B2功率超声振动系统的电声效率测量

本文用导纳圆图法和谐振导纳计算法，分别对用于超声清洗和塑料焊接的两个振动系统的电声效率进行了测量。结果表明在小信号和功率输出下，其电声效率基本相等。测量误差不超过±１５％。为通过电声效率和电功率测量，确定功率超声振动系统的输出声功率提供了可能途径     

功率超声换能器电声效率测试装置的研究

本文以单片机为测试工具，研制了一台测量功率超声换能器电声效率的测试装置，采用本装置可以能动地电声匹配电路电学参数的测量，方便，迅速地测出功率超声换能器在实际工作状态下的电声效率。     

螺杆紧固郎之万型振子的大振幅特性

对设计大功率超声振动系统,振子的大振幅特性是极其重要的。由于缺乏测量方法和合适的可变机械负载,大振幅特性从未测量过。采用瓦特表法和作者提出的可变机械负载阻,测量了最为有效和广泛应用的螺杆紧固郎之万型振子的大振幅特性,证明测量是成功的。作为一例,一个螺杆紧固的振子的最大机械输出功率大于1.5KW,在最佳声负载阻时,其电声效率高达96%。 一、引言 在大功率超声应用中,振子的大振幅特性(LAC)对于振动系统的合理设计是极其重要的。在超声处理中,往往要求给出振速和超声输出功率。大振幅特性(LAC)系指: (1)有效机械阻与振速的关…     

球壳换能器电声效率测量方法研究

换能器电声效率是高强度聚焦超声系统治疗剂量预测的重要参数。基于平面扫描法、辐射力天平法和自易法测量球壳聚焦换能器的输出声功率,同时测量换能器激励电功率,计算得到换能器电声效率。以1.1MHz的球壳换能器为被测对象,平面扫描法的相对扩展不确定度为14.21%,辐射力天平法的相对扩展不确定度为5.82%,自易法的相对扩展不确定度为15.30%。3种方法测量所得电声效率偏差在4%以内,实验证明3种方法在测量球壳聚焦换能器的电声效率时具有较好的一致性。     

功率超声换能器电声效率及辐射声功率的测量

在高频电功率计方法的基础上,本文提出了一种能够直接测量大功率压电超声换能器在实用状态下的辐射超声功率以及电声效率的新方法。与传统的高频电功率计法相比,本方法避免了介电以及机械损耗功率的测试,简化了测试步骤。     

A4 负载条件下功率换能器的特性研究

本文给出３种换能器系统在，有一定输入功率负载条件下输入电阻抗，电声效率的频率特性在某一工作频率处的功率特性，并与线性理论结果的趋势相一致，对大功率超声换能器的应用有一定指导意义。     

A4负载条件下功率换能器的特性研究

本文给出３种换能器系统在有、有一定输入功率负载条件下输入电阻抗、电声效率的频率特性，在某一工作频率处的功率特性，并与线性理论结果的趋势相一致，对大功率超声换能器的应用有一定指导意义     

微细超声工作台的设计与微振幅测量

微细超声工作台是微细超声加工机床与微细超声振动辅助加工机床的关键零部件,其振幅值直接影响加工精度与加工效率。传统的振幅测量方法很难准确的测出微细超声工作台的微振幅。基于精密微三维运动平台的高分辨率,提出了一种恒力控制的微振幅测量方法,成功的测量出能精确到0.1微米的微振幅。本文首先对微细超声工作台中的微细超声振动系统进行了理论设计,然后采用基于恒力控制的超声振幅测量方法,对不同功率作用下的微细超声振动系统的振幅值进行了测量。     

功率超声振动系统研究进展

本文对国内外近几年来在功率超声振动系统方面的研究进展情况作简要介绍，内容包括大功率纵振系统，弯曲振动和扭转振动系统，复合振动系统，大尺寸振动系统，在空气中产生功率超声的振动系统以及某些特殊用途的超声振坳系统等６个部分。     

大功率超声清洗机研制中的一些技术问题

本文介绍了微机控制的大功率超声清洗机研制的一些技术问题，探索了单片机在功率超声中的应用，提出了大功率超声振动子的一种新的设计方法，解决了一些影响振动子性能的关键问题，对于楔形工具头的超声振动子平均振幅的测量以及与同类机型的比较成为可能，文中还给出了部分比较曲线，实际测量证明，本文所述的系统比同类进口机平均振幅提高一倍以上，对工件的清效果明显优于进口机。     

A Novel Procedure for Receiver Noise Characterization

The noise figure at one value of source admittance, plus the variation of output noise power with source admittance, are sufficient for the complete noise characterization of a linear receiver. A standard noise generator of variable admittance is not required. A wide range of source admittances can be used.     

A General Formulation for Admittance of an Open-Ended Rectangular Waveguide Radiating into Stratified Dielectrics

Abstract

A general approach is presented for calculating the aperture admittance of a rectangular waveguide radiating into layered dielectric media. The two specific geometries of stratified, lossy dielectric media that are addressed terminate into either an infinite half-space or a perfectly conducting surface. The geometries describe two prevalent categories of layered dielectric composites and coatings that often are encountered in practical microwave nondestructive evaluation applications. Solutions are found initially by constructing a complete set of field components and subsequently enforcing the continuity of power flow across the aperture interface of the waveguide. Final results are presented as a superposition of transverse electric and magnetic components of the aperture admittance. The solutions presented allow the systematic calculation of admittance in the presence of arbitrary multilayer media, which in turn may be related to experimentaly measurable quantities of interest. With the practical assumption of dominant mode incidence on the aperture, the final expressions may be implemented without intense computational power, which often is desirable in practice where inaccuracies due to random errors and instrumentation sensitivity render incorporation of more rigorous solutions inefficient. Numerically simulated data also are presented to verify and interpret the results.     

露点法和中点法确定R407C压缩机性能测试工况点之比较

本文介绍了采用当中点和露点确定R4 0 7C压缩机性能测试工况点的方法 ,指出它们之间具有内在联系—结果可相互换算。同时对采用不同方法测得的压缩机制冷量和EER值进行了比较 ,结果表明采用露点法测得的制冷量和消耗功率通常比中点法低大约 5 % ,而计算出的EER相差不大。     

A study on the acoustic boundary admittance. Determination,results and consequences

The acoustic boundary admittance condition represents the stiffness, the mass and the damping behaviour of the surrounding structure. The harmonic analysis of small interior domains (e.g. vehicle cabin) is often carried out only by applying acoustically rigid boundaries since the admittances are unknown or unreliably determined by commonly applied methods. Determination using an impedance tube (or Kundt's tube) does not consider the real sound field; the calculation from the measured reverberation time provides an average admittance (and no phase information) of the whole boundary only. Beginning with the definition of the complex-valued boundary admittance, a brief review of the techniques to determine boundary admittances is followed by a boundary element based method that is suited to calculate the boundary admittances from a known sound pressure field. In addition to known methods, a formulation is found where the nodal admittance is calculated by the quotient of a nodal particle velocity divided by the nodal sound pressure. The nodal particle velocity can be calculated from a known sound pressure field solving a Dirichlet problem. The methods are applied to three simple examples. Finally, other examples are given to demonstrate how the boundary admittance can represent the fluid–structure interaction and phase angle of admittance influences the complex-valued eigenfrequencies.     

Electrical Conductivity and Complex Impedance Analysis of Ba<Subscript>2</Subscript>CrMo<Subscript>0.8</Subscript>W<Subscript>0.2</Subscript>O<Subscript>6</Subscript> Double Perovskite

Electrical properties of Ba ₂CrMo_0.8W_0.2O₆ double perovskite were investigated using admittance spectroscopy technique. According to impedance analysis, the material was modeled by an electrical equivalent circuit. Such analysis proves the presence of relaxation phenomenon in the compound. We also found that ac conductivity follows the Jonscher universal power law. Conduction process is found to be dominated by the thermally activated small polaron (SPH). The activation energy values, inferred from dc conductivity and from the temperature dependence of relaxation time, are closed to each other. Such result indicates that conduction process and relaxation phenomenon are related to the same defect.     

Comparative Study of Resistive and Inductive Superconducting Fault Current Limiters SFCL for Power System Transient Stability Improvement

This paper presents a comparative study of resistive and inductive superconducting fault current limiter (SFCL) for power systems transient stability improvement. Two applications of transient stability assessment are presented in this paper: The first shows the efficiency of the resistive and inductive SFCL in series with a generator, the second uses SFCL installed in series with a transmission line. SFCL can just be operated during the period from the fault occurrence to the fault clearing; the modeling and the effect of SFCL has been investigated to have higher benefits for the power system. In the present work, modification of the admittance matrix method is used for modeling of SFCL; Critical Clearing Time (CCT) has been used as an index for evaluated transient stability. The transient stability is assessed by the criterion of relative rotor angles, using the Runge–Kutta method. The effectiveness of the proposed method is tested on the WSCC3 nine-bus system applied to the case of three-phase short circuit fault in one transmission line. A simulation and comparison are presented in this document.     

An improved model of mutual admittances of tapped windings

The calculation of the equivalent admittances of windings tapped in sections, which are used as elements of high-accuracy measuring instruments (e.g., in inductive voltage dividers, magnetic current comparators, and transformers with minimum ratio errors), is considered. A comprehensive mathematical model of equivalent admittances is presented. It is derived from the measured mutual admittances of particular sections. The equivalent admittances of this model are dependent on the actual values of the mutual admittances as well as on the actual tap voltages. With the equivalent admittances it is possible to analyze, in a simple way, the ratio errors and the input admittance due to parasitic admittances and to calculate the accurate values of correcting admittances     

球面聚焦超声换能器的电声特性和测量方法的研究

研究介绍了圆形孔径的球面聚焦压电换能器的基本电声参数：输出声功率、辐射电导、电声效率、自由场发射电流(电压)响应、自由场电压灵敏度、有效面积、有效孔径、声焦距、声束宽度和阻抗(导纳)等电声特性及其测量方法,详细地论述了基于辐射力天平法和自易校准法的测量原理和方法,讨论了它们的内在联系。给出了换能器自易校准中的衍射修正系数和平均反射系数的公式、计算方法和系列数据图表。试验结果表明了测量原理和方法的合理性和可行性。     

A general formulation for admittance of an open-ended rectangular waveguide radiating into stratified dielectrics

A general approach is presented for calculating the aperture admittance of a rectangular waveguide radiating into layered dielectric media. The two specific geometries of stratified, lossy dielectric media that are addressed terminate into either an infinite half-space or a perfectly conducting surface. The geometries describe two prevalent categories of layered dielectric composites and coatings that often are encountered in practical microwave nondestructive evaluation applications. Solutions are found initially by constructing a complete set of field components and subsequently enforcing the continuity of power flow across the aperture interface of the waveguide. Final results are presented as a superposition of transverse electric and magnetic components of the aperture admittance. The solutions presented allow the systematic calculation of admittance in the presence of arbitrary multilayer media, which in turn may be related to experimentaly measurable quantities of interest. With the practical assumption of dominant mode incidence on the aperture, the final expressions may be implemented without intense computational power, which often is desirable in practice where inaccuracies due to random errors and instrumentation sensitivity render incorporation of more rigorous solutions inefficient. Numerically simulated data also are presented to verify and interpret the results.     

输电塔气动力系数和气动导纳风洞试验研究

输电塔结构的非定常抖振力与来流风速之间存在复杂的非线性关系,基于风洞试验得到的某1 000 k V格构式直线输电塔弹性模型的基底力以及参考高度处同步采集的风速时程,采用线性和高斯两种近似假定计算了非定常气动力系数并与试验值进行了比较;提出了包含结构气动阻尼效应在内的总气动导纳的概念,通过基底脉动力谱和来流脉动风速谱的比值对总气动导纳函数进行识别,并用基于频域相干函数对导纳函数的线性部分进行了估计。结果发现,风偏角线性近似所计算静气动力系数的偏差较高斯近似小;由于气动抖振力非定常性质明显,不考虑总气动导纳函数将高估输电塔模型的抖振响应;脉动风力与脉动风速间有较强的非线性关系,用线性导纳函数计算的抖振力谱将低估脉动风分量的影响。