Wearable textile-based sensor tag for breath rate measurement

Breath rate is an important vital sign for monitoring the well-being and detecting underlying illnesses related to the respiratory system. The spirometer is widely used for evaluating the health of the respiratory system by measuring lung capacity and respiration rate. Although this test yields accurate results, however, it is significantly inconvenient and invasive as the test subject must breathe through a tube inserted in the mouth. Therefore, this device is not suitable for continuous monitoring of respiration. In this paper a novel contact-less wearable breath rate measurement system is presented. The proposed sensor is based on a spiral resonator tag printed on a thin flexible textile substrate. The sensor exploits the body expansion and contraction during respiration to provide an estimate of the breathing frequency. This movement is measured by a microstrip probing loop that acts as the antenna of the reader. The reader operates at one frequency; the resonant frequency of the tag, and the sensing principle relies on the near-field coupling between the probe and the resonating tag at this frequency. The proposed sensor is characterized with its simple and light-weight design, can be easily integrated in garments, and its capability of providing continuous monitoring of the breathing rate. The proposed sensor has been tested through experimental measurements and the results matched measurements from a reference ground-truth breath rate sensor based on a nasal cannula equipped with a thermistor. The solution proposed in this work provides a novel contact-less technique for respiration rate estimation.