Target Microspheres Driving Based On Ultrasonic Near-field Acoustic Levitation

The development of world economy benefits from fossil fuels, such as coal, petroleum and natural gas, but which is almost over. Controllable nuclear fusion will provide us with a virtually inexhaustible source of clean, accessible energy. Inertial confined fusion (ICF) is one of effective method, which can realize controllable nuclear fusion. But how to support target pellet in laser radiation field is a problem. At present, the widespread use of the rod supports target pellet, baffling uniform radiation. However, magnetic levitation supporting must add magnetic material, which is effect on uniformity, stability and luminous efficiency of target pellet.To overcome these shortcomings, we propose a new method which combines ultrasonic near-field acoustic levitation and pneumatic driving. In this work, ultrasonic levitation system and pneumatic driving system are designed and tested, based on principle of acoustic levitation, influencing factors of levitation height, and control method of pneumatic driving.At first, vibration deformation of transducer is deduced by the theory of elastic mechanics. Then, radiation force generated by transducer is analyzed when circle plate is levitated. Finally, the levitation height formula of the special transducer with concave spherical surface is deduced and simplified. The formula demonstrates that the levitation height is related with amplitude of transducer, mass and radius of levitating object, and density of medium. The levitation height is changed by adjusting these factors.The ultrasonic transducer is the key components to realize near-field acoustic levitation. PZT-8is chosen as piezoelectric material. Duralumin and45#steel are chosen as front cover plate and back cover plate, respectively by specific application. The transducer is designed through theory, but acoustic field generated by transducer with concave spherical surface is unknown, so it is taken that the finite element parametric thoughts to design height and radius of concave spherical surface. The results demonstrate that height is2.5mm and radius is5mm are the best parametric. On this basis, the prototype is manufactured.Based on theory analyzed before, the ultrasonic levitation system is established and tested. The experimental results demonstrate that levitation height is growth, and disturbance is reduction with driving voltage increasing. On this basis, a radius coupling coefficient is introduced, to correct levitation height formula of the transducer with concave spherical surface. Load effect of resonance frequency is obtained by combining theory and experiment:resonance frequency is a little reduction with load mass increasing.Based on the ultrasonic levitation system, the pneumatic driving system is established and tested. The experimental results demonstrate that the pressure is the main factor which affected rotational speed of round sphere. The higher pressure is, the faster round sphere rotated. Eccentricity of outlet has a little effect on rotational speed of round sphere. Levitation height is reduction, and disturbance is growth with rotational speed increasing.Our work will provide a method that it realizes ICF target pellet non-contact supporting and controlling by the ultrasonic levitation and pneumatic driving.