Piezoelectric Tubular Composite Actuators And Their Applications

Piezoelectric composites are new type of transducer components developed in1970, which not only have the merits of piezoelectric ceramics, such as fast response,high precision, low power consumption, no electromagnetic interference, etc, but alsohavemeritsofhighflexibilityandgoodmechanicalprocessingproperties. Itovercomestheshortcomingsofpiezoelectricceramicsforbeingfragileandbeingdifficulttobefab-ricated into complex shapes. It is also easy to achieve impedance matching between thepiezoelectric composites and water or biological tissues. Piezoelectric composites havebeen widely used in acoustic transducers and medical ultrasonic imaging area. Amongthem, 1-3piezoelectriccompositesareextensivelyresearchedbecauseoftheirexcellentultrasonic character and easy fabrication process.The traditional 1-3 piezoelectric composites usually mix piezoelectric square orcylindrical columns with matrix. This paper uses piezoelectric tubes as the piezoelec-tric components to adapt to various applications. In addition to owning the merits oftraditional piezoelectric composites, the piezoelectric tubular composites require lowpoling and driving voltages and can be mixed with conductive matrix. Each piezoelec-tric tube can be controlled independently so it is easy for them to complete multi-modemotion. It utilizes electric field more efficiently than composites with interdigitatedelectrodes. Sheet shaped composites with short tubes can be applied to ultrasound andhigh-frequency vibration suppression. Sheet or block shaped composites based on longtubes can be used in occasions that require large displacement, such as shape control,medium and low frequency vibration and noise control, deformable mirrors and piezo-electric motors.Piezoelectric tubular composite actuators are studied in this paper. Firstly, the-oretical and FEM analysis on static and dynamic character of the composite actuatorare conducted in detail, followed by static and dynamic analysis on the four tubularcomposites in a particular driving mode. And a two phase traveling wave motor and apiezoelectric centrifugal pump are presented to illustrate the application of the piezo-electric tubular composite actuators. The main work and conclusions are as following:By use of electric field distribution model, the static and dynamic properties ofa single tube piezoelectric actuator were studied. By taking the piezoelectric strainas the thermal strain, the formulas of property parameters of the piezoelectric tubularcomposite were deduced with the rule of mixture models and the concentric cylinder models. The influence of non-uniform electric field on the piezoelectric coefficientswere studied. The formulas of density, dielectric constant, piezoelectric constants andYoung's modulus were given. The piezoelectric constants as functions of volumes frac-tion, aspect ratio, distribution density of the piezoelectric tubes and matrix materialswere discovered. By means of finite element software, piezoelectric coefficients andYoung's modulus matrix of the composite unit were derived and their change with thevolume fraction of ceramic materials were studied. Their values were compared withthe theoretical results. The stress, which is apt to cause damage to the composite, wassimulated under different loads. The vibration modes of the composite and the changeof its resonant frequencies with size parameters were analyzed.Under the condition that each piezoelectric tube is driven independently, a fourtubular composite actuator was invstigated. Theoretical analysis on its static and dy-namic character were conducted and formulas of bending deflection, output torque, andresonance frequencies were given. Compared with the traditional thin-wall theory, theanalysis in the paper is confirmed more reasonable. A prototype was fabricated andtested. By use of finite element analysis with ANSYS, theoretical analysis results wereverified. The character of the four tubular composite actuator was compared with theconventional single-tube actuator with quartered electrodes. It is confirmed that whenthetwokindsofactuatorsareinthesamesizeanddrivenbythesameelectricfieldinten-sity, four tubular composites actuator usually has better performance. In addition, fourtubular composites actuator have the advantages of large scalability, small electromag-netic radiation and low driving voltage. It is possible for tubular composite actuator tohandle with the defects of asymmetric structure of the piezoelectric tube in fabrication,which is an unconquerable problem in single-tube actuator, thus improving the drivingaccuracy. The tubular composite actuator can replace the conventional single-tube ac-tuator with quartered electrodes and work in scanning probe microscopes, piezoelectricmotors, piezoelectric gyroscopes, and even more extensive applications.A two phase traveling wave piezoelectric motor based on eight tubular compositeactuatorwasinvestigated. Theoreticalanalysisonthestaticanddynamiccharacteristicsof the eight tubular composite actuator was presented. A prototype motor was designedand fabricated. The test results of the motor character were in accordance with thetheoretical analysis well. The angular speed of the rotor possesses a good linearity withthe driving voltage amplitude. At static, the moving trace of the stator tip is not an idealcircle, which is caused by piezoelectric hysteresis. Motor can work in the vicinity ofthe resonant frequency. With a driving voltage of 200V_p-p at 5.0kHz, the motor can rotateatthehighestangularspeedof319rpmwithnoloadandproduceamaximumstalltorqueof1.6mNm, respectively. Whenthedrivingvoltageis160V_p-p withafrequencyof5.0kHz andpre-pressureof0.3N,themotor'smaximumefficiencyreaches12%,andthe maximum output power is 7mW.A novel centrifugal piezoelectric pump using piezoelectric tubular composite ac-tuator is introduced. It has no sliding parts and so is supposed to have higher efficiency.it is not sensitive to the quality of the pumping liquid as neither precision valve nor mi-cro channel is needed. Due to the independent control of each single piezoelectric tube,a variety of piezoelectric pumps may be derived from this structure. Its static and dy-namic characteristics were analyzed in theory. The static deflection, the output torque,resonant modes and the influence of liquid flow rate on the resonant frequency werestudied. A prototype was produced and performance testing was conducted. The ex-perimentsresultsshowthatwhenthedrivingvoltageis120V_p-p atfrequencyof232Hz,the pump can pump stilled water at a flow rate up to 7.7ml/min under a backpressureof 2.0kPa. With a driving voltage of 120V_p-p at 233.2Hz, the pump can pump stilledwater at a maximum flow rate of 8.6ml/min and sustain a maximum backpressure of5.4kPa, respectively.Based on the above researches, the following points are pioneering work of thisdissertation: (1)ThepiezoelectriccoefficientsandYoung'smodulusmatrixofthetubu-lar composites were discussed in detail, together with the stress and electric potentialdistribution under different loads. (2) Actuator made from four tubular composites issuperior to the traditional single-tube actuator with quartered electrodes, which can bereplaced in scanning tunneling microscope. (3) A two phase traveling wave piezoelec-tric motor was developed using eight tubular composite actuator. It usually outputslarger torque than the piezoelectric motors based on single tube actuator. (4) A nov-el centrifugal piezoelectric pump using piezoelectric tubular composite actuator is de-signed and it has advantages of simple structure, convenient control, stable output andhigh frequency operation.The results in this paper have both theoretical and practical value for optimized de-signofpiezoelectrictubularcompositeactuators, thepropertiesanalysisoftheactuatorsand exploration of applications of piezoelectric actuating technology.