On‐body calibration and measurements using personal radiofrequency exposimeters in indoor diffuse and specular environments

Abstract

For the first time, response of personal exposimeters (PEMs) is studied under diffuse field exposure in indoor environments. To this aim, both numerical simulations, using finite-difference timedomain method, and calibration measurements were performed in the range of 880-5875 MHz covering 10 frequency bands in Belgium. Two PEMs were mounted on the body of a human male subject and calibrated on-body in an anechoic chamber (non-diffuse) and a reverberation chamber (RC) (diffuse fields). This was motivated by the fact that electromagnetic waves in indoor environments have both specular and diffuse components. Both calibrations show that PEMs underestimate actual incident electromagnetic fields. This can be compensated by using an on-body response. Moreover, it is shown that these responses are different in anechoic chamber and RC. Therefore, it is advised to use an on-body calibration in an RC in future indoor PEM measurements where diffuse fields are present. Using the response averaged over two PEMs reduced measurement uncertainty compared to single PEMs. Following the calibration, measurements in a realistic indoor environment were done for wireless fidelity (WiFi-5G) band. Measured power density values are maximally 8.9 mW/m 2 and 165.8 mW/m 2 on average. These satisfy reference levels issued by the International Commission on Non-Ionizing Radiation Protection in 1998. Power density values obtained by applying on-body calibration in RC are higher than values obtained from no body calibration (only PEMs) and on-body calibration in anechoic room, by factors of 7.55 and 2.21, respectively. Bioelectromagnetics. 2016;9999:XX-XX.

Design and Calibration of A 60-GHz Personal Exposimeter for Exposure Assessment in Specular and Diffuse Environments

“…This indicates underestimation of the incident electric fields with respect to free space values. This conclusion is also obtained for exposure assessment at frequencies ≤6 GHz [6], [7]. Figure 6 shows the ratio of AA (response) for diffuse fields.…”

“…A large number of studies, for example [4]- [6], have investigated everyday life IPD measurements using personal exposimeters (PEMs) for frequencies lower than 6 GHz. PEMs measure the total electric fields near the body instead of the actual incident fields, and are consequently faced with large measurement uncertainties [7].…”

Personal Exposimeter for Radiation Assessment in Real Environments in the 60-GHz Band

“…This indicates underestimation of the incident electric fields with respect to free space values. This conclusion is also obtained for exposure assessment at frequencies ≤6 GHz [6,8]. Figure 6 compares the lowest simulated and measured PI 50 and PI 95 (which are measures for uncertainty of PE) of the response (R meas (φ)) of the PE consisting of 1, 2 and 3 antennas, according to the best combination of three antennas on the subject's forearm as shown in Figure 3.…”

“…For multiple plane waves incident on the antenna, the received power on the antenna is not necessarily equal to the sum of the incident powers induced by each single plane wave, since the incident plane waves can interfere with each other. Therefore, the received power (P r ) is calculated as a function of the incident electric fields (the sum of the induced voltages on the antenna) [6,17]. A realistic far-field exposure scenario in the 60-GHz band for an indoor environment (conference room of IEEE 802.11 standard [18]) is considered to determine the response of the simulated on-body antenna near the skin model.…”

“…For far-field exposures, the IPD limits are 1 mW/cm 2 (general public) and 5 mW/cm 2 (occupational exposure) averaged over 20 cm 2 of the exposed area [3]. Personal exposimeters (PEMs) have been used to measure the IPD in the 0.1-6 GHz range [4][5][6], for which a protocol has been developed [7]. PEMs' measurements are associated with a relatively large measurement uncertainty [8,9] as they measure the total electric fields near the body instead of the incident electric fields or the IPD for which exposure limits are issued [3].…”