Using CAPSENSE™ in a Wearable Textile Chest Belt for Respiration Sensing and Interaction Possibility.
Severin Bernhart, Harald Rieser, Vincent van Rheden, Rainer Matischek (2022): Using CAPSENSE™ in a Wearable Textile Chest Belt for Respiration Sensing and Interaction Possibility. In: Proceedings of the 2nd international “Salzburg Conference for Smart Materials”.
Textile sensor integration in clothing creates new fields of application because of their imperceptibility during human activity for gathering biometric data, especially in sports.  However, smart textiles pose new challenges for research and development. Textile capacitive sensors are used in numerous wear-able garments and are generally more robust than resistive sensors,  however, they are affected by exter-nal influences, e.g. temperature and moisture.  Within this work, we present the applicability and advantages of the CAPSENSE(TM) technology (CAPSENSE; Infineon) in an improved version of a wearable running stride and respiration sensor (SRS) (see Figure 1).
After experimenting with capacitive sensing solutions, e.g. capacitive voltage division and capacitive touch pins using an ESP32 chipset (Espressif Systems, China), it was decided to use a PSoC(TM) micro-controller unit (PSoC; Infineon) with integrated CAPSENSE function to measure the capacitance changes of the respiratory sensor. The PSoC enables parallel CAPSENSE input channels and thus the simultaneous determination of different measured values. Besides self-capacitance sensing, CAPSENSE additionally provides mutual-capacitance scanning between a Tx and Rx electrode for increased sensitivity and accuracy. In addition, an auto-calibration function is applied to counteract negative external influences, e.g. temperature and moisture. Therefore, we integrate a smart-textile sensor in parallel to the respiration smart-textile sensor as an input touch button to manually trigger the auto-calibration function at self-selected times.
Regarding the first pilot tests, CAPSENSE improves the respiration signal quality compared to the initial SRS. The signal quality is evaluated in an upcoming study regarding the signal-to-noise ratio. In addition, the textile input touch button will be evaluated according to proper functionality.
The investigated technology and the resulting prototype integrated into a chest strap enables further research and studies. The improved SRS will be used to examine if the runner can be guided towards a locomotor respiratory coupling by sound instructions provided by a smartphone application., The number of textile interaction buttons on the SRS can be increased to allow on-body touch interaction, which has proven effective and user-friendly while performing sports.  As such, CAPSENSE could enable a phoneless interaction to be holistically integrated into the sports experience.