A vibration piezoelectric energy-harvesting (PEH) sensor interface IC including high-efficiency power management and readout circuit for structural health monitoring is presented in this paper. The PEH interface consists of a parallel synchronized switched harvesting on inductor (SSHI) rectifier, and a novel duty cycle based maximum power point tracking (MPPT) circuit implemented with comparators and a switched capacitor. The comparators in both the SSHI and MPPT controllers are dynamically biased to provide fast response with low power. The switched capacitor based MPPT can tune the output voltage to suit the input effectively with a simple circuit structure. Moreover, the vibration frequency can be monitored to wake up the readout circuit when a certain threshold (20 Hz) is surpassed, indicating a possible catastrophic event. The readout circuit includes a low-power amplifier with dynamic bias, providing a programmable gain of 4/8/32/128 for the following 12-bit SAR ADC. The proposed system is implemented in a 55 nm standard CMOS technology. Experimental results show that a peak MPPT efficiency of 98.7% and up to 711% output power enhancement are achieved at 133 Hz resonance frequency. Moreover, the event driven wake-up of the readout circuit is successfully demonstrated. With a 11.3-bit ENOB achieved in the SAR ADC, the vibration frequency, temperature, and strain can be extracted from the proposed interface IC.

Multiple parameter environment monitoring via wireless Internet of Thing sensors is growing rapidly, thanks to low power techniques of the node. More importantly, the ever more complex and highly efficient energy harvesting systems enable long-term continuous monitoring in inaccessible environments without needing to change the battery. This paper reviews existing energy harvesting modalities, including photovoltaic, piezoelectric, pyroelectric, electromagnetic, and vibration, together with circuit techniques of interfacing power management circuits for energy harvesters. Moreover, techniques used to interface with multiple mode energy harvesters to obtain a stable output power with optimal power efficiency are discussed as an emerging direction. The state-of-the-art energy harvesting systems together with future development trends are provided.