SAR, SA, and Temperature Variation in the Human Head Caused by IR-UWB Implants Operating at 4 GHz

With the extensive use of wireless devices within or at close proximity to the human body, electromagnetic effects caused by the interaction between RF waves and human tissues need to be considered with paramount importance. The ultra-wideband (UWB) communication spectrum has recently been utilized in bio-telemetry applications, such as neural recording, brain-computer interfaces, and physiological data monitoring requiring high data rate and low power. This paper reports the electromagnetic effects of head-implantable transmitting devices operating based on impulse radio UWB wireless technology. Simulations illustrate the performance of an implantable UWB antenna tuned to operate at 4 GHz with an -10-dB bandwidth of approximately 1 GHz when it is implanted in a human head model. Specific absorption rate (SAR), specific absorption (SA), and temperature increase are analyzed to compare the compliance of the transmitting device with international safety regulations. The frequency- and age-dependent nature of the tissue properties, such as relative permittivity, is taken into account. The SAR/SA variation of the human head is presented with varying input power, different antenna orientations, and different signal bandwidths. We also present the percentage of SAR variation for each tissue type in the head model used for the simulations.