压电变压器的研究进展

压电变压器利用压电陶瓷材料自身的压电和逆压电效应来实现升降压，同传统的电磁变压器相比较，具有体积小、无电磁污染、升压比随工作频率和阻抗变化的特点。本文详细评述了用于压电变压器的铁电陶瓷材料的电畴特性、性能参数和掺杂改性的方法，以及压电变压器的变压原理、一般等效电路图和各种各样的压电变压器，分析了现阶段压电变压器存在的问题，并展望了压电变压器的发展方向。     

低温烧结PZT压电陶瓷研究进展

介绍了国内外在ＰＺＴ压电陶瓷材料低温烧结方面的研究进展，并对除低ＰＺＴ压电陶瓷材料烧结温度的各种方法进行了评述。     

锰掺杂对PMN-PT陶瓷介电和压电特性的影响

采用氧化物固相反应法制备了Mn掺杂0.67Pb（Mg1/3Nb2/3）O3-0.33PbTiO3陶瓷，研究了锰掺杂量对陶瓷相结构、介电和压电性能的影响。实验发现，随着锰掺杂量的增加，陶瓷焦绿石相含量的逐渐较少，材料变“硬”。即当锰掺杂量少于1.5mol％时，介电系数ε、压电常数d33和机械品质因数Qm逐渐增加，介电损耗tanδ减少。随着锰掺杂量的进一步增加，弛豫程度变得更加明显。当压电陶瓷组分中锰掺杂量为1.5mol％时，其介电和压电性能各为：ε=2300，kp=0.54，Qm=900，tanδ=0.004，d33=400pC/N，适于制作大功率压电陶瓷变压器。     

无铅压电陶瓷材料的研究进展

无铅压电陶瓷是当前压电铁电领域的研究重点。本文结合国内外有关无铅压电陶瓷方面的论文和专利，从两个方面综述了无铅压电陶瓷材料的研究进展：一是从掺杂改性的方面；二是从粉体的制备和工艺方面。文章分析和比较了各类无铅压电陶瓷材料的结构和性能，展望了无铅压电陶瓷今后的发展趋势。     

压电陶瓷变压器的发展——回顾与展望

文章简要介绍了压电变压器的工作原理 ,给出了压电变压器几个重要工作特性的数学表达式 ,并对压电变压器的发展过程进行了简要的回顾。在此基础上 ,文章着重对压电变压器在研发过程中所涉及的五个方面的问题进行了详细的探讨与说明 ,作者讨论了压电变压器等效电路模型的改进措施及压电变压各个特性的研究状况 ,分析和对比了各种用于制作压电变压器的压电材料的优缺点及其性能的改进方法 ,探讨了各种振动模式作用于压电变压器的效果 ,总结了压电变压器的制作工艺及结构对其特性的影响效果 ,给出了压电变压器的具体应用的例子 ,并指出了压电变压器今后的发展方向及有待解决的问题     

PLN—3型压电陶瓷材料组成对压电参数温度稳定性的影响

在适当的工艺条件下，改变铌锂锆钛酸铅（PLN）三元系压电陶瓷材料组成中的锆钛比，加取代改性物及外加改性添加物，获得了高温稳定的PLN－3型压电陶瓷材料。该材料常温性能优良，高温稳定性好，200℃时相对25℃时的性能参数变化较小，介电常数变化小于45％，谐振频率变化小于2．5％，机电耦合系数变化小于－3％。本文在大量实验的基础上叙述了PLN材料组成与材料压电参数温度稳定性的关系，并对其改性作用机理进行了探讨。     

压电陶瓷变压器研究和发展现状

概述了压电陶瓷变压器的原理和分类，介绍了各种振动模式的压电陶瓷变压器，并重点叙述了两种电极设计精巧的压电陶瓷变压器，对体型和膜型压电陶瓷变压器的研究进展现状进行了分析。     

高温,高频压电陶瓷材料研究进展

主要介绍了不同系列高温高频压电陶瓷材料的结构及性能特点,针对不同应用条件提出了相应的陶瓷材料系列,指出改性PbTiO_3压电陶瓷材料的研究是高温高频压电陶瓷研究工作的重要组成部分。     

铈掺杂对PZT压电陶瓷性能的影响

研究了铈掺杂对PZT(锆钛酸铅)压电陶瓷材料的相组成、微观结构、介电性能、压电性能及铁电性能的影响,并对实验结果做出物理机理的解释.实验结果表明,适量的铈掺杂有利于材料结构的致密,提高了体电阻率,解决了材料在高温高场下极化困难的问题,在铈掺杂量为0.4%(摩尔分数)时,制备出综合性能良好的PZT压电陶瓷:室温时εr=958,tgδ=0.24%,d33=239pC/N,Kp=0.45,Qm=886,适合制备大功率压电陶瓷.     

增材制造压电陶瓷研究进展

压电陶瓷是一种可以实现机械信号和电信号相互转换的功能陶瓷。由压电陶瓷与有机相构成的复合材料具有不同的宏观连接方式, 这不仅决定了压电器件广泛的应用场合, 而且推动了压电陶瓷材料和器件多样化的成型技术发展。与传统成型技术相比, 增材制造技术的最大优势在于无需模具即可实现外形复杂的小批量样品快速成型, 这与多样化的压电陶瓷及其器件研发需求十分契合, 同时因其样品后续加工量少、原材料利用率高、无需切削液的特点, 得到了学术界和工业界的广泛关注。在陶瓷材料增材制造领域, 功能陶瓷和器件的研究仍在增长期。本文从不同增材制造技术角度, 探讨和对比现阶段无铅和含铅压电陶瓷增材制造的发展历史、原料制备、外形设计、功能特性检测及试样的应用, 并根据现阶段各增材制造技术的优、劣势对其未来进行了展望。     

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.     

Heat transfer enhancement in distribution transformers using TiO2 nanoparticles

A transformer is an electrical device that transfers electrical energy between windings by electromagnetic induction while producing a considerable amount of heat in circuits. The heat produced in windings is removed by an appropriate heat transfer fluid such as liquid dielectrics. The cooling and insulating of a liquid dielectric depend on the properties of the oil filling the transformer. One of the approaches to enhance the thermal and dielectric properties of transformer oil is employing an appropriate nanoparticle in a transformer.In this paper, a three-phase distribution transformer is simulated three-dimensionally in order to study the heat transfer efficiency for pure oil (single phase) and nanofluid (TiO₂ nanoparticles- transformer oil). For both models, the electromagnetic field in solid sections and heat transfer in fluid and solid sections of the transformer are simultaneously investigated. The simulation results show that the presence of TiO₂ nanoparticles in the transformer oil increases the heat transfer coefficient, i.e. adding 1% (vol/vol) of TiO₂ nanoparticles to the transformer oil increases the Nusselt number from 2.17 to 2.49, while the maximum temperature of transformer components decreases from 47.20?°C to 43.05?°C.     

Flux-locked current source reference

The quantization of flux in a closed superconducting circuit is used to provide a stable reference current. A 10-mA current source is coupled through a toroidal transformer to a DC superconducting quantum interference device (SQUID) input, and the resulting signal is fed back as an error current. The result is a net flux linkage that exhibits short-term stability of 1 part in 10⁹/h. The net current is quantized with a step size of 59.4 nA, and it will exhibit the same stability as the flux provided the mutual inductance of the transformer remains constant. This current is passed through a precise 100-Ω resistor and compared against Zener diode references. The observed temperature coefficient for the flux transformer is 28.5±3 ppm/K at 4.2 K. Possible sources for the temperature dependence are discussed     

基于多物理场耦合及温升特性研究的变压器热点温度建模与仿真分析

变压器温升特性研究尤其是热点温度测算不但能够指导变压器工程制造,而且有利于掌握变压器的运行状态,从而避免热故障的发生并指导变压器动态增容。对现有热点温度计算方法进行改进,提出一种基于多物理场耦合的油浸式变压器温升模型。以500kV油浸式变压器为例,采用能量守恒原理分析变压器热特性,建立变压器温度场与流场的数学模型和物理模型,分析变压器的温升特性、物理参数和材料特性,应用流-固-热耦合温度场进行仿真计算。通过仿真计算和分析对热点温度的具体分布部位和数值有了更深入的了解。该方法比经验公式计算所得热点温度值的准确度提升了4%,为变压器热点温度计算提供了一种新的计算思路。     

Analysis of temperature rise for piezoelectric transformer using finite-element method

Analysis of heat problem and temperature field of a piezoelectric transformer, operated at steady-state conditions, is described. The resonance frequency of the transformer is calculated from impedance and electrical gain analysis using a finite-element method. Mechanical displacement and electric potential of the transformer at the calculated resonance frequency are used to calculate the loss distribution of the transformer. Temperature distribution using discretized heat transfer equation is calculated from the obtained losses of the transformer. Properties of the piezoelectric material, dependent on the temperature field, are measured to recalculate the losses, temperature distribution, and new resonance characteristics of the transformer. Iterative method is adopted to recalculate the losses and resonance frequency due to the changes of the material constants from temperature increase. Computed temperature distributions and new resonance characteristics of the transformer at steady-state temperature are verified by comparison with experimental results.     

Inverse magnetoelectric effect in ferrite-piezoelectric structures

A theory of the inverse magnetoelectric (ME) effect in bulk ferrite-piezoelectric composite materials is presented. Using the material equations and equations of motion, expressions for the frequency dependence of the inverse ME conversion coefficient and the voltage ratio in an ME transformer are obtained. These dependences exhibit a resonant character, with the ME response magnitude peaking at the resonance frequency. The ME transformer coefficient not only depends on the ME voltage coefficient and the number of turns in the induction coil, but is also influenced by the mutual orientation of the electric and magnetic fields and the sample geometry.     

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.     

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.     

A numerical study of the coupling coefficients for pot coretransformers

When a circuit containing a transformer is to be simulated, one must know the coupling coefficient or equivalent leakage inductances in addition to the other transformer properties. When other inductances in series with a transformer winding are large compared to the leakage inductance the leakage inductance may be neglected in a simulation. Otherwise, the coupling coefficient must be known or the simulation will be inaccurate. Since the degree of coupling depends on the nature of the winding as well as the core, and is difficult to estimate accurately, we have used numerical techniques to study the trends in coupling with geometric parameters for cores having cylindrical symmetry. Magnetic vector potential has been found using the TOPAZ2D finite element code, and then correspondingly interpolated numerical integration has given the inductances for an equivalent circuit. Results from our calculations show that although the magnetizing inductance changes greatly as a core saturates, the coupling coefficient changes slowly so long as some reasonable effective permeability remains. Actual values depend on the turns ratios and any air gaps present. For a typical pot core geometry without an air gap the coupling coefficient ranges from 0.997 to 0.999 for effective permeabilities from 600 to 1800. With air gaps the coupling coefficient drops, but stays even more constant with permeability     

Magnetic bead detection using nano-transformers

A novel scheme to detect magnetic beads using a nano-scale transformer with a femtoweber resolution is reported. We have performed a Faraday's induction experiment with the nano-transformer at room temperature. The transformer shows the linear output voltage responses to the sinusoidal input current. When magnetic beads are placed on the transformer, the output responses are increased by an amount corresponding to the added magnetic flux from the beads when compared with the case of no beads on the transformer. In this way, we could determine whether magnetic beads are on top of the transformer in a single particle level.