A hybrid energy scavenging sensor for long-term mechanical strain monitoring

We had previously reported a self-powered floating-gate level-crossing sensor/processor where the energy for sensing, computation and storage was extracted directly from the input strain variations. However, self-powering was found insufficient for wireless interrogation and configuration of the sensor. In this paper, we present a hybrid energy scavenging sensor where self-powering is employed for long-term ambient mechanical strain monitoring, whereas data digitization, framing, telemetry and high-voltage floating-gate configuration/programming are performed remotely using RF powering. As a hybrid energy scavenger, the sensor can seamlessly harvest working energy from both vibrations and RF signals under different working conditions. Therefore, the sensor does not experience any downtime and can continuously operate by recording key statistics of the ambient strain signals. Sensor prototypes with an integrated 13.56MHz RF interface have been fabricated in a 0.5-m standard CMOS process and the measured results verify the long-term autonomous monitoring capability of the sensor.