Design and Implementation of Interface Circuits Intended for Printed Piezoelectric Micropower Harvesters on Flexible Substrates

Abstract

Interface circuits with low power dissipation is proposed and implemented, which is useful for efficient AC/DC voltage conversion of thin-film piezoelectric micro-power stack mounted harvesters. The focus is on low-power (< 1 μW) elements consisting of printed PVDF-TrFE piezoelectric polymer on BaSrTiO3 coated flexible substrate with total thickness of the stack 3.1 μm. Using silver thin films as bottom and top electrodes, the samples exhibited stable piezoelectric rms voltage between 200 mV and 400 mV produced from functional area of ∼1.5 cm2 when stimulates it with sine-wave vibration with frequency of 50 Hz and intensity equivalent to mass loading between 1–80 g. The current registered from a single harvesting element is not greater than 1 μA. For this type of harvesters two power processing circuits intended are designed and built. The first circuit is a voltage doubler, for which the rectified output voltage is approximately equal to twice of the amplitude of the input voltage. The second circuit is a voltage quadrupler; as compared to the first one it provides higher voltage for charging a small and thin-size chip supercapacitor connected to the output port, but due to diodes voltage drops a smaller value of the energy efficiency can be obtained. For the implementation of the electronic circuits, low-power Schottky diodes with a forward voltage below 100 mV at current up to 0.1 mA are chosen. An experimental study to verify the efficiency of the proposed circuits is performed with laboratory made thin-film piezoelectric harvesters.