Analysis and optimization of thermoacoustic-piezoelectric energy harvesters: An electrical circuit analogy approach

The performance of standing and traveling wave thermoacoustic-piezoelectric energy harvesters are developed using an electrical circuit analogy approach. The harvesters convert thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The input thermal energy generates a steep temperature gradient along a porous medium. At a critical threshold of the temperature gradient, self-sustained acoustic waves are developed inside an acoustic resonator. The associated pressure fluctuations impinge on a piezoelectric diaphragm, placed at the end of the resonator. The resulting interaction is accompanied by a direct conversion of the acoustic energy into electrical energy. The behavior of these two classes of harvesters is modeled using an electrical circuit analogy approach. The developed models are multi-field models which combine the descriptions of the acoustic resonator and the stack with the characteristics of the piezoelectric diaphragm. The onset of self-sustained oscillations of the harvesters are predicted using the root locus method and SPICE software (Simulation Program with Integrated Circuit Emphasis). The predictions are validated against published results. The developed electrical analogs and the associated analysis approach present invaluable tools for the design and the optimization of efficient thermoacoustic-piezoelectric energy harvesters.