A series-SSHI-Phi interface circuit for piezoelectric energy harvesting with 163% improvement in extracted power at off-resonance

This paper presents the design and implementation of a series-SSHI-phi interface circuit for piezoelectric energy harvesting with improved operating frequency range. Adopting a nonlinear switching architecture, complex impedance matching can be achieved at off-resonance by introducing delay into switching timing. A buck-boost converter following the rectifier is used for resistive-load emulation and energy transfer. Implemented with a 0.25-μm CMOS HV process, experimental results with a commercially available piezoelectric device show a 56.1% improvement in 3-dB bandwidth compared to conventional series-SSHI interface. Furthermore, a 163% improvement in extracted power is demonstrated with -2% of frequency mismatch. When vibrating at resonant frequency of 126.7 Hz with 0.5 g acceleration and a 1.1-g tip mass, the harvester is able to extract 165 μW after considering the 12 μW of control power.