene/EC flakes in ethanol. The diluted dispersion was then drop-casted on to a TEM lacey carbon grid and tripled rinsed in isopropyl alcohol and dried with Ngl, where A is the (absorbance), α (absorption coefficient), Cg (concentration of graphene), and l is (path length of the spectroscopy), a graphene concentration of 3.5 mg/ml was measured. The previously reported absorption coefficient at wavelength of 660 nm (α660 = 2460 L/g-m) was used in the calculations8.Ultraviolet-Visible (UV-VIS) absorption spectroscopy (Cary 5000 G) was used to measure the optical absorbance of the graphene inks and quantify the graphene concentration. Using the Lambert-Beer law, A = αCIn order to find the annealing temperature and oxidation temperature of the graphene, Thermogravimetric Analysis (TGA) was employed. A Netzsch TGA instrument was used to obtain the spectra of mass percent versus temperature. The mass of the dried graphene flakes (black) was analyzed as the temperature increased from 25 °C to 1000 °C at a heating rate of 5 °C/min in air. TGA analysis revealed the decomposition peak of surfactant, ethyl cellulose, is around 250 °C and oxidation/decomposition of the graphene is 550 °C . All other external boundaries were under the adiabatic boundary conditions, if they are thermally insulating. Thermal properties of the substrates are κOX = 1.4 Wm−1 K−1, κSi = 100 Wm−1 K−1, κKapton = 0.12 Wm−1 K−1, and κAl2O3 = 32 Wm−1 K−1. Thermal conductivities of graphene interconnect are assumed at κ⊥ = 2 Wm−1 K−1 and κ|| = 50 Wm−1 K−1 for cross-plane and in-plane directions, respectively. These values are significantly lower than those of pristine graphene because of the nature of printed graphene. The thermal interface resistance between graphene interconnect and substrates Rint were fitted to be between 1.0 × 10−7 m2 K/W to 1.0 × 10−8 m2 K/W.In order to understand the heat dissipation and temperature distribution in our devices, we performed finite element simulations using COMSOL Multiphysics. In our thermal model, the bottom boundary of the substrate and the outmost surface of the silver pad (which were in contact with the probe) were kept at the ambient temperature under the isothermal boundary condition (The data generated and analyzed as part of this study are available from the corresponding authors upon reasonable request.Supplementary Information


A stretchable optical sensor can quantify the strain generated by human movement, which has been widely studied in the development of health monitoring systems, human–machine interfaces and wearable devices. This paper reports a graphene-added polydimethylsiloxane (PDMS) fiber, which has high tensile properties and good light transmittance suitable for detecting human movement. When the graphene-added PDMS fiber is stretched, the concentration of graphene per unit volume is constant, and the sensor uses the optical loss of the beam through the graphene PDMS fiber to detect the tensile strain. The fiber has excellent strain-sensing performance, outstanding sensitivity, a tensile property of 150%, and an excellent waterproofing performance. The linear response and repeated response in large dynamic range could reach 100% stability. The results show that the sensor can be used to detect human motion detection. These excellent properties indicate that the fiber has potential applications in wearable devices, soft robots and electronic skin. In recent years, flexible, stretchable and wearable sensor devices have received widespread attention ,6,7,8,9.In order to meet these needs, many studies have reported flexible, stretchable and highly sensitive strain or pressure sensors made of graphene polymer ,18,19,20This paper reports a graphene-added PDMS fiber with high tensile properties and good light transmittance. We studied the beam attenuation after passing through the graphene-added PDMS fiber to detect tensile strain. The optical loss is mainly caused by the absorption and scattering of graphene. The sensor can easily reach 150% strain, which shows the large range of human joint detection capabilities, including finger bending, wrist bending, elbow bending and knee bending. The muscle detection of human movement also exhibits excellent sensitivity including arm muscle relaxation and tension, the exhalation and inhalation of the human body. In addition, we demonstrated waterproof properties and tested the sensor changes in different environments. According to the results of this research, it is expected that people will be able to cost-effectively manufacture sensors that meet a variety of human needs.Single-layer graphene  with a purity of over 99% was acquired from Suzhou Tanfeng Materials Tech. Co. Ltd.  and was prepared by a chemical method. Poly tetra fluoroethylene (PTFE) tubes with different diameter sizes were bought from Oudelixin . Polydimethylsiloxane  was supplied by Dow Corning Co. Ltd.  The medical rubber gloves and the injection syringe were all purchased from a local hospital .A simple two-step method was used to prepare the graphene-added PDMS fiber. Firstly, the graphene powder was dispersed (5 mg/ml) in chloroform . After ultrasonic treatment for 6 hours, a well-dispersed solution was mixed with polydimethylsiloxane. Subsequently, the mixing solute on was mixed with a vortex and dried at 90 °C for 12 h in order to completely evaporate the chloroform. The mixing prepolymer was prepared by polydimethylsiloxane and a curing agent at a ratio of 10:1  by weight. The uniformly stirred PDMS mixture was degassed in a vacuum box. The High Power UV–Vis Fiber Light Source , which outputs 200 nm to 1600 nm light through a light guide, was used as the light source. The emission wavelength was 441.6 nm helium-cadmium laser. The sensor was coupled with two UV resistant quartz fibers (core: 600 μm) at each end, encapsulated with fixture equipment. Digital light power and an energy meter (PM100D) were used to measure the light intensity variation of the fiber optic sensor. The Laser Star Dual Channel (P/N 7Z01601) is a laser power meter, which is driven by window software. An Ocean Optics USB4000 spectrometer  measured the transmission spectrum and the spectral range was 200–1100 nm.c = We investigated the stretchability of the graphene-added PDMS fiber with a length of 3 cm and a diameter of 1 mm. The digital optical of graphene-added PDMS fiber is shown in In order to detect the optical properties of PDMS fibers, the optical properties of graphene-added PDMS materials were characterized by optical attenuation spectroscopy. We measured the transmission loss of PDMS fiber and graphene-added PDMS fibers in air, as shown in c = As shown in A represents the absorbance, k is the molar absorption coefficient, and the absorption property of graphene does not rely on the incident wavelength λ of visible light. ε is the strain, c is the concentration of graphene, and, under strain conditions, as, due to the constant volume, with absorption per unit length unchanged, c remains constant. T is the transmittance. The absorption of graphene leads to the attenuation of transmitted light intensity, and the change in strain attenuation can be expressed as:c is constant, the optical loss is proportional to the strain ε; when the strain ε is constant, the optical loss and the concentration c are linearly proportional.The absorption of graphene was linearly proportional to the length of the light passing through the PDMS fiber, as shown in The sensitivity of the sensor response is affected by the concentration of graphene and the length of the PDMS fiber. In our experimental test, the details of fiber fixation were as shown in Accompanied with the action of strain, the optical loss changed, as shown in In order to study the dynamic response of the sensor during stretching and releasing, we performed a cyclic test on a sensor with a graphene concentration of Due to its high flexibility, sensitivity and large strain range, the sensor can be directly attached to the human body to monitor its movement in real time. Because the graphene material has no wavelength selectivity in a visible light band, we can measure the optical loss through PDMS fibers with a single wavelength laser. Combined with the practical application of the sensor, we have improved the process of the optical fiber as shown in For large-strain detection of human motion, we attached sensors to human joints, as shown in −1.In addition, we also did some tests for smaller strains such as muscle movements, as shown in The stability of the sensor is necessary for practical applications. We soaked the sensor in water to monitor its optical response to water. In conclusion, we have demonstrated a simple, efficient and low-cost way to manufacture strain sensors with high tensile properties and sensitivity, made from graphene and polymer elastomers. Compared to the pure PDMS fiber, the composite fiber significantly enhances the optical sensing signal of the sensor, showing excellent sensitivity in the case of strain sensing. The tensile property of the sensor is 150%. This strain sensor was applied to practical applications to detect finger bending, wrist bending, elbow bending, knee bending and other motions of the human body in an all-round way. In addition, the optic fiber sensors could be used to monitor muscle movements and breathing. Moreover, we also researched the sensing capacity (bending strain) of this fiber sensor in water, and found that it has certain waterproof function. This study shows that the sensor fibers have a wide range of potential applications in flexible and stretchable devices.