Theoretical and numerical assessment of maximally allowable power‐density averaging area for conservative electromagnetic exposure assessment above 6 GHz

The most recent safety guidelines define basic restrictions for electromagnetic field exposure at frequencies more than 6 GHz in terms of spatial‐ and time‐averaged transmitted power density inside the body. To enable easy‐to‐perform evaluations in situ, the reference levels for the incident power density were derived. In this study, we examined whether compliance with the reference levels always ensures compliance with basic restrictions. This was evaluated at several distances from different antennas (dipole, loop, slot, patch, and helix). Three power density definitions based on integration of the perpendicular real part of the Poynting vector, the real part of its three vector components, and its modulus were compared for averaging areas of λ2/16, 4 cm2 (below 30 GHz) and 1 cm2 (30 GHz). In the reactive near‐field (d < λ/(2π)), the transmitted power density can be underestimated if an antenna operates at the free space exposure limit. This underestimation may exceed 6 dB (4.0 times) and depends on the field source due to different coupling mechanisms. It is frequency‐dependent for fixed‐size averaging areas (4 and 1 cm2). At larger distances, transmission can be larger than the theoretical plane‐wave transmission coefficient due to backscattering between the body and field source. Using the modulus of the incident Poynting vector yields the smallest underestimation. © 2020 Bioelectromagnetics Society.

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“…These aspects are discussed, e.g. in Hashimoto et al [2017], Laakso et al [2017], Neufeld et al [2018], and Neufeld and Kuster [2018].…”

Section: Objectivesmentioning

confidence: 99%

Limitations of Incident Power Density as a Proxy for Induced Electromagnetic Fields

Christ

Samaras

Neufeld

et al. 2020

Bioelectromagnetics

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“…Therefore, the power deposited in a human would be enhanced compared with the power at normal incidence [22], [26]. However, only a few studies [19], [27], [28] have computed the relationship between IPD and surface temperature elevation in 3-D local exposure scenarios but not for different incident angles, although this relates better to the rationale for relating the exposure guidelines and product safety standards. Furthermore, the effectiveness of APD should be confirmed for additional cases [19], [20].…”

Section: Introductionmentioning

confidence: 99%

Skin Temperature Elevation for Incident Power Densities From Dipole Arrays at 28 Ghz

et al. 2020

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The relationship between skin temperature elevation and incident power density (IPD) from radio-frequency near-field exposure at 28 GHz for different angles of incidence is evaluated computationally in this study. The averaging scheme of the IPD is crucial for determining the maximum allowable exposure levels of wireless equipment to comply with certain standards/regulations. However, it is still unclear which component of the IPD (i.e., the norm or normal component to the human body) is more related the temperature elevation. In the case of four-element dipole arrays, the distances between the model and the antenna were 15 and 30 mm in transverse-electric-and transverse-magnetic-like polarized waves, respectively, and in the case of eight-element dipole arrays, the distances were 45 mm from the center of the array. From our computational results for four-and eight-element dipole arrays, we confirmed that the normal component of the IPD provides better correlation with the surface skin temperature, regardless of angle of incidence, particularly for smaller angles of incidence (<30 •). The enhancement of the ratio of the temperature increase to IPD was observed around the Brewster's angle, which is mainly attributable to the difference in transmittance at the body surface. This exposure scenario may not occur as the antennahuman distance was too large to consider compliance at the closest distance. In terms of output power, the most restrictive condition for compliance is shown to be normal incidence, suggesting the importance of compliance for such exposure scenarios. Furthermore, the absorbed power density proved to be an appropriate metric to monitor in relation to skin temperature elevation.

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“…) as described in Chahat et al []. The mass of the fabricated phantom was approximatively 230 g. Note that this homogeneous phantom does model the structure of the skin and in particular, the stratum corneum, which was shown to contribute to the reflection coefficient of the skin [Neufeld et al, ; Ziskin et al, ].…”

Section: Methodsmentioning

confidence: 99%

Exposure Assessment in Millimeter‐Wave Reverberation Chamber Using Murine Phantoms

Fall

Lemoine

Besnier

et al. 2020

Bioelectromagnetics

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This study deals with the design and calibration of the first mode-stirred reverberation chamber (RC) in the 60-GHz-band adapted for in vivo bioelectromagnetic studies. In addition to the interface for electromagnetic and thermal dosimetry, the interfaces for lighting and ventilation were integrated into the RC walls while preserving acceptable shielding. The RC with mechanical and electronic steering capabilities is characterized in the 55-65 GHz range. To this end, murine skinequivalent phantoms of realistic shape were designed and fabricated. Their complex permittivity is within ±12% of the target value of murine skin (6.19-j5.81 at 60 GHz). The quality factor of the RC loaded with an animal cage, bedding litter, and five murine phantoms was found to be 1.2 × 10 4 . The losses inside the RC were analyzed, and it was demonstrated that the main sources of the power dissipation were the phantoms and mice cage. The input power required to reach the average incident power density of 1 and 5 mW/cm 2 was found to be 0.23 and 1.14 W, respectively. Surface heating of the mice models was measured in the infrared (IR) range using a specifically designed interface, transparent at IR and opaque at millimeter waves (mmW). Experimental results were compared with an analytical solution of the heat transfer equation and to full-wave computations. Analytical and numerical results were in very good agreement with measurements (the relative deviation after 90 min of exposure was within 4.2%). Finally, a parametric study was performed to assess the impact of the thermophysical parameters on the resulting heating. Bioelectromagnetics. 2020;41:121-135.

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Theoretical and numerical assessment of maximally allowable power‐density averaging area for conservative electromagnetic exposure assessment above 6 GHz

Cited by 21 publications

References 12 publications

Limitations of Incident Power Density as a Proxy for Induced Electromagnetic Fields

Limitations of Incident Power Density as a Proxy for Induced Electromagnetic Fields

Skin Temperature Elevation for Incident Power Densities From Dipole Arrays at 28 Ghz

Exposure Assessment in Millimeter‐Wave Reverberation Chamber Using Murine Phantoms

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