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.     

New technology for the design of advanced ultrasonic transducers for high-power applications

A new high-frequency ultrasonic transducer for wire bonding has been conceived, designed, prototyped and tested. In the design phase an advanced approach was used and established. The method is based on the two basic principles of modularity and iteration. The transducer is decomposed to its elementary components. For each component an initial design is obtained with finite elements method (FEM) simulations. The simulated ultrasonic modules are then built and characterized experimentally through laser-interferometry measurements and electrical resonance spectra. The comparison of simulation results with experimental data allows the parameters of FEM models to be iteratively adjusted and optimized. The achieved FEM simulations exhibit a remarkably high-predictive potential and allow full control on the vibration behavior of the ultrasonic modules and of the whole transducer. The new transducer is fixed on the wire bonder with a flange whose special geometry was calculated by means of FEM simulations. This flange allows the converter to be attached on the wire bonder not only in longitudinal nodes but also in radial nodes of the ultrasonic field excited in the horn. This leads to a nearly complete decoupling of the transducer to the wire bonder, which has not been previously obtained. The new approach to mount ultrasonic transducers on a welding-device is of major importance not only for wire bonding but also for all high-power ultrasound applications and has been patented.     

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.     

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.     

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。     

超声波显像管振动清洗机的研制

本文介绍一种无需任何清洗液且有别于常规超声波清洗机理的超声波显像管振动清洗机。从理论上分析说明超声波干振动清洗的机理和方法，阐明各超声参量的选取标准和超声振动系统中应注意的问题。     

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.     

Novel power MOSFET-based expander for high frequency ultrasound systems

The function of an expander is to obstruct the noise signal transmitted by the pulser so that it does not pass into the transducer or receive electronics, where it can produce undesirable ring-down in an ultrasound imaging application. The most common type is a diode-based expander, which is essentially a simple diode-pair, is widely used in pulse-echo measurements and imaging applications because of its simple architecture. However, diode-based expanders may degrade the performance of ultrasonic transducers and electronic components on the receiving and transmitting sides of the ultrasound systems, respectively. Since they are non-linear devices, they cause excessive signal attenuation and noise at higher frequencies and voltages. In this paper, a new type of expander that utilizes power MOSFET components, which we call a power MOSFET-based expander, is introduced and evaluated for use in high frequency ultrasound imaging systems. The performance of a power MOSFET-based expander was evaluated relative to a diode-based expander by comparing the noise figure (NF), insertion loss (IL), total harmonic distortion (THD), response time (RT), electrical impedance (EI) and dynamic power consumption (DPC). The results showed that the power MOSFET-based expander provided better NF (0.76 dB), IL (−0.3 dB) and THD (−62.9 dB), and faster RT (82 ns) than did the diode-based expander (NF (2.6 dB), IL (−1.4 dB), THD (−56.0 dB) and RT (119 ns)) at 70 MHz. The −6 dB bandwidth and the peak-to-peak voltage of the echo signal received by the transducer using the power MOSFET-based expander improved by 17.4% and 240% compared to the diode-based expander, respectively. The new power MOSFET-based expander was shown to yield lower NF, IL and THD, faster RT and lower ring down than the diode-based expander at the expense of higher dynamic power consumption.     

大功率单脉冲超声信号发生器的设计

为了提高探伤深度,实现混凝土大坝等散射强介质的超声检测,本文提出了一种成本低,小体积,结构简单的大功率单脉冲超声信号发生器,并给出了原理电路设计。所述装置利用控制电容充放电经脉冲变压器产生瞬时高压脉冲的新思路,克服了过去由于信号幅度限制功率上不去的困难。经实验验证该装置与现有的单脉冲信号发生器相比,探伤深度得到了很大提高,可用于混凝土结构构建的超声探伤。     

Ultrasound pressure distributions generated by high frequency transducers in large reactors

The performance of an ultrasound reactor chamber relies on the sound pressure level achieved throughout the system. The active volume of a high frequency ultrasound chamber can be determined by the sound pressure penetration and distribution provided by the transducers. This work evaluated the sound pressure levels and uniformity achieved in water by selected commercial scale high frequency plate transducers without and with reflector plates. Sound pressure produced by ultrasonic plate transducers vertically operating at frequencies of 400 kHz (120 W) and 2 MHz (128 W) was characterized with hydrophones in a 2 m long chamber and their effective operating distance across the chamber’s vertical cross section was determined. The 2 MHz transducer produced the highest pressure amplitude near the transducer surface, with a sharp decline of approximately 40% of the sound pressure occurring in the range between 55 and 155 mm from the transducer. The placement of a reflector plate 500 mm from the surface of the transducer was shown to improve the sound pressure uniformity of 2 MHz ultrasound. Ultrasound at 400 kHz was found to penetrate the fluid up to 2 m without significant losses. Furthermore, 400 kHz ultrasound generated a more uniform sound pressure distribution regardless of the presence or absence of a reflector plate. The choice of the transducer distance to the opposite reactor wall therefore depends on the transducer plate frequency selected. Based on pressure measurements in water, large scale 400 kHz reactor designs can consider larger transducer distance to opposite wall and larger active cross-section, and therefore can reach higher volumes than when using 2 MHz transducer plates.     

Piezoelectric multilayer transducers for ultrasonic pulse compression

This paper describes piezoelectric multilayer transducers for application in ultrasonic pulse compression systems. The transducers are constructed in such a way as to produce binary pulse sequences, in particular Barker-coded sequences. This is achieved by the polarization pattern of the active layers. Pulse compression is effected without any electronic circuitry by using a receiver transducer with a pattern corresponding to that of the transmitter.     

超声检测用窄脉冲探头高阻抗背衬的研制

利用一种简单的压力装置，制作与PZT压电晶片匹配的背衬块，最高声阻抗可达25．1×106kg·m-2·s－1用于试制窄脉冲探头，可以实现1.5周期的脉冲．     

Frequency and power dependence of ultrasonic degassing

We investigated the time variation of ultrasonic degassing for air-saturated water and degassed water with a sample volume of 100 mL at frequencies of 22, 43, 129, 209, 305, 400, 514, 1018, and 1960 kHz and ultrasonic power of 15 W. Ultrasonic degassing was evaluated by dissolved oxygen concentration. Ultrasonic degassing was also investigated at a frequency of 1018 kHz and ultrasonic powers of 5, 10, 15, and 20 W. The dissolved oxygen concentration varied with the ultrasonic irradiation time and became constant after prolonged ultrasonic irradiation. The constant dissolved oxygen concentration value depended on the frequency and ultrasonic power but not the initial dissolved oxygen concentration. The degassing rate at 101.3 kPa was higher in the frequency range of 200 kHz to 1 MHz. The frequency dependence of the degassing rate was almost the same as that of the sonochemical efficiency obtained by the potassium iodide (KI) method. Ultrasonic degassing in the frequency range of 22–1960 kHz was also investigated under reduced pressure of 5 kPa. Degassing was accelerated when ultrasonic irradiation was applied under reduced pressure. However, under a reduced pressure of 5 kPa, the lower the frequencies, the higher is the degassing rate. The sonochemical reaction rate was examined by the KI method for varying dissolved air concentrations before ultrasonic irradiation. Cavitation did not occur when the initial dissolved oxygen concentration was less than 2 mg·L⁻¹. Therefore, the lower limit of ultrasonic degassing under 101.3 kPa equals 2 mg·L⁻¹ dissolved oxygen concentration. A model equation for the time variation of dissolved oxygen concentration due to ultrasonic irradiation was developed, and the degassing mechanism was discussed.     

纵振驱动球面弯曲振动超声聚焦系统的聚焦特性*

为了将超声聚焦效应应用于工业加工中的冷却技术中,该文提出一种由夹心式换能器纵向振动驱动球面弯曲振动超声聚焦系统。基于基尔霍夫-亥姆霍兹声场理论分析了由换能器中心面纵向振动和球面弯曲振动组成的复合超声振动条件下的声场聚焦特性,并通过实验进行验证。研究结果表明,该聚焦系统具有显著的聚焦特性,球面弯曲振动将声能汇聚在声场焦区;当声场相位相同时,换能器中心面纵向振动和球面弯曲振动产生的声场在焦区发生叠加,可以进一步提高焦区声压;减小换能器中心面半径和球面曲率半径、增加球面开口半径可以增强复合超声振动的聚焦效果。     

高频聚焦换能器声场的激光测量法

本文描述了一种使用激光测振技术测量高频聚焦换能器声场布的方法，并给出了使用该方法对一种高频聚换能器进行测量的结果，通过理论计算对结果的正确性进行了验证。     

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.     

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.     

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。     

Review of the design of power ultrasonic generator for piezoelectric transducer

The power ultrasonic generator (PUG) is the core device of power ultrasonic technology (PUT), and its performance determines the application of this technology in biomedicine, semiconductor, aerospace, and other fields. With the high demand for sensitive and accurate dynamic response in power ultrasonic applications, the design of PUG has become a hot topic in academic and industry. However, the previous reviews cannot be used as a universal technical manual for industrial applications. There are many technical difficulties in establishing a mature production system, which hinder the large-scale application of PUG for piezoelectric transducers. To enhance the performance of the dynamic matching and power control of PUG, the studies in various PUT applications have been reviewed in this article. Initially, the demand design covering the piezoelectric transducer application and parameter requirements for ultrasonic and electrical signals is overall summarized, and these parameter requirements have been recommended as the technical indicators of developing the new PUG. Then the factors affecting the power conversion circuit design are analyzed systematically to realize the foundational performance improvement of PUG. Furthermore, advantages and limitations of key control technologies have been summarized to provide some different ideas on how to realize automatic resonance tracking and adaptive power adjustment, and to optimize the power control and dynamic matching control. Finally, several research directions of PUG in the future have been prospected.     

Progress in stacked piezocomposite ultrasonic transducers for low frequency applications

A stacked ultrasonic transducer comprises multiple individual layers connected mechanically in series and electrically in parallel to reduce the fundamental thickness mode resonance to a frequency corresponding to the transit time of the complete stack and the electrical impedance to a value which corresponds to that of the layers of the stack in parallel. In turn, this allows lower frequency resonant operation than would be possible with a single layer, and facilitates electrical impedance matching to typical transmission circuitry. On transmission, an ideal stack of uniform layers will have an output amplitude larger than that of the equivalent single layer by a factor equal to the . However, using conventional signal amplification circuitry on reception, the output voltage amplitude will be smaller than that of the equivalent single layer by a similar factor. In the past, stacks have commonly been assembled from layers of conventional piezoceramic material but more recently there have been reports of stacks of 1–3 piezocomposites and it is this type that is considered here. The work described in this paper is motivated by the need to operate at frequencies lower than are possible using conventional piezocomposite fabrication technology. Progress in comparison of experimental and simulated results is outlined and the highlights of a theoretical design study are presented. These show that although the general behaviour of a stacked structure is easily predicted, a rigorous theoretical analysis is essential to understand the detail of even a limited range of possible designs.