Radiative Near-Field Wireless Power Transfer to Scalp-Implantable Biotelemetric Device

Abstract

Monitoring of elevated intracranial pressure (ICP) is a lifesaving procedure. This article presents an ultrasmall batteryless implantable system for ICP monitoring comprising an off-body power transmitter (Tx) and in-body biotelemetric receiver (Rx). Due to the small implantable antenna (5.6 mm $\times 6$ mm $\times0.2$ mm = 6.72 mm3), the device exhibits dual-band characteristics (i.e., 915 and 1900 MHz) for simultaneous power transmission and data telemetry. The implant is powered wirelessly in the radiative near field (1900 MHz) for enhanced power transfer efficiency (PTE). Moreover, the structure demonstrates the measured peak gain values of −26.8 and −18.8 dBi with the impedance-matched bandwidths of 9.83% and 27.9% at 915 and 1900 MHz, respectively. The wireless PTE of the device was also analyzed in terms of distance variations, and a maximum PTE up to −25.9 dB at 20 mm ( $0.1267\lambda $ ) Tx–Rx separation was achieved. The rectifier attained a maximum power conversion efficiency of 82% at 2-dBm input power. Simulations using the finite-element method and finite difference time domain were performed to evaluate the biotelemetric implantable system. For validation, measurements were conducted in a saline-filled human head phantom, as well as in minced pork. The biotelemetric system yields good agreement between the measured and simulation results.