Respiration Monitoring Using a Flexible Paper-Based Capacitive Sensor

Abstract

Respiration is a key vital sign indicative of an individual's health. Current approaches of respiration sensing require direct contact with the body. Moreover, they are expensive and need bulky holter monitors for continuous realtime monitoring. In this study, we propose a low-cost capacitive sensor fabricated using screen printing of carbon paste interdigitated electrodes on paper substrate for respiration monitoring. Cellulosic paper provides a microporous network to trap exhaled breath. Respiration causes the dielectric constant of the paper to change, mostly as a function of breath humidity, which in turn changes the capacitance of the sensor. The interdigitated electrodes configuration is shown to provide better response time compared to resistive configuration. A simple phase sensitive detector-based circuit was used to convert the capacitance change into a measurable output voltage. The MSP430 microcontroller was used for data acquisition and voltage measurement. A graphical user interface was designed for real time respiration monitoring. Experimental results validate the performance of this sensor.