Analysis of Interface Material Noise in Non-contact Capacitive Sensing.

The thermal noise due to the resistivity of insulation materials can become a significant noise source in non-contact capacitive sensing, especially when measuring micro-volt-level physiological signals. Since both the impedance and the resistivity of practical insulation materials may be strongly frequency dependent, their thermal noise is often frequency dependent. This paper studies the impedance and noise behavior of different interface materials as function of frequency, by means of modelling, simulations, and experimental measurements. The results show that the inherent resistive noise of some fabrics (e.g., cotton, polyester) could outweigh the typical noise level of circuits for physiological sensing; and as a result, the interface noise can limit the quality of low-amplitude signal detection. Clinical Relevance- This study gives a guideline for material selection from the noise perspective in case of capacitive electrode sensing.