Simple method for measuring vibration amplitude of high power airborne ultrasonic transducer: Using thermo-couple

Vibration amplitude of transducer’s elements is the influential parameters in the performance of high power airborne ultrasonic transducers to control the optimum vibration without material yielding. The vibration amplitude of elements of provided high power airborne transducer was determined by measuring temperature of the provided high power airborne transducer transducer’s elements. The results showed that simple thermocouples can be used both to measure the vibration amplitude of transducer’s element and an indicator to power transmission to the air. To verify our approach, the power transmission to the air has been investigated by other common method experimentally. The experimental results displayed good agreement with presented approach.     

测定材料的缓冲防震性能

利用力学、机械传感器研究了不同缓冲材料与其他物体碰撞过程中瞬时作用力及其与碰撞初速度之间的关系,得到了材料的缓冲防震性能的动态变化曲线,并通过改变同种材料的厚度,发现该材料对缓冲作用的不同响应,并得到了一定材料在防震中的最佳缓冲厚度.     

Resonance tracking and vibration stablilization for high power ultrasonic transducers

Resonant frequency shift and electrical impedance variation are common phenomena in the application of high power ultrasonic transducers, e.g. in focused ultrasound surgery and in cutting. They result in low power efficiency and unstable vibration amplitude. To solve this problem, a driving and measurement system has been developed to track the resonance of high power transducers and to stabilise their vibration velocity. This has the ability to monitor the operating and performance parameters of the ultrasonic transducers in real time. The configuration of the system, with its control algorithm implemented in LabVIEW (National Instruments, Newbury, UK), ensures flexibility to suit different transducers and load conditions. In addition, with different programs, it can be utilised as a high power impedance analyser or an instantaneous electrical power measurement system for frequencies in the MHz range. The effectiveness of this system has been demonstrated in detailed studies. With it, high transducer performance at high power can be achieved and monitored in real time.     

Vibration amplitude and induced temperature limitation of high power air-borne ultrasonic transducers

The acoustic impedances of matching layers, their internal loss and vibration amplitude are the most important and influential parameters in the performance of high power airborne ultrasonic transducers. In this paper, the optimum acoustic impedances of the transducer matching layers were determined by using a genetic algorithm, the powerful tool for optimizating domain. The analytical results showed that the vibration amplitude increases significantly for low acoustic impedance matching layers. This enhancement is maximum and approximately 200 times higher for the last matching layer where it has the same interface with the air than the vibration amplitude of the source, lead zirconate titanate-pizo electric while transferring the 1 kW is desirable. This large amplitude increases both mechanical failure and temperature of the matching layers due to the internal loss of the matching layers. It has analytically shown that the temperature in last matching layer with having the maximum vibration amplitude is high enough to melt or burn the matching layers. To verify suggested approach, the effect of the amplitude of vibration on the induced temperature has been investigated experimentally. The experimental results displayed good agreement with the theoretical predictions.     

模式转换型超声塑焊振动系统的设计

基于弯曲振动理论和耦合振动理论,设计了一种新型大尺寸筒形超声塑焊振动系统。该振动系统由纵向振动换能器及变幅杆、弯曲振动金属圆盘和耦合振动圆筒四部分组成。换能器和变幅杆的纵向振动驱动圆盘的二次弯曲模式振动,圆盘的二次弯曲模式振动激励圆筒的纵向模式振动,实现了工具头在较高频率下谐振。实验结果表明,振动系统的测试频率与计算频率比较符合,在大信号下测试的纵-弯-纵振动模式转换效果很好。研究结果为高频大尺寸超声焊接系统的设计提供了思路。     

Load characteristics of high power sandwich piezoelectric ultrasonic transducers

Based on the equivalent circuit theory, the load characteristics of high power piezoelectric ultrasonic sandwich transducers are studied. Two types of loads are studied. One is liquid load as in ultrasonic cleaning, and the other is solid load as in ultrasonic drilling and machining. The effect of load and structure of the transducer on the resonance frequency of the transducer is analyzed. It is shown that the effect of load on the resonance frequency of sandwich transducers with different structures is different. For liquid load as in ultrasonic cleaning, the effect of the load on the resonance frequency of the sandwich transducer with symmetrical structure is the largest. It is the smallest for the transducer with its displacement node in the back metal cylinder. For solid load as in ultrasonic drilling and machining, the effect of the load on the resonance frequency of the sandwich transducer with its displacement node in the front metal cylinder is the largest. It is also the smallest for the transducer with its displacement node in the back metal cylinder. On the other hand, for some applications, such as ultrasonic drilling, when the lateral dimension of the tool is much less than that of the transducer, its effect on the resonance frequency of the transducer is small. The conclusions are useful in designing vibrating systems for different ultrasonic applications.     

Effects of high power ultrasonic vibration on the cold compaction of titanium

Titanium has widely been used in chemical and aerospace industries. In order to overcome the drawbacks of cold compaction of titanium, the process was assisted by an ultrasonic vibration system. For this purpose, a uniaxial ultrasonic assisted cold powder compaction system was designed and fabricated. The process variables were powder size, compaction pressure and initial powder compact thickness. Density, friction force, ejection force and spring back of the fabricated samples were measured and studied. The density was observed to improve under the action of ultrasonic vibration. Fine size powders showed better results of consolidation while using ultrasonic vibration. Under the ultrasonic action, it is thought that the friction forces between the die walls and the particles and those friction forces among the powder particles are reduced. Spring back and ejection force didn’t considerably change when using ultrasonic vibration.     

Optimization design of high power ultrasonic circular ring radiator in coupled vibration

This paper presents a new high power ultrasonic (HPU) radiator, which consists of a transducer, an ultrasonic horn, and a metal circular ring. Both the transducer and horn in longitudinal vibrations are used to drive a metal circular ring in a radial-axial coupled vibration. This coupled vibration cannot only generate ultrasound in both the radial and axial directions, but also focus the ultrasound inside the circular ring. Except for the radial-axial coupled vibration mode, the third longitudinal harmonic vibration mode with relative large vibration amplitude is also detected, which can be used as another operation mode. Overall, the HPU with these two vibration modes should have good potential to be applied in liquid processing, such as sonochemistry, ultrasonic cleaning, and Chinese herbal medicine extraction.     

Interdiffusion of Al-Ni system enhanced by ultrasonic vibration at ambient temperature

At ambient temperature, Al–1%Si wire of 25 μm diameter was bonded successfully onto the Au/Ni/Cu pad by ultrasonic wedge bonding technology. Physical process of the bond formation and the interface joining essence were investigated. It is found that the wire was softened by ultrasonic vibration, at the same time, pressure was loaded on the wire and plastic flow was generated in the bonding wire, which promoted the diffusion for Ni into Al. Ultrasonic vibration enhanced the interdiffusion that resulted from the inner defects such as dislocations, vacancies, voids and so on, which ascribed to short circuit diffusion.     

Window materials for high power gyrotron

The room temperature application of sapphire as window material at higher frequencies is not feasible since its absorption coefficient increases almost linearly with increasing frequency in the millimeter wavelength region. At cryogenic temperature the absorption coefficient value decreases only by a few factors (factor of 2 to 3) in the 90 – 200 GHz region. The earlier reported temperature squared dependence (decrease) in the absorption coefficient or the loss tangent value is totally absent in our broad band continuous wave data we are reporting here (at 6.5 K, 35K, 77K and 300K) and one we reported at conferences earlier. Our results are verified by another technique. We utilize our precision millimeter wave dispersive Fourier transform spectroscopic techniques at room temperature and at cryogenic temperatures The extra high resistivity single crystal compensated silicon is no doubt the lowest loss material available at room temperature in the entire millimeter wavelength region At higher millimeter wave frequencies an extra high resistivity silicon window or an window made with extra high resistivity silicon coated with diamond film would certainly make a better candidate in the future. A single free standing synthetic diamond window seems to have higher absorption coefficient values at millimeter wavelength region at this time although it is claimed that it possesses good mechanical strength and higher thermal conductivity characteristics. It certainly does not rule out the use of diamond film on a single crystal high resistivity silicon to improve its mechanical strength and thermal conductivityThis research program was supported by the U.S. Department of Energy, Office of Fusion Research. Authors acknowledge the loan of a synthetic diamond specimen from Dr. Kevin Gray of Norton Diamond Company     

功率超声设备频率振幅自动控制研究

本文根据差动变量器桥式电路补偿电学臂的原理，采用锁相环（PLL）及模拟乘法器等技术，进行功率超声设备频率振幅自动控制，结果表明，这种控制方法具有频率跟踪范围宽，负载知应能力强及系统性能稳定等功效。     

Automatic system for dynamic control of resonance in high power and high Q ultrasonic transducers

This paper describes the fundamentals, design criteria and electronic structure of a new frequency control system to keep permanently at resonance high Q ultrasonic transducers whose mechanical resonance band may vary within wide limits under normal operating conditions. The procedure developed is based on keeping constant at its zero value the phase of the motional admittance of the transducer by automatically and instantaneously adjusting the frequency of the driving signal provided by a voltage controlled oscillator. The characteristics of this system, especially the fact that the transducer is not an integral part of the feed-back loop of the oscillatory circuit and the frequency tracking mechanism does not depend directly on the magnitude of the motional variables of the transducer, offer some advantages in construction and performance with respect to the conventional motional positive feed-back systems.     

一种测量功率超声振动系统振速比的简单方法

本文提出了一种测量功率超声振动系统中振动速度比的简单方法。与传统的测量方法相比,本方法将力学量转变为电学量的测量,将绝对测量变成了相对测量,降低了对实验设备的要求,有利于提高测试精度。     

脆性光学材料的超声磨削实验研究

分别采用超声磨削和普通磨削加工方法加工了几种脆性光学材料,研究了几种主要工艺参数对工件加工表面粗糙度的影响。结果表明,超声频率和振幅、金刚石磨料粒度、切深、工具的横向进给速度和旋转速度等工艺参数对表面粗糙度的影响较大。通过比较发现,超声磨削方法比普通磨削方法具有更好的加工表面粗糙度,更高的材料去除率,以及更低的工具磨损量。     

An ultrasonic transducer for high power applications in gases

In the field of the generation of airborne ultrasound, we have described and analysed in a previous paper¹ a piezoelectric transducer based on a novel flexural vibrating stepped plate. This transducer has now been improved for high power applications, obtaining, with a remarkable increase in efficiency and directivity, sound pressure levels in free field greater than 160 dB.     

Characteristics of large capacity ultrasonic complex vibration sources with stepped complex transverse vibration rods

Configurations of large capacity ultrasonic complex vibration sources with multiple longitudinal transducers are proposed and studied. The ultrasonic complex vibration systems are effective and essential for new applications in various industries. The complex vibration source of 27 kHz consists of a complex transverse rod with a welding tip (aluminum alloy, stainless steel and titanium alloy), a complex vibration rod with a flange and stepped part for holding the system, a circular longitudinal vibration disk (aluminum alloy) and six bolt-clamped Langevin type PLT transducers. Three transducer pairs are driven simultaneously using three driving systems at phase difference 120 degrees, and almost circular vibration locus is obtained.     

Techniques for high power microwave sources at high average power

Experiments on CLIA (compact linear induction accelerator), capable of generating 750 kV and 10 kA into a matched load using magnetic switching to produce 60 ns long pulses, are described. As a first application, the authors used CLIA to drive a water-cooled L-band magnetron at repetition rates as high as 250 Hz with no breakdown or pulse shortening. This gives an average power of 6.3 kW. A short burst at 1 kHz demonstrates operation that would translate to an average power of approximately 25 kW. In this regime operation is not limited by gas build-up, electrode erosion or microwhisker depletion. Currently, the authors are operating on CLIA with a high current relativistic klystron. Beams with modulated current powers of approximately 1 GW have been generated at 100 Hz for bursts as long as 5000 pulses. It is concluded that there are no apparent obstacles to much higher average powers at higher peak powers     

Effects of high power ultrasonic vibration on temperature distribution of workpiece in dry creep feed up grinding

Temperature history and distribution of steel workpiece (X20Cr13) was measured by a high tech infrared camera under ultrasonic assisted dry creep feed up grinding. For this purpose, a special experimental setup was designed and fabricated to vibrate only workpiece along two directions by a high power ultrasonic transducer. In this study, ultrasonic effects with respect to grinding parameters including depth of cut (a_e), feed speed (v_w), and cutting speed (v_s) has been investigated. The results indicate that the ultrasonic vibration has considerable effect on reduction of temperature, depth of thermal damage of workpiece and width of temperature contours. Maximum temperature reduction of 25.91% was reported at condition of v_s = 15 m/s, v_w = 500 mm/min, a_e = 0.4 mm in the presence of ultrasonic vibration.     

Sound absorbing characteristics of fibrous metal materials at high temperatures

To study the effect of high temperatures on absorbing properties of fibrous metal materials, the calculations of effective density and effective bulk modulus are presented on basis of Dup‘ere’s model and Tarnow’s model. A modifying factor is presented to modify differences between real effective density and the effective density when the fibers regarded straight. The high temperatures effects on acoustic parameters are studied by thermodynamics theories and variable-property heat transfer. The surface specific acoustic impedances and normal incidence acoustic absorption coefficients are discussed theoretically. Finally, a measurement setup is built to verify the theoretical predictions. The experimental results fit the theoretical results well.