This paper examines the time and frequency response characteristics of two-arm micromachined thermal actuators. Two types of thermal actuators are considered: hot/cold arm actuators and ‘V’ or ‘chevron’ shaped actuators. A heat transfer equation governing the temperature profile along the thermal actuators is derived. Equations for the thermal time constants and the frequency responses are presented. The thermal time constants and frequency responses are measured experimentally and compared to analytical predictions.

This article investigates rectangular two-beam microelectromechanical thermal actuators and provides a method for their optimization. The thermal actuators investigated consisted of two asymmetric parallel arms,one thin and one wide. Under an electric current load, the thin arm heats and expands more than the wide arm, thereby bending the entire structure. Simplified models of the heat transfer mechanisms are used to determine the temperature profile. From the thermal expressions for expansion of the arms, equations are derived to predict the deflection as well as the buckling loads. Measurements of the actuator deflection as a function of voltage are presented. Design guidelines are introduced for optimization of a thermal actuator.

Surface-micromachined actuators made in multi-user MEMS processes (MUMPs) have been operated underwater without modifying the manufacturing process. Such actuators have generally been either electro-thermally or electro-statically actuated and both actuator styles are tested here for suitability underwater. This is believed to be the first time that thermal and electrostatic actuators have been compared for deflection underwater relative to air performance. A high-frequency ac square wave is used to replicate a dc-driven actuator output without the associated problem of electrolysis in water. This method of ac activation, with frequencies far above the mechanical resonance frequencies of the MEMS actuators, has been termed root mean square (RMS) operation. Both thermal and electrostatic actuators have been tested and proved to work using RMS control. Underwater performance has been evaluated by using in-air operation of these actuators as a benchmark. When comparing deflection per volt applied, thermal actuators operate between 5 and 9% of in-air deflection and electrostatic actuators show an improvement in force per volt applied of upwards of 6000%. These results agree with predictions based on the physical properties of the surrounding medium.

Force and power characteristics are experimentally measured for three types of toggling microthermal actuators: (i) standard two-arm thermal actuators, (ii) chevron or ‘V’ type actuators and (iii) chevron actuators with a toggle amplifier. Micro-Newton scale forces and micron scale displacements are experimentally measured using an off-chip probe. For each type of actuator, force versus deflection curves are measured to determine mechanical advantage and maximum ranges. For each type of actuator, work output versus input power curves are measured to determine actuator effectiveness. Different actuator designs are compared in terms of force, displacement, power and effectiveness.

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