Experimental Investigation On Near-field Acoustic Levitation

Nowadays, traditional clamping technology could no more be able to meet the demands required in semiconductor industry and precision machining field. Research of new non contact holding methods became a pressing problem at this stage. Near-field acoustic levitation (NFAL) means of suspending solid objects above the ultrasonic vibrator at very tiny distance by using ultrasonic waves with high power density. Compared with other suspension methods, NFAL has the advantage of preferable ability of electromagnetic interference resistance and stronger anti-static ability, thence, NFAL is more suitable for purification and super cleaning operations. While, there is still a lack of necessary knowledge and research on near-field acoustic pressure distribution, suspension requirements for complex shape objects still cannot be effectively addressed. At the same time, evaluation criterion for stability of clamping methods using NFAL is still a blank.In views of the problems raised above, the ultrasonic field brought about by a disc-shaped vibrator was taken as the research object in the dissertation. By designing and building relative test systems, distribution of the near-field acoustic pressure and the suspension state of a sample disc in the ultrasonic field was measured, then, analysis was taken based on experimental data. Results confirmed the practicability and credibility of the test systems. Main research contents and achievements of the dissertation are as follows.We have analyzed the phenomena of NFAL, discussed the causes of the levitated force, and by combining analysis of ultrasonic effects, we determined the measuring technical essentials and evaluation indexes of near-field acoustic pressure used for non-contact clamping. We have developed different acoustic pressure sensors of special structure, fully simulated the coupling acoustic field between the suspended object and surface of the ultrasonic radiator, and we have successfully measured the near-field acoustic pressure of a disc-shaped vibrator. The3D distribution model of the acoustic field was presented through processing the experimental data by curve fitting, which made the measurement results more reference and guidance for non-contact gripping.In order to observe the motion features of a suspended object, we for the first time designed a new strategy to collect the spatial features simultaneously by using orthogonal laser beams. Based on the strategy, a measuring system with two laser optics was built which helped a lot to the experiment; analysis and evaluation about sample discs’suspension state were also presented by actual measurement and data processing. We also built a6d.o.f. index system to evaluate the suspension stability.The works listed above have contributed to the understanding of NFAL, and the research results could provide support for applications of NFAL...