Electromagnetic Biosensing of Respiratory Rate

Continuous monitoring of respiratory rate is crucial in forecasting health crises and other major physiological instabilities. Current respiratory monitoring methods limit the mobility of the patient or require constant battery replacement. Wireless, wearable technology can collect continuous physiological data without immobilizing or inconveniencing patients, and human energy harvesting can be used to power these wearable sensors. In this paper, we explore this zero-net energy biosensor concept through simultaneous sensing and harvesting of respiratory effort. An off-the-shelf dc brushed motor is modified into a chest belt, and tested on a mechanical chest simulator as well as on 20 human subjects, using a spirometer as a reference. The electromagnetic biosensor is used to successfully harvest 7-70 μW from human subjects. On the mechanical chest, respiratory rate is detected with a mean absolute error of 0.00027 breaths/min with a standard deviation of 0.00019 breaths/min. For human subjects, respiratory rate is detected with a mean difference of 0.36 breaths/min with a standard deviation of 2.83 breaths/min (sitting), 0.23 breaths/min with a standard deviation of 2.64 breaths/min (standing), and 0.48 breaths/min with a standard deviation of 3.06 breaths/min (walking).