Mathematical modelling and experimental validation of an ultrasonic linear actuator

Abstract

This research presents a novel approach to the optimisation and experimental validation of a linear surface acoustic wave (SAW) actuator, emphasising advanced measurement techniques. The SAW-driven actuator comprises a stator and a slider. The stator is made of a 128° rotated, Y-cut, X-propagated LiNbO₃ piezoelectric substrate with comb-structured aluminium electrodes as interdigital transducers (IDT) patterned at both ends of the surface, called the delay line. The slider made of silicon material is placed on the active area of the delay line with an initial preload. A unique measurement methodology was employed to analyse the influence of preload and friction on the slider's motion, optimising key influential parameters such as preload force (5 mN) and coefficient of friction (0.45) for smooth actuation. This work integrates single-point and multipoint contact of the slider with the stator, which is analysed through a Multiphysics simulation environment, enabling precise tracking of the slider’s displacement and velocity in vertical and horizontal directions. A microfabricated MEMS SAW actuator was developed to validate the numerical predictions, and its electrical and mechanical properties were experimentally characterised using state-of-the-art measurement techniques. MATLAB and COMSOL simulations provided insights into the actuator’s response, which were subsequently validated by the movement of the slider. The experimental results confirmed that the slider achieved a steady-state speed of 0.3 m/s or more with a Rayleigh wave of 13.5 MHz and an amplitude of 12 nm. This study establishes an optimised balance between preload and friction for efficient motion, contributing to the miniaturisation of SAW actuators for applications of micromirror movement.