Exploration of planar capaciflector for wearable respiration monitoring

Abstract

Respiratory rate is an important physiological parameter, and its continuous monitoring plays
a key role in health management. This study aims to evaluate the application of planar capacitive sensors with active shielding, capaciflectors, in respiratory monitoring. Previous
studies have speculated that the change in sensor capacitance is mainly caused by skin
deformation during breathing, but this theory has not been experimentally verified. In this study, an integrated wireless capaciflector respiratory sensor was developed based on the Texas Instruments FDC2214 capacitance-to-digital converter (CDC). Through experimental tests on 10 adult male volunteers, the results showed that the increase in sensor capacitance caused by skin stretching ranged from 0.01 to 0.1pF, which was in the same order of magnitude as the capacitance change caused by breathing, confirming that skin deformation is the main source of respiratory signals. In addition, the study explored the effect of operating frequency (200kHz to 7MHz) on sensor sensitivity and found that the sensor sensitivity at 200kHz was about 1.2 times higher than that at other frequencies, showing its potential as an optimised frequency, but due to the small effect, the current frequency selection can be more based on the needs of electronic devices. The study also explored the effect of electrode size on sensor sensitivity. The results showed that the design with an electrode length of 16 mm and a spacing of 4 mm showed a sensitivity improvement of about 2 times in some subjects, which may be a potential optimised design. However, due to individual differences, it is necessary to expand the sample size for further research. This study provides an important design reference for the design of capaciflector-based respiratory monitoring sensors.

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Identifiers

ORCID for Neil White: orcid.org/0000-0003-1532-6452

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