DESIGN FEATURES OF DIFFERENT TYPES OF ULTRASONIC TRANSDUCER
DESIGN FEATURES OF DIFFERENT TYPES OF ULTRASONIC TRANSDUCER
Mariia Kireeva
PhD student of Department of Mechanical Engineering and Automation, Harbin Institute of Technology (Shenzhen),
China, Shenzhen
ABSTRACT
The article discusses the features, characteristics, purpose, scope and main modelling methods of ultrasonic transducers. During the research, special attention is paid to the design features of different types of ultrasonic transducers and analyze modern methods of ultrasonic transducers modelling by using software. In particular, the design characteristics of ultrasonic transducers are considered with a separated emphasis on the active element, the substrate and the wear-resistant plate. A description of an ultrasonic transducer for high-temperature industrial applications is also provided. The design features of electromagnetic ultrasonic transducer with extended inductance coil and capsule-type transducer are pointed out (are singled out separately).
Keywords: ultrasonic transducer, element, coil.
Introduction
Sound waves are a form of energy transfer in a state of mechanical vibration of an object. Ultrasound is a type of sound wave with an oscillation frequency above 20 kHz that cannot be heard by a human [1]. An ultrasonic transducer is a device to realize mutual conversion of mechanical and electrical energy.
Currently, ultrasound has been widely used in engineering and medicine for on-site material testing and imaging. In addition, ultrasonic technology has become one of the most widely used non-destructive testing methods. For example, non-destructive testing of technical elements at energy, chemical and oil refineries is playing an increasingly important role in improving safety and and extending the service life of installations. In particular, in order to find out the internal state of a material and determine the thickness of pipe wall or storage tank, this information is obtained by studying the behaviour of ultrasonic waves during their propagation inside the material, which depends on the internal flows in the studied material, that makes it possible to assess its condition [2].
The design of the ultrasonic transducer is focused on maximum performance in specific applications, which usually leads to a complex structure, expensive assembly and installation. A successful and cost-effective design of an ultrasonic transducer can be problematic for well-known reasons and traditionally depends on practical experience supplemented by using performance evaluation in computer modelling. Even if a simple piezoelectric device is considered, there are many possible designs. Moreover, the design of ultrasonic transducers for different applications can be great differences. For example, when developing ultrasonic sensors for sonar applications, the overall efficiency index of receive transmit or input loss is not important [3]. However, the input loss is a critical parameter for the design of biomedical probe. Therefore, knowledge of specific applications and areas of use are other key factors for the successful effective design of ultrasonic transmission system.
Taking into the above, the study of the features of the development and design of the ultrasonic transduser is a great practical importance and this determines the topic of this article.
The authors: Huang Wenmei, Wang Bowen, Heineken V.A., Lauversa M.K., Dekker R., Bobtsov A.A., Boikov V.I., Bushuev A.B. are working on the development of new methods and means of controlling the main parameters, as well as determining the suitability of the UP for operation in certain areas.
The works of Meleshko N.V., Konovalov N.N., Soyfer Yu.R., Makarov D.G., Pikalev E.M., Ma Xiaowen, Liu Yingchun, Ruan Jiaji, Tao Chenyang are devoted to the analysis of various types of piezoelectric materials used for high-temperature medium, as well as a review of the latest developments in the field of high-temperature piezoelectric materials.
Brozhovsky I., Bodnarova L., Pashkov P.V., Kirikov A.V., Yuan Jianren, Chang Yunfei, Cao Wenwu are working on improving the design of capacitive membrane ultrasonic transducers that can potentially be used for non-destructive ultrasonic testing and structural monitoring.
Nevertheless, despite the existing publications and extensive researches, the emergence of new materials, the complexity of electronics and the broad integration of breakthrough digital technologies necessitate regular updating and conducting new researches, the results of which would reflect and take into account new achievements and developments of scientific and technological progress.
Therefore, taking into account the above, the purpose of this article is to analyze the design features of different types of ultrasonic transducers and modern methods of modelling ultrasonic transducers using software.
I. Basic theoretical foundations of the ultrasonic transducer
In the first stage of the research, a more detailed generalized ultrasonic transducer scheme is considered, the main components of which are the active element, the substrate and the wear plate. (Figure 1).
Figure 1. Design characteristics of the ultrasonic transducer [4]
The active element is a piezoelectric or ferroelectric material that converts electrical energy, such as an excitation pulse from a flaw detector, into ultrasonic energy. The most commonly used materials are polarized ceramics, which can be processed in various ways to produce different wave modes. New materials such as piezoelectric polymers and composites are also used in applications that provide high advantages for improving the performance of sensors and systems [5].
Baking is usually a material with high attenuation coefficient and high density. It is used to control the vibration of the ultrasonic transducer frequency converter by absorbing the energy radiated from the back of the active element. If the acoustic impedance of the substrate is consistent with that of the active element, the result will be a strong attenuation converter. It shows a good band resolution, but may has low signal amplitude. When the acoustic impedance between the element and the substrate does not match, more acoustic energy will be reflected forward into the tested material. The end result is that the converter has a lower resolution due to the longer duration of the waveform. But it can have a higher signal amplitude or greater sensitivity [4].
Wear plate. The main purpose of the wear sensor plate is to protect the sensor element from exposure to the test environment. In the case of contact transducers, the wear plate must be made of a durable and corrosion-resistant material to withstand wear, such as steel [6].
II. Design features of ultrasonic transducer
2.1. Сonventional piezoelectric ultrasonic transducer
Тaking into account the basic theoretical provisions, using the example of specific practical tasks, we will consider the design features of the ultrasonic transducer.
The ultrasonic transducer shown in Figure 2 was designed for use in high-temperature industrial tests.
Technical characteristics of the ultrasonic transducer shown in Fig. 2:
1)The central frequency of the signal is 2.7-3 МНz with a minimum bandwidth of 3 dB 2.7 МНz (90%);
2)The ability to operate at temperatures up to 700-800 °C;
3)Continuous trouble-free operation for at least two years;
Figure 2. Ultrasonic transducer for high-temperature industrial tests [7]
36° Y-cut LiNbO3 is used as piezoelectric material in this ultrasonic transducer design. In order to work at a high temperature of 800°C, polycrystalline ceramics were selected as the backing. The acoustic model of porous media shows that porous 3% yttria-stabilized zirconia (YSZ) ceramics with a porosity of 25% and an average pore diameter of 200 µm provides optimal acoustic properties. Porous ceramics were made by using polyethylene spheres as a pore-forming agent.
TiBrazeORAl-665 soldering foil is recognized as the only candidate for connecting the LiNbO3 piezoelectric element with a porous zirconium substrate and an aluminium oxide layer [7].
The transducer shell or casing consists of several components, that enclose a multilayer structure consisting of a backing and a piezoelectric element. And provide electrical connections with two electrodes of a piezoelectric element. The key components of the design are: the casing, electrical insulators, leads and wires. All these elements maintain their mechanical properties at high temperatures and resist corrosion. The shell of the ultrasonic transducer takes into account the thermal expansion of each element.
All components of the ultrasonic transducer are fixed in the shell for easy carrying and protection of internal components from damage.
The two electrodes of the piezoelectric element are electrically connected to a live wire and a ground wire. The livewire from the pulsator applies an excitation voltage to the pulsator and is connected to the upper electrode of the piezoelectric element through the central rod of the converter. The electrical grounding is connected to the casing. Shell is connected to the extension ledge of the solder foil, which used to attach the piezoelectric element to the matching layer.
The transducer casing uses multiple electrical insulators to isolate the components. That conduct power from the components connected to the ground. Three ceramic insulators are made in the form of cylinders, discs and tubes. The goal is to separate the thin rod, disc connector and porous ceramic backing from the transducer shell respectively.
Each component of the converter has a different coefficient of thermal expansion. Consequently, as the temperature increases, the gap between the metal shell and the backing element will increase. In order to fill this gap at any temperature, a preloaded high temperature wave spring is included in the ultrasonic transducer [7].
2.2. Electromagnetic ultrasonic transducer
At the next stage, consider the design features of an electromagnetic ultrasonic transducer. It is a non-contact ultrasonic transmitter and receiver. The mechanism of the transducer includes the Lorentz force, magnetostrictive force and magnetic force. Compare with conventional piezoelectric ultrasonic transducer, the main advantage of electromagnetic ultrasonic transducer is that it does not need to connect the coupling clutch. Therefore, the measurement inconsistency caused by the use of the coupling clutch in the non-destructive testing process can be eliminated. At present, electromagnetic ultrasonic transducer is widely used in base metal defect detection, weld detection, thickness measurement and composite material detection, strength and reliability research of railway tracks and wheels, voltage measurement and high temperature detection.
Figure 3. Simplified design of the electromagnetic ultrasonic transducer with elongated inductors on the surface of the control object [8]
Figure 3 shows a simplified design of electromagnetic ultrasonic transducer with elongated inductors of a magnetic field source to excite a pulsed magnetic field. Including the designations on the image: 1 – body; 2, 3 – electric connectors; 4 – protector; 5 – flat hight-frequency inductor; 6 – source of magnetic polarizing field; 7, 8 – linear working sections of parallel conductors of hight-frequency inductor ; 9, 10 – two elongated inductors; 11, 12 – cores of ferromagnetic material; 13, 14 – ends of cores; 15 – control object (arrows show direction of propagation of excited ultrasonic pulses)[8].
The basis of electromagnetic ultrasonic transducer technology is the magnetostrictive effect for transmitting and receiving ultrasonic waves. The difference between an electromagnetic ultrasonic transducer and a conventional piezoelectric ultrasonic transducer is in the transmission and reception mode. The electromagnetic ultrasonic transducer transmits and receives ultrasonic wave through electromagnetic effect. Its energy is converted directly in the upper layer of the workpiece surface. So it does not need to contact with the workpiece and any binding medium. The probe structure of the electromagnetic ultrasonic transducer used to generate a Lamb wave in a ferromagnetic material is shown in Figure 4.
Figure 4. Mechanism of Lamb wave generated by magnetostrictive electromagnetic ultrasonic transducer [9]
The two main components of the electromagnetic ultrasonic transducer are an inductor and a magnet. The inductor is powered by a large alternating current pulse, and the magnet is designed to create a strong static magnetic flux within the depth of the sample surface directly under the electromagnetic ultrasonic transducer inductor.
2.3. Capsule-type electromagnetic ultrasonic transducer
To date, capsule-type electromagnetic ultrasonic transducer has become widespread and popular, since it allows for effective protection against external corrosion. The scheme of the capsule electromagnetic ultrasonic transducer is shown in Figure 5.
Figure 5. Capsule-type electromagnetic ultrasonic transducer [10].
As the figure 5 shows, the capsule-type electromagnetic ultrasonic transducer consists of a pair of cylindrical permanent magnets, a bobbin coil and an array of induction coils. A pair of cylindrical magnets is in a repulsive configuration with identical poles pointing towards each other. It is used to create a static magnetic field, the main axis of which is directed radially.
The bobbin coil is placed between a pair of permanent magnets and is driven by a transient current to generate a dynamic electromagnetic field inside the pipe. It is also used to capture the capsule-type electromagnetic ultrasonic transducer signal. That is, the electromotive force induced in the inductor can quickly detect external corrosion. The induction coil array is used to receive capsule-type electromagnetic ultrasonic transducer signals from different angles.
The advantage of a capsule-type electromagnetic ultrasonic transducer is that:
1)A pair of magnets of bobbin coil have the shape of a cylinder and are able to fit against the inner wall of the element under study. It leads to a reduction in lifting interference and an increase in conversion efficiency;
2)The generated electromagbetic fields, including static and dynamic magnetic fields, eddy currents and the resulting Lorentz force, are evenly distributed on the circumference. This leads to the uniform excitation of the incident ultrasonic volume wave along the circumference, which can improve the control efficiency.
Conclusion
Therefore, when summarizing the research results, the following conclusions can be drawn.
Ultrasonic transducer uses high-frequency sound waves to measure certain parameters. It has found a wide practical application in many industrial applications, including defect detection, thickness measurement and weld inspection. In addition, ultrasonic transducer is widely used in medicine. The ultrasonic waves generated by them help find specified targets, measure the distance between targets and transducers, determine levels or depths, the exact location of the intended target, as well as cut and weld parts and elements by soldering.
The design features of an ultrasonic transducer depend on their type, the tasks performed and the scope of use.
References:
- Meleshenko N.V. The ultrasonic testing of the welding joint by the probes and the phased arrays./ Meleshenko N.V., Konovalov N.N., Soyfer Y.R. // NDT World Review. - 2021. - Vol.24 -No.3(93). - pp.46-50.
- Leao-Neto. Development and Characterization of a Superresolution Ultrasonic Transducer / Leao-Neto, Jose P. // IEEE transactions on ultrasonics, ferroelectrics, and frequency control: a publication of the IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society. - 2022. - Vol.69 - No.2; -pp. 779-786.
- Chen F. Evaluating elongated grains with diffuse ultrasonic double scattering and rectangular transducers / Chen F., Chen S., Song Y., Li X. // The journal of the Acoustical Society of America. - 2022. - Vol. 151 - Issue 1 - pp 517-528.
- British Standards Institution. Ultrasonics. Transducers. Definitions and measurement methods regarding focusing for the transmitted fields / London: British Standards Institution - 2021.- 118 р.
- Ushakov V.M. Angle probes of ultrasonic testing of welded joints of energy facilities: a modern approach to the development and research / Ushakov V.M., Danilov V.N., Mikhalev V.V. // Russian journal of heavy machinery. - 2019. - No.10. - pp.9-13.
- Pyae P.A. Modeling a longitudinal-torsional transducer of an ultrasonic medical instrument / Pyae P.A., Grigoriev Y.V. // BMSTU Jurnal of mechanical engineering. - 2021. - № 5 (734). - pp. 3-8.
- Songling H. Theory and methodology of electromagnetic ultrasonic guided wave imaging / Songling H., Yu Zh., Zheng W., Shen W., Hongyu S. // Singapore: Springer. - 2020. - 287 р.
- Peter R. Hoskins. Diagnostic ultrasound: physics and equipment / edited by Peter R. Hoskins, Kevin Martin, Abigail Thrush. Boca Raton // FL: CRC Press. - 2019. - 354 р.
- Jiang X. High frequency piezo-composite micromachined ultrasound transducer array technology for biomedical imaging / Xiaoning Jiang, Sibo Li, Jinwook Kim, Jianguo Ma, Wenbin Huang. // New York, NY: ASME Press. - 2017. - 95 р.
- Hirao M. Electromagnetic acoustic transducers: noncontacting ultrasonic measurements using EMATs / Masahiko Hirao, Hirotsugu Ogi. // Tokyo: Springer. - 2016. -380 р.