Shape Memory Alloys (SMAs) exhibit temperature-dependent cyclic deformation. SMAs undergo reversible phase transformation with heating that generates strain which can be used to develop heat engine. In this study, we build upon the concept where environmental heat is first converted into mechanical energy through SMA deformation and then into electrical energy using a microturbine. This SMA heat engine was tailored to function as a miniature energy harvesting device for wireless sensor nodes applications. The results showed that 0.12 g of SMA wire produced 2.6 mW of mechanical power which was then used to drive a miniature electromagnetic generator that produced 1.7 mW of electrical power. The generated electrical energy was sufficient to power a wireless sensor node. Potential design concepts are discussed for further improvements of the SMA heat engine for the wireless sensing platform. Wireless sensing nodes are becoming ubiquitous addressing the requirements on variety of platforms including structural health monitoring, smart healthcare system, and industrial automation. The challenge with the implementation of wireless nodes lies in powering them over a long period of time, in most cases greater than 5 years. This need has driven research on the energy harvesters that can convert the locally available energy into electricity and replenish the storage media. Along this line of thought, we demonstrate here a thermal energy harvesting concept that has significant promise in the constant temperature environment. KeywordsConventional methods for low power energy harvesting from heat are mainly based upon the thermoelectric or pyroelectric effect. Thermoelectric (TE) devices convert temperature gradient across the device into electricity. Pyroelectric devices generate electricity in response to the alternating temperature variations. Pyroelectric materials have been reported to possess higher efficiencies compared to other thermal harvesters approaching up to 50% (Sebald, Pruvost, and Guyomar 2008 Roundy et al. 2004). However, TE devices require an effective heat sink which adds to the size, cost, and complexity of the device. In addition, the efficiency for these devices at temperatures below 200°C is below 5% and at temperatures below 100°C efficiency drops to much less than 1% (Ismail et al. 2009). This study focuses on an alternative heat energy recovery mechanism for applications where temperatures are less than 100°C. The mechanism is based on the shape memory alloy (SMA) that exhibits memory effect which translates into a mechanical force when driven beyond the austenite finish temperature. SMAs have been utilized in numerous actuations and sensing applications (Kudva 2004;Morgan 2004;Villanueva et al. 2010;Villanueva, Smith, and Priya 2011;Tadesse et al. 2012). They have also been explored for heat engine applications, where the first one was developed more than half a century ago (Banks 1975). Since then, several researchers have utilized the SMAs for converting heat

No abstract

No abstract