Location：Faculty&Staff > Faculty
Piezoelectric Materials and Actuators Group,
Ph.D. (1996～2000): Department of Electromechanical Control and Automation, Faculty of Mechatronic Engineering, Harbin Institute of Technology, China
Associate Professor (2003～now): School of Materials Science and Engineering, Tsinghua University, China
Part-time Academic Job
IEEE member, 《IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control》Permanent Reviewer,
1、Piezoelectric Material and Multilayer Piezoelectric Ceramic（MPC）
2、Piezoelectric Devices and Applications
3、Simulation, Optimization and Measurement of Piezoelectric Structures and Devices
1. A Fundamental Research on Some Key Techniques of Ultrasonic Motors
The traveling wave type and standing wave type of ultrasonic motors driven by the frictional mechanism are researched as major objects in this project. The project includes as follows: considering the dynamic models of the ultrasonic motors as electromechanical couple systems, studying some optimal design methods of the structures and optimizing control techniques using multivariable, miniaturizing and integrating of the drivers, as well as developing some new types of ultrasonic motors with the patent rights. The investigative contents of the project comprise also other key techniques: improving efficiency, increasing lifetime, enhancing control accuracy and reducing noise level of the ultrasonic motors. The implementation of the project will provide theoretical and technical foundation for industrialization of the ultrasonic motors in China.
2. Optimization design technology of novel piezoelectric micro motor
As to application and industrialization, we come up against the same problems about the development of the novel micro piezoelectric motor with an outer diameter smaller than 3mm. In this item, a new type of piezoelectric micro motor with a rod-shaped ceramic stator and higher output torque, superior to conventional piezoelectric motors with a film or cylinder stator, has been fabricated. According to the vibration theory and piezoelectricity, vibration model of the prototype motor was measured using scanning laser vibrometer PSV300 and miniature driving circuit with excellent impedance matching was designed. Through laser Doppler technology and FEM, its structure was also optimized. The maximum output torque can reach to 0.4mNm for stainless steel stator and 0.35mNm for copper stator. The preload is about 270mN and the resonant frequency 57 to 62 kHz. This kind of motor may be applied in the fields of military industry, mobile telephone, robots, medical appliances, and aerospace, etc.
3. Two-DOF Precision Piezoelectric Positioning System for Optical Adjustments
A two degree-of-freedom precision positioner driven by two ？15 mm ultrasonic motors, which use wobble vibration modes and four ring-shaped piezoelectric wafers for each one. The ultrasonic motors are mounted on the one side and driven by two AC input voltages with a 90 degree phase shift and around 40 kHz resonant frequency. The other side of the positioner will be tilted by a thrust force of the screws, which are connected to the output axis of the ultrasonic motors. The positioner is capable to produce a small tilting angle resolution, 0.002°, displacement resolution 20 nm and driving force ～1 Kg. This two degree-of-freedom precision positioner can be applied in the fields of optical communication, laser modulation, etc.
4. Special Piezoelectric Actuators with a Mechanical Position Feedback Ultrasonic motors with multi-points mechanical position feedback will be developed in this project. Among them, ？15 mm wobble ultrasonic motors and ？30 mm traveling wave ultrasonic motors are used to drive the fabricated MPF system, which has a fan-shaped movable element, disk-shaped mounted insulation plate with eight metallic points. Ultrasonic motors will stop at each contact point and restart by a high level from control system. The rotation time between two points is about 100 ms for ？15 mm ultrasonic motors and 150 ms for ？30 mm traveling wave ultrasonic motors. The outline of the circuit is about 70 mm ？50 mm and each circuit has two output terminals for two ultrasonic motors. Standard input voltage of the driver is 10～15VDC and input voltage of the motors is about 400Vp-p.
5. High Performance Multilayer Piezoelectric Transformer
Low-firing multiplayer piezoelectric transformer (MPT) was studied in Beijing Tsinghua University in the 1980’s. This kind of MPT has high voltage step-up ratio, low driving voltage and small size. Its voltage step-up ratio is ten times higher than that of conventional Rosen type single layer transformer. Recently, with the increasing requirement of backlight inverters of portable computers and other electronic instruments, the MPT has attracted significant interests. The low-firing MPT and its inverter have many advantages, such as a thin shape, small size, high transfer efficiency, non electromagnetic interference. A new type inverter used for the backlight driving of liquid crystal display in portable computer are being developed and commercialized.
6. Improve Aerodynamic Character of Aerofoil Using Micro-Oscillating Generator
Presently, applications of the piezoelectric microjet can be found in many fields of scientific instruments, industrial control, biomedicine, etc. Based on different injecting medium, there are two kinds of jet systems: piezoelectric liquid-jet and piezoelectric airflow-jet systems. The piezoelectric liquid-jet system has already been applied to the atomizing drug delivery system, biology mass spectrum analysis, jet printer, etc. while piezoelectric airflow jet system has many potential applications in the fields of electronic refrigeration, military industry, gesture rectification of micro/silicon planet, aerodynamic improvement of aerofoil, etc. A piezoelectric jet element with single nozzle is fabricated and measured in our group. Theoretical model of vibrating piezoelectric-metal composite shell used inside the piezoelectric micro airflow jet is established, and resonant frequency equations and vibrating displacement equations with axisymmetric vibration behavior can be obtained. Using energy method the resonant frequency of the vibrating composite structure is resolved. The detailed emulation calculation and experimental test are developed for the practical piezoelectric micro airflow jet. The experimental results of vibration modes, distribution of displacement and velocity are measured by Laser Doppler Vibrometer. The relationship between the vibrating amplitude and driving voltage is established. The geometrical parameter of the piezoelectric ceramic layer is optimized by FEM.
7. Research on diffuser/nozzle-based valve less piezoelectric pump
A simple structured micropump actuated by a piezoelectric ceramic actuator and fabricated with the silicon-based microelectromechanical system (MEMS) process is presented. The piezoelectric actuation has been employed for the deflection of the membranes because of its benefits, such as small size and no EMI in comparison with the other types, especially electromagnetic counterpart and so on. The micropump consists of silicon and glass by means of anodic bonding. The diffusers are used instead of passive check valves. To analyze the principle of the diffuser/nozzle-based valve less piezoelectric pump, and calculated the cone angle and diffusion ratio which have key influences on the pump performance using fluent software. The diffuser/nozzle-based valve less piezoelectric pump using conventional process has been fabricated by a master Miss. Li EZ in my group, see follows. And silicon-based micropump has been investigating by another doctoral candidate Mr. Wang BW in my group.
8. Various piezoelectric actuating elements and structures
Piezoelectric micro-structure (PMS) with a 5×5mm reflected face for a laser beam scanning has been fabricated using a conventional linear cutting process. This device consists of CuSn4-3 substrate, PZT5A piezoelectric bimorph, micro mechanical hinges, and reflected face. It can generate one-dimensional bending vibration modal shapes with various nodal lines, i.e. the 1st, 2nd and 3rd harmonic motion, which has been measured using Laser Scanning Vibrometer (LSV). The reflected face inside the device can be rotated with the dilatation of the piezoelectric bimorph. By means of analysis on slope coefficient of the reflected area, some factors that affect the scanning angle of the reflected face are investigated. The collected experimental data reveal that the maximum scanning angle of this piezoelectric micro structure ranges from -0.25° to +0.25° under an alternating current 5V. Such piezoelectric micro-structure can be optimized and, in the future, applied as an actuating element inside micro systems, laser modulation system, communication system. And the silicon based PMS and its application will be studied in the future.
9. Piezoelectric transducer for distance measurement
For the application of airborne distance sensing, a bimorph flexural structure is usually used. The maximum operation frequency is limited by the attenuation of sound waves in the air, which increases as the operation frequency increases, and is usually below 100 kHz for sensing distances up to 3 m. The operation frequencies also depend on the physical properties of the materials and transducer structure parameters. The ultrasonic performance of such a transducer, such a directivity of their beam and sound pressure at axial direction strongly depends on the vibration profiles of the transducer. A bimorph flexural PUT based on low-sintering piezoelectric ceramics PMN-PNN-PZT, which have high piezoelectric constant (d33>680pC/N), high electromechanical coupling factor (Kp=0.70～0.73), was fabricated.
10. Disk-Pivot Micro Piezoelectric Actuator Using Vibration Mode B11
Micro piezoelectric actuator using vibration mode B11 (Bmn, where m is the number of nodal circles, n is the nodal diameters) is designed. Different from conventional wobble-type ultrasonic motor using piezoelectric rod or cylinder, piezoelectric disc is used to excite wobble modes and metal cylinder stator is used to amplify the transverse displacement, metal rod rotor is actuated to rotate. The outer diameter of the actuator is 14 mm. There are features such as low drive voltage, micromation, and convenient control of wobble state by modifying the structure of stator, etc. Finite Element Analysis (FEA) of the stator has been made. It is found that the resonant frequency of vibration mode B11 is 49.03 kHz, which is measured at 45.7 kHz by the laser vibrometer and impedance analyzer. The rotation speed has been measured, which could be as high as 10071 rpm under an alternating current 100 V. Such piezoelectric actuator can be optimized and adjusted to fit practical conditions. It can be applied in the fields of precise instrument, bioengineering and other micro actuate system. Besides the above, 3 to 4 new types of micro motors with an outer diameter smaller 8mm and co-fired monolithic multilayer piezoelectric ceramic have been designed and studied by one postdoctor and two masters in my group.
11. Ultrasonic Motor with Slots on the Piezoelectric Vibration Converter
A vibration conversion type ultrasonic motor based on semiwave combined rod type piezoelectric vibrator is composed of rotor, stator, pre stretching mechanism and mechanical torque output mechanism. Said stator consists of the upper stator, piezoelectric plate, electrode plate and lower stator. Said rotor consists of friction disk in contact with the top end face of upper stator and a metallic disk adhered onto top surface of said friction disk. Said pre stretching mechanism is composed of rubber washer, spring washer and circular clip. Said mechanical torque output mechanism comprises shaft and upper and lower bearings.
The dynamic behavior of a vibration converter of an ultrasonic motor is described using finite element method. Tetrahedral finite elements with three dimensions are formulated with the effects of piezoelectric coupling. And the solution of the coupled electroelastic equations of dynamic motion is presented. The simulated response of the vibration converter is calculated, and shows excellent consistency with experimental results, which proved that finite element modeling is a good approach to optimize piezoelectric apparatus design. A gradual optimized method is employed to ascertain the most compatible structure.
12. Three-DOF multilayer piezoelectric micromanipulator with a probe
To satisfy the need for semiconductor, biomedicine, nanodevices, etc, micromanipulators have been considered as a key technique, which can manipulate objects in nana-scale. What’s more, they are small in size and can move smartly. The piezoelectric ceramics (PZT) is usually used as materials for micro-actuator, considering its simple structure, small size, lightweight and high resolution. We promote a novel model of 3-DOF multilayer PZT micromanipulator and simulate it with FEA (finite element analysis). States under different applied voltages were discussed, including the motion along axis Z and the rotation along axis X and the bisector between X-Y. After analyzing the distribution of stress, we propose some method, which helps to improve the capability of the micromanipulator. We also do some quantificational analysis about the micromanipulator, discovering that the relationship between the displacements of the probe and applied voltages is perfecting linear. Comparing the constant D defining the relationship of the displacements of the probe and applied voltages, it proves that the simulation is correct. We compare the capability between the single-layer and multi-layer PZT just only to show that the multi-layer PZT can reduce applied voltages producing the same displacement.
13. Vibration mechanism and multilayer structure of piezoelectric devices
The program focuses on the monolithic multilayer piezoelectric actuators and their applications, such as ultrasonic motors, automobile ejectors, etc. The outline of the prototype for automobile ejectors is 10x10x30 mm and ones of other ultrasonic motors are 2x2x3 mm to 5x5x4 mm. The monolithic multilayer structures are manufactured using tape casting technique. The vibration mechanism including vibration modes will be studied using scanning laser vibrometer and Finite Element Method. And the fatigue and other characters will also investigated using experimental and theoretical methods. Because of multilayer piezoelectric ceramic, the working voltage may be reduced from 200V inside previous prototypes to 20V. Only in this way, could transformer inside the circuit power be omitted and circuit outline scaled down. So the applications of piezoelectric actuators and motors could be expanded to more fields.
14. Ultra Slim Speaker (USS) based on Multilayer Piezoelectric Actuator
The thinner structure and lower power consumption are benefit for the customers. The ultra slim speakers studied in my group have such features as follows: ultra slim < 0.5 mm, small number of components, simple design, no magnetic field, lower power consumption. But now there are still challenges, for example, “spiky” frequency response, different application, high capacity load, processing technique, etc. I am supervising a master to overcome these problems and cooperating with some famous companies.
Awards And Honors
1998 1st Prize of China Instrument and Control Society Scholarship
Representative Publications (Optional)
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