Average absorption cross-section of the human body measured at 1–12 GHz in a reverberant chamber: results of a human volunteer study

Abstract

The electromagnetic absorption cross-section (ACS) averaged over polarization and angle-of-incidence of 60 ungrounded adult subjects was measured at microwave frequencies of 1-12 GHz in a reverberation chamber. Average ACS is important in non-ionizing dosimetry and exposure studies, and is closely related to the whole-body averaged specific absorption rate (WBSAR). The average ACS was measured with a statistical uncertainty of less than 3% and high frequency resolution for individuals with a range of body shapes and sizes allowing the statistical distribution of WBSAR over a real population with individual internal and external morphologies to be determined. The average ACS of all subjects was found to vary from 0.15 to 0.4 m(2); for an individual subject it falls with frequency over 1-6 GHz, and then rises slowly over the 6-12 GHz range in which few other studies have been conducted. Average ACS and WBSAR are then used as a surrogate for worst-case ACS/WBSAR, in order to study their variability across a real population compared to literature results from simulations using numerical phantoms with a limited range of anatomies. Correlations with body morphological parameters such as height, mass and waist circumference have been investigated: the strongest correlation is with body surface area (BSA) at all frequencies above 1 GHz, however direct proportionality to BSA is not established until above 5 GHz. When the average ACS is normalized to the BSA, the resulting absorption efficiency shows a negative correlation with the estimated thickness of subcutaneous body fat. Surrogate models and statistical analysis of the measurement data are presented and compared to similar models from the literature. The overall dispersion of measured average WBSAR of the sample of the UK population studied is consistent with the dispersion of simulated worst-case WBSAR across multiple numerical phantom families. The statistical results obtained allow the calibration of human exposure assessments made with particular phantoms to a population with a range of individual morphologies.

On the Measurable Range of Absorption Cross Section in a Reverberation Chamber

“…The theoretical contributions of the antenna and wall losses to the Q-factor are also shown. The wall contribution was estimated by fitting the high frequency ACS of the chamber to the model in (6); an effective conductivity of 0.35 MS/m gave the best leastsquares fit to the measured data. The antennas are the dominant loss mechanism below 2 GHz and have a significant effect up to 7 GHz.…”

“…Measurement of ACS is therefore also useful for material characterization, particularly at high frequencies [2] [5]. ACS is also very closely related to average whole-body specific absorption rate and has therefore recently been applied to the determination of human exposure to electromagnetic fields in diffuse environments [6] [7].…”

Rapid and accurate broadband absorption cross-section measurement of human bodies in a reverberation chamber

“…While the reverberation chamber measurement approach has limitations in its applicability due to the constraints of the technique it is highly complementary to the numerical simulation approach widely used in the literature for human exposure studies. The methodology reported here has subsequently been applied to a medium-scale empirical study of the variability of human exposure to electromagnetic fields due to internal and external morphological parameters [27].…”

Time domain technique for rapid, broadband measurement of human absorption cross section in a reverberation chamber

“…It is also useful in communications models, e.g. the effect of passengers on propagation in an aircraft [4,5]. Broadband measurements of ACS are important because (a) communication systems are moving to higher frequency bands, and (b) they can be related to body composition parameters for medical studies.…”