A Highly Sensitive Surface Acoustic Wave Sensor for Continuous Respiratory Monitoring

In this study, a novel surface acoustic wave (SAW) topology is proposed as a low-cost medical consumer electronics for continuous respiratory monitoring. The proposed sensing system works on the basis of humidity sensing without the need for an active layer, and it can be readily fabricated using a standard surface micromachining process. The SAW resonator comprises a set of arc-shaped interdigitated electrodes with an overall size of 250 mu m x 250 mu m at an operation frequency of 220 MHz. Due to this devised configuration, the generated acoustic waves by the transmitter electrodes are converged to a single point, resulting in the improvement of the sensitivity and response time. Thanks to the improved sensitivity, the monitoring system does not require an active layer. The behavior of the proposed system is evaluated by simulations and experimental measurements. The results indicate that the proposed system is capable to effectively and efficiently measure both respiratory rate and respiratory pattern, while the accuracy and reliability of the system is validated through concurrent measurements with a conventional respiratory monitoring belt.