频率自动跟踪超声波电源设计

针对超声波电源工作时负载状态改变,换能系统产生谐振漂移的问题,提出了一种基于STM32的频率自动跟踪超声波电源的设计。电源逆变电路采用带辅助网络的全桥结构,阻抗匹配电路选择了一种改进型的T型匹配网络,应用PWM移相调功技术控制电源的输出功率,通过数字鉴相技术得到电压电流的相位差作为电路谐振状态的反馈信号,结合STM32主控制器进行PI控制,调节PWM波的输出频率使电路始终工作于谐振状态,实现了谐振频率的自动跟踪。最后基于该设计方案,实际制作了一款应用于超声波清洗仪的电源,并通过实验验证了该电源具有输出功率稳定,负载适应性强,输出频率自动跟踪等特点。     

Optimization of a universal matchbox on an ultrasonic vibrating system

The main scope of the article is to investigate the effect of ferrite cores gap in a universal matchbox on an ultrasonic vibrating system. A gapped transformer mechanism in a universal matchbox has been thoroughly studied. Characteristics of an ultrasonic vibrating system have been recorded such as mechanical vibrations, inductance, resonant frequencies, current and voltage levels as the gap of ferrite cores gradually increases. In addition, the phase difference between the supplied voltage and the current is also computed and displayed in a Lissajous curve in order to determine the optimal gap between two ferrite cores in the universal matchbox. Explanations supplement the experiment results.     

超声换能器并联谐振频率的复合式跟踪方法研究

为了使超声换能器适应变化比较剧烈的负载,本文通过分析超声换能器在并联谐振频率附近工作时的频率特性和实际需求特点,利用变压器初级匹配方法得到了更好的频率特性,并对比了换能器空载和带负荷情况下的阻抗特性曲线,提出了复合式自动频率跟踪方法,空载时找到超声换能器最小电流的对应的频率点,加载过程中利用比例积分微分算法实现频率的快速跟踪。并对超声换能器在不同负载时的功率输出进行了实验,结果表明,复合式频率跟踪方法可以稳定地跟踪到超声换能器的并联谐振频率,能实现超声换能器的功率自调节,对提高换能器的工作效率和负荷适应能力具有实际的指导意义和应用价值。     

cMUT阵元的声学分析与环形扫描成像

电容式微机械超声换能器(cMUT)具有宽带宽、灵敏度高、机械阻抗低和与电子电路集成制造等优点.由于超声换能器声场设计的好坏决定了成像质量的优劣,为了明确阵元参数与辐射声场的关系,该文对不同的阵元参数进行了计算仿真.与压电陶瓷超声换能器的结构不同,cMUT阵元是由多个电容单元(cell)并联构成.因此分析了cell的半径...     

超声焊接全状态频率跟踪算法*

与超声塑料焊接相比，超声金属焊接负载重且变化剧烈，容易导致换能器出现无阻性点状态或者频率误跟踪。现有的频率跟踪方法往往只能在换能器有阻性点的状态下正常工作，在出现误跟踪时也无法自动复位。针对上述问题，本文基于梅森等效电路，推导出一种能够同时适配于谐振频率与反谐振频率，能够自行判断是否误跟踪频率跟踪算法。当换能器处于无阻性点状态时，算法将自动把跟踪目标变为相位差最小点，实现全状态频率跟踪。算法利用三个不同频率及其发波时换能器的电压电流相位进行计算，以此算出理想的频率跟踪步长和方向。最后通过MATLAB对算法进行仿真，验证算法在目标频率发生非线性变化时频率跟踪的效果。结果表明，新算法能够实现误跟踪的自复位和全状态频率跟踪，同时能在启动后10ms以内完成频率跟踪，跟踪精度达0.1hz。     

Reduction of acoustic radiation by impedance control with a perforated absorber system

A model of sound radiation from an infinite plate with an absorptive facing is proposed and investigated theoretically from the viewpoint of acoustic power. Acoustic characteristics on the plate surface are represented by impedance derived from iso-absorption curves. A parametric study is carried out to clarify the effect of the impedance on the acoustic power. Results derived from this model show that acoustic radiation depends on change in impedance as well as the absorption coefficient, and there is a possibility of reducing the radiation from vibrating surface by introducing an appropriate impedance surface. In order to realize this effect, a model using a perforated board with a back cavity attached to the vibrating surface is proposed, in which the motion of the perforated board is made equal to that of the vibrating surface. To obtain fundamental data, a theoretical study is performed under a simplified condition, assuming an infinite plane piston. The calculated results are compared to experimental data measured by using an acoustic tube. The results, which are in good agreement in the reduction effect, show that this system can achieve the reduction of radiated sound power at arbitrary frequencies.     

A finite element approach to a coupled structural-acoustic radiation system with application to loudspeaker characteristic calculation

The finite element method is applied to an elastic shell which is vibrating to generate acoustic radiation. A vibrating shell of revolution backed by an enclosure in its rear side is to radiate sound waves into a semi-infinite space in front. As a numerical example, some characteristics of a direct radiator type loudspeaker model are calculated and discussed. The driving point impedance and the far field sound pressure frequency characteristics are shown, together with the effects of the radiation and the enclosure.     

步进追频及恒振幅控制的超声电源设计

针对超声金属焊接过程中出现的负载变化导致谐振频率漂移和焊接振幅失恒问题,设计了一种基于步进追频及恒振幅控制的超声电源。在负载变化对谐振频率影响的研究基础上,根据FPGA-DDS步进追频原理设计了负载变化追频逻辑;结合全桥逆变电路的移相控制方式,研究了不同占空比下的最大输入电流与最大焊接振幅的关系,提出了基于输入电流反馈下的步进移相恒振幅控制方案;实验结果表明,负载变化追频逻辑实现了谐振频率快速变化下的动态实时追踪,解决了因频率失谐导致的焊接振幅非线性下降问题。同时,在加入了振幅闭环控制后,实现了焊接振幅相对极差稳定在10%以内。     

Electromechanical and pyroelectric properties in CoZn ferrite transducer

The system Co_0.6Zn_0.4Fe₂O₄ ferrite was prepared by the usual ceramic method. The resonant frequency and antiresonance of vibrating disc have been studied as a function of temperature. The decrease of resonant frequency with rising temperature was attributed to increase the interaction of domains with the applied AC field. The decrease of the ultrasonic wave velocity with the increase of temperature was ascribed to thermal lattice vibration, which facilitate the domains to interact at lower frequency of the applied AC field. The electromechanical coupling factor of the radial mode was fairly constant with rising temperature. The pyroelectric voltage measured at the transducer electric terminals increases with the increase of temperature. Ferrite transducer is useful for ultrasonic generation to be used in technology.     

Vibration analysis and sound field characteristics of a tubular ultrasonic radiator

A sort of tubular ultrasonic radiator used in ultrasonic liquid processing is studied. The frequency equation of the tubular radiator is derived, and its radiated sound field in cylindrical reactor is calculated using finite element method and recorded by means of aluminum foil erosion. The results indicate that sound field of tubular ultrasonic radiator in cylindrical reactor appears standing waves along both its radial direction and axial direction, and amplitudes of standing waves decrease gradually along its radial direction, and the numbers of standing waves along its axial direction are equal to the axial wave numbers of tubular radiator. The experimental results are in good agreement with calculated results.     

负载不匹配对大功率速调管输出特性的影响

 采用微波等效电路和3维电磁场计算软件研究了负载不匹配对大功率速调管输出腔的谐振频率、间隙阻抗和外观品质因数的影响。并采用1维大信号计算软件研究了负载不匹配对速调管效率的影响。对C波段速调管的研究表明：对于单间隙输出腔,负载不匹配对谐振频率影响较小,对间隙阻抗和等效外观品质因子影响较大,当负载驻波比为1.5时,谐振腔的谐振频率变化约35 MHz,间隙阻抗实部最大值变化为3 660~7 998 Ω,等效外观品质因子变化为36.9~93.5,中心频率处的效率下降4.6%。对于滤波器加载输出电路,负载不匹配对阻抗-频率特性和效率-频率特性有较大影响,当负载驻波比为1.5时,中心频率处的效率下降11.2%。当负载驻波比小于1.2时,负载失配对速调管性能的影响较小。     

短圆管换能器辐射阻抗

辐射阻抗是换能器最重要的辐射声场特性参数之一,影响着换能器的谐振频率、频带宽度、效率以及辐射声功率等。随着圆管换能器半径和高度的不断变化,想直接得到声场瑞利积分的解析解是十分困难的。该文通过建立经验公式模型来解决此问题。首先,通过有限元软件计算圆管换能器辐射阻抗的数值解。然后利用MATLAB工具进行曲线拟合。经过反复逼近拟合,建立圆管换能器辐射阻抗经验公式模型。与刚性扩展模型计算出的傅里叶级数解相比,经验公式模型在kr值从0.03~10范围内与有限元计算结果更为吻合,验证了经验公式计算辐射阻抗的准确性。同时,在圆管更低高径比情况下,经验公式模型仍可较准确地计算辐射阻抗。     

气流扬声器振动系统的设计原理

本文用等效电路方法分析了电动气流扬声器振动系统的特性,求得了气流扬声器的输入阻抗和位移振幅的频率特性,并把结果用于典型扬声器,说明用等效电路分析指导气流扬声器设计的作用。气流扬声器振动系统所需的电功率与其机械共振频率的四次方成正比,其声辐射主要限于共振频率以下,因而高频特性较差。求得了在共振频率以下,频率响应平直的最佳条件,实验表明,在最佳条件下,气流扬声器的高频特性随着磁隙中的磁感应强度的增加仍稍有提高。实验结果符合理论分析,测得气流扬声器喇叭喉部的声压级在不同情况下达181分贝或184.8分贝(零分贝等于2×10^-5牛顿/米²)。     

A passive means for cancellation of structurally radiated tones

The concept of cancellation of constant-frequency sound radiated from a vibrating surface by means of an attached mechanical oscillator is discussed. It is observed that the mass of a mechanical oscillator whose spring is attached to the vibrating surface will vibrate at comparatively large amplitudes and out of phase with that surface, provided that the surface vibrates at a frequency that is slightly higher than the oscillator's natural frequency. From this observation it is concluded that an oscillator's mass with a relatively small surface area can produce a volume velocity that is equal and opposite to that of the vibrating surface, resulting in cancellation of the sound radiated from the surface. Practical considerations in the design of such an oscillator are discussed, and the canceling performance from oscillators consisting of edge-supported circular disks is analyzed. An experimental canceling oscillator consisting of an edge-supported disk is described, and measurements made with this disk attached to a piston are shown to be in good agreement with analytical predictions. A tonal noise reduction exceeding 20 dB was demonstrated experimentally.     

用谐振来解释超声加工中的“局部共振”现象

本文采用机械阻抗方法分析了超声加工系统中出现的“局部共振”现象，通过对不同截面积比的变频杆和工具杆组合系统的计算，得出“局部共振”是超声加工系统的某些固有频率和工具杆固有频率相接近时的现象，此时整个系统仍是全谐振。     

基于改进PSO的超声雾化电源频率跟踪研究*

超声波雾化技术由于其良好的雾化效果获得了广泛关注，具有极大的研究价值和应用前景。但是在超声雾化的过程中，由于换能器的温度变化、刚度变化以及在水中的负载变化等因素，会产生谐振频率漂移的现象。当工作频率偏移谐振频率时，将造成换能器的工作效率降低和元器件损坏等问题。针对此问题，设计了基于改进粒子群算法优化PID参数的超声雾化电源频率跟踪算法，并对该算法进行频率跟踪的仿真验证和实验对比，在频率跟踪上实现了更好的效果，使换能器能够稳定工作在谐振状态，提高了电源的利用率。     

Non-linear acoustic radiation by an underwater vibrating spherical shell

I.IntroductionMostofthepublishedstudiesontheacousticwaveradiationfromelasticbodyconcen-tratedon1ineartheory.However,iftheamplitudeislargeandthefrequencyishigh,theresultingsoundwavepropagatinginthemediumwillgenerateconsiderablenonlineardistor-tion.Sothest.di.s[1]inthisfieldarelimited.Inthispaperwetreatedasphericalshell.Itconsistsoftwoaspects:oneisthestructuralresponseofasphericalshellinacousticfield.Becausethenonlineareffectofacousticwavecumulateswithpropagatingdistance,itisnegligibleonthesph…     

Development of non-destructive bond monitoring techniques for ultrasonic bonders

Simulation of an ultrasonic bonding tool was performed to formulate and analyse the relationships between the boundary conditions due to loading at the bond-tool interface and the measured parameters, such as the ultrasonic frequency and the input impedance variations during the bonding process. It is believed that improved process monitoring techniques can be developed based on the functional dependence between the ultrasonic frequency, input impedance variations and the boundary conditions at the bond-tool interface. Both experimental and simulation results obtained indicate that a strong dependence exists between the load, resonant frequency and the input impedance in an ultrasonic bonder. Resonant frequency was observed to increase as the loading on the bond surface increases.     

双泡模型共振频率的超声空化动力学研究

该研究旨在研究双泡模型的自然共振频率对超声空化的影响,通过理论计算研究了自然共振频率的影响因素,以及单频超声和双频超声与自然共振频率的关系。研究结果表明：气泡初始半径是影响自然共振频率的主要因素;低频驱动下的非线性波动程度会比高频的更加剧烈,当驱动频率等于气泡自然共振频率时,超声空化的效果更好;双频超声取气泡自然共振频率时超声空化效果远远优于单频超声驱动。该研究在超声医学和理解超声空化特性方面有着重要的意义。     

叠合结构超低频弯张换能器

研究了一种将多个椭圆弯张壳体在短轴方向进行机械叠合的超低频弯张换能器,每个弯张壳体采用超磁致伸缩材料进行驱动。推导了多个叠合壳体的等效电路,利用支路阻抗方法得到了换能器频率和阻抗的方程表达式。针对多个壳体叠合的结构复杂性,采用有限元方法计算并分析了叠合壳体换能器的多个结构点的振动位移分布,通过平动位移分布设计了活塞辐射面的结构参数。将有限元方法计算的换能器在空气中和水中的谐振频率与等效电路法计算的结果进行了对比,符合较好。研制了6个壳体叠合的超低频弯张换能器样机,换能器外形尺寸为Φ230×630 mm,重量为39 kg。换能器经湖上试验,水中谐振频率130 Hz,最大发送电流响应161.1 dB,最大发射声源级为180.4 dB,实现了超低频、小尺寸的发射能力。