Design of Contoured Microscale Thermomechanical Actuators

In this paper, we disclose how to contour the beams of microscale thermomechanical actuators (TMAs) in order to enhance the actuator's thermal and mechanical performance. In this approach, we vary the cross-section of the heated beams over the length of the beams. Using this approach, the stored strain energy and axial stiffness of the beam may be modified to achieve an optimized force-displacement relationship. Examples are provided to show that in some designs: 1) the maximum achievable thermal strain of a driving beam may be increased by 29%, 2) actuator stroke may be increased by a factor of four, and 3) identical force or displacement characteristics may be achieved with a 90% reduction in power. This paper presents the theory and models used to predict the thermal and mechanical behavior of the actuator. The theory and models were used to create a deterministic link between the actuator's design parameters and the actuator's performance characteristics. The theory and models were combined within a design tool that is posted at http://pcsl.mit.edu. The tool has been used to generate performance plots that enable designers to: 1) understand the quantitative relationships between design parameters and performance and 2) rapidly converge upon first-pass design parameters.1695