An Experimental Study of Levitation by Acoustic Holography

Abstract

There are various technologies for levitating and manipulating objects. For example, there are technologies using magnetic force or optical radiation force. In these technologies, the target objects are limited to magnetic materials or transparent dielectrics. On the other hand, the technology using acoustic radiation force can be applied to almost all solids and liquids. This technology is called acoustic tweezers. Acoustic holography has been studied with regard to acoustic tweezers. Acoustic holography is one of the methods to generate acoustic tweezers. In this method, many ultrasonic transducers arranged in an array are used. By adjusting the phase of each ultrasonic wave, various force fields can be generated and levitation objects can be realized. One of the problems of levitating objects using acoustic holography is that detailed performance such as the limit of size and weight of the target object has not been clarified. In order to solve this problem, it is necessary to establish a design method and to verify the performance of levitation experimentally. In this study, we designed the experimental device in order to use acoustic holography, and experimentally verified the performance of levitating objects by using the device. The experimental device we designed has 49 ultrasonic transducers, and each transducer can be driven with different phase and intensity. Therefore, acoustic holography can be used by using this device. First, we evaluated the feasibility of levitation by using objects of various densities and diameters. As a result, levitation was realized when the density of the objects were 23.5 kg/m³ or less. Second, we conducted the experiment to examine the relationship between the levitation height and the diameter of the object. As a result, it was found that the smaller the diameter of the object with respect to the wavelength, the higher the levitation height.