Passive temperature compensation in piezoelectric vibrators using shape memory alloy–induced axial loading

Piezoelectric materials have been widely studied as vibration energy harvesters in civil and mechanical systems, given their energy conversion ability and high mechanical to electrical coupling properties. Several external environmental effects, such as temperature, alter the performance of these transducers, thus limiting the longevity and the efficiency of the powered systems. Several techniques are applied to improve the harvesters’ properties and offset the environmental effects. These techniques include the optimization of the piezoelectric material, the use of matching networks to increase the power transfer, and, most importantly, the tuning of the harvester’s resonant frequency to match the fundamental frequency of the input excitation vibration, ensuring a maximum response. In this article, the effects of temperature variations on the energy harvesting characteristics of a bimorph cantilever lead zirconate titanate piezoelectric beam are studied. A proposed mechanical tuning, based on the application of an axial load to compensate the temperature effect, is presented. Mathematical models, which describe the combined effects of temperature and axial load on the natural frequency of the piezoelectric device, are derived. Finally, a fully passive temperature compensation mechanism is proposed. Experimental results are also shown to validate the presented results and the proposed concept.