Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> IV. SAR MEASUREMENT METHODOLGY <s> The interest in accurate dosimetric measurements inside phantoms that simulate biological bodies has burgeoned since several regulatory commissions began calling for or recommending the testing for compliance with safety standards of low power devices. This paper presents a newly developed, robot-based system that allows automated E-field scanning in tissue simulating solutions. The distinguishing characteristics of the system are its high sensitivity and its broad dynamic range (1 /spl mu/W/g to 100 mW/g) over the entire frequency range (10 MHz to over 3 GHz) used for mobile communications. The reproducibility of the dosimetric evaluations has been shown to be considerably better than /spl plusmn/5%. This has been accomplished by the use of an improved isotropic E-field probe connected to amplifiers with extremely low noise and drift characteristics in conjunction with digital processing of the data. Special emphasis has been placed on system reliability, user-friendliness and graphic visualization of data. <s> BIB001 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> IV. SAR MEASUREMENT METHODOLGY <s> There has been an explosive growth in the area of wireless communication. Over the world, hundreds of millions of subscribers are using mobile phones. International and national organizations have recommended limits for the protection of mobile phone users and standards are going to be established to certify the compliance of mobile phones with these limits. To ensure this conformity, numerical and experimental dosimetric analyzes are essential to evaluate the electric fields inside the user's head. These fields can not be measured near the mobile phone- the phantom interferes where they are a maximum and the use of interpolation and extrapolation is then necessary to evaluate the electric field components. This paper describes the interpolation and extrapolation methodologies, of the experimental sampled data in three dimensions, of the power absorbed in the whole volume of the head phantom. A new method to interpolate and extrapolate SAR measurements is presented. This technique, which is very fast and not very expensive in terms of required memory, is compared with other interpolation techniques which use splines or wavelets. <s> BIB002 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> IV. SAR MEASUREMENT METHODOLGY <s> This paper discusses the general suitability and possible limitations of an enhanced finite-difference time-domain (FDTD) simulation environment for straightforward and efficient RF design of complex transmitters. The study was conducted using a current commercially available multi-band mobile phone. Simulations were conducted in free space and with various dielectric loads, whereby different parameters were evaluated such as impedance, efficiency, far-field as well as near-field distributions of e-fields and h-fields, and the specific absorption rate (SAR). The results were compared to measurements. In addition, mechanical-design issues that showed a significant influence on the electromagnetic (EM) field behavior could be predicted by simulations and were experimentally reproduced. The accurate prediction of all essential performance parameters obtained by straightforward simulations suggests that appropriately enhanced software packages are suitable for device design in industrial research and development environments with few limitations, provided flexible graphical user interfaces (GUIs) and graded meshes combined with local grid-refinement schemes are available. <s> BIB003 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> IV. SAR MEASUREMENT METHODOLGY <s> The level and distribution of radiofrequency energy absorbed in a child's head during the use of a mobile phone compared to those in an adult head has been a controversial issue in recent years. It has been suggested that existing methods that are used to determine specific absorption rate (SAR) and assess compliance with exposure standards using an adult head model may not adequately account for potentially higher levels of exposure in children due to their smaller head size. The present study incorporates FDTD computations of locally averaged SAR in two different anatomically correct adult and child head models using the IEEE standard (Std. C95.3-2002) SAR averaging algorithm. The child head models were obtained by linear scaling of the adult head model to replicate the conditions of previous studies reported in the literature and also by transforming the different adult head models based on data on the external shapes of children's heads. The tissue properties of the adult and corresponding child head models were kept the same. In addition, modeling and experimental measurements were made using three spheres filled with a tissue-equivalent mixture to approximate heads of increasing size. Results show that the peak local average SAR over 1 g and 10 g of tissue and the electromagnetic energy penetration depths are about the same in all of the head models under the same exposure conditions. When making interlaboratory comparisons, the model and the SAR averaging algorithm used must be standardized to minimize controversy. <s> BIB004 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> IV. SAR MEASUREMENT METHODOLGY <s> This paper discusses the correlation between peak spatial-average specific absorption rate (SAR) and maximum temperature increase for antennas attached to the human trunk. Frequency bands considered are 150, 400, and 900 MHz, which are assigned for occupational communications. This problem is thoroughly investigated with the aid of Green's function. In particular, the effect of variation of thermal constants on the temperature increase is revealed by using one-dimensional model. Computational results suggests that one of the most dominant factors which affect the correlation between peak SAR and maximum temperature increase is blood flow in tissues. This is confirmed by considering a three-dimensional realistic human body model. Uncertainties caused by the calculation of peak SAR and the difference in the body model shape are also quantified <s> BIB005 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> IV. SAR MEASUREMENT METHODOLGY <s> Protocols and test procedures are specified for the measurement of the peak spatial-average SAR induced inside a simplified model of the head of users of certain handheld radio transceivers. These transceivers are intended to be used for personal wireless communications services, operate in the 300 MHz to 6 GHz frequency range, and are intended to be operated while held against the ear. The results obtained by following the protocols specified in this recommended practice represent a conservative estimate of the peak spatial-average SAR induced in the head of a significant majority of persons, subject to measurement and other uncertainties that are defined in this recommended practice. The results are representative of those expected during conditions of intended use of a handheld wireless device. It is not the intent of this recommended practice to provide a result representative of the absolute maximum SAR value possible under every conceivable combination of head size, head shape, handset orientation, and spacing relative to the head. The measurement of SAR induced in the external tissues of the head, e.g., the external ear (pinna), is not addressed in this document. This recommended practice also does not address the body SAR measurements typically required for wireless handsets. The following items are described in detail: measurement concepts, measurement techniques, instruments, calibration techniques, simulated-tissue (phantom) models, including homogeneous anatomically equivalent models of the human head and simple phantoms for validation of the SAR measurement system, and the limitations of these systems when used for measuring the spatial-peak mass-averaged SAR. Procedures for calibrating electric field (E-field) probes used for SAR measurements and assessing the SAR measurementand system uncertainties are provided in the annexes. This recommended practice is intended primarily for use by engineers and other specialists who are familiar with electromagnetic (EM) theory and SAR measurement techniques; it does not recommend specific SAR limit values since these are found in other documents. The benefits to the users include standardized and accepted protocols, validation techniques, and means for estimating the overall measurement uncertainty in order to produce valid and repeatable data. <s> BIB006 </s> Human Electromagnetic Field Exposure in Wearable Communications: A Review <s> IV. SAR MEASUREMENT METHODOLGY <s> Wearable electronics have become the norm over the last few years. Extensive use of wearable wireless devices (WWD) in greater proximity to the body has increased concern about potential biological effects due to the interaction of human tissues with electromagnetic (EM) fields. Human tissues absorb radiofrequency (RF) waves that are capable of affecting energy states at a molecular level, leading to unsafe effects. Remarkably, thermal effect due to the absorption of RF waves is a better biological manifestation than traditional specific absorption rate (SAR) values. In this study, we investigated the application of infrared thermography (IRT) to obtain temperature dynamics and reconstructed average SAR to evaluate the exposure compliance of WWDs. A microstrip-based monopole antenna was used to determine the biological effects of the interaction of EM waves with the body. SAR was obtained using EM field simulations and through reconstruction from thermal measurements with the use of bio-heat equations. The maximum average SAR on the skin was 50 mWkg-1 for the simulations and 54 mWkg-1 from reconstruction after IRT experiments. The maximum temperature change in both cases was observed to be less than 1 °C. The difference between the average SAR obtained through IRT and simulation tools was 8.9% on average. SAR determination from the information acquired using IR temperature dynamics can assess bio-compliance of modern wearable devices for various wireless applications. Bioelectromagnetics. 39:451-459, 2018. © 2018 Wiley Periodicals, Inc. <s> BIB007
Now, this section provides technical details on the standard methodology of SAR measurements for compliance tests. Manufacturers of EMF-radiating devices pay serious attention to the tests since any negative test result can require a design change that can negatively impact project cost and schedule  . A. Measurement Model 1) Complexity of SAR Modeling: The distribution of SAR in a biological body is complicated since the tissue constitution is differentiated by the body parts BIB005 . As such, computer simulations are often used to characterize the interaction between an antenna and a load for safety assessment. However, modeling of complex antenna-load structures to match realistic physical conditions using EMF simulations is not straightforward BIB002 BIB003 , and possible discrepancies between simulated and manufactured devices may undermine the accuracy of EMF safety assessment BIB001 . For this reason, although simulations are still popularly used to conduct initial evaluations BIB004 , the majority of EMF-emitting devices are tested using physical probes BIB006 . This setting with a physical probe is also known as a "conventional SAR measurement" system  . 2) Time-Average SAR Measurement: In a conventional SAR measurement system, a liquid-filled model is often used to represent electrical characteristics of body tissues on which a physical electric field probe is applied. Hence, in a conventional measurement setup, the invasiveness of the method, time consumed, and calibration requirements of the probe make the measurement cumbersome and inefficient BIB007 .