We present a self-powered interface external circuit design for multiple piezoelectric oscillators used in our recently developed low-frequency acoustic energy harvester. A synchronized switch harvesting on inductor (SSHI) interface circuit has exhibited a significant improvement in the energy harvesting efficiency of piezoelectric oscillator, compared with a standard circuit in AC/DC conversion. A self-powered SSHI interface circuit was developed to overcome the difficulties of typical SSHI, such as the requirements for external power and displacement sensor. The previous studies on self-powered SSHI only considered a single piezoelectric oscillator. The electrical response and operation of multiple piezoelectric oscillators in self-powered SSHI interface circuit has not been reported. In our previous study, multiple piezoelectric cantilever plates were installed in a quarter-wavelength tube resonator to harvest acoustic energy. The interface circuit for our acoustic energy harvester was not further discussed. In this study, a self-powered series-SSHI circuit (self-powered S-SSHI) for multiple cantilever piezoelectric plates has been studied by circuit simulation software Multisim. The simulation results indicate the total powers increase linearly with the piezoelectric plate numbers for both standard and self-powered S-SSHI circuits. The harvesting efficiency for multiple piezoelectric plates of self-powered S-SSHI is obviously higher than the standard circuit. The total maximum output power of 5 piezoelectric plates reaches 8.417 mW with the areal power density 0.421 mW/cm~2. This is 335.2% better than the standard circuit (1.934 mW with the areal power density 0.0967 mW/cm~2). Compared with the standard circuit, self-powered S- SSHI circuit significantly enhances the conversion efficiency by increasing the piezoelectric voltages and reducing the phase shifts between piezoelectric sources currents and voltages.
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