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 down- time 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-μm standard CMOS process and the measured results verify the long-term autonomous monitoring capability of the sensor.