Characterization and comparison of piezoelectric materials for transducing power from a thermoacoustic engine

Andrew Brian Evans Wekin

There is a growing need for small, reliable sources of electric power. A piezoelectric transducer coupled to a small scale thermoacoustic engine has the potential of producing high density power in a compact, lightweight system with no moving parts. The goal of this study is to identify and characterize some potential piezoelectric transducers for use in this thermoacoustic piezoelectric system. Four piezoelectric transducers are presented which represent a range of stiffness and electromechanical properties. All samples are tested to characterize their electrical and mechanical parameters and then driven by an acoustic device, or sound tube, over a range of frequencies and acoustic pressures to determine the operating conditions for maximum power output. One open and one closed standing wave thermoacoustic engine is also employed to generate power with each sample and these results are shown to correlate with the power output data from the sound tube. All results are tabulated to facilitate prediction of power output for any sample under given conditions. For open conditions, the most compliant sample has the highest power output. The 12x20mm PVDF (polyvinylidene fluoride) sample generates 12 µW on the open sound tube at a resonant frequency of 140 Hz with an acoustic pressure of 38.2 Pa RMS. This sample has an electromechanical coupling k2 of 0.0014, a mechanical Q of 16.84, a stiffness of 15.5 N/m and a power density of 250 W/m3. For closed conditions, the sample with the highest coupling has the highest power output. On the closed sound tube, the 15mm diameter PZT (lead zirconate titanate) disk generates 2.22 µW at a resonant frequency of 1500 Hz, with an acoustic pressure of 38.2 Pa RMS and an acoustic to electric efficiency of 17.2%. This sample has an electromechanical coupling k2 of 0.0319, a mechanical Q of 4.9137, a stiffness of 11600 N/m and a power density of 122.8 W/m3. This sample also generates the most power from the closed thermoacoustic engine: 177 µW at 470 Hz and 796 Pa RMS. The results show that mechanical Q is significantly lower for closed conditions for all samples; coupling coefficient k2 is higher for the closed conditions for the PZT disk and the PVDF samples but lower for the other samples; and the stiffness, resonant frequency, and damping of all samples are significantly higher in the closed conditions.

Characterization and comparison of piezoelectric materials for transducing power from a thermoacoustic engine

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