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Wireless drive of a piezoelectric plate by capacitorlike structure in electric resonance with an inductor Satyanarayan Bhuyan, Junhui Hu, and Chang Qing Sun Citation: J. Appl. Phys. 103, 094915 (2008); doi: 10.1063/1.2908183 View online: http://dx.doi.org/10.1063/1.2908183 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v103/i9 Published by the American Institute of Physics. Related Articles Polarization relaxation kinetics in ultrathin ferroelectric capacitors Appl. Phys. Lett. 102, 092901 (2013) Magnetic field tunable acoustic resonator with ferromagnetic-ferroelectric layered structure J. Appl. Phys. 113, 17C704 (2013) High power terahertz radiation source based on electron beam wakefields Rev. Sci. Instrum. 84, 022706 (2013) Comparative study of tip cross-sections for efficient galloping energy harvesting Appl. Phys. Lett. 102, 064105 (2013) Diagonal control design for atomic force microscope piezoelectric tube nanopositioners Rev. Sci. Instrum. 84, 023705 (2013) Additional information on J. Appl. Phys. Journal Homepage: http://jap.aip.org/ Journal Information: http://jap.aip.org/about/about_the_journal Top downloads: http://jap.aip.org/features/most_downloaded Information for Authors: http://jap.aip.org/authors Downloaded 07 Mar 2013 to 202.6.242.69. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions JOURNAL OF APPLIED PHYSICS 103, 094915 共2008兲 Wireless drive of a piezoelectric plate by capacitorlike structure in electric resonance with an inductor Satyanarayan Bhuyan, Junhui Hu,a兲 and Chang Qing Sun School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore 共Received 13 December 2007; accepted 14 February 2008; published online 9 May 2008兲 A new technique of wirelessly transmitting electric energy to piezoelectric components is explored. In the design, an ac electric field is focused to a piezoelectric plate placed between plate-shaped live and needle ground electrodes which form a capacitorlike electric field generator in series with an inductor. The transmission of electric energy is enhanced when the capacitorlike electric field generator and inductor are in electric resonance. Experimentally it has been found that the real output power delivered to the piezoelectric plate depends on the electrode pattern, vibration mode, and electrical load of the piezoelectric component and the electric field focused by the needle ground and live electrodes. When the operating frequency is close to mechanical resonance frequency of the piezoelectric plate operating in the thickness vibration mode, a maximum output power of 0.264 W and energy conversion efficiency of 1.02% have been achieved with an input voltage 150 Vrms and 10 mm electrode separation. © 2008 American Institute of Physics. 关DOI: 10.1063/1.2908183兴 I. INTRODUCTION Piezoelectric actuators are devices capable of converting electric energy into mechanical displacements. They have various applications due to their compact size, high precision positioning, low power consumption, high output force, and high-power density properties. There has been remarkably rising interest in the applications of piezoelectric actuators such as precision positioning,1–10 particle manipulations,11–13 vibration control,14,15 etc.16,17 In the existing driving circuits, electric energy is applied to the actuators via lead wires soldered on the electrodes of piezoelectric components. However, this method of applying electric energy has some limitations. At large vibration and high input voltage, the soldered points melt and this causes the breakdown of actuators. The lead wires also hinder the applications of piezoelectric actuators in rotary mechanisms. Therefore, there is a need to investigate wireless electric energy transmission to piezoelectric actuators. Earlier, a new technique of wireless electric energy transmission was proposed by the author.18 In the technique, ac electric field from a plate-shaped live electrode is focused to a piezoelectric plate by using a needle ground electrode. But the output power of the driven piezoelectric plate is not high enough. In order to drive a highpower piezoelectric plate wirelessly by an electromagnetic wave and widen the application range of piezoelectric actuators, the wireless drive of piezoelectric plates needs to be investigated further. The wireless drive of piezoelectric plates is experimentally investigated by using the electric resonance of a capacitorlike electric field generator and an inductor in series. In the capacitorlike electric field generator, the ac electric field is focused to a needle ground electrode from a plate-shaped live electrode through a piezoelectric plate placed in between a兲 Author to whom correspondence should be addressed. Electronic mail: [email protected]. 0021-8979/2008/103共9兲/094915/5/$23.00 them. The technique enables a relatively large output power delivered to the piezoelectric plate. The effects of operating frequency, electric load, electrode pattern, vibration mode, and position of the piezoelectric plate on the real output power delivered to the electric load are studied in order to optimize the electric energy transmission to piezoelectric plates. II. EXPERIMENTAL SETUP, CONDITIONS, AND OPERATING MECHANISM To transmit a relatively large electric energy to piezoelectric components, a capacitorlike electric field generator in series with an inductor is used as shown in Fig. 1共a兲. With a brass plate-shaped live electrode, a stainless steel needle ground electrode is used to form the capacitorlike electric field generator. In the electric field generator, the ac electric field is focused to a needle ground electrode from a plateshaped live electrode through a piezoelectric plate placed in between them. When the electric field generator and inductor are in electric resonance, the transmission of electric energy is enhanced because of the large voltage across the capacitorlike structure. Two types of piezoelectric plates are used in the experiment. The upper and lower surfaces of the piezoelectric plates are covered with silver metal electrodes. Figure 1共b兲 shows the configuration of plate A which has whole electrode on its top and bottom surfaces and only has output section P. Figure 1共c兲 shows the configuration of the plate B, which has two electrically separated sections P and Q. A resistance load is connected across the two electrodes of section P for measuring the real power which section P delivers. The experiments are performed under the following conditions. All the experimental piezoelectric plates are made of same ceramic material lead zirconate titanate 共PZT兲 with a size of 30⫻ 8 ⫻ 2 mm3, and are poled along the thickness direction. The electrode length ratio of section Q to P of plates A and B is 0:1 and 5:1, respectively. The live electrode 103, 094915-1 © 2008 American Institute of Physics Downloaded 07 Mar 2013 to 202.6.242.69. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 094915-2 J. Appl. Phys. 103, 094915 共2008兲 Bhuyan, Hu, and Sun FIG. 1. 共Color online兲 共a兲 Experimental setup to drive piezoelectric components wirelessly, 共b兲 configuration of plate A, and 共c兲 configuration of plate B. area is 30⫻ 30 cm2. The ground electrode is a metal needle whose tip is assumed to have zero area. The medium between the live and ground electrodes is air. The inductances 共L兲 are 1.50 and 1.46 mH for piezoelectric plates A and B, respectively, and thus the electric field generator and inductor are in resonance. To prevent the shift of resonance frequency due to heat generation, the temperature rise of the piezoelectric plate is kept below 10 ° C in the experiment. Unless otherwise specified, the piezoelectric plate is placed equidistantly in between the live and needle ground electrodes positioned perpendicular to each other, the ac input voltage applied to the series of electric field generator and inductor is 150 Vrms, distance between the live and needle ground electrode is 10 mm, and plates operate in the thickness vibration mode. Table I shows the measured resonance frequencies and equivalent circuit parameters from section P of plates A and B by an impedance analyzer 共HP4194A兲. When the capacitorlike electric field generator and inductor are in electric resonance, the current flowing through the electric field generator is very large. Thus at resonance, a relatively large ac electric field can be focused to a needle ground electrode from the plate-shaped live electrode through a piezoelectric plate placed in between them. The piezoelectric plate is polarized in the thickness direction. When an ac electric field penetrates the piezoelectric plate, a mechanical vibration can be stimulated in the piezoelectric plate by the converse piezoelectric effect. When the frequency of ac electric field is close to mechanical resonance frequency of the piezoelectric plate, a mechanical resonance can be excited in the plate. This mechanical resonance can generate a relatively large voltage across the output electrodes due to the piezoelectric effect. III. EXPERIMENTAL RESULTS AND DISCUSSION Figures 2共a兲 and 2共b兲 show the frequency characteristics of the output power of both piezoelectric plates A and B operating in the thickness vibration mode, placed inside the capacitorlike electric field generator. Figure 2共a兲 represents the result when the electric field generator is electrically resonant with the inductor. Figure 2共b兲 represents the result without the inductor. It is observed that at the resonance frequencies of 772 and 782 kHz of plates A and B, respectively, a maximum output power is achieved. When the frequency of ac electric field is close to mechanical resonance frequency of the plate, a relatively large vibration can be excited in the plate by the converse piezoelectric effect. This mechanical resonance generates a relatively large voltage at the section P by the piezoelectric effect. It is also seen that when the electric field generator and inductor are in electrical resonance the output power of the piezoelectric plate is significantly higher than that of the electric field generator with- TABLE I. Parameters of the section P of piezoelectric plates. Piezoelectric plates Resonance frequency f r 共kHz兲 Equivalent resistance Rm 共⍀兲 Equivalent inductance Lm 共mH兲 Equivalent capacitance Cm 共pF兲 Clamped capacitance Cd 共pF兲 Plate A Plate Ba 772 782 42 286 16.3 117 2.52 0.368 712.2 202.8 a Section Q is open circuit. Downloaded 07 Mar 2013 to 202.6.242.69. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 094915-3 Bhuyan, Hu, and Sun J. Appl. Phys. 103, 094915 共2008兲 FIG. 3. 共Color online兲 Dependence of the output power on the electrical load and electrode length ratio at resonance frequency of the thickness vibration mode. FIG. 2. 共Color online兲 Frequency characteristics of the output power of piezoelectric plates A and B at the optimum load resistance for 共a兲 electric field generator with inductor and 共b兲 electric field generator without an inductor. out an inductor. When the electric field generator is in series electric resonance with an inductor, the voltage across the capacitorlike structure is eight times greater than the ac source voltage. Thus at resonance, a relatively large amount of ac electric field can be focused to the needle ground electrode and hence a relatively large electric energy can be transmitted to the piezoelectric plate placed in between the live and needle ground electrodes. Therefore, for a given input ac voltage Vin, the output power is larger for an electric field generator which is in electric resonance with an inductor. Figure 3 shows the dependence of output power at resonance on the electrical load for the piezoelectric plates, operating in the thickness vibration mode. It is seen that the output power at resonance reaches the maximum at an optimum load resistance. For plate B whose electrode length ratio of Q to P is 5:1, the output power at resonance reaches the maximum at 1365 ⍀ and the maximum output power is 0.264 W. The equivalent circuit of the plates is shown in Fig. 4, which can be used to explain these results. When the load resistance RL is not much larger than 1 / 共Cd兲, the output voltage V0 increases with RL for a given voltage Vs. When RL is much larger than 1 / 共Cd兲, the load branch can be regarded as open circuit. So, V0 is constant and the output power 共V20 / RL兲 decreases as the electrical load RL increases.19 Figure 5 shows a comparison of the maximum output power between the plates operating in various resonance modes for different electrode length ratio of Q to P. The maximum output power is measured when the electric field generator is in resonance with an inductor for different resonant modes. The optimum load of each measuring point depends on the resonance mode and electrode length ratio. It is seen that a high output power is achieved for large electrode length ratio of Q to P, and the maximum output power at resonance of plate B 共electrode length ratio Q: P = 5:1兲 is higher than that of plate A 共electrode length ratio Q: P = 0 : 1兲. When the electrode length ratio of Q to P increases, FIG. 4. Equivalent circuit of the piezoelectric plate. Vs is the source voltage, V0 is the output voltage, Cd is the clamped capacitance, and Lm, Cm, and Rm are the equivalent inductance, capacitance, and mechanical resistance, respectively. Downloaded 07 Mar 2013 to 202.6.242.69. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 094915-4 Bhuyan, Hu, and Sun FIG. 5. 共Color online兲 Effect of the electrode length ratio on the maximum output power of plates operating in different resonance modes when the electric field generator is in electric resonance with the inductor. The maximum power is for frequency and electrical load. the clamped capacitance 共Cd兲 of section P decreases. Then, 1 / 共Cd兲 increases with the decrease of Cd for a given frequency. This increases the output voltage V0. When the change of RL is not very large, the output power increases as the output voltage V0 increases. Hence the output power at resonance of plate B is higher than that of the plate A. Figure 6 shows the effect of vibration modes on the output power at the optimum load and resonance frequency. The output power is measured for plate B when the electric field generator is in electric resonance with an inductor. It is seen that the output power of the piezoelectric plate operating in the thickness vibration mode is significantly higher than that of the plate operating in the width and length extensional vibration modes. Thus, the vibration mode has an effect on the output power of the piezoelectric plate. Figure 7 shows the dependence of the output power at resonance on the distance between the lower surface of piezoelectric plate and needle ground. The output power is measured for plates A and B operating in the thickness vibration mode, when the electric field generator and an inductor are in electric resonance. It is seen that the maximum output power increases with the decrease in the distance between the piezoelectric plate and needle ground for a given input ac voltage. This is because the electric field at the piezoelectric plate increases as the plate is moved towards the needle ground. Figure 8共a兲 shows frequency characteristic of the energy conversion efficiency 共the ratio of the real power delivered to the electrical load resistor to real power supplied by the ac input voltage source兲 at the optimum electrical load resis- J. Appl. Phys. 103, 094915 共2008兲 FIG. 6. Effect of vibration modes on the output power of plate B when the electric field generator is in electric resonance with the inductor. tance of piezoelectric plates A and B, operating in the thickness vibration mode. It is seen that when the electric field generator and inductor are in electric resonance an efficiency of 1.02% has been achieved for plate B at the resonance frequency of 782 kHz and electric load resistance of 1365 ⍀ which is lower than that of the efficiency of 1.18% achieved FIG. 7. 共Color online兲 Dependence of the maximum output power on the distance between the piezoelectric plate and needle ground electrode. The maximum power is for frequency and electrical load. Downloaded 07 Mar 2013 to 202.6.242.69. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 094915-5 J. Appl. Phys. 103, 094915 共2008兲 Bhuyan, Hu, and Sun IV. CONCLUSIONS In this work, an improved method of wireless drive of a piezoelectric plate is explored by using the electric resonance of a capacitorlike electric field generator and an inductor in series. In the capacitorlike electric field generator, the ac electric field is focused to a needle ground electrode from a plate-shaped live electrode through a piezoelectric plate placed in between them. When the capacitorlike electric field generator and inductor are in electric resonance, the wireless electric energy transmission can be enhanced. The technique enables a relatively large output power delivered to the piezoelectric plate. The output power attains the maximum at the resonance of piezoelectric plate and the plate with properly divided electrode has a larger output power than the one with whole electrode. The real output power achieved by the piezoelectric plate depends on the electrode pattern, vibration mode, and electrical load of the piezoelectric component, and the electric field focused by the needle ground and live electrodes. At resonance frequency of 782 kHz, a maximum output power of 0.264 W and energy conversion efficiency of 1.02% have been achieved by the piezoelectric plate operating in the thickness vibration mode with a needle ground electrode, input voltage of 150 Vrms, and 10 mm electrode separation. Methods of increasing the transmission power and energy conversion efficiency will be investigated further theoretically and experimentally. W. G. Cady, Piezoelectricity 共McGraw-Hill, New York, 1946兲, p. 45. T. Ikeda, Fundamentals of Piezoelectric Materials Science 共Ohm Publishing Co., Tokyo, 1984兲, p. 209. 3 A. Kumada, Jpn. J. Appl. Phys., Suppl. 24 739 共1985兲. 4 K. Nakamura, M. Kurosawa, and S. Ueha, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 40, 402 共1993兲. 5 S. Ueha and Y. Tomikawa, Ultrasonic Motors 共Oxford University Press, Oxford, 1993兲, p. 1. 6 S. Lin, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 44, 1189 共1997兲. 7 K. Yao, B. Koc, and K. Uchino, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 48, 1066 共2001兲. 8 Y. Chen, T. Zhou, Q. Zhang, X. Cheng, and S. Chen, Ultrasonics 39, 667 共2002兲. 9 J. R. Friend, J. Satonobu, K. Nakamura, S. Ueha, and D. S. Stutts, IEEE Trans. Ultrason. Ferroelectr. Freq. Control 50, 179 共2003兲. 10 J. L. Pons, Emerging Actuator Technologies 共Wiley, Chichester, 2005兲, p. 46. 11 W. T. Coakley, D. W. Bardsley, and M. A. Grundly, J. Chem. Technol. Biotechnol. 44, 42 共1989兲. 12 J. Wu, J. Acoust. Soc. Am. 89, 2140 共1991兲. 13 S. Gupta and D. L. Feke, Ultrasonics 35, 131 共1997兲. 14 G. Gibbs and C. Fuller, J. Acoust. Soc. Am. 92, 3221 共1992兲. 15 J. S. Yang and X. Zhang, Int. J. Appl. Electromagn. Mech. 16, 29 共2002兲. 16 D. L. Miller, W. L. Nyborg, and C. C. Whitcomb, Science 205, 505 共1979兲. 17 P. Muralt, A. Kholkin, M. Kohli, and T. Maeder, Sens. Actuators, A 53, 398 共1996兲. 18 S. Bhuyan and J. H. Hu, Appl. Phys. Lett. 91, 26, 共2007兲. 19 J. H. Hu, H. L. Li, H. L. W. Chan, and C. L. Choy, Sens. Actuators, A 88, 79 共2001兲. 1 2 FIG. 8. 共Color online兲 共a兲 Frequency dependence of energy conversion efficiency at the optimum electrical load of piezoelectric plates and 共b兲 dependence of efficiency on the electrical load when the electric field generator is in electric resonance with the inductor. without inductor. Due to the internal resistance of the inductor, the efficiency achieved with inductor is less than that achieved without inductor. Figure 8共b兲 shows the dependence of efficiency on the electrical load, when the electric field generator and inductor are in electric resonance for piezoelectric plate B operating in the thickness vibration mode. It is seen that the energy conversion efficiency depends on the electrical load and a maximum efficiency of 1.12% is achieved for plate B at the resonance frequency of 782 kHz and electric load resistance of 1450 ⍀. Downloaded 07 Mar 2013 to 202.6.242.69. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions