Development of a Piezoresistive Pressure Sensor Using an in-House Pulsewave Simulator to Ensure Detection of Full Pulse Waveform on Diverse Populations

Abstract

Flexible and skin mountable wearable health monitoring devices have gained much attention in recent years due to their non-invasive approach to continuous monitoring of weak human physiological signals. In general, ultra-sensitive pressure sensors can be categorized by the operation mechanism into piezoresistive, capacitive, triboelectric, and piezoelectric sensors. Specifically, piezoresistive sensors has drawn much attention because of their fast response, broad detection range, simple structure, and relative simplicity of the signal measuring system. Despite the success of the past efforts in acquiring the full pulse waveform of the human heartbeat, their signal acquisition requires utilization of unwearable measuring equipment. In this study, the central research objective will be to do finite element analysis to optimize the design, and then to fabricate, test and finally verify wearability of the full system (including the signal acquisition portion) on the wrist. A piezoresistive pressure sensor capable of precise monitoring of arterial pulse waveform allows detection of not only the pulse but also possible irregularities in its waveform that can be potentially the harbingers of various medical conditions. Modeling of the sensor’s micro-features showed micro-features with the shape of a pyramid, size of 100 μm, angle of 50-60 degrees and spatial configuration of 1 per 300 μm realizes high sensitivity and signal level (1 mA for pulse waveform detection from the wrist). This helps to eliminate the dependability of the sensor response read-out on complex and unportable measuring devices such as sourcemeters. Furthermore, fabrication of the conductive micro-patterned sensor has been accomplished by the standard micro-fabrication techniques including photolithography and wet etching. Methods such as electrospinning, bipolar exfoliation of graphene and electrostatic spray deposition were used to ensure long term stable conductivity and operation of the device. After the fabrication, this piezoresistive sensor was fully calibrated and characterized by a developed pulse waveform simulator to ensure viability of the system to detect the full pulse waveform from the wrist with various amplitudes of excitation signal (accounting for diverse human population with different pulse strengths). The detailed results will be discussed during the presentation.