Determination of optimal crystallographic orientations for LiNbO₃ and LiTaO₃ bimorph actuators

The actuators for precise positioning based on bimorph structures of piezoelectric LiNbO3 and LiTaO3 crystals are considered. The optimal orientations of the actuator plates ensuring the highest possible displacements are determined by the extreme surfaces technique and the finite-element method. The simulated displacements for optimal orientations of LiNbO3 and LiTaO3 plates are compared with those obtained experimentally for manufactured LiNbO3 and LiTaO3 actuators, whose orientations are not optimal. As is shown, the optimal configuration of the actuator allows us to significantly increase its displacement for both LiNbO3 and LiTaO3 specimens.

A piezo driver for piezoelectric bimorph actuators in micro-positioning application

Piezo driver for piezoelectric bimorph actuators is the key component for micro-positioning application. Hysteresis nonlinearity of piezoelectric bimorph actuators limits the performance of micro-positioning systems. A novel piezo driver was developed with Prandtl-Ishlinskii (P-I) model and correction network. The combination of P-I model and correction network can describe the rate-dependent hysteresis. Experiments were performed to validate the proposed piezo driver. The results show that the piezo driver can compensate the hysteresis of the piezoelectric bimorph actuator in the frequency range of 0.1 Hz to 10 Hz, and the accuracy of micro-positioning have been greatly improved.

Optimization of MEMS Actuator Driven by Shape Memory Alloy Thin Film Phase Change

At the microscale, shape memory alloy (SMA) microelectromechanical system (MEMS) bimorph actuators offer great potential based on their inherently high work density. An optimization problem relating to the deflection and curvature based on shape memory MEMS bimorph was identified, formulated, and solved. Thicknesses of the SU-8 photoresist and nickel-titanium alloy (NiTi) was identified that yielded maximum deflections and curvature radius based on a relationship among individual layer thicknesses, elastic modulus, and cantilever length. This model should serve as a guideline for optimal NiTi and SU-8 thicknesses to drive large deflections and curvature radius that are most suitable for microrobotic actuation, micromirrors, micropumps, and microgrippers. This model would also be extensible to other phase-change-driven actuators where nonlinear and significant residual stress changes are used to drive actuation.

Temperature Homogenization of Co-Integrated Shape Memory—Silicon Bimorph Actuators

The high work density and beneficial downscaling of shape memory alloy (SMA) actuation performance provide a basis for the development of actuators and systems at microscales. Here, we report a novel monolithic fabrication approach for the co-integration of SMA and Si microstructures to enable SMA-Si bimorph microactuation. Double-beam cantilevers are chosen for the actuator layout to enable electrothermal actuation by Joule heating. The SMA materials under investigation are NiMnGa and NiTi(Hf) films with tunable phase transformation temperatures. We show that Joule heating of the cantilevers generates increasing temperature gradients for decreasing cantilever size, which hampers actuation performance. In order to cope with this problem, a new method for design optimization is presented based on finite element modeling (FEM) simulations. We demonstrate that temperature homogenization can be achieved by the design of additional folded beams in the perpendicular direction to the active beam cantilevers. Thereby, power consumption can be reduced by more than 35 % and maximum deflection can be increased up to a factor of 2 depending on the cantilever geometry.