Modeling and analysis of dual-output piezoelectric transformer operating at the thickness-shear vibration mode.

In our previous study, the multioutput piezoelectric transformer operating at the thickness-shear vibration mode was proposed and experimentally investigated. By designing a new construction of support and lead wire connection, a power density of 52.7 W/cm3 and a total output power of 169.8 W were achieved at a temperature rise less than 20 degrees C. In this work, a theoretical model was developed for the dual-output piezoelectric transformer operating at the thickness-shear vibration mode. The equivalent circuit parameters of the piezoelectric transformer were derived. Based on this, the impedance characteristics, equivalent inductance, capacitance ratio, voltage gain, and efficiency of the piezoelectric transformer were calculated. The theoretical results were verified by experimental data. Furthermore, the effect of the transformer size on the voltage gain, efficiency, output power and power density, and the effect of the load of one output on the voltage gain of another output were analyzed. Some useful guidelines were achieved by these analyses.     

High-power, multioutput piezoelectric transformers operating at the thickness-shear vibration mode

In this study, a piezoelectric transformer operating at the thickness shear vibration mode and with dual or triple outputs is proposed. It consists of a lead zirconate titanate (PZT) ceramic plate with a high mechanical quality factor Qm and a size of 120 x 20 x 4 mm3. The PZT ceramic plate is poled along the width direction. The electrodes of input and output parts are on the top and bottom surfaces of the ceramic plate and separated by narrow gaps. A new construction of support and lead wire connection is used for the transformer. At a temperature rise less than 20 degrees C and efficiency of 90%, the piezoelectric transformer with dual outputs has a maximum total output power of 169.8 W, with a power of 129.5 W in one output and 40.3 W in another. The one with triple outputs has a maximum total output power of 163.1 W, with a power of 36.9 W in the first output, 13.0 W in the second output and 113.2 W in the third output. The maximum efficiency of the piezoelectric transformer with dual outputs and triple outputs is 98% and 95.7%, respectively. The voltage gains of the transformers are less than one, and different outputs have different gains. Also, there is a driving frequency range in which the load resistance of one output has little effect on the voltage gain of another output.     

Theoretical modeling of a thickness-shear mode circular cylinder piezoelectric transformer

We propose a piezoelectric transformer operating with thickness-shear modes of a circular cylinder and perform a theoretical analysis on the transformer. An exact solution from the three-dimensional equations of piezoelectricity is obtained. The output voltage, input admittance, and efficiency of the transformer are determined. The basic behaviors of the transformer are shown by numerical results.     

Modeling and analysis on ring-type piezoelectric transformers

This paper presents an electromechanical model for a ring-type piezoelectric transformer (PT). To establish this model, vibration characteristics of the piezoelectric ring with free boundary conditions are analyzed in advance. Based on the vibration analysis of the piezoelectric ring, the operating frequency and vibration mode of the PT are chosen. Then, electromechanical equations of motion for the PT are derived based on Hamilton's principle, which can be used to simulate the coupled electromechanical system for the transformer. Such as voltage stepup ratio, input impedance, output impedance, input power, output power, and efficiency are calculated by the equations. The optimal load resistance and the maximum efficiency for the PT will be presented in this paper. Experiments also were conducted to verify the theoretical analysis, and a good agreement was obtained.     

Theoretical analysis of a ceramic plate thickness-shear mode piezoelectric transformer

We perform a theoretical analysis on a ceramic plate piezoelectric transformer operating with thickness-shear modes. Mindlin's first-order theory of piezoelectric plates is employed, and a forced vibration solution is obtained. Transforming ratio, resonant frequencies, and vibration mode shapes are calculated, and the effects of plate thickness and electrode dimension are examined.     

High power universal piezoelectric transformer

This study describes a multilayer piezoelectric voltage and power transformer that has one direction poling, operates in a wide-frequency range and delivers both step-up and step-down voltages by inverting the electrical connections. In this design, the input and output electrodes are on the same side of the disk and are isolated from each other by a fixed isolation gap. The electrode pattern is a ring/dot structure such that it uses radial mode for both input and output part that are built-in on the same ceramic disk. A prototype transformer was fabricated of size 15 x 2.78 mm2 having mass of 3.8 gm. In the step-down configuration at the constant output power of 6 W, the transformer characteristics across a 100 omega load were found to be efficiency = 92%, gain = 0.21 input voltage = 110 V(rms), and temperature rise = 20 degrees C from the room temperature. In the step-up configuration at the constant output power of 5 W, the transformer characteristics across a 5 komega load were found to be efficiency = 97%, gain = 9.5, input voltage = 16 V(rms), and temperature rise = 8 degrees C from the room temperature. A detailed equivalent circuit analysis of the transformer was done, and the results were found to be in excellent agreement with the experimental results.     

Modeling of a disk-type piezoelectric transformer

In this paper, an electromechanical model for a disk-type piezoelectric transformer (PT) is proposed. To establish this model, vibration characteristics of the piezoelectric disk with free boundary conditions are analyzed in advance. Based on the vibration analysis results of the piezoelectric disk, the operating frequency and vibration mode of the PT are chosen. Then, electromechanical equations of motion for the PT can be derived based on Hamilton's principle, which can be used to simulate the coupled electromechanical system for the transformer. Voltage step-up ratio, input impedance, output impedance, input power, output power, and efficiency can be calculated by the equations. Thus, the optimal load resistance and the maximum efficiency for the PT are also calculated in this paper. Finally, experiments were conducted to verify the theoretical analysis, and good agreement was obtained.     

High power universal piezoelectric transformer.

This study describes a multilayer piezoelectric voltage and power transformer that has one direction poling, operates in a wide-frequency range and delivers both step-up and step-down voltages by inverting the electrical connections. In this design, the input and output electrodes are on the same side of the disk and are isolated from each other by a fixed isolation gap. The electrode pattern is a ring/dot structure such that it uses radial mode for both input and output part that are built-in on the same ceramic disk. A prototype transformer was fabricated of size 15 x 2.78 mm2 having mass of 3.8 gm. In the step-down configuration at the constant output power of 6 W, the transformer characteristics across a 100 ohms load were found to be efficiency = 92%, gain = 0.21 input voltage = 110 Vrms, and temperature rise = 20 degrees C from the room temperature. In the step-up configuration at the constant output power of 5 W, the transformer characteristics across a 5 kohms load were found to be efficiency = 97%, gain = 9.5, input voltage = 16 Vrms, and temperature rise = 8 degrees C from the room temperature. A detailed equivalent circuit analysis of the transformer was done, and the results were found to be in excellent agreement with the experimental results.     

Magnetoelectric coupling, efficiency, and voltage gain effect in piezoelectric-piezomagnetic laminate composites

The magnetoelectric (ME) effect of piezoelectric-magnetostrictive laminate composites, which is a product tensor, has been studied. Based on piezoelectric and piezomagnetic constituent equations, the longitudinal-mode vibration and equivalent circuits have been derived. The effective magnetoelectric coupling coefficient, voltage-gain, and output efficiency have been determined. Our results show: (i) that there is an extreme high voltage gain effect of >260 under resonance drive: the induced ME voltage is much higher than the input voltage to the coils for magnetic excitation; (ii) that there is an optimum ratio of the piezoelectric to piezomagnetic layer thicknesses, which results in maximum effective magnetoelectric coupling; and (iii) that the maximum output efficiency of magnetoelectric laminate at resonance drive is ∼98%, if eddy currents are neglected. This high ME voltage gain effect offers potential for power transformer applications.     

Power density of piezoelectric transformers improved using a contact heat transfer structure

Based on contact heat transfer, a novel method to increase power density of piezoelectric transformers is proposed. A heat transfer structure is realized by directly attaching a dissipater to the piezoelectric transformer plate. By maintaining the vibration mode of the transformer and limiting additional energy losses from the contact interface, an appropriate design can improve power density of the transformer on a large scale, resulting from effective suppression of its working temperature rise. A prototype device was fabricated from a rectangular piezoelectric transformer, a copper heat transfer sheet, a thermal grease insulation pad, and an aluminum heat radiator. The experimental results show the transformer maintains a maximum power density of 135 W/cm(3) and an efficiency of 90.8% with a temperature rise of less than 10 °C after more than 36 h, without notable changes in performance.     

Vibration distribution in output sections of a piezoelectric transformer operating at thickness shear mode

In this study, the vibration distribution along the width direction in the output section of a piezoelectric transformer operating at the thickness shear vibration mode is investigated experimentally and theoretically. It is experimentally found that the vibration of output section has a spatial gradient and attenuates as the distance from the input section increases. A theoretical model is developed to estimate the vibration attenuation in the output section, which provides the guidelines of optimizing the transformer and explains some important phenomena such as the nonuniform temperature distribution in piezoelectric transformers. The larger the load resistance, the larger the vibration gradient is. At the resonant frequency, the vibration gradient decreases with increasing the width of the input or output section, and it changes little with the length and thickness of the transformer when the load resistance matches with the piezoelectric transformer. The vibration gradient increases with increasing the length or decreasing the thickness when the load resistance is constant, in which the load does not match with the transformer.     

Nonlinear processing of the output voltage of a piezoelectric transformer

Reducing the size of power supplies raises the problem of new components that could be better candidates for integration. In this field, electromagnetic transformers may be replaced with significant benefit by piezoelectric transformers (PT). In a PT, the input electrical energy is transferred to the output by an acoustical means, using the direct and converse effects of piezoelectric materials. Its main advantages over an electromagnetic transformer are no magnetic noise generation, small size, high power density, and high efficiency. This paper deals with an innovative technique that produces a significant improvement of the power capability of piezoelectric transformers. This technique is based on a particular output voltage processing of the PT. Its effect is a vibration level reduction of the PT structure while keeping the output power practically constant. Vibration level is a critical parameter that determines the maximum power capability of a given PT. Thus, the new processing reduces significantly the losses of the PT. Both theoretical predictions and experimental results show that the increase of the power capability may reach 200%.     

Weakly nonlinear behavior of a plate thickness-mode piezoelectric transformer

We analyzed the weakly nonlinear behavior of a plate thickness-shear mode piezoelectric transformer near resonance. An approximate analytical solution was obtained. Numerical results based on the analytical solution are presented. It is shown that on one side of the resonant frequency the input-output relation becomes nonlinear, and on the other side the output voltage experiences jumps.     

Multilayer piezoelectric ceramic transformer with low temperature sintering

The low-fired high performance piezoelectric ceramics used for multilayer piezoelectric transformer were investigated. Based on the transient liquid phase sintering mechanism, by doping suitable eutectic additives and optimizing processing, the sintering temperature of the quaternary system piezoelectric ceramics with high piezoelectric properties could be lower to about 960–1000°C. The low-temperature sintering multilayer piezoelectric transformer (MPT) has been developed. Some characteristics of MPT were systemically studied. The measurements include the frequency response of input impedance, frequency response of phase difference between input voltage and current, frequency shifting with load, input impedance changing with load, phase difference between input voltage and current shifting with load, and phase difference between input voltage and vibration velocity. The vibration modes and resonance characters of MPT were measured by a Laser Doppler Scanning Vibrometer. Several kinds of MPT with high voltage step-up ratio, high power density, high transfer efficiency and low cost have been industrially produced and commercialized. It reveals a broad application prospect for back-light power of liquid crystal display and piezo-ionizer etc.     

Nano piezoelectric/piezomagnetic energy harvester with surface effect based on thickness shear mode

BackgroundEnergy harvesters with piezoelectric materials are widely discussed for the new kinds of smart structures. However, reports on the energy harvesters at the nano scale which have large potential applications in the future are rather limited.MethodsIt’s well known that the surface or interface stress can affect the mechanical properties of nanostructures. This work proposes the nano energy harvester with piezoelectric/piezomagnetic structure, in which the thickness-shear mode is considered by the surface stress model.ResultsThe vibration motion and output power density are derived and calculated. The peak value of the power density can be enlarged by increasing the residual surface stress and the surface effect on the nano-plate energy harvester can be influenced by both the surface piezoelectric and piezomagnetic elastic constants. Moreover, the harvesting ability can be improved by increasing the thickness of the piezoelectric layer.ConclusionThe capability of the energy harvester depends on the residual surface stress and the surface material constants. The proposed model provides the possibility of applying nano composite structures to the energy harvester.     

Modeling and fabrication of a piezoelectric vibration‐induced micro power generator

Abstract

In this paper, theoretical and experimental study on a piezoelectric vibration‐induced micro power generator that can convert mechanical vibration energy into electrical energy is presented. The mechanical‐electrical energy conversion mechanism is a voltage between two capacitors, which belong to the mechanical and the piezoelectric equivalent circuits, respectively. To verify the theoretical analysis, two clusters of transducer structures are fabricated. Piezoelectric lead zirconate titanate (PZT) material is chosen to make the energy conversion transducer. The desired shape of the piezoelectric generator with its resonance frequency in accordance with the ambient vibration source is designed by finite element analysis (FEA).

Experimental results show that the maximum output voltages are generated at the first mode resonance frequencies of the structure. The overall conversion efficiency is measured to be 33%. The experimental results coincide with the theoretical analysis.     

Analyses of the temperature field in a bar-shaped piezoelectric transformer operating in longitudinal vibration mode

In this study, a theoretical model of the steady-state temperature field in a bar-shaped piezoelectric transformer operating in longitudinal vibration mode is developed, and the characteristics of the temperature field are analyzed numerically. Being different from previous work, the effects of the stress distribution and the relative positions of input and output parts on the internal loss distribution are taken into account in this model. Using this model, the temperature rise and its distribution are calculated, and the effects of ambient temperature, internal loss distribution, size, heat dissipation coefficient, and heat conductivity of the transformer on the temperature rise are estimated. The calculated temperature rise and its distribution agree quite well with the experimental data. It is found that the allowable output power of the transformer should be reduced markedly when the ambient temperature increases to maintain a reasonable working temperature for the piezoelectric material of the transformer. It also is found that decreasing wavelength, making internal loss distribution uniform, and increasing the ratio of perimeter to area of the cross section (for example, decreasing the cross-sectional area and using a thin plate structure), decrease the temperature rise for a given internal loss per unit volume. Furthermore, it is revealed that the heat dissipation coefficient has a remarkable effect on the temperature rise at a large internal loss, and the variation in the heat conductivity of the piezoelectric material has little effect on the temperature rise.     

Modeling and analysis of circular flexural-vibration-mode piezoelectric transformer

We propose a circular flexural-vibration-mode piezoelectric transformer and perform a theoretical analysis of the transformer. An equivalent circuit is derived from the equations of piezoelectricity and the Hamilton's principle. With this equivalent circuit, the voltage gain ratio, input impedance, and the efficiency of the circular flexural-vibration-mode piezoelectric transformer can be determined. The basic behavior of the transformer is shown by numerical results.     

p-Type polymer-hybridized high-performance piezoelectric nanogenerators

Enhancing the output power of a nanogenerator is essential in applications as a sustainable power source for wireless sensors and microelectronics. We report here a novel approach that greatly enhances piezoelectric power generation by introducing a p-type polymer layer on a piezoelectric semiconducting thin film. Holes at the film surface greatly reduce the piezoelectric potential screening effect caused by free electrons in a piezoelectric semiconducting material. Furthermore, additional carriers from a conducting polymer and a shift in the Fermi level help in increasing the power output. Poly(3-hexylthiophene) (P3HT) was used as a p-type polymer on piezoelectric semiconducting zinc oxide (ZnO) thin film, and phenyl-C(61)-butyric acid methyl ester (PCBM) was added to P3HT to improve carrier transport. The ZnO/P3HT:PCBM-assembled piezoelectric power generator demonstrated 18-fold enhancement in the output voltage and tripled the current, relative to a power generator with ZnO only at a strain of 0.068%. The overall output power density exceeded 0.88 W/cm(3), and the average power conversion efficiency was up to 18%. This high power generation enabled red, green, and blue light-emitting diodes to turn on after only tens of times bending the generator. This approach offers a breakthrough in realizing a high-performance flexible piezoelectric energy harvester for self-powered electronics.     

Novel method for driving the ultrasonic motor

This paper reports a novel driving method for an annular plate-type ultrasonic motor. Instead of the direct current/alternating current (DC/AC) converter type driver using a conventional electromagnetic transformer, a compact disc-type piezoelectric transformer is used to obtain a high voltage output for driving the ultrasonic motor. The piezoelectric transformer is operated in the radial vibration mode at resonance frequency close to the resonance frequency of the ultrasonic motor. Later, it was found that the piezoelectric transformer could drive the ultrasonic motor, even if their resonance frequencies are not exactly the same by incorporating a matching network in the circuit. The maximum speed of the ultrasonic motor obtained by using this driving method is over 300 rpm. It is believed that the results of this study will have impact on the integration and miniaturization of the ultrasonic motor and its driving circuit.