Design and Construction of a Piezoelectric Transducer for Acoustic Levitation

Abstract

Sound can levitate objects of different sizes in air and water. This feature allows cells, liquids, or compounds to be handled without being touched or contaminated. Acoustic levitation is usually achieved through one or more piezoelectric transducers. Among different types of piezoelectric transducers, the Langevin-type transducer, formed by pairs of piezoelectric ceramics rings sandwiched between two loading masses and coupled by a central bolt, is one of the most used transducers in acoustic levitation. The piezoelectric materials, when excited with a specific electrical potential, respond by deforming mechanically. Thus, the transducer acts as an actuator, generating displacement amplitudes that depend on the frequency. At the resonance frequency, the displacement of the transducer face is maximum. In this work, we design and fabricate a piezoelectric transducer to assembly a single-axis acoustic levitator capable of levitating objects larger than the acoustic wavelength. This approach is fundamental for developing a new generation of levitation devices called “acoustic robots.” A numerical model based on the Finite Element Method was employed for simulating and designing the transducer. Then the transducer parts were machined in a mechanical workshop, and the transducer was assembled and characterized. The designed Langevin transducer consists of two piezoelectric ceramics pressed between two metallic aluminum cylindrical masses and a mechanical amplifier composing the transducer body. The characterization of the Langevin transducer was done by measuring its electrical impedance curve. As a result, resonant frequency response was found around 21.560 kHz with a minimum impedance of 95 Ω and the anti-resonance frequency at 21.685 kHz with a maximum impedance of 81.502 kΩ. The transducer successfully levitated a polyacetal disk of 3.1 mm radius, 2 mm thickness, and a mass of 85 mg.