Surface Acoustic Wave Motor Research Articles

Rayleigh wave excitation with an elliptical reflector for high-power ultrasound

This study proposes a Rayleigh wave transducer with an elliptical reflector for high-power ultrasound (ELIPS). In contrast to conventional transducers using IDT with single crystal piezoelectric plates or wedge transducers, our ELIPS enables high-power Rayleigh wave excitation in the megahertz range, which will be useful for applications such as surface acoustic wave (SAW) motors, SAW tactile devices, and SAW atomizers. The driving principles of the transducer are Rayleigh wave excitation with a transverse wave source and transverse wave focusing with a dilatational wave source and an elliptical reflection surface. The effectiveness of this mechanism was confirmed with an FEM simulation, and the Rayleigh wave excitation was validated using a prototype transducer. Finally, the high-power characteristics were examined, and a maximum vibration amplitude of 15.5 nm at 1.0 MHz was successfully obtained. It should be noted that this vibration amplitude is not a saturated value, and a much higher value could be realized with higher input power.

Friction Layer Analysis of a Surface Acoustic Wave Motor

Abstract This study applied appropriate assumptions to simplify a surface acoustic wave (SAW) motor model, as well as the elastic friction layer concept to analyze the two-dimensional contact problem. The effect of inertial force was factored into the equation of motion for the friction layer; the relationship between external force and the displacement of the friction layer surface was determined via Fourier transform; and the displacement field under different loads was analyzed using numerical methods. Based on the friction theory proposed by Armstrong, the relative velocity of the friction layer between the slider and stator was considered in the relationship between the normal and tangential forces acting on both contact surfaces. Finally, the deformation and the contact forces acting on the friction layer were evaluated by assuming the displacement of the stator substrate.

Characteristic measurement of a surface acoustic wave nano-stepping motor by using a fiber-optic Michelson interferometer

The actuation technique of a surface acoustic wave motor with nanometer scale linear motion was experimentally investigated in this study. The surface acoustic wave motor comprised a stator made of a Y+128° cut, X-propagation lithium niobate substrate with silicon sliders and an array of pillar projections manufactured using semiconductor fabrication techniques. Two sets of interdigital transducers deposited on the substrate were used to generate Rayleigh waves with a driving frequency of up to 9.7 MHz. The surface acoustic wave motor was driven by friction exerted on the contact area between the slider and the surface acoustic waves in a retrogressive elliptical locus. The stepping motion of the surface acoustic wave motor was measured directly using a fiber-optic Michelson interferometer through demodulation with a digital signal processing method. A displacement of several nanometers was achieved at each step during the experiment.

Contributions to the development of an axisymmetric SAW motor with a stator made from non-piezoelectric material

Surface acoustic wave (SAW) motors offer great potential due to their high blocking forces, high positioning accuracy and simple design. As established SAW motors have a plane stator made by piezoelectric single crystals, designers have nearly no influence on changing material properties like the friction coefficient or brittleness. Furthermore, the efficiency decreases with rising travel length, caused by components of the SAW passing the slider. This article presents the theory of Rayleigh waves on cylindric rods in axial direction of propagation. Based on this, a new axisymmetric motor structure with a stator made from non-piezoelectric base material, which could avoid the problems mentioned above, was analytically characterized. Furthermore, a prototype of a plane SAW motor made from non-piezoelectric steel is presented. SAW were generated by small piezoelectric units made from lead zirconate titanate (PZT). At the working frequency of 3.85 MHz a SAW with an efficiency of 17% was generated. An idling speed of 29 mm s−1 and a blocking force of 0.19 N were measured therewith. Finally, we present a SAW generation by thick film technology. This technology allows the manufacture of piezoelectric units on cylindric rods that are necessary for the mentioned axisymmetric SAW motors. Our prototypes are compared to numeric models.

Dual friction-drive SAW motor utilizing cylindrical shaft as external load driver

This work presents an ingenious mechanism using dual frictional-drive (DFD) for surface acoustic wave (SAW) linear motor resulting in significantly compact and lightweight design. The device uses two synchronous Rayleigh waves propagating on two 128° rotated y-cut x-propagated lithium niobate (LiNbO3) piezoelectric stators facing each other and driving a cylindrical slider held tightly between the stators in translational motion. By reversing the direction of propagation of both the SAWs, the direction of motion of the slider can be reversed. The experimental results of the proposed SAW motor demonstrate the novel mechanism to form the device where the slider is attaining a steady state velocity of 1.28 m/s for a continuous wave excitation of frequency 13.5 MHz.

Investigating translational motion of a dual friction-drive surface acoustic wave motor through modeling and finite element simulation

This study presents the investigation of translational motion of a surface acoustic wave (SAW) linear motor employing dual friction drive (DFD) through mathematical modeling and finite element simu...

Excitation of Rayleigh wave with sapphire/LiNbO3 mechanical integration for surface acoustic wave motor

The surface acoustic wave (SAW) motor, as a type of traveling wave ultrasonic motor, has been studied for years. A Rayleigh wave is excited by a unidirectional interdigital transducer (U-IDT) in a lithium niobate stator. Through frictional force, a driven slider can achieve linear motion. At the contact surfaces of the stator and slider, one problem observed is the lack of tolerance to wear. Owing to the large mohs hardness, a novel approach to the fabrication of a sapphire stator is investigated to improve frictional durability. In the novel sapphire stator, the Rayleigh wave, generated by the lithium niobate U-IDT transducer, is transmitted to the sapphire stator surface through pure mechanical integration. Through measurement results, the sapphire stator is evaluated via the admittance characteristics of the wave excitation unit, the normal vibration of the Rayleigh wave, and the horizontal vibration velocity of the Rayleigh wave.

Recent developments of piezoelectric motors with diverse operating principles

This article presents an extensive review of the developments in the field of piezoelectric motors involving different operational concepts. The review is carried out for ultrasonic motors and surface acoustic wave motors using resonant vibrations of piezoelectric substrates. The traditional upbringings of ultrasonic motors using standing and travelling waves along with surface acoustic wave driven motors are presented. Further this research work gives a scope to understand the recent development of various driving principles and different characteristics of piezoelectric motors.

Finite Element Simulation of a SAW Motor based on Dual Friction-Drive

The paper presents a finite element simulation and analysis of a dual friction-drive surface acoustic wave (SAW) motor. The SAW motor consists of a cylindrical slider placed between two identical lithium niobate (LiNbO3 or LN) stators facing each other. Typically the LN stator contains an interdigital transducer (IDT) fabricated on either side of it so that the application of sinusoidal voltage excitation to the IDT generates travelling Rayleigh SAW on the surface of the stator. The SAWs propagating in the two stators interact with the slider and under the preload applied on the stators the generated frictional force drives the slider. The direction of motion of the slider can be reversed by reversing the direction of SAWs. Finite element simulation of the motor is carried out to study the characteristics such as displacement and velocity of the slider for sinusoidal excitation.

Modelling and Finite Element Simulation of a Surface Acoustic Wave Driven Linear Motor

The paper presents modeling and finite element simulation of a surface acoustic wave (SAW) linear motor. A SAW linear motor works on the principle of friction drive provided by SAW propagating on a piezoelectric stator. The SAW motor comprises of a cubical slider driven by Rayleigh wave generated on a piezoelectric substrate using an interdigital transducer (IDT) fabricated on the stator. In the study, a lithium niobate piezoelectric substrate is used as the stator on which aluminum IDTs are fabricated at the two edges and a cuboid slider is placed in the path of SAW propagation along with a preload. The characteristics such as displacement, velocity and forces acting on the slider for different amplitudes of wave excitations are studied. The slider in the SAW motor can move both in forward and reverse directions and the motor attains a saturated velocity with the continuous wave excitation.

Stator optimization and evaluation method in a surface acoustic wave motor

The interdigital transducer (IDT) of a surface acoustic wave (SAW) motor comprises two unidirectional IDTs (U-IDTs), including a driving IDT (D-IDT) and a reflector IDT (R-IDT). In order to improve the conductance of the U-IDT, the distance between the D-IDT and the R-IDT will be adjusted. The novel U-IDT will be investigated by simulation and some measurements. The novel stator will be fabricated by the basic semiconductor planar process. On the other hand, a stator evaluation method for the SAW motor will be reported. Lastly, through the calculation of the wave power, the measured vibration amplitude and stator recycle efficiency will be unified.

J1130104 弾性表面波モータの実負荷特性測定について([J113]次世代アクチュエータシステム)

A surface acoustic wave (SAW) motor is small and low in profile with high speed and large thrust in linear motion. Hence the performance has been evaluated from transient response even though the reliability is rather low. We tried to measure the thrust directly using loading mass. Difficulty of thrust evaluation by loading mass is tiny size of the slider in mm dimensions and huge thrust in several N. Moreover, the moving distance of the SAW motor is short in a few cm. Hence the SAW motor has to be stopped before the mechanical system for the measurement becoming in static condition. The loading mass was connected with steel wires even though the wires were elastic. But we cannot use bulky material for mass connection due to small size. By evaluating the stretch of the steel wire, the speed vs. load was successfully measured. The loading force was estimated from the wire elasticity and the stretching value from the measurement using two sets of laser Doppler velocimeter (LDV). We successfully proved that the actual SAW motor thrust is 60 % larger than that of the estimated value from transient response; 4.0 N against 2.5 N for example.

2205 弾性表面波モータの薄型化について(センサ・アクチュエータ(2))

Surface acoustic wave motor has been investigated and then its superior performances such as high speed, high thrust, quick response and so on are demonstrated. However, for high performance operationg of the SAW motor, huge laboratory setup are required. From the view point of low-profile elements of the motor, namely, thin stator and thin slider, low-profile actuator system should be designed.

Study of Piezo-Induced Surface Vibration in Solids Using Atomic Force Probe

Piezo-induced surface vibrations in solids with nanometer amplitude are detected and analyzed. The vibrations are excited by the piezo element using a PZT component, which attached to the target material and controlled by a signal generator. The detections of such vibrations are carried out using the atomic force probe (AFP). The AFP is a very sensitive instrument utilizing a nano-tip connected to a cantilever to detect vibrations through an interaction of atomic force between the tip and the target surface with sub-nanometer resolution, about 30 times more precise than the piezoelectric sensor for the same signal detection. The glass material has been chosen as the target solid. The enhancement effect of the vibrations in the glass slice around resonance frequency is confirmed, the maximum amplitude appears at 7.4 kHz. The piezo-induced vibration will be employed in our future research for developing piezo-induced and laser-induced surface acoustic wave (SAW) motor.

5PM3-PMN-023 マイクロ表面テクスチャによる表面弾性波モータの駆動力の向上(OS6 マイクロナノトライボロジー,ポスターセッション)

Surface Acoustic Wave (SAW) motor is an actuator driven by friction force, in which larger driving force is generally required. To reply such requirement, larger driving area is expected theoretically. On the other hand, driving force of the SAW motor decreases by adhesion of wear particles at the at the contact interface. In this study, larger driving force is realized with larger driving area by introducing surface texture and hard coating such as DLC and W-DLC for controlling behavior of wear particles.

Theoretical and visualization study of laserinduced surface acoustic wave on annular stator

The mechanism of laser-induced surface acoustic wave (SAW) on annular stator is theoretically and experimentally studied. An annular stator with groove arrays is specifically designed. The physical model of laser-induced SAW on the stator is established, and the key factors influencing the wave amplitude are disclosed. We introduce a new kind of visualization method to detect laser-induced SAW on the copper-made annular stator, under a pulsed laser of 1053 nm wavelength, 30 ns pulse width and 1 mJ pulse energy. The results show that when the location of the irradiating laser spot is near the groove arrays, the SAW propagating towards the groove will be attenuated and absorbed immediately by the groove arrays, while the SAW away from the groove can keep propagating along the stator surface. In this way, the one-way propagation of laser-induced SAW is successfully acquired. In the contrast experiments, the laser-induced SAW travels in both directions on a copper ring without groove arrays, resulting in a chaotic state of the surface acoustic wave. The one-way SAW induced by pulsed laser on the annular stator will be used in the laser-driven SAW motor in the future.

2P1-G05 高温環境での利用を考慮したクリップ型両面駆動SAWモータの試作(超環境ロボット・メカトロニクス)

Surface acoustic wave motor has been investigated and then its superior performances such as high speed, high thrust, quick response and so on have been demonstrated. In case of application for high temperature environment, linear guide-less construction will be better for actual application, For the linear guide-less design, preload mechanism using clip is tested. Successfully, the operation of SAW motor is confirmed, the speed was low.

Two-Dimensional Motor Based on Surface Acoustic Wave

With the development of high precision processing, the miniaturization demand of motors with super-precision positioning and simple fabrication become an urgent problem. This paper illustrates a surface acoustic wave (SAW) motor for two-dimensional positioning. The SAW motor include a SAW stator and a slide. In order to realize the two-dimensional moving, four Interdigital Transducer (IDTs) are fabricated on the four directions of a 0.5-mm thick, 128°YX- LiNbO3substrate. Comparing the aluminum material, the copper material selected to be used as IDT in our experiment has many advantages. Each of the four copper IDTs has 10 straight finger pairs in a simple repeating pattern, the IDT aperture is 10mm and the pitch is 400μm. The SAW stator is fabricated by the lift-off process. The dimension of the device is 29mm (width) X29mm (length). The slide consists of three ruby balls with the diameter of 1mm and an plastic disc with the thickness of 0.5mm and the diameter is 8mm. With the four radio frequency driving sources, two-dimensional motion is possible. The maximum speed of the slide that was placed on the SAW propagating surface was 5mm/s when the applied driving power was 28W and the applied driving frequency was 9.6MHz. The experiments indicate the two-dimensional motor based on SAW would be applicable to miniature motor and improve the resolution.

Surface Acoustic Wave Motor

In an energy recovery type surface acoustic wave motor, an increase in energy efficiency at the time of energy recovery and supply is achieved by adjusting phase change. A surface acoustic wave motor comprises: a surface acoustic wave substrate; a slider provided with an applied pressure; a driving interdigital electrode connected to an external power supply for generating a driving surface acoustic wave on a surface so as to drive the slider by a frictional force which is generated on a contact surface of the slider with the surface acoustic wave substrate based on the surface acoustic wave and the applied pressure; recovery interdigital electrodes placed forward and backward in the direction of travel of the surface acoustic wave for recovering energy of a surface acoustic wave unused to drive the slider, and for using that energy to generate a surface acoustic wave; and phase adjusting means for matching the phase of a surface acoustic wave generated by the recovery interdigital electrodes to the phase of the driving surface acoustic wave generated by the driving interdigital electrode.

204 二次元弾性表面波モータのための駆動面設計に関する研究(学生賞III,一般講演)

204 二次元弾性表面波モータのための駆動面設計に関する研究(学生賞III,一般講演)