THERMAL ENERGY CONVERSION BY COUPLED SHAPE MEMORY AND PIEZOELECTRIC EFFECTS

A new concept of thermal-to-electric energy conversion by coupling shape memory effect (SME) and direct piezoelectric effect (DPE) is proposed, and two prototypes of thermal energy harvesters are fabricated and tested experimentally. First is a hybrid laminated composite consisting of TiNiCu shape memory alloy (SMA) and Macro Fiber Composite (MFC) piezoelectric. This composite had 0.1 cm3 of active materials and harvested 75 μJ of energy for a temperature variation of 60 °C. The second prototype is a SME/DPE "machine" which uses the thermally induced linear strains of SMA and bends a bulk PZT ceramic plate through a specially designed mechanical structure. The SME/DPE "machine" with 0.2 cm3 of active material can harvest 90 μJ at heating and 60 μJ at cooling by 20 °C. In contrast to usual pyroelectric materials, the proposed harvester is compatible with small and slow temperature variations. The integration into MEMS using sub-micron multilayers of active materials is currently under way.