**A Novel Capacitance-Based In-Situ Pressure Sensor for Wearable Compression Garments**

#### **Steven Lao, Hamza Edher, Utkarsh Saini, Je**ff**rey Sixt and Armaghan Salehian \***

Energy Harvesting and Vibrations Lab, Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada; sblao@uwaterloo.ca (S.L.); hedher@uwaterloo.ca (H.E.); utkarsh.saini@edu.uwaterloo.ca (U.S.); jasixt@uwaterloo.ca (J.S.)

**\*** Correspondence: salehian@uwaterloo.ca

Received: 20 September 2019; Accepted: 29 October 2019; Published: 31 October 2019

**Abstract:** This paper pertains to the development & evaluation of a dielectric electroactive polymer-based tactile pressure sensor and its circuitry. The evaluations conceived target the sensor's use case as an in-situ measurement device assessing load conditions imposed by compression garments in either static form or dynamic pulsations. Several testing protocols are described to evaluate and characterize the sensor's effectiveness for static and dynamic response such as repeatability, linearity, dynamic effectiveness, hysteresis effects of the sensor under static conditions, sensitivity to measurement surface curvature and temperature and humidity effects. Compared to pneumatic sensors in similar physiological applications, this sensor presents several significant advantages including better spatial resolution, compact packaging, manufacturability for smaller footprints and overall simplicity for use in array configurations. The sampling rates and sensitivity are also less prone to variability compared to pneumatic pressure sensors. The presented sensor has a high sampling rate of 285 Hz that can further assist with the physiological applications targeted for improved cardiac performance. An average error of ± 5.0 mmHg with a frequency of 1–2 Hz over a range of 0 to 120 mmHg was achieved when tested cyclically.

**Keywords:** capacitive pressure sensors; in-situ pressure sensing; sensor characterization; physiological applications; cardiac output
