In this paper, a new micro electro-thermal actuator with bidirectional vertical motion is introduced, analyzed and tested. In traditional vertical electro-thermal actuators, the arms of actuators are fabricated with different widths to provide high and low electrical resistance for the hot and cold arms. Applying electrical current to the arms results in different thermal expansions between the hot and cold arms, which force the tip of the device to bend. The new bidirectional vertical thermal actuator (BVTA) eliminates the parasitic electrical resistance of the cold arm through the use of a ‘U’ shape structure. This U-shape structure provides a larger deflection with improved electrical efficiency due to the use of an active return current pass. The U-shape actuator is more beneficial in applications such as variable capacitors where a larger deflection is needed to increase the tuning range. For analysis and design purposes, an effective method to transfer the continuous system to a lumped model is presented. Simulation and test results are provided to show the deflection and effects of the design parameters on the actuator performance.
Electrothermal actuators have a very promising future in MEMS applications since they can generate large deflection and force with low actuating voltages and small device areas. In this study, a lumped model of a two-hot-arm horizontal thermal actuator is presented. In order to prove the accuracy of the lumped model, finite element analysis (FEA) and experimental results are provided. The two-hot-arm thermal actuator has been fabricated using the MUMPs process. Both the experimental and FEA results are in good agreement with the results of lumped modeling.
Strong shock waves can be generated by pulse discharge in water. Study of the pressure characteristics and attenuation law of these waves is highly significant to industrial production and national defense construction. In this research, the shock-wave pressures at several sites were measured by experiment under different conditions of hydrostatic pressure, discharge energy, and propagation distance. Moreover, the shock-wave pressure characteristics were analyzed by combining them with the discharge characteristics in water. An attenuation equation for a shock wave as a function of discharge energy, hydrostatic pressure, and propagation distance was fitted. The experimental results indicated that (1) an increase in hydrostatic pressure had an inhibiting effect on discharge breakdown; (2) the shock-wave peak pressure increased with increasing discharge voltage at 0.5 m from the electrode; it increased rapidly at first and then decreased slowly with increasing hydrostatic pressure; and (3) shock-wave attenuation slowed down with increasing breakdown energy and hydrostatic pressure during shock-wave transfer. These experimental results were discussed based on the mechanism described.
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