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Stochastic analysis of the absorbed power density (APD) on skin surface exposed to radiation of halfwave dipole at 10, 30 and 90 GHz and for different antenna‐body distances is presented. Skin tissue is modeled as a half‐space consisting of one layer (skin) or three layers (skin, fat and muscle) whose permittivities and conductivities are uncertain. Deterministic part is based on numerical solution of Pocklington equation via Galerkin Bubnov Indirect Boundary Element method (GB‐IBEM) and numerical integration of the corresponding field integrals. Uncertainty from tissue electric parameters is propagated to APD via non‐intrusive Stochastic Collocation method (SCM) in order to compute stochastic moments of APD. For 1‐layered model APD stochastic moments are computed with 3 deterministic simulations. On the other hand APD mean and variance for 3 layered model are successfully computed with 13 deterministic simulations while skewness and kurtosis require 85 deterministic simulations. The ratio of APD standard deviation and mean decreases with frequency thus indicating that the uncertainty in the tissue electric properties has smaller effect on APD uncertainty at higher frequencies. Finally, sensitivity analysis carried out for both 1‐layered and 3‐layered models indicates the same conclusions. At 10 GHz skin permittivity and conductivity are the two most important parameters. However, as frequency increases the impact of skin conductivity prevails. This indicates that in frequency range 10–90 GHz the APD uncertainty quantification and sensitivity analysis can be carried out by using only 2‐dimensional stochastic model. Key Points: The reported values for tissue permittivity and conductivity are scattered, thus introducing the uncertainty in the output absorbed power density (APD)Stochastic Collocation can assure the computation of APD stochastic moments with good accuracy at relatively low number of simulationsSensitivity analysis shows that the impact of the inner layers' permittivity and conductivity is negligible [ABSTRACT FROM AUTHOR]

This paper proposes a method to reduce phantom shell effects that occur during the absorbed power density (APD) derivation using a negative permittivity material (NPM). In this study, APD is examined as a primary parameter to assess the effectiveness of the proposed method, especially following the introduction of APD above 6 GHz, in accordance with 2020 ICNIRP guidelines. As the frequency increases, the impact of the phantom shell can affect APD measurement results. To investigate this, a dipole antenna operating in the $6\sim 10$ GHz frequency range was used as the radiation source. Therefore, this study proposes a method to reduce effects by using NPM. The selection of the NPM is achieved through input impedance calculations method. Simulation results indicate that before applying the proposed method, the APD difference between the presence and absence of the phantom shell ranged from 20.6% at 6 GHz (W/ shell =100, W/o shell =82.9 W/m2) to 69.3% at 10 GHz (W/ shell=52.3, W/o shell=30.9 W/m2). After applying the method, these differences reduced to 6.9% at 6 GHz (proposed method=77.2, W/o shell=82.9 W/m2) and 13.5% at 10 GHz (proposed method=35.1, W/o shell=30.9 W/m2). This study is the first to highlight the impact of phantom shell effects on APD, revealing potential overestimations in the 6-10 GHz range and suggesting that these effects may worsen at higher frequencies. The proposed method effectively addresses these issues within current standards while providing insights for future standards development in higher frequency bands.

Background/Aim: The widespread use of fifthgeneration 5G millimeter-waves (MMW) generates concern about potential adverse health effects. The latest international guidelines for MMW exposure adopt an absorbed power density (APD) of 200 W/m2 to avoid a local temperature rise of 5˚C in human tissues as an operational adverse health effect threshold. However, because APD is estimated by simulations using human tissue models, it is unknown whether a similar value can be confirmed for living tissues. The aim of this study was to investigate the relationship between APD and skin temperature rise in vivo, and to validate the estimated values. Materials and Methods: The rat dorsal skin was locally exposed to a 26.5 GHz quasiMMW (qMMW) for 18 min using a patch antenna. The qMMW exposure intensities estimated by dosimetry were set to 0-500 W/m2 of APD. The temperatures in the dorsal skin and rectum were simultaneously measured during exposure. Results: The qMMW-induced local temperature increase at different sites. The dorsal skin temperature increased by approximately 11.3˚C at a maximum intensity of 500 W/m2, but the rectal temperature increased by only 0.6˚C, indicating highly localized effects of exposure to rats. A significant correlation was observed between APD and skin temperature rise. The relationship provided a linear regression model, and a temperature rise of less than 5˚C was estimated in the skin exposed to 200 W/m2 of APD. Conclusion: These results suggest that the operational threshold for the MMW exposure guidelines is valid under the present experimental conditions using rats. [ABSTRACT FROM AUTHOR]

This study presents an investigation of clothed human skin exposure to obliquely incident electromagnetic waves at 60 GHz. We clarified the combined impacts of the cloth material, incidence angle, and polarization on the assessment of transmittance and absorbed power density (APD) at the skin surface. A Monte Carlo simulation was conducted considering the thickness variation of the cloth material and skin tissue. For the case of transverse magnetic™ wave exposure, the transmittance increases with increasing incident angle up to the maximum transmittance angle in the range from 60 to 80°, which is known as the Brewster effects, regardless of textile materials and air gap between cloth and skin. The air gap results in a periodic fluctuation of the APD, where the variation is almost within 1 dB when the incident power density is constant and the incident angle is smaller than 40°. Our results also show that as the air gap increases to 2.5 mm, i.e., half-wavelength at 60 GHz in the air, the APD within the skin surface covered by typical cloth materials increases up to 40% compared with that of bare skin. Although the use of several cloth materials may increase the transmittance and APD in oblique incidence scenarios, all the results of the APD do not exceed the basic restriction for local exposure, demonstrating that the current guidelines for human exposure to electromagnetic fields are appropriate for preventing the excessive exposure at 60 GHz considering the impacts of oblique incidence angles and cloth materials.

Background/aim: The widespread use of fifth-generation 5G millimeter-waves (MMW) generates concern about potential adverse health effects. The latest international guidelines for MMW exposure adopt an absorbed power density (APD) of 200 W/m 2 to avoid a local temperature rise of 5°C in human tissues as an operational adverse health effect threshold. However, because APD is estimated by simulations using human tissue models, it is unknown whether a similar value can be confirmed for living tissues. The aim of this study was to investigate the relationship between APD and skin temperature rise in vivo, and to validate the estimated values., Materials and Methods: The rat dorsal skin was locally exposed to a 26.5 GHz quasi-MMW (qMMW) for 18 min using a patch antenna. The qMMW exposure intensities estimated by dosimetry were set to 0-500 W/m 2 of APD. The temperatures in the dorsal skin and rectum were simultaneously measured during exposure., Results: The qMMW-induced local temperature increase at different sites. The dorsal skin temperature increased by approximately 11.3°C at a maximum intensity of 500 W/m 2 , but the rectal temperature increased by only 0.6°C, indicating highly localized effects of exposure to rats. A significant correlation was observed between APD and skin temperature rise. The relationship provided a linear regression model, and a temperature rise of less than 5°C was estimated in the skin exposed to 200 W/m 2 of APD., Conclusion: These results suggest that the operational threshold for the MMW exposure guidelines is valid under the present experimental conditions using rats., (Copyright © 2023, International Institute of Anticancer Research (Dr. George J. Delinasios), All rights reserved.)

Microwave-assisted extraction (MAE) is a promising technique for the extraction of flavonoid compounds from plants. However, it is difficult to scale up due to the complex mass transfer involved. This has prompted the study of parameters for scaling up the system by considering energy-related parameters, i.e. the nominal power density and the absorbed power density ( APD). Modeling of MAE of flavonoid compounds from cocoa ( Theobroma cacao L.) leaves using the film theory model was performed for this purpose. Operating parameters such as the sample particle size, the solvent-to-feed ratio, and the microwave irradiation power were also included in the kinetic study. The APD exhibited its aptitude as scaling-up parameter as it can characterize both the extraction kinetics and the extraction yields of MAE. Furthermore, it can be used as a reference for predicting the optimum extraction time of MAE under various heating conditions. [ABSTRACT FROM AUTHOR]

Abstract: The intrinsic microwave power and energy required for optimizing MAE was investigated for the extraction of active compounds from cocoa (Theobroma cacao L.) leaves at various extraction scales. To carry out this investigation, an optimization method based on absorbed power density (APD) and absorbed energy density (AED) were developed based on the extraction mechanism of MAE using sequential single factor experiments. The optimized results are consistent with those obtained by the conventional optimization method using response surface methodology (RSM) and also comparable with that of the optimized Soxhlet extraction. The main advantage of the method is that the intensive optimum conditions obtained at solvent to feed (S/F) ratio of 50ml/g, APD of 0.3W/ml and AED of 300J/ml are capable of determining the specific optimum operating conditions (S/F ratio, power, time) of the MAE at various scales of 100–300ml with great accuracy. [Copyright &y& Elsevier]

Abstract: A modeling technique based on absorbed microwave energy was proposed to model microwave-assisted extraction (MAE) of antioxidant compounds from cocoa (Theobroma cacao L.) leaves. By adapting suitable extraction model at the basis of microwave energy absorbed during extraction, the model can be developed to predict extraction profile of MAE at various microwave irradiation power (100–600W) and solvent loading (100–300ml). Verification with experimental data confirmed that the prediction was accurate in capturing the extraction profile of MAE (R-square value greater than 0.87). Besides, the predicted yields from the model showed good agreement with the experimental results with less than 10% deviation observed. Furthermore, suitable extraction times to ensure high extraction yield at various MAE conditions can be estimated based on absorbed microwave energy. The estimation is feasible as more than 85% of active compounds can be extracted when compared with the conventional extraction technique. [Copyright &y& Elsevier]

The problem of determining electromagnetic fields (EMF), absorbed power density (APD), and specific absorption rate (SAR) inside arbitrarily shaped biological bodies is considered. The biological bodies are assumed as the human body or human brain illuminated by a plane wave, and EMF, APD, and SAR are calculated inside the biological bodies. The EMF, APD, and SAR theoretical derivation inside the biological bodies by a three-dimensional transmission line matrix (TLM) method with asymmetrical condensed node is given. The combination of the method of moment (MoM) and generalized multipole technique (GMT) is used to determine the field inside the biological bodies. A complete dispersion analysis is given for the TLM and combination of MoM and GMT. In TLM, wave amplitudes inside electric and magnetic field components represent the electromagnetic field. The correct mapping between the wave amplitudes and field components is described by the cell boundary mapping. The combination of MoM and GMT method is based on domain integral representation of the field inside the body. Both methods involve an iterative minimization of the defect between the number of cells and the field calculated by integral representation. The two algorithms are compared. The methods employed the same initial guess and a priori information that the characteristic function is nonnegative. [ABSTRACT FROM AUTHOR]

This study presents an investigation of clothed human skin exposure to obliquely incident electromagnetic waves at 60 GHz. We clarified the combined impacts of the cloth material, incidence angle, and polarization on the assessment of transmittance and absorbed power density ( APD ) at the skin surface. A Monte Carlo simulation was conducted considering the thickness variation of the cloth material and skin tissue. For the case of transverse magnetic™ wave exposure, the transmittance increases with increasing incident angle up to the maximum transmittance angle in the range from 60 to 80°, which is known as the Brewster effects, regardless of textile materials and air gap between cloth and skin. The air gap results in a periodic fluctuation of the APD , where the variation is almost within 1 dB when the incident power density is constant and the incident angle is smaller than 40°. Our results also show that as the air gap increases to 2.5 mm, i.e., half-wavelength at 60 GHz in the air, the APD within the skin surface covered by typical cloth materials increases up to 40% compared with that of bare skin. Although the use of several cloth materials may increase the transmittance and APD in oblique incidence scenarios, all the results of the APD do not exceed the basic restriction for local exposure, demonstrating that the current guidelines for human exposure to electromagnetic fields are appropriate for preventing the excessive exposure at 60 GHz considering the impacts of oblique incidence angles and cloth materials., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict ofinterest., (Copyright © 2022 Li and Sasaki.)

The introduction of new dosimetric quantities, in particular, epithelial or absorbed power density for frequencies above 6 GHz, in exposure guidelines and safety standards requires the development of new experimental assessment procedures for compliance testing. In this study, we propose to approximate the peak spatial-average absorbed power density (psS ab ) using the same measured data and algorithms that are used for determining the peak spatial-average specific absorption rate psSAR, which is currently limited to frequencies up to 10 GHz. The uncertainty component for the transformation of psSAR to psS ab was evaluated as less than 0.55 dB (13.5%) for any source as close as 0.02 λ from the tissue simulating media. The approach is easy to implement and allows determining compliance with the basic restrictions of the latest safety guidelines. In the next project, we will expand dosimetric probes, phantoms, and procedures for frequencies above 10 GHz. © 2021 Bioelectromagnetics Society., (© 2021 Bioelectromagnetics Society.)