Graphene has attracted much attention for the realization of high-speed photodetection for silicon photonics over a wide wavelength range. However, the reported fast graphene photodetectors mainly operate in the 1.55 μm wavelength band. In this work, we propose and realize high-performance waveguide photodetectors based on bolometric/photoconductive effects by introducing an ultrathin wide silicon−graphene hybrid plasmonic waveguide, which enables efficient light absorption in graphene at 1.55 μm and beyond. When operating at 2 μm, the present photodetector has a responsivity of ~70 mA/W and a setup-limited 3 dB bandwidth of >20 GHz. When operating at 1.55 μm, the present photodetector also works very well with a broad 3 dB bandwidth of >40 GHz (setup-limited) and a high responsivity of ~0.4 A/W even with a low bias voltage of −0.3 V. This work paves the way for achieving high-responsivity and high-speed silicon–graphene waveguide photodetection in the near/mid-infrared ranges, which has applications in optical communications, nonlinear photonics, and on-chip sensing. The use of a silicon−graphene plasmonic waveguide has enabled the realization of fast and sensitive photodetectors that operate at the wavelength of 2 µm. In order to satisfy the demands for the applications in optical communication and optical sensing, there is the need to extend silicon photonics to wavelengths beyond 1.55 µm. However, it is a challenge to create high-performance photodetectors at these wavelengths. Now, Daoxin Dai and coworkers from Zhejiang University and Southeast University in China have proposed and realized a silicon−graphene hybrid plasmonic waveguide photodetector that operates at 2 µm with a responsivity of ~70 mA/W and a 3-dB bandwidth over 20 GHz. In this design, efficient light absorption in graphene is enabled by using a hybrid plasmonic waveguide with a wide thin silicon ridge core and a metal cap that serves as a signal electrode. However, the realization of high-performance silicon-based waveguide photodetectors beyond 1.55 μm still faces challenges. For example, the reported GeSn8 and ion-implanted silicon9 photodetectors still operate in the limited wavelength band of <2.5 μm, while III−V photodetectors10 are unsuitable for monolithic integration on silicon. As an alternative, two-dimensional materials12  provide a promising solution because of their broad operation wavelength band and advantage of avoiding material and structure mismatch in the design and fabrication. At present, black-phosphorus photodetectors have limited bandwidths of ~3 GHz18, and their fabrication is not easy. In contrast, large-size graphene sheets are commercially available and can be transferred/patterned easily in the wafer process line19. Recently, several fast silicon−graphene waveguide photodetectors at 1.31/1.55 μm have been reported with a high bandwidth of ~100 GHz21. Among these photodetectors, the metal−graphene−metal (MGM) configuration is widely used, since the high mobility of graphene facilitates high-speed operation. However, MGM graphene photodetectors32 usually have limited responsivities when operating at low bias voltages. For example, in ref. 20, the reported responsivities are <170 mA/W at −0.4 V and <400 mA/W at −0.6 V for mono-layer and bi-layer graphene photodetectors, respectively. In addition, for the 40 GHz graphene-semiconductor heterostructure (GSH) photodetector reported recently33, the responsivity is also very low (~11 mA/W). More recently, a graphene-insulator-graphene (GIG) photodetector was reported with an improved responsivity of 0.24 A/W and an estimated 3 dB bandwidth of 56 GHz. Unfortunately, the working bias voltage is as high as 10 V34. Therefore, high-speed and high-responsivity graphene photodetectors with low bias voltages are still highly desired. Notably, very few results have been reported for the realization of graphene waveguide photodetectors beyond 1.55 μm, even though light absorption in graphene is present in this range. For the reported surface-illuminated mid-IR graphene photodetectors40, the responsivity is low due to the limited light absorption, which is well known. For the mid-IR graphene waveguide photodetectors reported in recent years43, the measured bandwidths are very limited . To the best of our knowledge, currently, high-speed  silicon−graphene waveguide photodetectors have not been reported for the mid-IR range beyond the wavelength band of 1.55 μm.Currently, it is desirable to extend the wavelength band of silicon photonicsIn this paper, we propose and demonstrate high-speed and high-responsivity silicon−graphene waveguide photodetectors beyond 1.55 μm by utilizing a hybrid plasmonic waveguide with an ultrathin wide silicon ridge. With this novel design, the light absorption in graphene is enhanced while the metal absorption loss is reduced simultaneously, which helps to greatly improve the responsivity. Here, the wide metal cap in the middle and the MGM sandwiched structures are introduced as the signal electrode and the ground electrodes, respectively, so that one can achieve reduced graphene-metal contact resistances  and a large 3 dB bandwidth. A mechanism analysis confirms that the photothermoelectric (PTE) effect dominates the photoresponse under zero bias, while the bolometric (BOL)/photoconductive (PC) effects become dominant when a bias voltage is applied. When operating at 2 μm, the present graphene photodetector has a responsivity of ~70 mA/W and a measured 3 dB bandwidth of >20 GHz (which is setup-limited). Meanwhile, the present photodetectors also work very well at 1.55 μm. The measured responsivity is approximately 0.4 A/W for a bias voltage of −0.3 V and an optical power of 0.16 mW, while the 3 dB bandwidth is over 40 GHz (setup-limited).2O3 insulator layer, a graphene sheet, and a metal cap. The metal cap in the middle is used as the signal electrode, while the ground electrodes are placed far away from the silicon ridge to avoid high metal absorption loss. In particular, here, we introduce the MGM sandwiched structure for the ground electrodes in order to achieve reduced graphene-metal contact resistances, which helps achieve a large 3 dB bandwidth44. For previous silicon−graphene hybrid plasmonic waveguide photodetectors, the center metal strip exhibits high absorption of light even though the light−graphene interaction can be enhanced27, in which case the undesired metal absorption without any contribution to the photocurrent generation is even higher than the desired graphene absorption. As a result, the responsivity is usually limited27. This problem can be alleviated partially by reducing the width of the center metal strip . However, this reduction in width introduces a high graphene-contact resistance, which consequently leads to a reduction in the responsivity and the bandwidth. In this paper, a silicon−graphene hybrid plasmonic waveguide is proposed with a wide silicon ridge, as shown in Fig. 29 so that the light absorption in graphene is enhanced due to the weak mode field confinement in the vertical direction45. Furthermore, for the hybrid photonic-plasmonic mode46 supported in the present waveguide, the metal absorption loss is low even when a relatively wide metal strip is chosen to achieve a low metal−graphene-contact resistance. Meanwhile, the center metal strip  on top of the silicon ridge still helps improve the light absorption in graphene due to the strong localized field. In this way, the present hybrid plasmonic waveguide can simultaneously realize low metal loss and high absorption in graphene. In addition, the silicon ridge height is chosen to be as small as 50 nm, which helps to avoid damage to the graphene sheet during the fabrication processes. As shown in Fig. 24 and demonstrated in refs. 30.Figure 0 mode of the thin-silicon photonic waveguide and then coupled to the quasi-TE0 mode of the silicon−graphene hybrid plasmonic waveguide46 with a low coupling loss. Figure 0 mode in the present silicon−graphene hybrid plasmonic waveguide as the waveguide dimensions vary. Here, a finite-element method mode-solver tool (COMSOL) is used (see more details in Supplementary Note η(L) = ηg(1 − 10αL−0.1), where L is the propagation distance, α is the mode absorption coefficient in dB/μm, ηg is the ratio of the graphene absorption to the total absorption, i.e., αg and αm are the absorption coefficients of the graphene sheet and the metal strip, respectively). Since only the graphene absorption contributes to the photocurrent, one should maximize the ratio ηg so that the graphene absorption is more dominant than the metal absorption to improve the responsivity. Figure ηg and the results for the absorption coefficients  as the ridge width wsi varies from 0.5 to 4.0 μm. Here, the width and height of the metal strip are chosen as wm = 200 nm and hm = 50 nm, respectively. As shown in Fig. ηg increases when choosing a wider ridge. When the ridge width wsi is chosen to be larger than 3 μm, the ratio ηg is higher than 70%. Meanwhile, it is noted that the absorption coefficients  decrease when choosing a wider ridge, which is simply due to more optical confinement in the silicon region and weaker light−matter interaction in the absorption regions. As a result, one needs to choose a longer absorption length to achieve sufficient absorption in the photodetector, which prevents fast responses due to the RC-constant limitation. Fortunately, the light absorption can be enhanced greatly by reducing the silicon core height hsi, as shown in Fig. αg, αm) for the cases with different silicon core heights of hsi = 220, 160, and 100 nm are given. From this figure, one sees that the absorption coefficients αg and αm increase by more than 100% when the core height hsi is reduced from 220 to 100 nm. This result is attributed to the stronger evanescent field for the case with a thinner silicon core. Meanwhile, the graphene absorption ratio ηg increases slightly as the core height hsi decreases. As a result, an ultrathin silicon core is preferred to achieve strong light absorption so that one can use a short absorption section. Here, we choose hsi = 100 nm for our devices based on the feasibility of the fabrication processes. To avoid a long carrier transit time between the electrodes, the ridge width is chosen as wsi = 3 μm. With this design, the absorption coefficients are  =  dB/μm, and the graphene absorption ratio ηg is approximately 70%.Note that the thin-silicon photonic waveguide and the silicon−graphene hybrid plasmonic waveguide are polarization-sensitive. Here, we consider the case of TE polarization; thus, a TE-type grating coupler is used to achieve efficient fiber-to-chip coupling. The input light is coupled to the TEηg and the absorption coefficients  on the width wm and height hm of the metal strip. Here, the dimensions of the silicon ridge are wsi = 3 μm and hsi = 100 nm. It can be seen that a high ratio ηg can be achieved by choosing a narrow metal strip, which is simply due to a significant reduction in the metal absorption. For example, when choosing wm = 100 nm, the metal absorption coefficient is as small as αm = 0.019 dB/μm, while the ratio ηg is as high as ~90%. However, the graphene absorption coefficient αg also decreases to some degree when the metal strip becomes narrow. Therefore, to have a sufficiently high graphene absorption coefficient and a high absorption ratio ηg, we choose wm = 200 nm in our design, which also makes the fabrication relatively easy and guarantees a low graphene-metal contact resistance for the middle electrode. The absorption coefficients  can also be further enhanced by reducing the metal thickness, as shown in Fig. ηg also decreases. Therefore, we choose hm = 50 nm as a trade-off.Figure wm = 200 nm, hm = 50 nm, wsi = 3 μm, and hsi = 100 nm, the calculated electric field distribution 0 mode is shown in Fig. 7 V/m for 1 mW optical power, which helps enhance the light absorption in graphene. For the present design, we calculate the total graphene absorption η(L) as the propagation distance L varies from 0 to 50 μm, as shown in Fig. wm = 200 nm when the length L is 50 μm. For a metal width of wm = 300 nm, the total graphene absorptance is close to a saturated value of 51.4% when the length L is 20 μm, which occurs because the metal absorption increases. In contrast, when wm = 100 nm, the total graphene absorption increases to 78.7% (not yet saturated) when the length L increases to 50 μm, which is due to the relatively low absorption coefficients . With such a design, the present silicon−graphene hybrid plasmonic waveguide achieves the best result among the results of the reported silicon−graphene hybrid waveguides (which were developed for 1.55 μm). For a direct comparison, the silicon−graphene hybrid plasmonic waveguide is also designed optimally for 1.55 μm , including the processes of electron-beam lithography, ICP etching, AlVG is set to less than 4.0 V to avoid the breakdown of the Al2O3 nanolayer. Figure VG and bias voltages Vb. For Device A, the Dirac voltage VDirac is approximately 3.2 V  =  V and  V, respectively, the graphene sheet is highly doped. As a result, the bolometric coefficient β is large49; thus, the BOL effect becomes the dominant mechanism. In Fig. VG, Vb) =  V and  V, respectively, the graphene sheet is lightly doped. As a result, the bolometric coefficient β is small49; thus, the BOL effect is suppressed. Meanwhile, the lifetime of the photogenerated carriers in graphene becomes long because of the low doping level49. In this case, the density of the photogenerated carriers is sufficiently high, and the PC effect becomes the dominant mechanism for the photoresponse.In order to better understand the mechanisms of the photodetectors, we also provide theoretical calculations for the Fermi level Vb| increases from 0 to 0.3 V, the dominant mechanism for the photoresponse changes from the PTE effect to the BOL effect or the PC effect, depending on the applied gate voltage. Meanwhile, the responsivity increases significantly if the gate voltage is controlled well. Figure Vb = −0.3 V when choosing VG = ~1.9 V (the BOL effect) and ~3.2 V (the PC effect). The responsivities for the BOL and PC modes are 35.0 and 25.5 mA/W, respectively, when the input optical power Pin is ~2.2 mW. When the input optical power Pin decreases to 0.28 mW, the responsivities increase to approximately 52.1 and 30.0 mA/W for the BOL mode (VG = ~1.9 V) and the PC mode (VG = ~3.2 V), respectively. Since MGM-type graphene photodetectors often have a high dark current  is much lower than the dark current (~3 mA). Thus, some notable noise was observed at high frequencies in the measurement, as shown in Fig. fmax in the measurement is up to 20 GHz, which is limited by the 2 μm optical modulator (with a 3 dB bandwidth of 10 GHz) available in the lab.The frequency responses of the devices were measured by using a setup combining a commercial 10 GHz optical modulator and a vector network analyzer , as shown in Fig. VDirac larger than 4.0 V . Figure Vb = 0.6 V, which was characterized with the help of an erbium-doped fiber amplifier at 1.55 μm. The measured 3 dB bandwidth is higher than 40 GHz . This device was further used to receive high-bit-rate data with the setup shown in Supplementary Fig. Vb = 0.6 V and VG = 2.8 V. It can be seen that the eye diagram is open with a bit rate as high as 30 Gbit/s. More details are provided in Supplementary Note To verify the high bandwidth of the present waveguide photodetector, we characterized the third device (Device C) on the same chip, as shown in Fig. 35, a silicon−graphene photodetector was demonstrated with a responsivity of 6.25 mA/W at 10 μm and an estimated 3 dB bandwidth of >1 GHz at 1.03 μm. In ref. 36, a silicon−graphene photodetector was reported with responsivities of 0.6−0.076 A/W for an input optical power of 2.5−50 μW. For the device in ref. 36, the measured 3 dB bandwidth was higher than 50 GHz at 0.8 μm, and the responsivity was 2−11.5 A/W for an ultralow optical power in the wavelength range of 3−20 μm. For the waveguide photodetector reported recently43, the measured 3 dB bandwidths were on the scale of kHz or not given. In contrast, the present photodetectors  have a responsivity of 70 mA/W (at −0.3 V and 0.28 mW) and a setup-limited 3 dB bandwidth of >20 GHz.Here, we provide a comprehensive comparison of the performances of the reported silicon−graphene photodetectors beyond 1.55 μm, as shown in Table 33. More recently, the device demonstrated in ref. 20 showed a 3 dB bandwidth of over 110 GHz and 100 Gbps data reception. Similarly, the present silicon−graphene hybrid waveguide photodetector also demonstrates a high 3 dB bandwidth of >40 GHz, which is setup-limited.We further compare the reported silicon−graphene photodetectors in a wavelength band of 1.55 μm, because abundant measurement results are reported in this band, as shown in Fig. 33 when operating at a low bias voltage, e.g., |Vb| < 0.3 V. It is well known that, for MGM photodetectors, the responsivities are usually positively correlated with the bias voltages Vb49 and negatively correlated with the input optical powers Pin36. Meanwhile, it is usually desirable to be able to detect a low optical power with a low bias voltage because this helps to reduce the dark currents and suppress the shot noise. In Fig. Vb = ±0.3 V unless no data are provided in the literature. Three graphene photodetectors with a responsivity of >100 mA/W have been reported recently30. For the photodetector reported in ref. 28, the responsivity is estimated to be ~150 mA/W (at 0.3 V) with Pin = 0.025 mW according to the responsivities given for the cases of Vb = 0 and 1.2 V. The other photodetector in ref. 30 has a responsivity of ~140 mA/W (at 0.3 V) with Pin = 0.56 mW, which is estimated from the responsivities given for the cases of Vb = 0 and 0.4 V. In ref. 20, the responsivities are proportional to the bias voltage and are ~375 mA/W and ~150 mA/W when operating with Vb = −0.3 V for Pin of 0.08 and 0.6 mW, respectively. For the present photodetector (Device C) operating at a low bias voltage Vb = −0.3 V, the responsivity at 1.55 μm is as high as ~0.4 A/W with Pin = 0.16 mW, which is the highest value among the results of the various reported high-speed graphene photodetectors. In addition, the tunneling photodiode in ref. 34 with an estimated bandwidth of 56 GHz is not included in Fig. Pin = 0.42 mW. However, a high bias voltage results in large power consumption and cannot be supported by low-voltage CMOS drivers. In summary, the present silicon−graphene waveguide photodetector works well with a high responsivity and a high bandwidth.On the other hand, most of the reported graphene photodetectors have a responsivity of less than 100 mA/Wb = −0.3 V for Pin = 0.28 mW. In order to verify the ultrafast photodetection capability, we have also measured the frequency responses of the present waveguide photodetector operating at 1.55 μm. It is shown that the measured 3 dB bandwidth is >40 GHz (which is still limited by the setup). Meanwhile, the measured responsivity is approximately 0.4 A/W at Vb = −0.3 V for Pin = 0.16 mW, which has some advantages over other photodetectors33. It is well known that MGM graphene photodetectors usually suffer from a low signal-to-noise ratio due to the high intrinsic large dark current. Fortunately, this issue can be alleviated partially for the present device, which has relatively high responsivities at low bias voltages. In this paper, Device A at 2 μm has an NEP of 61.7−72.7 pW/Hz1/2, which is slightly better than that of commercial infrared photoconductive PbSe detectors (80 pW/Hz1/2)51. For the present 2 μm waveguide photodetectors with large bandwidths, there are some important application scenarios, e.g., 2 μm optical communications3, monitoring of a 2 μm pulsed laser system in mid-infrared time resolved spectroscopy52, nonlinear photonics4, and lab-on-chip sensing7. In short, the present work paves the way for achieving high-responsivity and high-speed near/mid-infrared waveguide photodetectors on silicon, which will play an important role in various applications. In future works, more efforts should be dedicated to introduce special junction structures to reduce the dark current and further extend the operation wavelength band.In this paper, we have proposed and demonstrated novel silicon−graphene hybrid plasmonic waveguide photodetectors beyond 1.55 μm, which are realized by introducing an ultrathin wide silicon ridge core region with a metal cap at the top. With this design, the light absorption in graphene is enhanced while the metal absorption loss is reduced simultaneously. This design greatly facilitates effective optical absorption in graphene over a short length. Metal−graphene−metal sandwiched electrodes have also been introduced to reduce the metal−graphene-contact resistance, which helps improve the response speed. For the fabricated photodetectors, the mechanism has been revealed from the IV characteristics operating at different gate voltages. It has been shown that the dominant mechanism for the present photodetectors is the PTE effect at zero bias voltage and the BOL or PC effect at nonzero bias voltages, which help achieve high-speed responses. For the fabricated photodetector operating at 2 μm, the measured 3 dB bandwidth is >20 GHz , while the responsivity is ~70 mA/W at Vhsi = ~100 nm, an etching depth of het = ~50 nm, and a ridge width of wsi = 3 μm. A 90-nm-thick aluminum gate electrode (with an ohmic contact) was fabricated by utilizing lift-off processes. A 10-nm-thick Al2O3 layer was deposited on the SOI ridge waveguide by using an atomic-layer deposition (ALD) process. The bottom layer of the side ground electrodes was made of 15/50-nm-thick Ti/Au hybrid thin films. Then, a single-layer graphene sheet was transferred onto the chip and patterned by EBL and ICP etching processes. Finally, a 50-nm-thick Au layer was deposited and patterned to form the narrow signal electrode and the top layer of the side ground electrodes.The ultrathin silicon core layer was obtained from a standard 220-nm-thick SOI wafer. A thermal oxidation process was used to obtain an ~100-nm-thick silicon top layer from a standard 220-nm-thick lightly p-doped SOI wafer. EBL and ICP processes were used for the fabrication of the silicon ridge waveguide with a silicon thickness of The CVD-grown graphene was obtained from ACS material LLC . A 300-nm-thick film of PMMA was spin-coated on the graphene/copper film at 4000 rpm. The PMMA/graphene/copper film was floated on aqueous ammonium persulfate (60 mg/mL) to remove the copper and rinsed in deionized water. Then, the film was transferred onto the chip. The graphene-covered chip was dried, baked, soaked in acetone and rinsed with isopropanol.Pin was estimated according to the measured coupling efficiency of the grating coupler (~10.5 dB at 2 μm) and the power splitting ratio of the directional coupler (~1 dB at 2 μm). More details on the optical power analysis are provided in Supplementary Note The responsivities of the photodetectors were characterized by using low-frequency measurements. Continuous-wave light from a fiber laser was modulated with a frequency of 0.2 kHz by a chopper and then coupled to the optical waveguide by using an on-chip grating coupler. The photocurrent was then amplified and recorded by using a preamplifier and a lock-in amplifier (see Supplementary Fig. Supplementary Material


To guarantee proper cellular viability and an accurate geometry, it is mandatory to control all these factors. Despite internal factors, such as printing pressures, temperatures or speeds, being well-controlled in actual bioprinters, there is a lack in the controlling of external parameters, such as room temperature or humidity. In this sense, the objective of this work is to control the temperature and humidity of a new, atmospheric enclosure system for bioprinting. The control has been carried out with a decoupled proportional integral derivative (PID) controller that was designed, simulated and experimentally tested in order to ensure the proper operation of all its components. Finally, the PID controller can stabilize the atmospheric enclosure system temperature in 311 s and the humidity in 65 s, with an average error of 1.89% and 1.30%, respectively. In this sense, the proposed atmospheric enclosure system can reach and maintain the proper temperature and humidity values during post-printing and provide a pre-incubation environment that promotes stability, integrity and cell viability of the 3D bioprinted structures.Bioprinting is a complex process, highly dependent on bioink properties  and environmental conditions (mainly temperature, humidity and CO Bioprinting is a booming technology that could revolutionize regenerative medicine . It has w/v). For this reason, several processes can be associated to uncontrolled bioprinting conditions. Some of them are related to the stability and integrity of 3D bioprinting structures [It is important to know that hydrogels are very sensitive to external changes  because of their high-water content , Poietis®  or 3D-Discovery BioFactory® , control the air flow to minimize biological contamination using High Efficiency Particle Arresting (HEPA) filters [As far as the authors know, no previous studies have focused on designing, developing and testing an atmospheric enclosure system for bioprinting that could control these critical parameters to assure the integrity and stability of the 3D structure together with the viability of its cells during the post-printing stage. Instead of generating an atmospheric enclosure system, other authors propose to control these atmospheric parameters by reducing bioprinting time, bioprinting into a water-based bath or reducing air flow [ filters ,11,12. H filters , so larg filters ,13.2, which increases the complexity of PID controllers due to the cross-coupling effects among these three variables [2 variable was left out of the scope of this work for two main reasons. Firstly, it is not expected that cells produce significant CO2 emissions during post-printing, so its concentration should remain stable in the global system. Additionally, the cross-coupling interaction of CO2 with temperature and humidity will make difficult the optimization of the PID parameters and, consequently, will decrease the robustness and stability of the final PID controller. Hence, we focus our interest on developing a stable and robust PID controller of the two main variables involved in the post-printing stage of bioprinting—temperature and humidity.Proportional integral derivative (PID) controllers are commonly used in atmospheric enclosures of other fields, e.g., neonatal ,15,16 orariables ,29. It hariables . With thTherefore, the main objective of this work is the design, development and validation of a temperature and humidity PID controller for an atmospheric enclosure system with bioprinting purpose. This atmospheric enclosure system could control the post-printing stage independently of the bioprinting technique used. For this purpose, theoretical, simulated and experimental studies have been performed to assure a proper functioning of the proposed system.®, and different area dimensions are shown in The designed atmospheric enclosure system is a sub-divided parallelepipedal with different areas: a bioprinting sub-chamber, a climatic conditions generation sub-chamber and an electronic/mechanic components sub-chamber. All designing was done using Autodesk Inventor®  UNO boards, all connected to a Raspberry®  Pi 3, and the whole system was controlled by a personalized Python® version 3.9  script. This script provides the user full live control over the bioprinter atmospheric enclosure parameters while temperature, humidity and CO2 data are shown.Bioprinter control is divided into three different processes: bioprinter mechanical control, atmospheric enclosure control and data visualization. All three processes were individually controlled by Arduino2 is injected from an external AquaMedic®  CO2 pressurized bottle when a Blau®   electro valve is opened. Likewise, the type and location of every one of the sensors used is shown in The control of proper atmospheric conditions inside the enclosure needs generation and sensorization of each one of the inner parameters. In this sense, temperature is generated with two 200-W electrical finned resistances, humidity is produced with cold vaporization of water in a tank using a piezoelectrical transducer and, finally, CO2 are modified and then exit to the enclosure atmosphere again. This process is continuously repeated, creating an air conditioning flow until the atmospheric parameters’ target values are reached.The main area of the atmospheric enclosure system is the climatic conditions generation sub-chamber. All generation apparatuses were placed in this area to produce the appropriate atmospheric conditions. This sub-chamber is a separated area of the enclosure connected by 4 air inlets/outlets, 2 inlets with axial fans and 2 outlets, as shown in To ensure a sterile environment at the beginning of the bioprinting process, the bioprinter sub-chamber is sterilized by action of four UV LED panels (420 nm and 440 mW) incorporated in the bioprinter sub-chamber. After this process, air is introduced into the system from outside, passed through a HEPA filter and generates positive pressure to prevent the entry of contaminating external agents.2 pressurized bottle and two CO2 sensors for future purposes, they have not been used in this study. Although the proposed atmospheric enclosure system has a COvC is the volumetric air heat capacity (J/kg∙°C); V is the inner air volume (m3); hT is the inner temperature (°C); aG is the air mass flow that a fan extracts from the chamber to the generation sub-chamber (m3/s); 3); pC is the air-specific heat (1006 J/kg∙°C); cT is the generation sub-chamber air temperature (°C); nQ is the heat dissipation capacity (J/s); 0T is the external temperature (°C); R is the enclosure thermal resistance (°C∙s/J); nd is the inner humidity (g/kg); cd is the external humidity(g/kg); nD is the enclosure humidity gain (g/s).The purpose of this work is to control the inner temperature and humidity of an atmospheric enclosure system. In this sense, the inner heat balance and water mass balance equations are the general non-lineal differential equations used in temperature and humidity control processes ,22. In tX as G1(s) and G2(s) are temperature and humidity terms, respectively. Transfer functions for the PID controller were obtained applying the Laplace transform to Equations (1) and (2). Defining SISO test to study inner temperature when heater (electric resistance) was switched on.SISO test to study inner humidity when humidifier (cold mist humidifier) was switched on.MIMO test to study coupling of inner temperature and humidity ,29.A comparative between theoretical and experimental behaviors  of the atmospheric enclosure was proposed. For this purpose, the different experimental behaviors of each parameter (inner temperature and humidity) were tested and determined. To obtain data for the experimental transfer function, single input, single output (SISO) and multiple inputs, multiple outputs (MIMO) tests were performed as follows:Initial inputs and target values for all tests are shown in ® R2018b System Identification Toolbox™. This tool is commonly used to obtain mathematical models of dynamic systems from experimental input and output data. As such, Matlab® R2018b Simulink™ was used to simulate and compare both theoretical and experimental transfer functions.Experimental transfer functions were obtained from test data using the MatlabVariations in temperature and humidity can change bioprinting materials’ properties and affect the cellular viability, stability and integrity of 3D bioprinted structures. To minimize variations, a PID controller was added to the atmospheric enclosure system. PID controller algorithms are widely used in feedback control systems and are mathematically expressed as :(5)u(t)=® R2018b  to tune all PID parameters using process input/output signals. All these calculations were done through a simulation block diagram implemented in Matlab® R2018b Simulink™, which follows the standard structure shown in A good PID control system can provide the atmospheric enclosure with the necessary stability in the shortest time. In this sense, the Ziegler–Nichols closed-loop method was used in Matlab® R2018b System Identification Toolbox™. All possible types in this toolbox were used: one pole (P1), two poles (P2), three poles (P3), one pole and one zero (P1Z), two poles and one zero (P2Z), three poles and one zero (P3Z), two poles sub-damped (P2U), three poles sub-damped (P3U), two poles and one zero sub-damped (P2ZU), three poles and one under-damped zero (P3ZU), one pole and one integrator (P1I), two poles and one integrator (P2I), three poles and one integrator (P3I), one pole and one delay (P1D) and two poles and one delay (P2D) transfer functions.The workflow was performed as Yinping et al.  in theirNext, both transfer functions’  block diagrams were designed and evaluated. Finally, theoretical and experimental transfer functions were analyzed, obtaining the first Kp , Ki  and Kd (derivative controller) values using the Ziegler–Nichols method. Then, this first PID tuning was tested and manually re-tuned to limit overshoots produced by the Ziegler–Nichols method.To validate the atmospheric enclosure system, several tests were performed using the former calculated Kp, Ki and Kd values. Finally, to check the quality of calculated PID, an experimental error (6) was calculated.The following temperature (7) and humidity (8) theoretical transfer functions were obtained once inherent constants of the system were replaced in Equations (3) and (4).The experimental transfer function for temperature was obtained from a SISO test with laboratory environmental conditions set to 22 °C and 50% relative humidity. In the tests, actuators (electric heat resistance) were powered on or off when the inner temperature registered by sensors was below or above the target temperature (37 ± 1 °C). Data acquisition from sensors takes 700 s (test time) to assure a complete study with enough data.® R2018b for this transfer function was 99.49%.The experimental transfer function, Equation (9), is calculated from the selected fitting plot for electric heater switching, the one pole and one delay (P1D) plot a. The ac® R2018b for this transfer function was 99.03%.Using previously described methodology for SISO tests, the plot that best fit the humidity behavior b was oneA slightly variation between the experimental and theoretical transfer functions (Equations (7) and (9) vs. Equations (8) and (10)) can be observed; an exponential function is multiplied to the proportional constant. Albright et al.  explain ® R2018b model from these data that extract the transfer function with a specific accuracy (model). These graphs represent the first approach of the solution that will be used as input of ® R2018b Simulink™. Additionally, two delay blocks have been added to this diagram to simulate the delay of sensors while reading in experimental functions. An open-loop block diagram  to compaThe dependency between temperature and humidity means that control could be a hard task when they are actuating at the same time. Wang et al.  exposed Analyzing Using the before-mentioned methodology, a MIMO test was performed on the atmospheric enclosure system to obtain the inherent values of the system. Laboratory environmental conditions were set to 22 °C and 50% relative humidity and the target values were the same as those used in the previous MIMO tests. Analyzing all obtained plots, P1D with delay models were the ones that best fit the temperature and humidity behaviors . The ass® R2018b model from these data that extract the transfer function with a specific accuracy (model). These graphs represent a former approach to the final solutions that will integrate other elements, such as the response time of the sensor, which will be exposed in Previous results of our theoretical transfer functions cannot be considered good enough to describe our system. Interrelations between variables, non-linearity, high hysteresis or real-time variations are some reasons why temperature and humidity are complex systems to control. In this sense, performing temperature and humidity tests without any kind of control system variables will provoke high fluctuation and poor stabilization of the system. Therefore, to design a good PID controller, natural fluctuations of variables were considered in the new system modelling.® R2018b Pidtool toolbox, PID controller values of transfer functions (11) and (12) were obtained. This tool provides two different PID behavior adjustments: response velocity and long-time stabilization. PID values (Using the MatlabD values  were obt®/Simulink™.The block diagram shown in Results from the experimental test using a decoupled PID controller of temperature and humidity can be seen in ® R2018b calculates the theoretical transfer function for the temperature with a 95.01% accuracy that can justify these differences between the theoretical and experimental values.The temperature behaviors for the theoretical and the real system are very close. The objective of this work is to determine the optimum PID controller values of an atmospheric enclosure system for bioprinting. Specifically, we propose to control temperature and humidity to improve the integrity, stability and cell viability of 3D bioprinted structures. In order to design and develop our atmospheric enclosure, three components of the system were analyzed and compared with previous studies: the mathematical model, the transfer functions and the block diagram, but it was also analyzed whether to use coupled or uncoupled variables. The similarity between the proposed atmospheric enclosure system and greenhouses or animal buildings suggests that the mathematical model used by Daskalov et al.  and AlbrAccording to the bibliography, there is no agreement about the best way to control temperature and humidity. So, some authors propose coupled controllers ,32,33 whOnce the type of controller was chosen, the next step was the composition of block diagram, whose main element will be the system’s plant transfer function for temperature and humidity. Previous studies proposed different types of transfer function to control temperature and humidity: some of them without delay ,32 and oRegarding the block diagram, three different blocks have been used: control, plant and delay. Although this diagram is quite common , in the Finally, the global performance of our atmospheric enclosure system is pretty good. In this sense, low stabilization time and errors were obtained in the experimental tests. Other authors presented a temperature stabilization time of 2760 s for a 4 °C increment , 600 s fIn this work, a PID controller for temperature and humidity control of an atmospheric enclosure system for bioprinting was designed, developed and tested. Theoretical and experimental transfer functions for temperature and humidity were calculated and verified. The results show that the proposed atmospheric enclosure system is capable of stabilizing temperature and humidity in 311 s and maintaining target values with an average error of 1.89% and 1.29% for temperature and humidity, respectively. Hence, the proposed atmospheric enclosure system for bioprinting could improve post-printing environmental conditions to increase the integrity, stability and cell viability of 3D bioprinted structures. 2 control is needed in addition to temperature and humidity. In this sense, the next step of this study will be analyzing the system’s behavior after the inclusion of carbon dioxide as well as the interrelation with temperature and humidity. Additionally, bioprinters usually have a heat/cool cartridge in the extruder to control the bioink temperature. So, the addition of this heat/cool source inside the atmospheric enclosure to simulate bioprinter performance while extruding will be another future development.As commented, to guarantee a proper atmospheric enclosure system for bioprinting, a CO


This stacked structure is deposited in the high resistive Si wafer substrate, and the hexagon radiator itself is a sandwich structure, which is composed of gold hexagon structure and two multilayer graphene stacks. The proposed antenna characteristics i.e., tunability of frequency, the efficiency corresponding to characteristics modes, and the tuning of absorption spectra, are evaluated by full-wave numerical simulations. Besides, the unity absorption peak that was realized through the proposed geometry is sensitive to the incident angle of TM-polarized incidence waves, which can flexibly shift the maxima of the absorption peak from 30 THz to 34 THz. Finally, an equivalent resonant circuit model for the investigated antenna based on the simulations results is designed to validate the antenna performance. Parametric analysis of the proposed antenna is carried out through altering the geometric parameters and graphene parameters in the Computer Simulation Technology (CST) studio. This clearly shows that the proposed antenna has a resonance frequency at 33 THz when the graphene sheet Fermi energy is increased to 0.3 eV by applying electrostatic gate voltage. The good agreement of the simulation and equivalent circuit model results makes the graphene-metal antenna suitable for the realization of far-infrared sensing and imaging device containing graphene antenna with enhanced performance.Plasmonic antennas are attractive optical components of the optoelectronic devices, operating in the far-infrared regime for sensing and imaging applications. However, low optical absorption hinders its potential applications, and their performance is limited due to fixed resonance frequency. In this article, a novel gate tunable graphene-metal hybrid plasmonic antenna with stacking configuration is proposed and investigated to achieve tunable performance over a broad range of frequencies with enhanced absorption characteristics. The hybrid graphene-metal antenna geometry is built up with a hexagon radiator that is supported by the Al Plasmonic innovation has appeared to be an essential field for exploring the potential outcomes of future photonics technologies. Various new research platforms have emerged after the investigation of its possible applications, including biosensing and imaging, biotech, astronomy, security, remote sensing, and optical communication . Among a2/V·s and 108 cm/s Fermi velocity at low temperatures [The ongoing curiosity in the graphene plasmonics opens up the prospects to counterpart these impairments. Graphene is an allotrope of carbon, which has been revealed in recent years, having a monoatomic thickness and being purposely used as the nanomaterial in different fields . Carbon eratures . The eleeratures . Alternaeratures . The exteratures .In recent years, cutting-edge nanofabrication technologies have empowered substantial improvement in developing optical antennas that are intended for tunable optoelectronic and photonic devices . GraphenA significant obstacle for accomplishing perfect absorption in fabricated graphene antennas is lower carrier mobility despite the stimulating forecasts and alluring features of graphene tunable antennas. Similarly, the low carrier mobility is due to polymethyl methacrylate (PMMA) residues in processed graphene samples or trapped impurities during the synthesis process. However, in theoretical works, the unpatterned and passivated graphene sheets with higher carrier mobility are adopted for predicting unity absorption ,21. The An effective way to achieve broadband tunable absorption enhancement is by integrating graphene with metallic plasmonic antennas. Feng et al.  use the The ultra-thin and small geometry of graphene antennas is highly dispersive with frequency-dependent properties. There is no accurate formulation and conventional hypothetical models for developing the connection among the graphene antenna performance and various related antenna characteristics. The approach based on full-wave numerical modeling is a method for characterizing the antenna performance. Still, with monoatomic thickness, it will surely require huge computing resources in the event when high accuracy is required during simulation . The typIn this article, a novel graphene-metal hybrid stack antenna is demonstrated to achieve enhanced absorption by designing graphene stacks with gold hexagon structure in a stacking manner. The proposed graphene antenna has tunable operational bandwidth, starting from 30 to 34 THz. The stacking symmetry provides a slow-wave structure, in which an efficient interaction of graphene plasmons takes place with the metallic plasmons in gold structure. The investigated antenna possesses tunable resonance behavior at a broad range of frequencies due to graphene tunable conductivity. The conductivity of the graphene layers in the stack is tuned by increasing the Fermi energy of the graphene sheet upon applying electrostatic gate voltage. The detailed study and operational mechanisms of the graphene-metal antenna are carried out through the parametric optimization of geometric and graphene parameters, which illustrate the tunable resonance behavior along with improvement in the overall performance. Additionally, the antenna performance and efficiency are also intensively investigated with different TM -modes excitation. The absorption enhancement is attributed to the stacking geometry of the antenna. Furthermore, an equivalent circuit model that is based on PEEC and transmission line method is modeled for the graphene patch and graphene-metal hybrid plasmonic antenna to validate the proposed geometric model. Good agreement is found between the numerical simulation results with the equivalent circuit model. Moreover, c = chemical potential), scattering rate (τ = relaxation time), frequency, and temperature. In particular, the electrical properties of graphene are dependent upon these parameters, with the change in these parameters producing a shift in surface conductivity due to the dispersive nature of graphene. According to Kubo’s formula [q represents the electron charge, incident waves angular frequency is ω, T denotes the effective carrier temperature in kelvin, and T = 293 K, ħ = h/2π is the reduced Planck constant, Fermi–Dirac distribution is τ (relaxation time) denotes the collision frequency, and Boltzmann’s constant is represented by kB. The surface impedance of graphene is inversely proportional to conductivity and it can be considered by using boundary conditions sZ = 1/gσ. Moreover, the conductivity of graphene has two parts, intraband and interband transitions [The two-dimensional graphene material exhibits very outstanding electrical properties because of the mono-atomic thickness, where it allows for the propagation of surface plasmons modes at far-infrared frequencies. The surface conductivity model, electromagnetic wave propagation in single and multi-layer graphene, and also the effect of multi-layer graphene stacking on surface conductivity, along with the extraction of effective complex graphene permittivity, is investigated in this section. Kubo’s formula can be employed to calculate the surface conductivity of an infinite graphene sheet. The edge effects are not considered, which is experimentally proved in , stating formula , the surcµ is the Fermi level  of the graphene sheet, damping constant is represented by cΓ = Fq ħv2/cµµ, where the Fermi velocity is Fv = 106 m·s−1, and electron mobility is being denoted by µ = 104 m2·V−1s−1. On the other hand, interband part of graphene conductivity dominates at high frequencies and it can be formulated asIn the infrared region, intraband contributions control the properties of graphene. If the intraband part of graphene conductivity is taken into consideration, and then in the absence of a magnetic field and eliminating the spatial dispersion effect. The surface conductivity of graphene can be approximated by the Drude model ,(3)σintt,m,b denotes top, middle, bottom layers), It is worth pointing out that in this article, multi-layers of graphene in stack form are deposited on the top of the dielectric substrate, and a gold metal layer is to be sandwiched between two graphene stacks by forming hybrid graphene-metal antenna stack configuration. Each graphene stack is composed of three layers of graphene. Consequently, to calculate the conductivity of multi-layer graphene, it is assumed as the three layers of graphene were closely situated inside the stack. The effect of the dielectric substrate is strictly removed to find the conductivity of the tri-layer graphene stack. The approach of electrostatic gate bias  is being through ,(8)ns=2cµ) are recognized for each of the graphene sheets, the complex conductivity of the graphene stack metal-hybrid structure can be extracted asOnce the Fermi energies (sn of the film. Equation (8) correlates the carrier density and chemical potential of graphene. Contrarily, the carrier density is generally associated with the applied external electrostatic bias field. Consequently, the chemical potential is identified with applied biasing voltage through carrier density [cµ and gV is given by [gV is the bias voltage applied across graphene sheets. cµ = 0.1 is low; however, as the chemical potential is raised to cµ = 0.4 eV, the conductivity obtained almost spans a wideband of frequency. Additionally, the increase in chemical potential provides tunable conductivity characteristics.Chemical potential is a basic factor that can be progressively controlled by either chemical doping or electrostatic gate biasing. It should be noted that the chemical potential of the monolayer graphene depends on the carrier density  density . The gat density . In a gr density . The expgiven by ,(11)EF=The thickness of graphene is supposed to be very thin, with the goal of getting the volumetric conductivity of graphene. Assuming dependence of time-harmonic on all EM fields, the equivalent complex permittivity can be derived from Maxwell’s equation ne sheet .(12)εg to the antenna geometry reduces the electrical (quantum) tunneling from the sandwich graphene-metal stack to the graphene reflector [2 substrate functions as a reflector, where the absorption of the stacked antenna structure can be expressed as A graphene-based stack metal hybrid antenna is designed in the infrared region, specifically at 33 THz in the far-infrared region. or layer  between eflector , and theeflector . The golT = 300 k, respectively. Furthermore, increasing the surface conductivity of graphene by applying gate voltage across graphene stack results in the high interaction of metallic plasmons with graphene plasmons, which in turn increases the absorption in the graphene-metal antenna.The structure is simulated through a finite-difference time-domain (FDTD) computational solver in CST studio to hypothetically investigate the optical characteristics of the proposed design. A linearly polarized transverse magnetic (TM) plane wave . The incidence waves have the angular polarization ‘θ’ in the x-axis direction with a frequency range of 28–34 THz, in order to excite the graphene-metal antenna structure. In the simulation setup, the x-axis boundary is set to a perfect electric conductor, while a perfect magnetic conductor boundary is applied along the y-axis. The thickness of graphene is set to ≈1 nm, because the stack is composed of three graphene layers. To get better performance, the characteristics parameters of graphene are optimized by setting the chemical potential value as 0.3 eV, relaxation time as 0.1 ps, and temperature sppk propagating along the hexagon is related by sppk = n/R, where R is the radius of the hexagon and n is the mode order. In the considered frequency range, the surface plasmon in graphene approximately satisfies The dimensions of the designed antenna model are 15 × 15 um, but to perform parametric study and analyze the effect of various geometric parameters, i.e.,  on the performances of the antenna are systematically studied. Larger absorption is achievable by employing multilayer graphene with metallic and dielectric stackings. The proposed graphene-metal antenna has unique and exceptional functionalities; which, firstly, it can highly confine the electric field and enhance absorption, and secondly, it provides the tunability of surface plasmon resonance at a wide range of far-infrared frequneices. L represents the length, D denotes the diameter of the proposed antenna, and Equation (13) delivers a rough estimation of surface plasmon resonance and the tuning of resonance frequency with Fermi energy instead of varying the geometrical size of the graphene antenna. This property of graphene antenna makes it more useful then metallic optical antennas. Similarly, the plasmon resonance of nanoantennas can be firmly affected by using different dielectric substrates. Accordingly, in the proposed investigation, the graphene-metal antenna is designed on the stacked substrate, thereby surface plasmon resonance happens at2O3 layer and SiO2 is represented by oscillator 2. The charges in χ1(t) in oscillator 1 can be legitimately excited by the incident radiation source, and the charges χ2(t) can only be excited by the near field coupling of oscillator 1, they fulfill the following coupled equations [γ1 and γ2 are the damping rates in the oscillators 1 and 2, while ω1 and ω2 are the angular frequencies of the resonance modes in both oscillators, respectively. δ describes the detuning of resonance frequency from the dark plasmonic state to the radiative state. k represents the coupling coefficient between the dark plasmonic mode and radiative plasmonic modes. At the same time, g is the geometric parameter that represents the strength of coupling between the radiative plasmonic mode with the incident infrared radiation. Solving Equations (15) and (16), the susceptibility for the proposed antenna model can be expressed, as [The broadly utilized coupled oscillator model ,48 is adquations ,(15)χ¨1ssed, as ,(17)χe=d is the thickness of the stacked profile, aγ is the total absorption rate, while oA is directly related to oscillator strength. The transmission of the second oscillator should be blocked (γ2 = 0) and the mode damping rate γ1 should be equal to the absorption rate aγ in order to get unit absorption at the resonance frequency (ω), thus satisfying the critical coupling condition.Finally, the Lorentz profile for the absorbance at a resonant frequency can be directly calculated from the dispersion relation for the coupled Lorentz oscillator model ; the absThe graphene-metal antenna that was investigated in this article resonates at a broad range of frequencies  as graphene exhibits metal-like properties at the infrared region. Normally, various complex numerical and theoretical techniques are used to study the resonance behavior, performance, and validate the graphene antenna simulation results. For this purpose, an equivalent circuit model for the graphene-metal stacked antenna is developed. First, a simple graphene patch is analyzed while using a circuit model based on the partial element equivalent circuit (PEEC) technique to determine the resistance and inductance of graphene sheets. Second, the unit cell PEEC model is considered for a stack graphene hexagon patch to determine the resonant frequency. Lastly, the RLC equivalent circuit model is developed for the graphene-metal hybrid antenna to study the performance characteristics and resonance behavior.A PEEC method is employed in order to understand the surface resistance and inductive behavior of graphene stack at the top of gold hexagon functioning as a graphene radiator. The proposed PEEC method states that a normal graphene patch is composed of the addition of many PEEC cells. The cells are either rectangular or triangular for the graphene patch. Here, the hexagon symmetry is divided into rectangular cells, which is the most convenient way, and several systematic solutions exist for the equivalent circuit calculation . The PEEz = 0, and it can be formulated asHowever, the above equation relates to the tangential electric field and surface electric current through the surface conductivity of graphene. The impedance of the graphene sheet can be directly determined from the surface conductivity by considering impedance boundary condition at l) and width (w) can be expressed by applying the PEEC model on one rectangular unit cell, being expressed bygV at the unit cell PEEC equivalent circuit and neglecting the interband contribution of surface conductivity. The total surface resistance can be calculated, asThe From Equation (25), it is clear that, when intraband conductivity is considered, the reactance in Equation (23) is always positive, while L = pL + rL, p denotes the unit length of a single cell. Additionally, the propagation constant in both branches of the circuit model can be related to impedance and admittance bySurface plasmon resonant frequency for the graphene hexagon stack shape patch can be straightly calculated from the subsequent equivalent circuit model. effl is the effective length of the resonator and m is the integer. Finally, excluding losses i.e., (R = 0) and combining Equations (29) and (30) determines the resonant frequency for graphene hexagon through the proposed circuit model.Thus, the dispersion relation of the graphene hexagon patch can be determined as,2O3) between the graphene reflector and the first graphene stack, which can be expressed as l is the thickness of the Al2O3, respectively. Similarly, the reflection coefficient (Γ) can be determined from the input impedance, as,In this section, the transmission line (TL) model and the corresponding RLC resonant equivalent circuit model are developed to analyze the performance of the designed antenna, respectively, in The resonance frequency of the proposed RLC equivalent circuit can be formulated as,L is the inductance, R is the resistance corresponding to the resonance frequency of the circuit, and S11) frequency response, the quality factor at a random point in the frequency range can be expressed by the following equationFrom Equation 34), it is clear that the resonance frequency of the circuit is dependent on the values of L and C. Furthermore, the quality factor is studied for the proposed RLC circuit, which has an inverse relationship to antenna bandwidth. Accordingly, unloaded quality factor , it is cFrom Equation (36), it can be seen that the quality factor is directly related to the bandwidth of the antenna at the resonance frequency a’ value at the frequency ‘af’ with reflection magnitude can be calculated asThe correction coefficient ‘The graphene-metal plasmonic antenna has been excited with plane wave having a frequency range of 30–34 THz, in investigating the characteristic performance of the proposed graphene-metal stack antenna. The parametric optimization of the graphene and the corresponding frequency responses are obtained while using Finite-difference time-domain (FDTD) solver in the CST studio. In achieving better results, the mesh grid in numerical simulations is set to the minimum cell size of 0.02 um, therefore, generating a fine mesh across the geometry. Furthermore, in the RLC equivalent circuit that is illustrated in The multilayer graphene complex conductivity that is dependent on the frequency is calculated through the Kubo formula, as depicted in S11), as shown in S11 value of −30 dB, as represented by the blue line in the S11 value −22.5 dB. The shifting of frequency is due to the effective coupling between graphene plasmons and metallic plasmons. This effect is noticeable at high frequencies ranges, which also provide the frequency tunability feature to metallic nanoantennas. The chemical potential and relaxation time of the graphene stacks is set to 0.3 eV, and 0.3 ps, while the thickness of the gold hexagon layer is 0.4 um, while the thickness of the Al2O3 separation layer is 0.5 um. Finally, placing the second graphene stack on the top of the gold layer completes the hybrid geometry of the proposed antenna, and the structure becomes a slab of repeating substrate, metal, and graphene stacks, as illustrated in The surface plasmon resonance of the proposed simulated graphene-metal stack antenna is described by the reflection coefficient (FE), plays a significant role in controlling the complex surface conductivity of graphene. The chemical potential of the graphene sheets is tuned in the range of 0 eV to 0.3 eV by applying external electrostatic gate voltage across the graphene sheet, as shown in S11 is improved along with frequency tuning. At 32 THz, the resonance peak touches the −10 dB line, which ensures the antenna matching condition. This dramatic right shift of the frequency is directly related to the chemical potential of graphene layers in stacks. Additionally, the S11 resonance peaks accomplish better values as the chemical potential raises. With the chemical potential of 0.3 eV, the antenna attains the resonance peak with S11 of −23 dB at 33 THz. It should be noted that the value of S11 at 0.3 eV in Chemical potential, which is also known as Fermi level , the dissipated and radiated contributions are denoted by subscripts l and r. The dissipation impedance matrix Zl describes the complex surface conductivity of graphene. Similarly, the modal input admittance can be expressed with respect to the characteristic current [In this section, characteristic mode analysis has been demonstrated to reveal the total and modal input impedance and efficiency of the proposed graphene-based antenna. The natural resonant capability of complex graphene-based structures is directly related to the linear superposition of decomposed modes of impedance and radiation efficiency. Multiple modes of the antenna resonance can be acquired by solving integral equations on the antenna geometry in a single simulation, which has the advantage of less computational requirements. Furthermore, the impedance matrix of graphene-based antennas is very dissimilar from that of optical metallic antennas. The desired substrate properties should be carefully taken into consideration, along with the lossy and reactive behavior of the dielectric substrate material. The characteristic modes of the graphene-based antenna can be calculated by resolving the eigenvalues for the impedance matrix  . While the second and fourth modes are excited with the same waves, but with the wave vector propagating parallel to the antenna surface (y-polarized). The total input impedance of the proposed antenna is investigated based on characteristic modes with different excitation modes. Furthermore, at 0.3 ps the input impedance becomes more significant and the resonance of the antenna appears at 32.6 THz, because the wave vector is propagating parallel to the antenna surface. The higher input impedance is obtained at 0.7 ps, which is also in good agreement with resonance frequency with a small redshift. However, at mode 4, when the relaxation time is set to 1 ps, the antenna has zero reactance at the desired frequency, as shown in The modal input admittance outcomes from the simulation also expose the resonant condition of the proposed graphene-metal antenna. Additionally, radiation efficiency analysis that is based on the characteristic mode method is analyzed since efficiency is the key factor of the graphene antenna. 2O3 spacer. Using a substrate layer between the mirror and first graphene stack provides a wide range of tunable surface plasmons excitation in the graphene layers. When incident light strikes the top graphene stack, it then excites plasmons propagating modes along with the excitation of localized surface plasmons in the gold metallic structure. These localized surface plasmons trap the light energy in the near field, which leads to stronger EM confinement and enhanced absorption. The graphene surface that is below the gold layer can absorb some of the light from the interaction of graphene and gold plasmons and it can achieve unity absorption. The interband absorption of the stacked graphene can be greatly enhanced by the effect of metal doping and the increase of the Fermi energy with bias voltage. In the proposed stacked structure, the resonance S11 is totally caused by the graphene-metal sandwich, if the total absorption of the antenna is designed at frequency S11 can be greatly enhanced by increasing the FE through the electrostatic doping [FE = 0.3 eV is obtained through a potential of 5 V.The optical absorption enhancement of graphene-based antennas, along with the tuning of optical absorption at the broad spectral range, particularly far-infrared, stays problematic and provides an extremely exhaustive task. The limitation of low optical absorption in the graphene-based antenna is overcome by employing multilayer graphene in stacking configuration in the antenna geometry. The proposed technique allows for the antenna to achieve higher absorption along with tunability at the broad spectral range, even at terahertz to mid-infrared. The graphene stack on the top of the gold hexagon has the advantage of exciting surface plasmons propagating modes, which results in high EM field confinement. Furthermore, the absorption of multilayer graphene is enhanced by sandwiching the gold hexagon between graphene stacks, which also allows for the propagation of plasmons and plasmonic light trapping to increase the absorption. The acquired unity absorption  is tunable in a band starting from 30 THz to 34 THz. The tunability is realized by applying gate voltage across the graphene reflector being separated by the first graphene stack with an insulator Alc doping . This tuc doping ,(42)σ. From The coupling coefficient and quality factor with different relaxation time are calculated from the equivalent circuit parameters, as presented in 2O3 is deposited on the top of the graphene hexagon patch and it will be subjected to the previous photo-lithography procedure to make the Al2O3 hexagon layer. Secondly, the graphene-gold sandwich structure is to be fabricated on the top of the Al2O3 hexagon. For the graphene stacks, the synthesis and transfer process will be repeated. Later, the gold hexagon layer will be deposited on the first graphene stack, followed by the photolithography and metal etching to construct the gold hexagon. Finally, the second graphene stack will be transferred to the top of the antenna, which will complete the fabrication of the proposed antenna.The complex geometric structure of the proposed graphene-metal stack hybrid antenna has great realization in the application, such as infrared sensing and imaging due to the enhanced absorption characteristics far-infrared region. This section is focused on the practical consideration of the proposed graphene-metal antenna and antenna integration with optoelectronic devices for various photonic utilizations. For the practical implementation, the complex fabrication techniques of the graphene-based antenna may raise specific challenges. Regarding the fabrication process, a high-quality multi-layer graphene can be grown on copper foil through the chemical vapor deposition (CVD) process. Once the multilayer graphene is grown, then graphene can be transferred on the desired silicon/silica substrate with the aid of polymethyl methacrylate (PMMA) by using the transfer process. To this stage, the substrate containing graphene sheets is subjected to a photolithography process to pattern graphene into a hexagon structure. First, the chrome mask will be fabricated. As the size of the antenna is in micrometers, it can be easily patterned through photo-lithography with high precision under mask aligner environment. After the patterning process, the unwanted area of the graphene is etched away to obtain a hexagon patch of composed graphene layers. In this way, simple graphene hexagon patch plasmonic antennas could be realized. However, for the graphene-metal stack model, certain additional steps of fabrication are needed in order to complete the proposed structure. Now, taking it one step further, a layer of Al2 substrate. The tuning of chemical potential, which results in frequency reconfiguration, can be realized by applying an electrostatic gate voltage. Additionally, the tuning range of chemical potential 0 eV to 0.4 eV can be practically realized, as this range met the theoretical limit of the maximum Fermi energy level for various substrates.Additionally, the performance of the proposed antenna greatly depends upon the graphene chemical potential and relaxation time. In the simulation of the proposed graphene-metal antenna, the graphene is tuned with the relaxation time range broadly used in the literature ,57 obtaiIn conclusion, an efficient hybrid graphene-metal plasmonic antenna comprised of a multilayer graphene stacks, has been investigated in order to analyze the resonance tunability and enhancement of optical absorption. The simulated reflection spectra reveal that the hybrid stack structure of the plasmonic antenna has a surface plasmon resonance at 33 THz when the chemical potential is 0.3 eV. The resonance of the antenna can be dynamically tuned by controlling the chemical potential of graphene through electrostatic gating. The resonance peak is actively tuned from 30 THz to 34 THz when the chemical potential has been increased from 0 eV to 0.3 eV. The addition of graphene layers in stack formation results in the absorption enhancement and reaching almost unity. The unity absorption realized with the proposed graphene-metal hybrid structure due to the synergistic effect of localized surface plasmons enhancement between gold and graphene. Additionally, the high absorptivity is broadly tunable when the incidence angle of the excitation source is varied from 0° to 90°. Moreover, the study of the antenna with characteristics mode analysis provide a physical understanding of the hybrid plasmonic antenna. It is shown that the integral equation solver accurately determined the input impedance and radiation efficiency using characteristic modes. Finally, an equivalent resonant circuit model is designed to validate the proposed hybrid design. The excellent agreement of the simulation results with equivalent circuit model results illustrates that hybrid plasmonics antenna is highly applicable for infrared sensing and imaging applications.


Idiopathic pulmonary fibrosis (IPF) is a fibroproliferative disorder limited to the lung. New findings, starting from our proteomics studies on IPF, suggest that systemic involvement with altered molecular mechanisms and metabolic disorder is an underlying cause of fibrosis. The role of metabolic dysregulation in the pathogenesis of IPF has not been extensively studied, despite a recent surge of interest. In particular, our studies on bronchoalveolar lavage fluid have shown that the renin–angiotensin–aldosterone system (RAAS), the hypoxia/oxidative stress response, and changes in iron and lipid metabolism are involved in onset of IPF. These processes appear to interact in an intricate manner and to be related to different fibrosing pathologies not directly linked to the lung environment. The disordered metabolism of carbohydrates, lipids, proteins and hormones has been documented in lung, liver, and kidney fibrosis. Correcting these metabolic alterations may offer a new strategy for treating fibrosis. This paper focuses on the role of metabolic dysregulation in the pathogenesis of IPF and is a continuation of our previous studies, investigating metabolic dysregulation as a new target for fibrosis therapy. Idiopathic pulmonary fibrosis (IPF) is a severe chronic interstitial lung disease (ILD) of unknown aetiology , limitedThe role of metabolic dysregulation in the pathogenesis of IPF has not been investigated in detail. Several years ago, our research group applied proteomic methods to the bronchoalveolar lavage (BAL) fluid of IPF patients, observing the alteration of certain molecular mechanisms linked to metabolism and fibrosis ,19,20,21Although IPF is considered to be limited to the lungs and most pathogenetic hypotheses centre on the respiratory system, our results and those of other authors suggest that the disease has systemic elements. We focus on these aspects in the present paper, in particular on the role of metabolic dysregulation in the pathogenesis of IPF.Proteomic and bioinformatic analysis performed by us on the BAL from IPF patients compared with the BAL of other ILDs, and healthy controls highlighted various dysregulated proteins related to transcriptional factors such as NF-kB, PPAR-γ and c-myc. In particular, the interactomes showed fatty acid binding protein 4 (FABP4), retinol binding protein 4 (RBP4), haptoglobin (HP), apolipoprotein AI (APOAI) and zinc-alpha-2-glycoprotein (ZA2G), related to PPAR-γ; while angiotensinogen (ANGT), surfactant A2 (SP-A), alpha-2-HS-glycoprotein (FETUA), alpha-1-antichymotrypsin (AACT), peroxiredoxin 1 (PRDX1), beta 2 microglobulin (B2M), glutathione S transferase 1 (GSTP1) and transthyretin (TTHY) were related to NF-kB. C-myc was linked to PRDX1, albumin (ALBU) and annexin II (ANXA2) deregulation ,18. ThesIn 2013 and 2014, our proteomic studies on the BAL of IPF patients, compared with the profiles of healthy smoker and non-smoker controls, reported a dysregulation in proteins involved in the RAAS . In partMoreover, the production of ANGT and Ang II observed in white adipocyte tissue reveals the role of RAAS in promoting adipocyte hypertrophy and decreasing the number of small insulin-sensitive adipocytes . These dSOD2 mRNA expression was markedly suppressed in both systemic sclerosis-ILD and IPF fibroblasts, compared with non-ILD controls, leading to an increasing trend in ACTA2 mRNA expression and cell proliferation [Our proteomic studies found dysregulated proteins such as HPT, transferrin, PRDX1, PRDX5, GSTP1, CERU and ALBU in the BAL of IPF patients; these proteins are related to hypoxia, oxidative stress and iron metabolism ,19. The feration .The hypoxic stimulus characterizing IPF also leads to pulmonary hypertension (PH) by progressive vasoconstriction and vascular remodelling. Indeed, hypoxia induces the proliferation and differentiation of pulmonary artery adventitial fibroblasts into myofibroblasts that ultimately, stimulate the recruitment of inflammatory cells and the release of key regulators. The proliferation and differentiation of pulmonary artery adventitial fibroblasts during chronic hypoxia are mainly dependent on the signal transduction of the p38 pathway and its downstream mediator, HIF-1 .Studies on mesenchymal stem/stromal cells, also used in IPF therapy , have shAnother possible source of reactive oxygen species in IPF is the accumulation of iron in the lower respiratory tract, also reported to be induced by smoking. Disordered iron regulation, as our findings suggested, may play a central role in the pathogenesis of oxidative stress-induced microscopic injury, triggering epithelial cell damage and fibroblast proliferation . PatientAn intriguing interactome that we observed in our work on IPF concerned FABP4, RBP4, HP, APOAI and ZA2G, related to peroxisome proliferator-activated receptor gamma . This inRBP4, another protein that we found dysregulated in BAL samples, is a cytokine primarily produced by adipose tissue and connected to PPAR-γ. It is the main transport protein for retinol in the blood. Thus, RBP4 is known to regulate lipids, glucose metabolism and insulin resistance . RetinolTranscriptional factor PPAR-γ, related to our differential proteins, is the master regulator of adipogenesis and has antifibrotic effects initiated by blocking TGF-β in organs such as the skin, lung and heart . In adipThe action of PPAR-γ is likewise seen in lipofibroblast differentiation, where it prevents oxidative lung injury, promoting mesodermal differentiation and antioxidant defences. PPAR-γ is also reported to indirectly stimulate lung surfactant production, so that the lung can adapt to atmospheric oxygen . PPAR-γ An even greater number of studies highlight the lipid metabolic dysregulation in the onset and development of IPF, focusing on PPAR-γ action and the production of adiponectins and leptins . Serum cInterestingly, in line with our findings regarding LXR/RXR and FXR/RXR and the differentiation and activation of macrophages in IPF , Venosa Lipid metabolism depends on proper mitochondrial function and correct interaction between mitochondria and ER. Correct outer mitochondrial membrane fusion is therefore essential to connect the intracellular network in order to regulate and meet cell metabolic demands. In turn, mitochondrial fusion is required for oxidative phosphorylation, mitochondrial DNA biogenesis, mitophagy regulation and metabolic adaptation. Chung et al. reported that mitochondrial fusion and lipid metabolism are closely linked to regulate alveolar epithelial cell II injury and subsequent fibrotic remodelling by damaging surfactant lipid production. Surfactants are a lung surface-active lipoprotein complex, containing about 90% lipids, that reduces lung surface tension, prevents the alveoli from collapsing, and plays a critical role in immune regulation ,92. Capohttps://portal.genego.com/) in order to build the interactome reported in Proteomics coupled with systems biology studies, performed on BAL samples from patients with IPF, healthy controls, other ILDs and different phenotypes of IPF, has brought to light a number of interesting molecules that seem to be involved in the onset of fibrosis via mechanisms related to metabolic dysfunction ,19,20,45Following this suggestion, we also performed a bioinformatic analysis on MetaCore software by the tool “Drug look up for your data” visualizing specific drug molecules  related Based on our own as well as other findings, a fine balance between lipid metabolism and wound healing mechanisms leading to fibrosis is suggested in IPF onset and development. Lipid metabolism as well as glucose anabolism and catabolism are dramatically subject to certain environmental and genetic influences, which may alter their equilibrium, leading to metabolic or fibrotic disorders. To corroborate these observations, various widespread diseases associated with the onset of fibrosis, including IPF, cirrhosis, hepatitis, non-alcoholic steatohepatitis, chronic kidney disease, myocardial infarction, heart failure, diabetes and scleroderma, share common metabolic pathways ,94,95,96Mitochondrial dysregulation is linked to lipid accumulation in the lungs, influencing the lipid composition of pulmonary surfactant, which is reported to be an extracellular lipid reservoir, uniquely susceptible to direct and continuous exposure to environmental oxidants, inflammatory agents and pathogens. Surfactant lipids have been recognized as bioactive molecules that maintain immune quiescence in the lung but can be remodelled by the inhaled environment into neo-lipids, which mediate key roles in inflammation, immunity and fibrosis. Since surfactant composition is sensitive to circulating lipoproteins, the lipid milieu of the alveoli should be recognized as susceptible to diet and common systemic metabolic disorders .Idiopathic pulmonary fibrosis has long been considered to be limited to the lung compartment, although different pathways related to metabolic alterations in IPF are also typical of diseases affecting other organs. Fibrosis is thought to begin in the lung as microvascular injury, leading to endothelial cell damage and alveolar epithelial injury, accompanied by the release of cytokines, chemokines and growth factors, and the induction of the coagulation cascade, triggering positive feedback that amplifies all these molecular responses . HypertrAll the metabolic pathways described are implicated in the pathogenesis of IPF through the induction of the onset and development of fibrosis. Little data are available on the IPF of metabolic pathways, leading to alterations in lipid and glucose metabolism and mitochondrial dysfunctions. Research is increasingly focusing on this new view of IPF as a systemic disorder. The altered metabolism of carbohydrates, lipids, proteins and hormones has been documented in the lung, liver and kidney fibrosis. Correcting these metabolic alterations is becoming a new strategy for antifibrotic therapies. Understanding the pathology of IPF from different but interconnected points of view, namely the exposome, genetic predisposition and dysregulated metabolic pathways, could be the key to a holistic picture of this disease.