Piezoelectric Transformer Research Articles

Concurrent operational modes and enhanced current sensitivity in heterostructure of magnetoelectric ring and piezoelectric transformer

A heterostructure possessing two concurrent operational modes: current sensing (CS) mode and current transduction (CT) mode and an enhanced current sensitivity associated with the CT mode is proposed by combining a magnetoelectric ring (MER) with a piezoelectric transformer (PET). The MER is a ring-shaped magnetoelectric laminate having an axially polarized Pb(Zr, Ti)O3 (PZT) piezoelectric ceramic ring sandwiched between two circumferentially magnetized, inter-magnetically biased Tb0.3Dy0.7Fe1.92 (Terfenol-D) short-fiber/NdFeB magnet/epoxy three-phase magnetostrictive composite rings, while the PET is a Rosen-type PZT piezoelectric ceramic transformer. The current sensitivity (SI) and magnetoelectric voltage coefficient (αV) of the heterostructure in the two operational modes are evaluated theoretically and experimentally. The CS mode provides a large SI of ∼10 mV/A over a flat frequency range of 10 Hz−40 kHz with a high resonance SI of 157 mV/A at 62 kHz. The CT mode gives a 6.4-times enhancement in resonance SI, reaching 1000 mV/A at 62 kHz, as a result of the amplified vortex magnetoelectric effect caused by the vortex magnetoelectric effect in the MER, the matching of the resonance frequencies between the MER and the PET, and the resonance voltage step-up effect in the PET.

Improvement of burst-mode control of piezoelectric transformer based DC/DC converter

Burst-mode operation is adopted sometimes in piezoelectric transformer based converters for two major purposes: (1) to achieve voltage regulation in DC/DC converters and (2) to achieve dimming control in backlight inverters. Burst-mode control enables the converter to operate at a constant switching frequency as well as to maintain good efficiency at light load conditions. However, in practice, the piezoelectric transformer cannot instantly stop vibrating in the burst-mode due to its high quality factor. The delay in the output voltage change resulting from this behavior influences the accuracy of the regulation. This paper proposes a control strategy to make the piezoelectric transformer stop more quickly so as to enhance the accuracy of burst-mode control. The proposed method only modifies the control signal of the burst-mode driving circuit. The proposed control strategy is verified by experiments in a step-down 9 W DC/DC converter.

On the nonlinear behavior of a multilayer circular piezoelectric plate-like transformer operating near resonance

We studied the weakly nonlinear behaviors of a simply-supported multilayer circular piezoelectric plate-like transformer (MCPPT) operating near resonance, where the MCPPT consists of a multilayer circular piezoelectric compound plate with four piezoelectric layers polarized in different directions. Nonlinear effects of large deformations near resonance are considered; it is shown that on one side of the resonant frequency, the output-input relation becomes nonlinear, and the other side, the output voltage becomes multivalued.

Electromechanical characteristics of piezoelectric ceramic transformers in radial vibration composed of concentric piezoelectric ceramic disk and ring

A new type of piezoelectric ceramic transformer in radial vibration is presented. The piezoelectric transformer consists of a pairing of a concentric piezoelectric ceramic circular disk and ring. The inner piezoelectric ceramic disk is axially polarized and the outer piezoelectric ring is radially polarized. Based on the plane stress theory, the exact analytical theory for the piezoelectric transformer is developed and its electromechanical equivalent circuit is introduced. The resonance/anti-resonance frequency equations of the transformer are obtained and the relationship between the resonance/anti-resonance frequency, the effective electromechanical coupling coefficient and the geometrical dimensions of the piezoelectric transformer is analyzed. The dependency of the voltage transformation ratio on the frequency is obtained. To verify the analytical theory, a numerical method is used to simulate the electromechanical characteristics of the piezoelectric transformer. It is shown that the analytical resonance/anti-resonance frequencies are in good agreement with the numerical results.

Fabrication of high-power piezoelectric transformers using lead-free ceramics for application in electronic ballasts

CuO is doped into (Na(0.5)K(0.5))NbO(3) (NKN) ceramics to improve the piezoelectric properties and thus obtain a piezoelectric transformer (PT) with high output power. In X-ray diffraction patterns, the diffraction angles of the CuO-doped NKN ceramics shift to lower values because of an expansion of the lattice volume, thus inducing oxygen vacancies and enhancing the mechanical quality factor. A homogeneous microstructure is obtained when NKN is subjected to CuO doping, leading to improved electrical properties. PTs with different electrode areas are fabricated using the CuO-doped NKN ceramics. Considering the efficiency, voltage gain, and temperature rise of PTs at a load resistance of 1 kΩ, PTs with an electrode with an inner diameter of 15 mm are combined with the circuit design for driving a 13-W T5 fluorescent lamp. A temperature rise of 6°C and a total efficiency of 82.4% (PT and circuit) are obtained using the present PTs.

Optimization of Piezoelectric Resonance Effect in a Piezoelectric Transformer Plasma Source

Optimization of the piezoelectric resonance effect in a piezoelectric transformer plasma source (PTPS) is investigated. The PTPS utilizes a piezoelectric transformer (PT) effect to generate large electric potentials and aid in plasma formation in the plasma source. Finite-element simulations are used in conjunction with observations of device operation in order to optimize the PT effect used by the plasma source. Simulations were used to determine optimal crystal rotation for electromechanical coupling and evaluate the geometry of the plasma source in order to maximize the generated voltage. Input impedance measurements and an estimate of the mechanical quality were used to verify the effectiveness of device construction changes to reduce mechanical clamping.

Bulk piezoelectric ceramic transformers

In this contribution, we present a review on the various bulk piezoelectric ceramic transformers based on planar vibration modes. The studied transformer shapes include rectangular bar, rings and discs (e.g. disc ring dot) homogeneously poled in the thickness direction. Electrical parameters like transformation ratio, efficiency and input and output power are measured and modelled as a function of frequency and resistive load in the secondary circuit. Analytical modelling has been performed for the ‘Rosen type’ and ‘ring dot’ disc or ring transformers as well as for the bar transformers and several other geometries. Finite element analysis modelling has been performed for the set of other more complicated disc transformer geometries. An overview of the results on the studied transformers is presented, including data on transformation ratio, efficiency and optimum load.

Modeling and Simulation of Three Level Piezoelectric Transformer Converters

This paper proposes a modeling and simulation of three level piezoelectric transformer converters. The increasing utilization of piezoelectric transformers (PT) in power electronics requires fundamental analysis and design of PT power converters. In addition, the possibility of overcoming the essential limitations of PT power ability by a combined operation of PTs needs to be examined. These studies could provide wide opportunities for PT exploitation in power electronic circuits. The electrical circuit and model of piezoelectric transformers (PTs) ELS-60 is developed. Rosen-type PT and many other non-isolated conversion circuits have the inherit problem of the common neutral between the input and output that make it difficult to connect the output in series like the magnetic transformer. A new method based on the bootstrap method is proposed to solve the aforementioned problem. A new circuit for output summation of voltage level in the output side of each PT is developed. The impact of load and output filter capacitor on the conversion ratio and resonant frequency is discussed. The paper finally proposes a multilevel concept for many PT connected together for voltage summation. The method proposed can be applied to other multiple conversion circuits, which are based on common neutral between the input and output. The MATLAB/SIMULINK software used to design the required circuit diagram.

Charged-Particle Emission and Self-Biasing of a Piezoelectric Transformer Plasma Source

The piezoelectric transformer (PT) plasma source (PTPS) is a compact radio-frequency-driven plasma source developed for near-space and microspacecraft propulsion. The PTPS utilizes the PT effect to aid in plasma production and acceleration of charged particles to create thrust. Charged-particle emission measured with a Faraday cup and a retarding potential analyzer is presented. Low emitted ion energies are explained by self-bias of the PT output due to charged-particle transfer from the plasma to the PT surface. Finally, self-neutralization of the PTPS was investigated for a PTPS isolated from the vacuum chamber ground.

Digital Holographic Method for Piezoelectric Transformers Vibration Analysis

The paper describes a holographic method for vibration analysis in nanometer range. The method was successfully applied on different types of piezoelectric transformers and the measurement results are introduced. To proof the reliability of the method it was done a comparing simultaneous measurement of a piezoelectric component by the holographic method and the well-established single-point interferometric method. Results showing the minimal deviation of both methods are presented in the final part of the paper.

Finite Element Modeling of Ring-Shaped Piezoelectric Transformer

In this work, we developed a finite element package to investigate the dependence of electromechanical coupling coefficient on ring-shaped piezoelectric transformer parameters, and proposed how to design the transformer in achieving optimum efficiency using the ceramic PZT-5H as an application. The ring transformer firstly used full driven electrode to observe piezoelectric vibration characteristic with varying the ring dimensional (structural) parameters. Then, with the optimized ring parameters, electrode layout was designed in accordance to the distribution of electrical potential within the ring transformer, where both alternating and non-alternating electrode layouts were considered. From the calculation, results showed that the piezoelectric vibration characteristic strongly depends on the ring-shaped transformer dimension. Specifically, with increasing piezoelectric ceramic thickness and the width between inner- and outer-ring-radius, the resonance frequencies of the transformer decrease. On the other hand, in terms of the electrode layouts, the alternating electrode was a better choice in obtaining desired resonance frequency mode, as it provides larger electromechanical coupling coefficient than the non-alternating electrode. These results are in agreement with previous experimental investigation, where applicable.

The Piezoelectric Properties of (Na0.5K0.5)NbO3-K5.4Cu1.3Ta10O29Ceramics with Various K5.4Cu1.3Ta10O29Doping and Sintering Temperatures

(1-X)<TEX>$(Na_{0.5}K_{0.5})NbO_3-XK_{5.4}Cu_{1.3}Ta_{10}O_{29}$</TEX> (NKN-KCT) lead-free piezoelectric ceramics have been synthesized by the conventional solid state sintering method, and their sinterability and piezoelectric properties were investigated. Typically, this material is sintered between 1,025 and <TEX>$1,100^{\circ}C$</TEX> for 2 hours to achieve the required densification. Crystalline structures and Microstructures were analyzed by X-ray diffraction and scanning electron microscope. The density, dielectric constant (<TEX>${\varepsilon}_r$</TEX>), piezoelectric constant <TEX>$d_{33}$</TEX>, electromechanical coupling factor <TEX>$k_p$</TEX> and mechanical quality factor <TEX>$Q_m$</TEX> value of the NKN ceramics depended upon the KCT content and the sintering temperature. In particular, the KCT addition to NKN greatly improved the mechanical quality factor <TEX>$Q_m$</TEX> value. The ceramic with X = 1.0 mol% sintered at <TEX>$1,050^{\circ}C$</TEX> exhibited optimum properties (<TEX>${\varepsilon}_r$</TEX>=246, <TEX>$d_{33}$</TEX>=95, <TEX>$k_p$</TEX>=0.38 and <TEX>$Q_m$</TEX>=1,826). These results indicate that the ceramic is a promising candidate material for applications in lead free piezoelectric transformer and filter materials.

A verification and parametric analysis of an analytical model of a flexural vibration mode piezoelectric transformer

In this paper, a circuit model equivalent to that proposed in a previous work was verified through experimental and finite element methods. On the basis of this verified model, the impact of the parameters on the electrical characteristics of a circular flexural vibration mode piezoelectric transformer was systematically investigated through the orthogonal experiment design method. Some interesting and valuable rules were found. Additionally, the research process showed that the orthogonal experimental design method itself can partly act as an optimization design method for the circular flexural vibration mode piezoelectric transformer design.

Optic and Piezoelectric Coupling in the Sol-Gel PLZT Electroceramics

PZT ceramic system with presence of La contents, have been proposed and prepared using sol gel sintering method for practical application of photostriction, which is the superposition of photovoltaic and piezoelectric effects. Such a ceramics produced by conventional mixing oxide method does not exhibit photostrictive properties due to the defects and inhomogeneous distribution of grains and pores. In this study, an investigated lanthanium(III) doped PZT ceramics were obtained by sol-gel technique from the organometallic precursors. It was found that fabricated material were effective in the enhancement of photovoltaic and photostrictive properties. Consequently, lanthanium influence deviation of piezoelectric parameters were studied as a function UV light illumination. For the determination lighting dependancy of the transformation parameters the resonant and antiresonant method was implemented. The improved Piezoelectric Transformer structure successfully changed gain characteristics proportionally to light intensity. The authors invention of a light driven output gain adjustment in Piezoelectric Transformers (PT) yields a novel “smart” multifunctional wireless device. This new created application area can be utilized in self-adopting shutters in photo cameras due to improved sensitivity to surrounding illumination conditions.

Magnetic and Piezoelectric Properties of the Fe&lt;sup&gt;3+&lt;/sup&gt; Doped PLZT Electroceramics

For the growing interest in developing of more attractive multiferroic and magnetoelectric ceramics an alternative is a double-doped Pb(Zr1-xTix)O3- material with trivalent lanthanum and iron ions. Such material has a structure based on ABO3 perovskite and properties depending on the chemical and structural composition. In the present work the results of the preparation and characterization of Fe3+- modified 9/65/35 PLZT ceramics have been reported. Two samples of Pb0,91(La1-zFez)0,09(Zr0,65Ti0,35)0,9775O3 ceramics, for different Fe ions concentration (z = 0,0 and 0,5 at.%), were prepared from the MOM derived powders and sintered by the hot uniaxial pressing methods. To analyze the obtained ceramics properties the XRD, SEM and also application oriented dielectric and magnetic measurements were performed. The Fe3+ substitution at the La-site of PLZT has shown many interesting and unusual dielectric, piezoelectric and magnetic properties. The obtained material was proposed to implement into Piezoelectric Transformer structure to change gain characteristics proportionally to magnetic field intensity.

Optimal Design and Test of Ultrasonic Vibration System

Ultrasonic vibration system is the chief component of USM machine tool. Whether products are precisely machined is lie on the performance of the system. To design good performance of ultrasonic vibration system, finite element method is used to analyse the dynamic performance of the system based on theoretic calculation. The dynamic performance of transformer and transformer with tool is analysed respectively, including natural vibration characteristic and harmonic characteristic. The result of FEA is compared with theoretic calculation. The parametric optimization design technique of the finite element analysis package ANSYS is applied to optimize the structure dimension of the piezoelectric transducer and transformer with tool. Then amplitude of the optimized system and the previous system is compared based on laser-CCD sensor for micro-displacement. The optimized system is more superior and has larger amplitude. Last some round holes are machined on kentanium YG8, monocrystalline silicon, PZT. And machining effect of single Micro-USM is got by the test.

Analytical modeling of a sandwiched plate piezoelectric transformer-based acoustic-electric transmission channel

The linear propagation of electromagnetic and dilatational waves through a sandwiched plate piezoelectric transformer (SPPT)-based acoustic-electric transmission channel is modeled using the transfer matrix method with mixed-domain two-port ABCD parameters. This SPPT structure is of great interest because it has been explored in recent years as a mechanism for wireless transmission of electrical signals through solid metallic barriers using ultrasound. The model we present is developed to allow for accurate channel performance prediction while greatly reducing the computational complexity associated with 2- and 3-dimensional finite element analysis. As a result, the model primarily considers 1-dimensional wave propagation; however, approximate solutions for higher-dimensional phenomena (e.g., diffraction in the SPPT's metallic core layer) are also incorporated. The model is then assessed by comparing it to the measured wideband frequency response of a physical SPPT-based channel from our previous work. Very strong agreement between the modeled and measured data is observed, confirming the accuracy and utility of the presented model.

Power enhancement of piezoelectric transformers by adding heat transfer equipment

It is known that piezoelectric transformers have several inherent advantages compared with conventional electromagnetic transformers. However, the maximum power capacity of piezoelectric transformers is not as large as electromagnetic transformers in practice, especially in the case of high output current. The theoretical power density of piezoelectric transformers calculated by stress boundary can reach 330 W/cm(3), but no piezoelectric transformer has ever reached such a high power density in practice. The power density of piezoelectric transformers is limited to 33 W/cm(3) in practical applications. The underlying reason is that the maximum passing current of the piezoelectric material (mechanical current) is limited by the temperature rise caused by heat generation. To increase this current and the power capacity, we proposed to add a thermal pad to the piezoelectric transformer to dissipate heat. The experimental results showed that the proposed techniques can increase by 3 times the output current of the piezoelectric transformer. A theoretical-phenomenological model which explains the relationship between vibration velocity and generated heat is also established to verify the experimental results.

Self‐organization in a piezoelectric transformer‐based excimer lamp

AbstractAn excimer lamp constructed using a piezoelectric transformer (PT) has been developed and studied in our laboratory. The excimer lamp is based on the excitation of a dielectric barrier discharge (DBD) generated by a PT surface that induces a high voltage due to the piezoelectric effect. Spectroscopic measurement in the vacuum ultraviolet (VUV) region was performed for the excimer lamp filled with a He‐Xe mixture and Ar. Emission spectra having a peak at 172 and 126 nm were found, which were respectively radiated from the ${\rm{Xe}}_2^\ast$ and ${\rm{Ar}}_2^\ast$ excimers returning to their ground states. A self‐organization phenomenon (SOP) was also recognized in the He and Ar DBD. Static and time‐resolved observations of the self‐organized patterns were performed using single reflex and ICCD cameras, respectively. The formation of self‐organized patterns in argon requires a small amount of air as an additive. In time‐resolved observation, we found dark spots arrayed hexagonally in a weak emission on the PT surface, whose arrangement coincides well with that of bright hexagonal filaments. The dark spots are considered as the traces of accumulated charges on the dielectric electrode, which interrupt the hexagonally filamentary discharges. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(10): 44–53, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10397

Measurement of piezoelectric transformer vibrations by digital holography

A method for the measurements of the out-of-plane displacement on the surface of vibrating object is presented herein. This method is based on frequency-shifted time-averaged digital holographic interferometry, employing the principle of phase shifting. This approach allows for significant noise reduction, which results in high sensitivity of measurements. This method makes it possible to measure vibrations with amplitudes in the nanometer range over the whole measured surface. This method was applied to the visualization of the out-of-plane vibration modes of piezoelectric transformers. The amplitude and modal shapes were measured with a very high resolution. Furthermore, aspects influencing the measurement errors are discussed and the measurement results by holographic method were compared with the well-established single-point laser interferometry measurement method.