Empirical and theoretical dosimetry in support of whole body radio frequency (RF) exposure in seated human volunteers at 220 MHz

Abstract

This study reports the dosimetry performed to support an experiment that measured physiological responses of seated volunteer human subjects exposed to 220 MHz fields. Exposures were performed in an anechoic chamber which was designed to provide uniform fields for frequencies of 100 MHz or greater. A vertical half-wave dipole with a 900 reflector was used to optimize the field at the subject's location. The vertically polarized E field was incident on the dorsal side of the phantoms and human volunteers. The dosimetry plan required measurement of stationary probe drift, field strengths as a function of distance, electric and magnetic field maps at 200,225, and 250 cm from the dipole antenna, and specific absorption rate (SAR) measurements using a human phantom, as well as theoretical predictions of SAR with the finite difference time domain (FDTD) method. A NBS (National Bureau of Standards, now NIST, National Institute of Standards and Technology, Boulder, CO) 10 cm loop antenna was positioned 150 cm to the right, 100 cm above and 60 cm behind the subject (toward the transmitting antenna) and was read prior to each subject's exposure and at 5 min intervals during all RF exposures. Transmitter stability was determined by measuring plate voltage, plate current, screen voltage and grid voltage for the driver and final amplifiers before and at 5 min intervals throughout the RF exposures. These dosimetry measurements assured accurate and consistent exposures. FDTD calculations were used to determine SAR distribution in a seated human subject. This study reports the necessary dosimetry to precisely control exposure levels for studies of the physiological consequences of human volunteer exposures to 220 MHz.

Thermal Mechanisms of Interaction of Radiofrequency Energy With Biological Systems With Relevance to Exposure Guidelines

“…Several recent studies at the Air Force Research Laboratory at Brooks AFB, TX, by Adair and colleagues have measured thermoregulatory responses to extended (45-min) RF exposures of human volunteers under controlled environmental conditions. These studies measured a variety of sensory and thermophysiological endpoints (Adair et al 1998(Adair et al , 1999(Adair et al , 2001Allen et al 2005) in subjects exposed to RF energy at frequencies of 100, 220, 450, and 2,450 MHz at levels that considerably exceeded ICNIRP and IEEE exposure guidelines. These studies are the first, and apparently only, measurements of physiological responses of humans exposed for extended periods to RF energy of substantial parts of their bodies, conducted under carefully controlled environmental conditions.…”

Thermophysiological responses of human volunteers to whole body RF exposure at 220 MHz

“…It was mapped across three 80 Â 80 cm planes (located 2.0, 2.25, and 2.5 m from the dipole) with National Bureau of Standards (NBS, now NIST) E field and H field probes. The PD across the dorsal aspect of a seated standard human, as measured with the NBS E field probe at 2.25 m from the dipole antenna, is illustrated in Figure 5 of an accompanying study [Allen et al, 2005]. The average PD across the subject was calculated as 11.6 AE 0.53 mW/cm 2 (116.…”

“…The average whole body SAR was determined to be 0.78 W/kg and the average normalized SAR was 0.045 (W/kg)/(mW/cm 2 ) [Durney et al, 1986]. For details of the empirical and theoretical dosimetry, see Allen et al [2005].…”

Calculation of Whole-Body Sar From a 100 MHZ Dipole Antenna

“…Various numerical simulation techniques are now available and provide alternative effective methods to determine SAR distributions in highly sophisticated millimeter-resolution anatomically based models. Among those techniques, the finite-difference time-domain (FDTD) method has become the most widely used method for bio-electromagnetic applications [7][8][9][10][11].…”