Characterization of Coated Piezo-resistive Fabric for Respiration Sensing

Electro-resistive band (ERB) or conductive elastomer can be also used as non-invasive bio-potential sensors. This stretchable conductive material gained acceptance in health monitoring systems due to their low cost, low power consumption and high flexibility. ERBs can be polarized with a current source to generate a voltage signal directly proportional to the change of length. However, the sensors require close contact with the patient's skin to monitor bio-mechanical movements adequately. Direct contact with human skin causes inconsistent current leakage and result in low SNR. Isolating the ERB is important to avoid current leakage, provide protection by overstretching and easiness of wearing. However, not all stretchable material suitable to use as ERB substrate. In this work, we have compared two different conductive elastomers (rubber and fabric) stretched using a breathing simulator machine to compare the material performance. We have coated the ERBs with 3 different coating materials: Pinkysil, Transil and silicone tape, as well as raw bands. We have processed and analyzed all the collected signals using a wide range of measurements and calculations such as linearity, baseline change, Total Harmonic Distortion (THD), Signal to Noise Ratio (SNR), correlation coefficient and phase difference. We have discovered from the final results that the silicone tape serves as a good isolator material and shows reliable and consistent results. The conductive rubber also shows less noise and distortion across stretching in shorter stretch applications compared to the conductive fabric.