Wireless performance of a fully passive neurorecording microsystem embedded in dispersive human head phantom

This paper reports the wireless performance of a biocompatible fully passive microsystem implanted in phantom media simulating the dispersive dielectric properties of the human head, for potential application in recording cortical neuropotentials. Fully passive wireless operation is achieved by means of backscattering electromagnetic (EM) waves carrying 3^rd order harmonic mixing products (2f₀±f_m=4.4-4.9 GHz) containing targeted neuropotential signals (f_m≈1-1000 Hz). The microsystem is enclosed in 4 μm thick parylene-C for biocompatibility and has a footprint of 4 mm × 12 mm × 500 μm. Preliminary testing of the microsystem implanted in the lossy biological simulating media results in signal-to-noise ratio´s (SNR) near 22 (SNR≈38 in free space) for millivolt level neuropotentials, demonstrating the potential for fully passive wireless microsystems in implantable medical applications.