Research On A New Near - Field Acoustic Suspension System

As early as in1886, there were studied on ultrasonic levitation. At that time, according to the experiments, it found that the dust particles can suspend at the resonant cavity in the acoustic waves. Under the acoustic radiation force, ultrasonic suspended make the object is suspended. It can be divided into near-field acoustic levitation and standing wave suspension. This paper mainly studies the near-field acoustic levitation.In recent years, near field acoustic levitation has gained much attention. It is the use of high intensity acoustic field that the acoustic radiation pressure and the suspended matter gravity is phase equilibrium, so that objects were suspended in the acoustic field. In the field of the precise machining, especially for the surface of the device which had higher requirement and had a wide application. For example, in the semiconductor industry, the wafer surface roughness and cleanliness requirements is very high. Therefore, it has an important significance for the study of near field acoustic levitation technique. There have been many scholars have conducted research on near field acoustic levitation system front, Professor Whymark was first discovered near field acoustic levitation. American Chu of Yale University and Apfel is derived and calculated near-field acoustic levitation of the radiation pressure and levitation force. Ueha and the Hashimoto study the relationship between near-field acoustic levitation force and surface of sound source amplitude, height of suspension, reach a conclusion that when the suspended objects is planar, the suspension height is proportional to sound source surface displacement amplitude, and is inversely proportional to the square root of suspended matter density. Since then, they have study on the near-field acoustic levitation system stability, laying the foundation for the application of near-field acoustic levitation in industry. The German scholar Reinhart established the near field of ultrasonic levitation system that the radiation surface is concave, used as a non-contact fixture, but the suspension is not stable, so there is no use in industrial production.By reading literature, find the key issue of the near-field acoustic levitation technique is how to improve the stability of suspension system and how to increase the acoustic levitation force. For the above problem, this paper did the research and discuss at the following: (1)According to the principle of plane wave reflection and transmission when the normal incident, conclude that in the near-field acoustic levitation system, when the incident wave spread to the surface of suspended matter in the surface, there was almost the total reflection. According to the acoustics theory, the calculation method of circular piston sound radiation pressure in an infinite baffle. We obtained the formula of exponential type rotary actuator disk surface acoustic radiation pressure.(2)Through the analysis, know if the radiator surface displacement amplitude or vibration velocity is larger, can obtain bigger acoustic levitation force. So how to obtain larger surface vibration velocity or amplitude, through a lot of reading literature, found that the use of high amplitude ultrasonic transducer can get a larger surface vibration velocity or amplitude. The large amplitude of ultrasonic transducer is composed of the ultrasonic transducer and ultrasonic horn. This paper used the longitudinal composite piezoelectric transducer, through the principle and design of ultrasonic transducer, it obtained the calculation formula of the vibration velocity distribution, the stress distribution and the frequency equation of the longitudinal composite piezoelectric transducer. Through calculation, it obtained the size of the ultrasonic transducer when the working frequency is20kHz.This paper use amplitude bar with a conical transition section, according to the principle and design of ultrasonic horn, obtained the displacement node, horn formulas of amplification coefficient, shape factor of the ultrasonic horn. When the ultrasonic horn had work at the20kHz, it calculated the size of the ultrasonic amplitude transformer.Finally, using the finite element software, analysis of the vibration amplitude of ultrasonic transducer, and obtained its resonant frequency.(3)By using the finite element software, calculate the exponential type rotary actuator disk near field acoustic suspension system resonance frequency, and get the distribution curves of displacement index type near the surface rotating excitation disc at0.5mm by choosing the path. Then, through experiments are consistent with the calculated resonant frequency and finite element software. And through the displacement tester get the three-dimensional displacement distribution of the index type rotating excitation disc. Finally, by loading the coupled fluid solid boundary conditions, obtained the acoustic field distribution of the index type rotary actuator disk, and compared its distribution with the disk surface pressure. By comparing, it obtained this conclusion that exponential rotational excitation disc surface acoustic radiation pressure is greater than the surface of the disk near the acoustic radiation pressure.