Investigation of the Long-Term Reliability of a Velostat-Based Flexible Pressure Sensor Array for 210 Days

Pressure sensors are subjected to continuous force and stress that may affect the operation of the sensor in the long run. Reliability is a crucial factor that must be considered when designing and fabricating any sensor. It is essential to test the material used in the sensor to assess the reliability of the complete product. In this work, we report the long-term reliability of a flexible pressure sensor mat using a carbon-impregnated polymer, velostat, which is a flexible, light, and thin polymer composite material with piezoresistive properties. We focus on the analysis of the performance of a flexible pressure sensor array under long-term and repeated loading. Tests were performed every fortnight for 210 days. We have observed that the material characteristics of the velostat material change on repeated application of pressure up to a certain time frame. For a given loading, once the material settles, the change in resistance of the material becomes consistent for a given application of pressure. We have also analyzed the changes in the parameters associated with the 2-parameter model, and have analyzed the effect of crosstalk on the sensor matrix for different pitch lengths to select the best pitch that will give us the minimum crosstalk. We have observed that the error rate of the sensor pixels decreased by 53 percentage points in 210 days. The results obtained from the experimental tests for reliability reveal a practical possibility of implementing velostat-based pressure sensors in wearable and healthcare devices and provide steps to take while calibrating an as-fabricated velostat-based sensor.