A Comparison of the Human Skin Temperature Response from a Horn Antenna and Open-Ended Waveguide using Experimental and Computer Simulated Local Radiofrequency Field Exposures at 6 GHz

Abstract

We evaluated skin temperature responses to localized 6 GHz radiofrequency electromagnetic field (RF-EMF) exposures on the human forearm using a horn antenna and open-ended waveguide at 5 cm (1 wavelength at 6 GHz) from the tissue surface. Reflection coefficients (S11) were measured experimentally for both antennas with the skin surface or RF absorbing pad at 5 cm from the aperture. Skin temperatures were measured continuously using a thermal camera and reported at baseline and end-exposure or time-matched sham (30-min). The reflection coefficient for the horn antenna was 4.3 dB [95% confidence limits: 5.8, 2.8] lower than the waveguide in the forearm condition and 3.5 dB [5.0, 2.0] lower than the horn in the RF absorber condition (both P<0.001). Final skin temperature was 7.4°C [6.6, 8.2] higher with the horn (39.1°C [38.6, 39.7]) and 4.6°C [3.8, 5.5] higher with the waveguide (36.3°C [35.8, 36.9]) compared to the sham condition (31.7°C [31.1, 32.3]) and the horn was 2.8°C [2.0, 3.6] higher than the waveguide (all P<0.001). Final skin temperature was also 0.7°C [0.4, 1.0] higher for every 1°C increase in baseline temperature (P<0.001). The horn antenna more efficiently transferred RF-EMF energy into the tissue, producing higher peak steady-state skin temperature responses than the waveguide, consistent with electromagnetic simulations showing a greater peak 10-g averaged specific absorption rate and smaller 2-dimensional beam shape on the skin surface for the horn. These findings will allow us to further optimize our exposure system for future human experiments assessing biological responses to 6 GHz RF-EMF exposures.