The application of shape memory alloys (SMA) for actuators is still limited to a couple of particular prototypes, and only a few commercial actuators are available. One of the main reasons is the lack in robustness regarding substantial fatigue and changes in boundary conditions. In order to improve the life time behavior and reduce the fatigue of SMA actuators, a self-sensing control strategy is presented. Based on resistance feedback, the heating power at full contraction is controlled in order to avoid overheating without reducing the operating voltage. This allows fast actuation without thermal overload of the SMA. The concept was proved experimentally. Life time tests show a considerable increase in life cycles and reduce of fatigue.

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Our contribution will describe the basic fundamentals of shape memory alloys. Emphasis will be given to specific characteristics for the use of shape memory wires in actuators. The investigation of shape memory wires in actuators includes qualitative and quantitative benchmarking based on measurements at different test beds. To display applicability of shape memory wires for different tasks, the main focus will be on the influence of different bias forces, the determination of performance, and the possibility of position control without position sensors.

The deposition of a single-layer piezoelectric thin film on superelastic shape memory alloys has been experimentally investigated. Therefore, the ultrasonic-assisted hydrothermal method was used for preparing a crystalline thin film on various NiTi-based substrates without an additional buffer layer between substrate and thin film. The deposited layers were crystallographically characterized by scanning electron microscopy, X-ray diffraction, and piezoresponse force microscopy. Due to the hydrothermal synthesis with ultrasonic assistance, the PbZrO 3 thin film-in general antiferroelectric-exhibits ferroelectric hysteresis loops, which has been experimentally tested.

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