Beyond the Scalp: Numerical SAR and Performance Comparison of Two 4-Band PIFAs for Brain Implants

We compare the radiation performance and the specific absorption rate (SAR) of two brain-implantable PIFAs operating in the Medical Device Radiocommunication Service (MedRadio) band (401–406 MHz), Wireless Medical Telemetry Service (WMTS) band (1427–1432), and Industrial, Scientific and Medical (ISM) bands (902–928 MHz and 2400-2483.5 MHz). The two antennas have the same total thickness and occupy the same volume, but one is based on a single substrate layer and the other also includes superstrate. A feature shared by the two antennas was that the maximum SAR occurred at the interface between the biocompatible encapsulation layer and the surrounding tissues, whereas neither antenna performed superior to the other in terms of SAR or the radiation performance considering all four operating frequencies.