Piezoelectric-Based Respiratory Monitoring: Towards Self-Powered Implantables for the Airways

Wearable and implantable technology for respiratory monitoring has created the potential for continuous collection of respiratory parameters for healthcare and other applications. However, battery life, form factor, and user burden impose practical constraints that affect user acceptance and therefore clinical utility. This work introduces a wireless self-powered sensing system for airway monitoring that uses an array of piezoelectric cantilevers that functions as both the respiratory flow sensor and the energy harvester that powers the system. The cantilevers are excited by airflow in the airway, and the harvested energy from the cantilevers is stored in a capacitor. Once a threshold energy is available in the capacitor, a load switch closes and enables a low frequency oscillator that functions as a data-less transmitter. The signal coming from the sensing system is received by an external software-defined radio (SDR), and the rate at which this signal is received is mapped to the respiratory conditions in the airway. A benchtop testing system that incorporates a lung simulator, a data acquisition system, and a hot wire anemometer was created to validate the sensor. Results show that the signal reception rate is affected by the breathing rate and volume, demonstrating the potential for a self-powered, miniaturized, passive implantable device for continuous respiratory health monitoring.