音響ホログラフィによる物体浮揚に関する検討

抄録

Optical tweezers are well known as methods for trapping and manipulating objects. They are often used when the target objects are μm order or less. In contrast, acoustic-based methods (acoustic tweezers) are used when the target objects are mm order. Acoustic holography has been studied with regard to acoustic tweezers. Acoustic holography is one of the methods used to generate acoustic tweezers. Various force fields are generated in the space by adjusting the phases of ultrasonic transducers arranged in an array in this method. In this study, we designed the experimental setup in order to use acoustic holography, and experimentally verified the performance of levitating objects by using the setup. First, in order to use acoustic holography, we designed the experimental setup. In this setup, 49 ultrasonic transducers were arranged in a square shape. By sending signals from the FPGA board to the transducers, desired force fields are formed. Each transducer can be driven with different phase and intensity. By using this setup, ultrasonic waves were focused on a certain point, and the sound pressure at the point was measured. Only 25 transducers were used because of dynamic range of microphone. The measured sound pressure was 1930 Pa. If this pressure works perpendicularly to the surface of a 3.5 mm diameter sphere, the force will be balanced with the gravity acting on the object of the density of 2740 kg/m³. Second, in order to verify the performance of levitating and manipulating objects, I measured the sound pressure distribution when on creating a force field to levitate objects. The shape of the force field was the twin trap. The twin trap is the force field that horizontally sandwiches objects. As a result, the styrofoam elliptical plate with a mass of 0.3 mg can be levitated at a height of 86 mm.