Mobile phones: a trade-off between speech intelligibility and exposure to noise levels and to radio-frequency electromagnetic fields

When making phone calls, cellphone and smartphone users are exposed to radio-frequency (RF) electromagnetic fields (EMFs) and sound pressure simultaneously. Speech intelligibility during mobile phone calls is related to the sound pressure level of speech relative to potential background sounds and also to the RF-EMF exposure, since the signal quality is correlated with the RF-EMF strength. Additionally, speech intelligibility, sound pressure level, and exposure to RF-EMFs are dependent on how the call is made (on speaker, held at the ear, or with headsets). The relationship between speech intelligibility, sound exposure, and exposure to RF-EMFs is determined in this study. To this aim, the transmitted RF-EMF power was recorded during phone calls made by 53 subjects in three different, controlled exposure scenarios: calling with the phone at the ear, calling in speaker mode, and calling with a headset. This emitted power is directly proportional to the exposure to RF EMFs and is translated into specific absorption rate using numerical simulations. Simultaneously, sound pressure levels have been recorded and speech intelligibility has been assessed during each phone call. The results show that exposure to RF-EMFs, quantified as the specific absorption in the head, will be reduced when speaker-mode or a headset is used, in comparison to calling next to the ear. Additionally, personal exposure to sound pressure is also found to be highest in the condition where the phone is held next to the ear. On the other hand, speech perception is found to be the best when calling with a phone next to the ear in comparison to the other studied conditions, when background noise is present

Robust, wearable, on-body antenna relying on half mode substrate integrated waveguide techniques

A compact, robust, wearable antenna for body-worn applications in the 2.4 GHz Industrial Medical and Scientific band is designed, fabricated and tested. This novel compact textile cavity backed slot antenna combines a half-mode substrate integrated waveguide topology with an additional row of shorting vias for miniaturization. Excellent free space performance is achieved with a measured 4.6 % impedance bandwidth, maximal gain of 4.7 dBi and radiation efficiency of 81.3 %. On-body measurements reveal minimal frequency detuning when the antenna is worn by a test subject as well as a negligible impedance bandwidth reduction to 4.5 %. The low calculated Specific Absorption Rate of 0.51 W/kg averaged over 1 g of tissue demonstrates high antenna body isolation. Therefore, this design is an attractive option as antenna in smart textile systems