Uniaxial Annular Clamping Force Of Ultrasonic Levitation Device

Acoustic levitation is the technology that the sample stable suspend in the acoustic field.This technology use the acoustic radiation force that generated by high intensity acoustic standing wave fields balance the gravity of samples. Acoustic levitation has a very unique application in many research field or engineering field such as the analysis of tiny samples or droplets,containerless processing, the ground space simulation, space simulation and so on.Acoustic levitation device consists of three parts,ultrasonic generator, ultrasonic transducer and acoustic reflector. Currently there are two commonly used acoustic levitation device, single-axis acoustic levitation and three-axis acoustic levitation. Single-axis acoustic levitation is simple and convenient design, but less stable suspension. The device has good suspension stability, but its high development cost, design and operation is rather complicated and not use the application.Three-axis acoustic levitation has good stable suspension, but its high development cost, design and operation in a complex way, not conducive to applications.In this paper, based on the principle of acoustic levitation, we analysis the structure of various types of devices,and design the single-axis acoustic levitation that has annular clamping force by changing the reflector and emitter. This device improve the function of the single-axis acoustic levitation.This study covers the following aspects:(1) Based on acoustic levitation theory, the structure of the single-axis acoustic levitation is analysised. By change the reflector and emitter,the single-axis acoustic levitation generate the annular clamping force. By this way, stable suspension is improved;(2) The paper study the characteristics of two kinds of acoustic levitation's resonator-the plane reflector-emitter and the convex reflector-emitter, by the finite element method,and calculate the acoustic field and the acoustic radiation force in those resonantor. The acoustic pressure and acoustic radiation force distribution in various resonantor are simulated by Matlab tool, and the three physical factors are discussed;(3) Under the one dimension design theory assumption, the frequency equation half-wave is derived. According to the frequency equation the sandwich piezoelectric transducer (lead titanate) which meet this research needs is designed, the whole set of ultrasonic levitation device is designed, processed and studied experimentally.This research showed that: (1) The standing-wave field of the plane reflector-emitter single-axis acoustic levitation is of axial symmetry, satisfy the Helmholtz equation and boundary conditions, the acoustic field and the acoustic radiation force in resonantor show periodic change in the vertical direction, and can not produce acoustic radiation force gradient.in the horizontal direction. In the homologous sample circumstances, the acoustic radiation force in plane reflector-emitter resonantor decreases with increasing incident frequency and transmitter radius. The smaller the vibration mode, the greater the acoustic radiation force.(2) In the resonantor of convex reflector-emitter single-axis acoustic levitation, the sound field distribution also meet the Helmholtz equation and boundary conditions, the acoustic field and the acoustic radiation force in resonantor not only present periodic change in the vertical direction, but also produce acoustic radiation force gradient. in the horizontal direction. The possibility that the sample divorced from levitation region greatly reduced because the levitation samples in ring clamping force field of this resonantor.(3)For certain resonantor of convex reflector-emitter acoustic levitation, the transmitter radius is definite, the sum of convex transmitter height and reflector height is half-wavelength. A series of peaks of maxium acoustic radiation force has appeared with the convex transmitter radius, incident frequency and vibration mode.(4)The plane reflector-emitter acoustic levitation has been experimentally studied by using two cylindrical piezoelectric ceramic transducer. The results show that acoustic levitation device can suspendhree samples on the groud condition,but suspension stability is poor in the horizontal direction,and the sample is easy to divorce from the levitation area.