Simulation And Experiment Research Of Ultrasonic Standing Wave Levitation Performance

Ultrasonic standing wave levitation, one of non-contact support technologies,can be used to simulating the environment of outer space on the Earth,provides an ideal experimental environment with microgravity for biochemistryand materials science, and overcomes the problems caused by the traditionalcontact operation, such as surface damage of precision components. Ultrasonicstanding wave levitation make use of the ultrasonic wave to form a high-intensityultrasonic standing wave trap (acoustic radiation force) between the transducer andthe reflector, and the levitated particle will be captured and suspended in the soundfield. When the length between the transducer and the reflector is exactly an integermultiple of a half wavelength, the sound field produces resonance and form a stablestanding wave.Firstly, this paper analyzes the acoustic wave equation in the ideal medium,and derives the distribution of the velocity of medium particle and the soundpressure in the plane wave field. Combined with Gor’kov’s time average potentialtheory, this paper provides the expression of parameters used to measure the soundsuspension ability (relative time average potential, relative elasticity coefficient),the expression of axial acoustic levitation force, and predict the stable levitatedposition of ultrasonic standing wave levitation. Through constructing the modelof collision, this paper points out the theory of acoustic levitation based onmomentum conservation theory.Secondly, this paper discusses the influence of structure parameters (the lengthbetween the transducer and the reflector, the reflection surface diameter andthe radiation surface diameter) of acoustic levitation system with a plan reflector onthe suspension ability, and then, optimizes the structure parameters. According tothe focusing effect of concave spherical surface，the single-axis acoustic levitationsystem is designed with a concave reflector. In the realization of two layersuspension points, the structure parameter of the acoustic levitation device isoptimized to obtain a better ability of levitation. The acoustic field is simulated,respectively to determine the stable levitated position and relative elasticity coefficient at the different cavity length when the reflection surface is a plane and aconcave spherical surface. Relative time-average potential is presented with Finiteelement analysis software ANSYS and Matlab software, from which the levitationability of the levitation system can be compared.Finally, Acoustic levitation experiment device is established according to theprinciple of single-axis acoustic levitation. The suitable ultrasonic power andultrasonic transducer are selected. The finite element analysis software ANSYS isused for the modal analysis of the ultrasonic transducer. The resonant frequencyof transducer is measured by an impedance analyzer and the amplitude of thetransducer surface is measured by a high performance single point laser vibrometer.At last, levitation experiment of the foam ball with2mm in diameter is carried outto test the suspension ability and stability of the acoustic levitation device.