Quality Factor Optimization of Inductive Antennas for Implantable Pressure Sensors

Inductive antenna design for passive wireless implantable use presents several challenges not currently addressed. A small form factor is desired for minimally invasive implantation and monitoring, and a low frequency is necessary for effective through-body power transfer. However, a small inductor limits sensitivity to changes in capacitance at low-frequency operation. It is thus necessary to optimize the inductor for maximal sensitivity while satisfying tight area and low frequency constraints. Here, a design methodology is presented for planar circular spiral inductors used with capacitive pressure sensors to form a passive wireless implantable pressure sensor. Several analytical expressions are collected to find the optimal geometric parameters that maximize the quality factor and sensitivity of the sensor frequency response. The analysis is validated through comparison with field solvers and wireless measurements of fabricated devices.