Analysis and Design of Power Processing Circuits for Thin Film Piezoelectric Energy Harvesters on Flexible Polyethylene Terephthalate Substrates

Piezoelectric potassium niobate based harvesters with active films' thickness between 200 nm and 400 nm are fabricated by vacuum radiofrequency (RF) sputtering on plastic polyethylene terephthalate substrates. Using gold electrodes at the opposite sides of the samples, they show piezoelectric rms voltage between 300 mV and 600 mV generated from 3 cm2 area, according to the film's thickness. The obtained current from a single harvester is up to $1\ \mu A$. An AC/DC power processing circuit topology intended for this type of piezoelectric energy harvesters is proposed and investigated. A DC/DC monolithic low-power converter is connected between the output port of the bridge rectifiers with smoothing capacitor and the load (such as rechargeable battery or supercapacitor (SC)) in order to properly regulate the rectified voltage. Experimental tests, conducted by using the synthesized piezoelectric energy harvesters on flexible substrates, validate the theoretical analysis and results.