Advantages and challenges of relaxor-PbTiO3 ferroelectric crystals for electroacoustic transducers – A review

Relaxor-PbTiO₃ (PT) based ferroelectric crystals with the perovskite structure have been investigated over the last few decades due to their ultrahigh piezoelectric coefficients (d₃₃ > 1500 pC/N) and electromechanical coupling factors (k₃₃ > 90%), far outperforming state-of-the-art ferroelectric polycrystalline Pb(Zr,Ti)O₃ ceramics, and are at the forefront of advanced electroacoustic applications. In this review, the performance merits of relaxor-PT crystals in various electroacoustic devices are presented from a piezoelectric material viewpoint. Opportunities come from not only the ultrahigh properties, specifically coupling and piezoelectric coefficients, but through novel vibration modes and crystallographic/domain engineering. Figure of merits (FOMs) of crystals with various compositions and phases were established for various applications, including medical ultrasonic transducers, underwater transducers, acoustic sensors and tweezers. For each device application, recent developments in relaxor-PT ferroelectric crystals were surveyed and compared with state-of-the-art polycrystalline piezoelectrics, with an emphasis on their strong anisotropic features and crystallographic uniqueness, including engineered domain–property relationships. This review starts with an introduction on electroacoustic transducers and the history of piezoelectric materials. The development of the high performance relaxor-PT single crystals, with a focus on their uniqueness in transducer applications, is then discussed. In the third part, various FOMs of piezoelectric materials for a wide range of ultrasound applications, including diagnostic ultrasound, therapeutic ultrasound, underwater acoustic and passive sensors, tactile sensors, acoustic tweezers and ultrasonic motors, are evaluated to provide a thorough understanding of the materials’ behavior under operational conditions. Structure–property–performance relationships are then established. Finally, the impacts and challenges of relaxor-PT crystals are summarized to guide on-going and future research in the development of relaxor-PT crystals for the next generation electroacoustic transducers.     

Turning of Microgrooves Both With and Without Aid of Ultrasonic Elliptical Vibration

Microgroove, as a form of surface texturing, has a wide array of industrial applications. However, the use of conventional methods to machine microgrooves leads to a number of problems including large burrs, high cutting forces, and poor machining quality. In this paper, ultrasonic elliptical vibration cutting is used to assist microgrooves turning on cylindrical workpiece surfaces. The elliptical locus in the cutting process is generated by a newly designed 2D resonant ultrasonic vibrator. A series of microgrooves cutting experiments without and with the ultrasonic elliptical vibration-assistance is performed to verify the effects of the ultrasonic elliptical vibrations as compared to the ordinary cutting method. The generated cutting forces, burr suppression action, and microgroove surface quality are compared for the two classes of processes. Comparison results show the effectiveness of elliptical vibration-assisted microgroove cutting in reducing cutting forces and improving microgrooves machining quality for difficult-to-cut materials. The results also show that ultrasonic elliptical vibration-assisted cutting improves the microgroove turning process with respect to cutting forces, microgroove surface roughness, and burr formation for difficult-to-cut materials.     

金属熔体在超声场中凝固的研究

本文综述了超声场对金属凝固过程的影响，着重总结了声空化、声流所起的作用，同时介绍了超声在新材料制备中的应用。     

Surface roughness evaluation via ultrasonic scanning

Despite extensive applications of ultrasonic waves to various nondestructive testing and evaluation of materials, scattering of focused ultrasonic waves due to surface roughness has not been fully investigated. This paper presents an analytical and experimental evaluation of surface roughness measurement using focused ultrasonic beams. The characteristics of focused ultrasonic waves are analyzed by using the impulse response method with a sine-modulated Gaussian pulse as source. First, the beam profile in the focal plane of the focused ultrasonic transducer is analyzed both numerically and experimentally. Second, peak amplitude distribution and reflected waveforms from a flat surface with various incident angles are analytically generated and compared with experimental results. Then, the peak amplitudes of the ultrasonic waves reflected from cusped surfaces which are easily found among machined surfaces are analyzed and compared with experimental data for the first time. The analysis shows good agreement between analytical and experimental results. The excellent correlation between the measurements using a profilometer and the proposed ultrasonic system demonstrates a good potential for surface roughness measurement by ultrasonic sensing.     

Experimental investigation and process optimization of the ultrasonic welding applied to papers

Ultrasonic welding is a serious candidate in the development of methods to assemble papers and paperboards without using additional substances. However, the ultrasonic welding of papers remains a technological challenge considering the low weldability of lignocellulosic materials. This study aims to investigate on the ultrasonic welding process applied to papers in order to identify the processing conditions which favor the formation of strong welded joints. To reach such purpose, an experimental strategy was developed by combining the characterization of welded materials and the monitoring of process parameters. Experimentations were performed using a reference paper displaying a good weldability to specifically highlight the contribution of process parameters. Results indicate that the process is highly sensitive to vibration amplitude, power supplied by the high frequency generator, and sample thickness. Power seems to be a reliable indicator of the severity of the process. A strong decrease in the strength of the welded joints is observed when working with low thicknesses. It seems that the layers coated on top of papers are the main part of the material contributing in the development of adhesion at the welding joint. Overall, instrumenting the device has led to a better understanding of the ultrasonic welding of papers.     

Fabrication and characterization of piezoelectric micromachined ultrasonic transducers with thick composite PZT films

Ferroelectric microelectromechanical systems (MEMS) has been a growing area of research in past decades, in which ferroelectric films are combined with silicon technology for a variety of applications, such as piezo-electric micromachined ultrasonic transducers (pMUTs), which represent a new approach to ultrasound detection and generation. For ultrasound-radiating applications, thicker PZT films are preferred because generative force and response speed of the diaphragm-type transducers increase with increasing film thickness. However, integration of 4- to 20-microm thick PZT films on silicon wafer, either the deposition or the patterning, is still a bottleneck in the micromachining process. This paper reports on a diaphragm-type pMUT. A composite coating technique based on chemical solution deposition and high-energy ball milled powder has been used to fabricate thick PZT films. Micromachining of the pMUTs using such thick films has been investigated. The fabricated pMUT with crack-free PZT films up to 7-microm thick was evaluated as an ultrasonic transmitter. The generated sound pressure level of up to 120 dB indicates that the fabricated pMUT has very good ultrasound-radiating performance and, therefore, can be used to compose pMUT arrays for generating ultrasound beam with high directivity in numerous applications. The pMUT arrays also have been demonstrated.     

An ultrasonic technique for the determination of casting-chill contact during solidification

Heat transfer between a solidifying aluminium alloy casting and a mould is dominated by the thermal resistance created by the interface. Interfacial heat transfer occurs by conduction through the atmosphere between the two surfaces and by conduction through the points of actual contact. (Heat transfer by radiation is probably significant only for ferrous castings.) The extent of real physical contact between two surfaces is difficult to quantify. This paper explains a method, using ultrasonic flaw detection techniques, whereby an estimate of the propagation of an ultrasonic signal through a casting-chill interface is used to infer the degree of actual contact occurring between them.In experiments involving casting and solidification of an aluminium alloy onto a copper chill the technique was found to give information for the first two seconds of the casting process only. In this time a peak in ultrasound transmission was observed, correlating to a maximum in the area of casting-chill contact, followed by a decrease in the ultrasound transmission that corresponded to actual contact areas between the casting and the chill in the region of 5 to 10%.     

Innovative focused ultrasound-based sealing method of flexible packaging films—Principles and characteristics

A key process to package goods is the closure procedure. It ensures the good protection against the environment and vice versa. Ultrasonic sealing presents the advantage of converting locally ultrasound into heat, which is optimal for temperature sensitive goods. The disadvantages remain, however, the equipment cost, the noise generation, and the process sensitivity to materials. It is necessary to develop a sealing process to decrease the acquisition cost of the sealing equipment and cover a wide range of polymer films. This paper focuses on a new sealing method based on high-intensity focused ultrasound. The principles and characteristics of this process are discussed and underpinned with experimental results. Both the acoustic and thermal effects of the sealing process are summarized. A study of the process parameter impact on the seam strength in static and dynamic operating is proposed. Low-density polyethylene films with a carrier layer of bi-oriented polypropylene and polyethylene terephthalate are used. A first test bench generates point-shaped seam. The heat generation is recorded with an infrared thermography system. A second test bench, a horizontal form fill and seal machine, produces longitudinal seams. The seam quality is controlled by tensile test and tightness test. A quick heating of the polymer films is found. Point seams and longitudinal seams are successfully generated. The seams behave similarly to the ones generated with ultrasonic sealing process. However, the sealing velocity is limited to 3 m/min. This work provides a summary of the characteristics and principles of the new sealing method in packaging applications.     

20世纪功率超声在国内外的发展

本文就强超声的产生系统 ,强超声在液体媒质中的主要作用机理以及多种多样超声处理技术和应用在国内外近百年来的发展概况作一简要回顾 ,同时涉及一些领域的最近发展     

An ultrasonic technique for the determination of casting-chill contact during solidification

Heat transfer between a solidifying aluminium alloy casting and a mould is dominated by the thermal resistance created by the interface. Interfacial heat transfer occurs by conduction through the atmosphere between the two surfaces and by conduction through the points of actual contact. (Heat transfer by radiation is probably significant only for ferrous castings.) The extent of real physical contact between two surfaces is difficult to quantify. This paper explains a method, using ultrasonic flaw detection techniques, whereby an estimate of the propagation of an ultrasonic signal through a casting-chill interface is used to infer the degree of actual contact occurring between them.In experiments involving casting and solidification of an aluminium alloy onto a copper chill the technique was found to give information for the first two seconds of the casting process only. In this time a peak in ultrasound transmission was observed, correlating to a maximum in the area of casting-chill contact, followed by a decrease in the ultrasound transmission that corresponded to actual contact areas between the casting and the chill in the region of 5 to 10%.     

超声处理污泥的影响因素讨论

超声处理污泥问题是一种超声技术新的应用的尝试,在已经进行的研究工作的基础上,介绍了超声处理污泥的机理、特点,就其影响的几大主要因素——频率、声强、功率、反应器的设计与换能器类型、污泥自身因素等进行分析。对于超声处理污泥这种极其复杂的过程,进一步讨论了超声技术处理污泥存在的问题和今后的发展方向。     

REMOVAL OF PARTICULATE CONTAMINANTS USING ULTRASONICS AND MEGASONICS: A REVIEW

ABSTRACT

Sonic cleaning is a commonly used technique for removal of particles from surfaces. The theory of particle removal using ultrasound is reviewed. Effects of cavitation and acoustic streaming are discussed. Experimental results using ultrasonics and megasonics (ultrasonic cleaning near 1 MH_z) from the literature are reviewed. Emphasis is placed on removal of fine particles from silicon surfaces for semiconductor manufacturing applications.     

超声联合臭氧用于废水处理的研究进展

臭氧（O3）是一种强氧化剂，具有良好的杀菌消毒和降解污染物的能力，但臭氧与有机物的反应是选择性的。超声降解水体中有机污染物是近年来兴起的一项极具发展前景的新型水处理技术，能有效地降解废水中的难降解有机污染物。将超声与臭氧进行联合使用，可以提高降解有机物的效率。文章介绍了超声／臭氧联用技术降解有机物的机理．综述了国内外超声／臭氧联用技术在废水处理中的研究进展。并指出超声联合臭氧技术今后需解决的问题和发展方向。     

Ultrasonic Transducer Sensitivity and Model-Based Transducer Characterization

It is shown that the role that an ultrasonic piezoelectric transducer plays in both generating and receiving ultrasound in an ultrasonic nondestructive evaluation (NDE) measurement system can be completely described in terms of the transducer's electrical impedance and open-circuit, blocked force receiving sensitivity. Furthermore, it is shown that both of these quantities can be obtained experimentally via a model-based approach and purely electrical measurements. The measurement of sensitivity uses a method originally developed for lower-frequency acoustic transducers. However, it is shown that at the higher frequencies found in ultrasonic NDE applications electrical cabling effects play an important role and must be compensated for in determining the transducer sensitivity. Examples of experimental measurement results using these new approaches are given.     

面向电子制造的功率超声微纳连接技术进展

为满足电子制造与封装对新材料与工艺的迫切需求,尤其是高功率、高温服役、高集成度以及高可靠性等新型器件的连接难题,开发了面向电子制造的功率超声微纳连接技术。从固相键合、超声复合钎焊和超声纳米连接3个方面,综述了面向电子制造的功率超声微纳连接技术的原理方法、优势与应用场合。功率超声由于其表面清洁、声流和空化作用,将大幅提升冶金反应速率,有效解决了传统TLP反应温度高时间长,以及Cu和Al等金属的易氧化等问题,甚至攻克了Al2O3,AlN,SiC等陶瓷基板的难润湿以及低温纳米颗粒烧结驱动力不足的难题。综述了该领域多年来的研究成果,聚焦电子制造中的功率超声微纳连接技术,从固相连接领域的引线键合、室温超声金属连接和超声增材制造,到钎焊领域的超声低温软钎焊、超声中高温连接以及超声瞬态液相连接,最后针对第三代半导体高功率器件简述了超声纳米连接,探讨了功率超声微纳连接技术的研究进展及趋势。     

超声破穿冰块的方法

本文提出了超声破块的新方法，对冰块样品的实验表明，利用５Ｗ／ｃｍ＾２声强的超声可以达到３００ｍｍ／ｍｉｎ的破穿速度，作者介绍了这种实验方法，并认为：喷射声空化场的空化集中效应是超声破穿冰块的作用机制，最后，预测了这种超声破穿方法在冰处理工程上的应用。     

A survey of developments in ultrasonic NDE of concrete

The goal of this paper is to develop an understanding of the current state of ultrasonic nondestructive evaluation in the concrete community. Methods supplemental to the less than satisfactory procedure specified in ASTM C-597 are discussed. It is hoped that such an understanding, in conjunction with a feeling for the nature of reinforced concrete as a material, will promote research interest in this important field. Following an introductory problem statement, a literature review concerning the existing use of stress waves for the nondestructive evaluation of concrete is presented. An examination of current practice is offered. Next, new approaches are selected and reviewed from the current literature. In all cases, these are approaches that have been successful in applications to advanced engineering materials other than concrete. Where appropriate, potential benefits and pitfalls of each new technique, as applied to concrete, are discussed     

Ultrasonic Transducer Sensitivity and Model-Based Transducer Characterization

It is shown that the role that an ultrasonic piezoelectric transducer plays in both generating and receiving ultrasound in an ultrasonic nondestructive evaluation (NDE) measurement system can be completely described in terms of the transducer's electrical impedance and open-circuit, blocked force receiving sensitivity. Furthermore, it is shown that both of these quantities can be obtained experimentally via a model-based approach and purely electrical measurements. The measurement of sensitivity uses a method originally developed for lower-frequency acoustic transducers. However, it is shown that at the higher frequencies found in ultrasonic NDE applications electrical cabling effects play an important role and must be compensated for in determining the transducer sensitivity. Examples of experimental measurement results using these new approaches are given.     

Piezoelectric films for high frequency ultrasonic transducers in biomedical applications

Piezoelectric films have recently attracted considerable attention in the development of various sensor and actuator devices such as nonvolatile memories, tunable microwave circuits and ultrasound transducers. In this paper, an overview of the state of art in piezoelectric films for high frequency transducer applications is presented. Firstly, the basic principles of piezoelectric materials and design considerations for ultrasound transducers will be introduced. Following the review, the current status of the piezoelectric films and recent progress in the development of high frequency ultrasonic transducers will be discussed. Then details for preparation and structure of the materials derived from piezoelectric thick film technologies will be described. Both chemical and physical methods are included in the discussion, namely, the sol-gel approach, aerosol technology and hydrothermal method. The electric and piezoelectric properties of the piezoelectric films, which are very important for transducer applications, such as permittivity and electromechanical coupling factor, are also addressed. Finally, the recent developments in the high frequency transducers and arrays with piezoelectric ZnO and PZT thick film using MEMS technology are presented. In addition, current problems and further direction of the piezoelectric films for very high frequency ultrasound application (up to GHz) are also discussed.     

Controlling Cell Behavior Through the Design of Polymer Surfaces

Polymers have gained a remarkable place in the biomedical field as materials for the fabrication of various devices and for tissue engineering applications. The initial acceptance or rejection of an implantable device is dictated by the crosstalk of the material surface with the bioentities present in the physiological environment. Advances in microfabrication and nanotechnology offer new tools to investigate the complex signaling cascade induced by the components of the extracellular matrix and consequently allow cellular responses to be tailored through the mimicking of some elements of the signaling paths. Patterning methods and selective chemical modification schemes at different length scales can provide biocompatible surfaces that control cellular interactions on the micrometer and sub‐micrometer scales on which cells are organized. In this review, the potential of chemically and topographically structured micro‐ and nanopolymer surfaces are discussed in hopes of a better understanding of cell–biomaterial interactions, including the recent use of biomimetic approaches or stimuli‐responsive macromolecules. Additionally, the focus will be on how the knowledge obtained using these surfaces can be incorporated to design biocompatible materials for various biomedical applications, such as tissue engineering, implants, cell‐based biosensors, diagnostic systems, and basic cell biology. The review focusses on the research carried out during the last decade.