Testbed for Simulating Pulsewaveform for Development of Wearable Piezoresistive Pressure Sensors

Abstract

Due to their non-invasive method of continuous monitoring of weak human physiological data, flexible and skin-mountable wearable health monitoring devices have attracted a lot of attention in recent years. According to their mode of operation, ultra-sensitive pressure sensors can generally be divided into piezoresistive, capacitive, triboelectric, and piezoelectric sensors. Particularly, piezoresistive sensors have received a lot of attention due to its rapid response, wide detection range, straightforward structure, and comparatively easy signal measuring system. Although previous attempts to obtain the complete pulse waveform of the human heartbeat were successful, their signal capture required the use of unwearable measuring equipment. In order to resolve this shortcoming of the current supposedly wearable systems, we outline three requirements for a sensor to be wearable (i.e. could be paired with a simple and compact signal acquisition device). The first of these is the sensitivity; through a complete literature review we determine the lower limit of sensitivity that if obtained, the sensor can acquire the pulsewaveform from the body peripheries such as wrist or ankle. Second is the response time of the sensor. The piezoresistive sensor must have a shorter response time than the period of fastest heartbeat. And lastly is the cyclability; the durability tests of the sensor must show ample stability and consistency in the signal output after operation for months.To verify that the sensors pass the requirements above, we have custom-built a testbed capable of measuring these three characteristics. The testbed specifically makes use of a secondary pressure sensor to confirm the sensitivity. Secondly, by using an encoder instead of merely relying on a sensor's rise or fall time, it is capable to more accurately determine the response time of the sensor. Furthermore, because the testbed is motorized, it is streamlined to mimic operation over an extended cycles.Finally, in this study we fabricated an exemplary piezoresistive pressure sensor using environmentally friendly materials and tested it in the testbed and then mounted it on the wrist of a human subject and acquired the pulsewaveform with a simple and wearable signal acquisition device to confirm the capability as a wearable pulsewave monitoring device. The details of this study will be presented in the meeting.