Theoretical And Experimental Study Of Noncontact Handling And Transportation System Based On Near Field Acoustic Levitation

Near field acoustic levitation (NFAL) has been used in non-contact handling andtransportation of small objects to avoid contamination. In semiconductor manufacturing andmicro-assembly, it is difficult to handle and transfer the wafer or component of MicroElectromechanical System (MEMS) due to their fragility and surface sensitive characteristics.Classical processes usually contain mechanical contacts, which may result in the destructionof fragile parts or cause some degree of surface damage. Also, particles are generated andthus contaminate the working space. The major advantage of NFAL lies in the fact that anymaterial, insulator or conductor, magnetic or non-magnetic, can be manipulated by acousticlevitation and transportation without physical contacts.The noncontact wafer handling and transportation systems based on NFAL have beenstudied in this dissertation. We have built theoretical models, designed and optimized thedriving parts and built up the experimental systems. We have also tested and analyzeddynamic performances during handling and transporting process. Experimental data matchwell with theoretical calculations, thus proves the accuracy and reliability of our theoreticalmodel. The main research content and achievements are as follows.Based on viscous fluid equations of motion, we have studied the mechanism of near fieldacoustic levitation. We have built theoretical model of gas squeeze film considering flexuralboundary condition, gas inertia and edge effect. Solving such nonlinear partial differentialequation, high resolution central scheme has been developed in numerical solutions, and approximate analytical solutions have been studied by equivalent method. By accounting theflexural mode shape of the vibrator, we have extended the applications of the theoreticalmodel. By accounting gas inertia and edge effect, accuracy of the model has been improvedgreatly. With high order solutions, our model can provide quantitative analysis for squeezefilms, including velocity and pressure distributions, levitation forces and driving forces.We have built dynamic models of noncontact systems, including the coupling effect ofrail, gas film and levitated object. The relationship between traveling waves and forces hasbeen studied. Static and transient responses have been solved by finite differential method.According to velocity and pressure distributions of the gas film, we have calculated restoringforces and moments with small eccentric and inclination. Consequently we have discussedthe anti-disturb ability of the gas film generated by vibrators with different cross sections,which provide theoretical basis and optimization method for transducer design.Piezoelectric transducers have strong electrical-mechanical coupling. The coupled FEAmodel with transducer and large surface vibrator has been built in this dissertation.Simulations have been performed to get mode shapes, amplitude distributions andimpedances, which are used for design of the driving part. The coupling has been proved bymeasurement. Moreover in simulations, dimension sensitivity on electrical-mechanicalcharacteristics has been discussed, which provide a general method for optimizingtransducers used in NFAL.Finally, noncontact levitation and transportation systems have been built for experimentalresearches. To serve wafers of different size, we have set up two levitation device with tworadiuses, thus enhanced the contrast of different conditions and reliability of data. In thedesign of transportation systems, electrical and mechanical impedance matching has beendiscussed. Optimal matching program can be achieved by experimental debugging. Fortesting of dynamic performance during levitation and transportation, measuring systems havebeen built, which provide powerful data for comprehensive evaluation of noncontact systems. Compared with experimental data, our theoretical model has the highest precision, with erroraround5%. Good agreement with experiment enables the theoretical model to quantitativelyexplain the NFAL mechanism, predict dynamic response inside the squeeze film, and finallyhelp design the noncontact transportation systems effectively. Meanwhile, by large amount ofexperimental tests, key techniques of design and manufacturing have been concluded, forexample, precise requirements in dimensions to guarantee traveling wave generation andtransporting. At this point, it provides a theoretical foundation for practical applications.