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Shape-memory-alloy (SMA) has attracted considerable attention in recent years as a smart and efficient material, due to its unique properties. SMA microactuators became one of the potential solutions for unresolved issues in microelectromechanical systems (MEMS). This paper presents a thermomechanical behavior analysis of bimorph SMA structure and studies the effect of varying the SMA layer thickness, the type of stress layer and its thickness, and the processing temperature on the displacement of the microactuator. Furthermore, the analyzed results were verified by experimental work, where the fabrication of the SMA microactuators followed the standards of the MEMS fabrication process. SiO, SiN and Poly-Si were used as stress layers. The fabrication results showed that the bimorph SMA structure achieved maximum displacement when SiO was used. The SMA structure with dimensions of 10 mm (length) × 2 mm (width) × 80 µm (thickness), had maximum displacement of 804 µm when 4.1 µm of SiO layer was deposited at a temperature of 400 °C. [ABSTRACT FROM AUTHOR]

This paper reports a study on wireless radiofrequency (RF) power transfer to and heat generation in micropatterned coils for wireless control of thermally-driven microdevices. Inductor-capacitor circuits with the planar spiral coils act as RF receivers as well as frequency-sensitive wireless heaters that selectively produce heat when resonated with external RF magnetic fields. Electrical and thermal characterizations are performed using two sets of microfabricated circuits with varying numbers of turns and fill ratios defined in the spiral coils. The measurements in electrical parameters of the circuits, coupling coefficient, power transfer efficiency, and heat generation have been evaluated and parameters show good consistency between them. These tests reveal maximum power transfer efficiency and steady-state temperature of ~35 and 99 °C, respectively, for the coil with a fill ratio of 0.55. The reported results will serve as a basis for the design of the wireless heater, which provide a promising path to radio-control of thermoresponsive actuators such as shape-memory alloys and hydrogels. [ABSTRACT FROM AUTHOR]