Abstract
This paper reports the design, fabrication and performance of MEMS-based piezoelectric bidirectional conveyors featuring 3D printed legs, driven by linear travelling waves (TW). The structures consisted of an aluminium–nitride (AlN) piezoelectric film on top of millimetre-sized rectangular thin silicon bridges and two electrode patches. The position and size of the patches were analytically optimised for TW generation in three frequency ranges: 19, 112 and 420 kHz, by the proper combination of two contiguous flexural modes. After fabrication, the generated TW were characterized by means of Laser–Doppler vibrometry to obtain the relevant tables of merit, such as the standing wave ratio and the average amplitude. The experimental results agreed with the simulation, showing the generation of a TW with an amplitude as high as 6 nm/V and a standing wave ratio as low as 1.46 for a device working at 19.3 kHz. The applicability of the fabricated linear actuator device as a conveyor was investigated. Its kinetic performance was studied with sliders of different mass, being able to carry a 35 mg silicon slider, 18 times its weight, with 6 V of continuous sinusoidal excitation and a speed of 0.65 mm/s. A lighter slider, weighting only 3 mg, reached a mean speed of 1.7 mm/s at 6 V. In addition, by applying a burst sinusoidal excitation comprising 10 cycles, the TW generated in the bridge surface was able to move a 23 mg slider in discrete steps of 70 nm, in both directions, which is a promising result for a TW piezoelectric actuator of this size.
Highlights
The field of micro-electro-mechanical systems (MEMS) comprises a great variety of sensors and actuators that represent a rising platform for several applications, such as telecommunications, chemistry, biosensors or automotive engineering [1,2]
The benefits associated with miniaturization allowed for improved performance, compact size, low power consumption, array configurations and low manufacturing costs in MEMS sensors
ultrasonic motors (USM) are devices based on a rotor or slider pressed against a stator surface, where elastic vibrations induce rotational or linear movement by friction between surfaces [7,8,9]
Summary
The field of micro-electro-mechanical systems (MEMS) comprises a great variety of sensors and actuators that represent a rising platform for several applications, such as telecommunications, chemistry, biosensors or automotive engineering [1,2]. The use of piezoelectric films for an all-electrical actuation scheme, integrated into the monolithic fabrication process, allowed for a further step into the miniaturisation of efficient motors In this regard, TW-based bidirectional rotatory motion in the millimetre scale was demonstrated using thin-film PZT on silicon rotors with teeth by two degenerate orthogonal modes [26]. Tellers et al [28] proposed a different approach, where an array of PZT-actuated micro-hammers worked as a linear conveyor, capable of transporting 2 mg masses at 1 mm/s with 5 V excitation and positional errors as low as 2%, without speed control.
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