This study aims to examine the effect of annealing conditions on nitinol (NiTi) characteristics and applies this knowledge to fabricate a NiTi-copper shape memory alloy bimorph actuator. The effect of the annealing conditions was investigated at various temperatures, i.e., 500, 600, and 650°C, for 30 min. With the characterizations using x-ray diffraction, energy dispersive spectroscopy, and differential scanning calorimetry techniques, the results showed that annealing temperatures at 600 and 650°C were able to appropriately form the crystalline structure of NiTi. However, at these high annealing temperatures, the oxide on a surface was unavoidable. In the fabrication of actuator, the annealing at 650°C for 30 min was chosen, and it was performed at two pre-stressing conditions, i.e., straight and curved molds. From static and dynamic response experiments, the results suggested that the annealing temperature significantly affected the deflection of the actuator. On the other hand, the effect of pre-stressing conditions was relatively small. Furthermore, the micro gripper consisting of two NiTi-copper bimorph actuators successfully demonstrated for the viability of small object manipulation as the gripper was able to grasp and hold a small plastic ball with its weight of around 0.5 mg.

This work proposes a novel and simple fabrication process of a nickel-copper thermal bimorph actuator. This new fabrication process employs only two-step electroplating technique that is easy, cheap and compatible for various materials. In this study, the total thickness of fabricated cantilever actuator is around 80 μm, i.e. 30±10 and 50±10 μm for nickel and copper, respectively, and its length is equal to 22.5 mm. For actuator’s width, it is varied as 258±7, 351±7 and 447±7 μm. After heating by applying current through the actuator’s structure, the actuator bends up due to the elongation mismatch between copper and nickel elements. It is found that the deflection becomes larger for a narrower actuator. From the experiments, the deflection at current of 2.5A for 258±7 μm wide actuator is approximately equal to 4 mm. In addition, the response of all actuators is faster than 1 Hz. With obtained large deflection and fast response, the fabricated actuators are viable to employ for flow control applications.

In this work, a magnetic membrane actuator that involves simple fabrication process and low cost is developed based on electroplating technique, and its dynamic performance is examined. The magnetic actuator consists of an element of soft ferromagnetic material embedded in PDMS circular membrane. It is driven by attracting the soft ferromagnetic element using external magnet that is attached on a shaft of electrical motor. When the shaft is rotated, the magnet will move back and forth towards the membrane. In this study, the nickel element as a soft ferromagnetic material is designed as a simple circular disk with four straight arms, and it is fabricated into three different thicknesses, i.e. 49±3, 70±7 and 100±6 μm, while PDMS thickness is fixed at 280±33 µm. The dynamic performances of 2-cm membrane actuators are examined using a capacitive sensor in the actuating frequency range of 40-240 Hz. The experimental results show that there are two motion patterns, i.e. small and strong oscillations, where the transition frequency is approximately at 100 Hz. In addition, with the increment of nickel element’s thickness, gain and peak frequency, where gain peaks occur, increase while peak-to-peak amplitude decreases.