Design, characterization and perspectives of shape memory alloy elements in miniature sensor proof of concept

The use of shape memory alloys (SMAs) has found numerous applications in several different areas. In particular, in the mini/micro actuation field, SMAs have the advantage of having high power to weight ratio, improved reliability and reduced complexity in the design of the active mechanism. In recent years, several devices have been developed that use SMAs to promote free recovery (null forces), constrained recovery (partial displacement) or work-producing devices. In all these cases, forces and/or displacements are produced by the SMA element upon a heating/cooling cycle. This paper presents an experimental investigation on the potentiality of using SMA in the development of self-contained temperature sensors. The current work proposes some proof of concept devices based on both the one-way and the two-way shape memory effect exhibited by the same NiTiCu alloy wire. The results of the thermal and mechanical characterizations of the SMA element are reported. The choice of the shape of the SMA element, core of the sensor activation, and of the configuration of the whole device are presented in different variations for the one-way and two-way configurations. Finally, a functional investigation of the assembled sensors illustrates their features in terms of operating temperature and cycling effect. The proposed design concepts confirms the effectiveness of SMA in the light-weight technology and they show some examples of sensor applications in miniature scale that can be calibrated in terms of operating temperature, overall dimensions and SMA strain-to-output transducing method. © 2014 Elsevier B.V. All rights reserved.