Co-investigator Anantha Chandrakasan
Vibration-based machine health monitoring provides an efficient real-time method for tracking the health of industrial motors, thereby achieving predictive maintenance and avoiding machine downtime. Vibration sensors are attached to the vibrating motors, and periodically transmit data indicative of machine health. To power such monitors, we demonstrate a vibration-based energy harvesting system. It extracts power from 50Hz industrial motors and comprises a co-designed MEMS-based transducer and associated low-power management circuit.
The MEMS-based energy harvester can generate about 1 mW output power under matched load at resonance. However, its high quality-factor results in significant reduction in output power and voltage at off-resonance conditions. The system is made resilient to manufacturing variations which cause a mismatch between the harvester’s natural resonance and the motor frequency by using the interface power electronics. A Meissner oscillator circuit is used to achieve battery- less cold-start from low harvester-voltages at off-resonance. A regular operation circuit is designed to operate once the cold-start circuit generates above-1V output voltage (Vout). This circuit employs an H-bridge to interface the harvester whose FETs are switched based on current-feedback. The load-storage element is toggled between the two ports of the harvester to synthesize the desired load-current at any frequency. The circuit thus accomplishes conjugate-impedance matching for efficient power extraction from the harvester. Further, it can tune the harvester’s source reactance to electrically shift its resonance to achieve increased bandwidth of operation.
The IC implemented in the Taiwan Semiconductor Manufacturing Company (TSMC) 180nm process is co-designed with the harvester achieves cold-start from 150mV-peak AC-voltage from the harvester at 5% off-resonance (10x state-of-the- art). The H-bridge circuit is able to deliver 800 μW to the load at 71% efficiency at resonance. It is also able to perform frequency tuning to account for manufacturing tolerances (A first low- power IC demonstration for this application).