Monitoring Wrist Pulse Wave With a Cantilever-Type Microwave Capacitive Sensor

This paper proposes a low-cost planar microwave sensor able to monitor the wrist pulse wave (WPW) when it is in contact with the anterior part of the wrist, near the radial artery. The device is a highly sensitive two-port capacitive sensor based on a cantilever that moves as a consequence of the blood flow in the radial artery. Due to this motion, the transmission coefficient varies at the rhythm imposed by the heartbeat rate. Thus, by considering either the phase or the magnitude of the transmission coefficient at a specific (operating) frequency, the WPW can be sensed. The device is implemented in a bracelet-type structure to slightly press the sensor on the wrist, as required for a faithful measurement. The associated required electronics of this sensor are very simple and low cost (especially when the device operates in magnitude) and, contrary to radar-type sensors, the device can monitor the WPW regardless of the position or potential movement of the patient under test. As compared to optical methods, the proposed system is not affected by factors such as ambient light conditions or skin tone. The prototype device is able to detect subtle variations in pulse waveforms, a crucial aspect for assessing cardiovascular health.