Disk-type Piezoelectric Transformer Research Articles

An Electromechanical Model for Clamped-Edge Bimorph Disk Type Piezoelectric Transformer Utilizing Kirchhoff Thin Plate Theory.

In this paper, an analytical solution for a clamped-edge bimorph disk-type piezoelectric transformer with Kirchhoff thin plate theory is proposed. The electromechanical equations for transient motions are first derived, and coupled expressions for mechanical response and voltage output are obtained. For the case of excitation around the first resonant frequency, the resulting equations are further simplified. There are analytical solutions for a mechanical response, voltage, current, and power outputs. According to the analytical model, the output voltage is affected by the inner radius of the input and output electrodes, the radius of the piezoelectric transformer (PT), and the thickness ratio between the lead zirconate titanate (PZT) layer and the substrate. When the inner radius of the input electrode approaches zero (electrode becomes circular shape), it achieves maximum output voltage at the first resonance frequency excitation. On the contrary, when the inner radius of the output electrode approaches zero, the output voltage reaches its minimum value. Voltage ratios remain constant as the disk radius changes, and the first resonance frequency is inversely proportional to the square of the disk radius. The voltage ratio is fixed even with the miniaturization of the PT.

Disk-type piezoelectric transformer of a Na0.5K0.5NbO3–CuNb2O6 lead-free ceramic for driving T5 fluorescent lamp

Lead-free (Na0.5K0.5)NbO3 (NKN) ceramics doped with 1mol% CuNb2O6 (CN) ceramics were prepared using the conventional mixed oxide method, with a sintering temperature of 1075°C. Microstructural analyses of the NKN–01CN ceramics were carried out and compared, using X-ray diffraction (XRD). NKN–01CN ceramics sintered at 1075°C not only exhibited excellent ‘hard’ piezoelectric properties of kp=40%, kt=45%, k33=57%, a ferroelectric property of Ec=23kV/cm, and an extraordinarily high mechanical quality factor (Qm) of 1933 but also showed excellent stability with temperature (TCF=−154ppm/°C). The piezoelectric transformer was simplified, using an equivalent circuit, and analyzed, using MATLAB; the simulation data agreed well with the experimental results. An efficiency of 95.7% was achieved for the NKN–01CN piezoelectric transformer with load resistance of 20kΩ. An 8W T5 fluorescent lamp was successfully driven by the NKN–01CN piezoelectric transformer.

디스크형 압전 변압기의 전극 대칭성에 따른 전기적 특성

본 연구에서는 직경이 50mm, 두께가 4.5mm인 디스크형 압전 변압기의 구동부와 발전부의 전극에 대한 대칭성을 고려하여 2, 4 및 8등분으로 각각 분할하였다. 이렇게 분할된 압전 변압기에 부하저항을 변화(<TEX>$100{\Omega}{\sim}10_{K\Omega}$</TEX>)시키면서 전기적 특성을 측정하고, 이를 토대로 한 압전변압기의 승압비 및 효율에 관한 메카니즘을 정량적으로 해석하였다. In this study, a disk-type piezoelectric transformer was fabricated. Its diameter was 50 mm and thickness was 4.5 mm. The driving and generating electrode with their gap of 1mm were fabricated on the top surface. But the common electrode was fabricated on the whole bottom surface. The electrode surface of driving and generating part on the top surface was divided into 2, 4 and 8 pieces. The electrical characteristics with its electrode variation was measured in the range of load resistance of <TEX>$100{\Omega}{\sim}10_{K\Omega}$</TEX>. We investigated quantitively the influence of the set-up voltage ratio.

Radial vibration mode of 0.71Pb(Mg1∕3Nb2∕3)O3–0.29PbTiO3 single crystal and its applications

Ferroelectric single crystal (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 (PMNT) has attracted considerable attention for its outstanding piezoelectric properties after poled along the ⟨001⟩ or ⟨101⟩ directions and it is being actively applied to various ultrasonic devices. However, almost all previous applications focus on the longitudinal extension, transverse extension, thickness extension and thickness shear vibration mode. Here, we investigated the radial vibration mode of the ⟨001⟩ poled 0.71Pb(Mg1∕3Nb2∕3)O3–0.29PbTiO3 single crystal. Both the finite element simulation and experimental results have shown that the performance of radial vibration mode is excellent. The coupling coefficient of radial vibration mode can reach 0.84 and the anisotropy of the circular plate is very weak after it was poled along the ⟨001⟩ direction. Based on this mode, we further designed and fabricated a disk-type piezoelectric transformer and the open circuit voltage step-up ratio reached about 50 with no spurious vibration mode around the resonance frequency. All these have shown that the radial vibration mode of PMNT single crystal is also promising and useful for other piezoelectric device applications.

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.

Crescent-shaped Input Type 원형압전변압기의 특성 연구

This paper presents a new disk-type piezoelectric transformer. The input side of the transformer has a crescent-shaped electrode and the output side has a focused poling direction. The piezoelectric transformers operated in each transformer's resonance vibration mode. The electrodes and poling directions on commercially available piezoelectric ceramic disks were designed so that the planar or shear mode coupling factor <TEX>$(k_p\;k_{15})$</TEX> becomes effective rather than the transverse mode coupling factor <TEX>$(k_{31})$</TEX>. ANSYS finite element code was used to analyze transformer behavior and to optimize electrode and poling configurations. The voltage step-up ratio of the proposed transformer has been markedly improved in comparison with that of the equivalent rectangular(Rosen) type. A single layer prototype transformer, <TEX>$20\sim30mm$</TEX> in diameter and <TEX>$1.0\sim3.5mm$</TEX> thick, was fabricated, such as step-up ratio, power transformation efficiency, and temperature were measured. While the transformer was driving a Cold Cathode Fluorescent Lamp(CCFL), the temperature field of the transformer was also observed.

디스크형 압전변압기의 전극 면적비에 따른 구동 메카니즘에 관한 연구

본 연구에서는 직경이 50[㎜], 두께가 4.5[㎜]인 디스크형 압전 변압기의 구동부와 발전부의 전극 면적비를 각각 1.4:1, 2:1 및 3:1로 분할하여, 부하 저항을 변화(100[Ω]～70[㏀])시키면서 전기적 특성을 측정하고, 이를 토대로 한 압전변압기의 승압비에 관한 메카니즘을 정량적 및 정성적으로 해석하였다. In this study, a disk-type piezoelectric transformer was fabricated. Its diameter was 50[㎜] and thickness was 4.5[㎜]. The driving and generating electrode with their gap of 1[mm] were fabricated on the top surface. But the common electrode was fabricated on the whole bottom surface. The electrode surface ratio of driving and generating part on the top surface was the range of 1.4:1 to 3:1. We investigated the electrical characteristics with the variation of its thickness and the electrode surface ratio of driving and generating part in the range of load resistance of 100[Ω]～70[㏀]. From the experimental results, their influence on the set-up voltage ratio were investigated quantitively and qualitatively.

Design of a Circular Piezoelectric Transformer with Crescent-Shaped Input Electrodes

In this study, a new disk-type piezoelectric transformer design is proposed. The input side of the transformer has a crescent-shaped electrode and the output side has a focused poling direction. The electrodes and poling directions on commercially available piezoelectric ceramic disks were designed so that the planar or shear mode coupling factor (kp or k15) becomes effective rather than the transverse mode coupling factor (k31). ATILA finite element code was used to analyze transformer behavior and to optimize electrode and poling configurations. The voltage step-up ratio of the proposed transformer has been markedly improved in comparison with that of the equivalent rectangular type. A single layer prototype transformer, 25.4 mm in diameter and 1.0 mm thick, operated at 92.8 kHz, was fabricated and its characteristics, such as step-up ratio and power transformation efficiency were measured. While the transformer was driving a cold cathode fluorescent lamp (CCFL), the temperature field of the transformer was also observed.