Respiratory Activity Monitoring by a Wearable 5.8 GHz SILO With Energy Harvesting Capabilities

In this work, the design and the realization of a pocket-size sensor for breath rate detection are presented. Exploiting the self-injection locking radar technique, it is possible to perform FM-to-AM demodulation that allows the detection of the voltage peaks at the output of the sensor's receiving part. If compared with existing solutions, this device is of reduced dimensions and fully wearable; in fact, it can be worn by the user at a certain distance from the body at the chest position, and work without the need of any dedicated remotely synchronized anchor nodes nor bulky analyzers to be carried close by. As a more distinctive peculiarity, the receiving circuit is designed as an RF-to-DC rectifier in order to also enable the possibility to harvest energy that can be exploited, for instance, to feed a microcontroller unit and a transceiver with the aim of sending wirelessly the breath rate data to a laptop or a smartphone. Circuit simulations are corroborated by measurements in order to ensure the feasibility of the proposed solution.