Development of Biocompatible MEMS Wireless Capacitive Pressure Sensor

Abstract

The objective of this research was to develop a wireless pressure sensor useful for monitoring bladder pressure. The wireless sensor consists of an active capacitive element and an inductor coil. The changes in pressure are related to the changes in the resonant frequency of the internal sensor. The existing pressure sensors have inductors formed on both sides of the substrate. The changes in internal capacitance of these sensors are related to the changes in pressure by impedance matching of the internal LC circuit. The deviation in bladder pressure is an important variable in evaluating the diseased state of the bladder. The inductor designed for this application is a spirally wound inductor fabricated adjacent to the capacitor. The external sensing uses equivalent changes in internal LC. The resonant frequency of the internal sensor is defined by the deformation of the plate, causing the plate to touch the dielectric on the fixed capacitive plate, which is reflected as changes in capacitance(C). The deformation of the plate has been modeled using Finite Element Analysis. The finite element analysis optimizes the dimensions of the design. Remote sensing is achieved through inductive coupling and the changes in pressure are determined. The device is tested for pressures ranging from 0–150 mmHg, bladder pressure. The RF Telemetry system has been modeled using Sonnet. The frequency range is between 100–670 MHz which is in compliance to that specified by Federal Communications Commission (FCC) regulations.