Performance Of A Proposed Obliquely Incident Noncontact SAW Motors

Surface acoustic wave(SAW)motors are a special kind of ultrasonic motors,where surface acoustic waves are generated through interdigital transducers(IDTs).Therefore,in addition to the advantages of ordinary ultrasonic motors(such as high output force,high speed,etc.),the SAW motors have some other merits,such as precise positioning at the nanoscale,easy miniaturization,etc.To overcome the deficiency of contact-type SAW motors,noncontact SAWs were proposed,where SAWs at the stator generate acoustic waves in the fluid layer between the stator and the rotor.The acoustic streaming in the fluid drives the rotor.Since the non-contact SAW motors do not rely on the friction between the rotor and stator as the driving force,they have the advantages of no friction loss,longer life and higher speed compared to the contact SAW motors.These advantages enable the non-contact SAW motors to be applied in some special situations,such as microfluidics,on-chip laboratories and other special fields,etc.In previous noncontact SAW motors,the stator is placed horizontally at the bottom of the fluid layer.In this paper,a non-contact rotary motor driven by obliquely incident SAWs is proposed,and the performance of the motor is studied and analyzed.The thesis is composed of the following four parts:In the first chapter,the research background and the characteristics of SAW motors are introduced firstly,and then,the development history of the motors,from one dimension to two dimensions and three dimensions,from linearity to rotation,from contact type to non-contact type,is briefly summarized.Finally,the problems faced by different types of motors are discussed.The second chapter introduces our ideas on how to optimize the design of noncontact SAW motors.Two aspects are considered:(1)The optimization of the IDT structure.A better structure of IDTs can greatly improve the efficiency of the motor in converting the input electrical power into the SAW energy.(2)The optimization of the incident angle of the SAWs.By adjusting the angle of the SAW propagating in the fluid layer,acoustic waves propagating parallel to the liquid surface can be obtained,so that most of the SAW energy can be converted to the kinetic energy of the rotor.In the third chapter,the non-contact rotary motor driven by obliquely incident surface acoustic waves is studied experimentally.Firstly,the experiments are carried out under different excitation voltages and incident angles.It is found that the angular speed of the motor is the highest when the inclination angle is equal to 66°.Then,the influence of the rotor diameter on the motor performance is studied with the incident angle being 66°.It is found that: for the motors driven by parallel IDTs,the rotor with a smaller diameter can obtain a larger angular velocity.For the motor driven by Focused-IDTs,the performance is affected by the relation between the rotor diameter D and the offset X,which is the staggered distance between the central axes of the two Focused-IDTs.Finally,we study the influence of different types of Focused-IDTs on the motor,including parallel IDTs and Focused-IDTs,bidirectional IDTs and SinglePhase Unidirectional Transducers(SPUDTs),and Focused-IDTs with the focusing angle being 40° and 60°.The experiments indicate that the SPUDTs with the focusing angle of 40° have better performance.The fourth chapter summarizes the whole paper and points out the research work that can be carried out in the future.