Modeling and Optimization of Inductively Coupled Wireless Bio-Pressure Sensor System Using the Design of Experiments Method

This paper presents an approach for modeling and design of inductively coupled wireless bio-pressure sensor system for chronic intracardiac pressure monitoring. Making use of recent advances in microelectromechanical systems and semiconductor technology, bio-pressure sensor is developed as a series LC resonant circuit with a featured pressure-dependent capacitance working at the medical implant communication service band of 402-405 MHz for wireless sensing without power consumption. The microfabricated sensor consists of a planar spiral gold (Au) coil, a series capacitor, an SU-8-based frame structure, and an encapsulated bio-compatible PDMS membrane. Bio-pressure sensor is designed with a small footprint of 3.2 mm × 3.2 mm for reducing the bleeding and infection risks in surgery. With a limited footprint and desired working frequency, there are many mutually dependent geometry parameters with numerous combined groups of values involved in the full optimization of the system. In order to maximize the performance of system under the design requirements, RF characteristics that affect inductive sensitivity and pressure sensitivity are theoretically analyzed first, and then design of experiments method is applied to model and optimize 3-D electromagnetic models of sensor and sensor system on the derived RF characteristics. The large number of combined groups of values in factorial simulations is thus reduced to a few performance-related design factors. By monitoring the induced peak impedance of the readout coil, the pressure-dependent resonant frequency of the sensor can be detected and measured. The experimental results show that the optimized wireless sensor system has a relatively high average pressure sensitivity of 5.3 KHz/mm Hg at a telemetry distance of 10 mm demonstrating its potential for intracardiac pressure monitoring.