Dec 12, 2018

A Numerical Assessment of the Human Body Effect in the Transmission of Wireless Microphones

Eugenia Cabot, Ivica Stevanovic, Niels Kuster, and Myles H. Capstick, Microwave and Optical Technology Letters, Volume 61, Issue 3, pp. 809–817, March 2019, online 05 December 2018, doi: 10.1002/mop.31623

Many mobile devices, including wireless microphones, are operated in the near proximity of the human body, which modifies the radiation conditions and absorbs some of the power of the device and, therefore, introduces additional losses in the radio communication link due to the body. With the introduction of more and more wireless services, there is a decrease in the spectrum available for professional wireless microphones – such as those used in TV studios, theaters, and concert venues – in the ultra-high-frequency (UHF) range traditionally used in these applications. Additional spectrum is available only at higher frequencies, however, users are concerned that performance will be degraded, leading to noisy or dropped audio. The question is, to what extent is this concern justified? We address this question in this paper, where we characterize the body loss in wireless microphones over a wide frequency range spanning from the very high frequencies (VHF, 235 MHz) to the super high frequencies (SHF, 6 GHz) using 3D numerical electromagnetic simulations of three realistic human anatomical models that cover a range of body mass indices and for two microphone types, hand-held and body-worn.

Results of this work were also included in the Electronics Communications Committee (ECC) Report 286: “Body effect of handheld and bodyworn audio PMSE equipment” published in September.

The scientific and technical impact of the study can be summarized as:

  • Finite-difference time-domain (FDTD) simulations were performed with SEMCAD X to numerically characterize body loss and shadowing of hand-held and body-worn microphones 
  • The obstruction due to the presence of the human body causes the total radiated power (TRP) of a body-worn or hand-held wireless microphone to be less than that of the same microphone in space case
  • Body loss decreases as a function of frequency but is more weakly correlated with body size (BMI) is weak, thus the three  anatomical models used in the study represent good coverage of wireless microphone users; user size exerts influence on the shadowing ratio, but only on the order of 2 to 3 dB
  • Typical postures and positions of the user’s hand on the hand-held microphone and typical placements of the body-worn microphone on the user’s body were used in the simulations; the position of the hand on the microphone and the proximity of the microphone to the body are key factors influencing body loss