Efficient Calibration of Velostat-Based Flexible Pressure Sensor Matrix

Regular plantar pressure monitoring is required for diabetic, wheelchair-bound and bed-ridden individuals. It has been shown that peak plantar pressure for diabetics increases significantly and progressively, and requires regular monitoring for early detection and intervention. Sensor matrices of capacitative, resistive, and piezoelectric transducers are most commonly used for measuring areal pressure. Calibration for such medical devices is crucial for reliability and repeatable results. In this work, we elaborate on the calibration challenges of a
$32\times 32$
velostat-based sensor matrix, and demonstrate calibration strategies suitable for a manufactured product. We show that
$2N$
parameters can be used to calibrate an
$N\times N$
sensor matrix instead of
$2N^{2}$
. We observe the accuracy of calibration of a
$32\times 32$
sensor matrix by comparing the total detected weight of 35 participants at a static load with their reported weight, with 4.2% mean error and 3.1% median error. For participants in the 50–85 kg weight range, the difference was always within ±5%. Further, upon drawing contour plots and using the pressure distribution information, we were able to distinguish participants with possible foot ulcers and flat feet.