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Micromachines
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Acoustic Transducers and Their Applications, 2nd Edition
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Acoustic Transducers and Their Applications, 2nd Edition

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "A：Physics".

Deadline for manuscript submissions: 10 July 2025 | Viewed by 12134

Special Issue Editors

Dr. Songsong Zhang

E-Mail Website
Guest Editor
School of Microelectronics, Shanghai University, Shanghai 200444, China
Interests: piezoelectric material; MEMS device process; piezoelectric transducer design; acoustic sensing model; acoustic device algorithm and system-level application
Special Issues, Collections and Topics in MDPI journals
Dr. Liang Lou

E-Mail Website
Guest Editor
School of Microelectronics, Shanghai University, Shanghai 200444, China
Interests: piezoelectric material and devices; MEMS; acoustic transducer; acoustic sensor
Dr. Qiaozhen Zhang

E-Mail Website
Guest Editor
College of Information, Mechanical and Electrical Engineering, Shanghai Normal University, Shanghai 200234, China
Interests: intelligent sensing technology and system; RF micro-acoustic devices for mobile communication; modeling and simulation of piezoelectric thin-film micro-acoustic devices
Special Issues, Collections and Topics in MDPI journals
Dr. Xing Haw Marvin Tan

E-Mail Website
Guest Editor
Institute of High Performance Computing, A*STAR, Singapore 138632, Singapore
Interests: piezoelectric transducer design and simulation; piezoelectric material property extraction; bulk acoustic wave (BAW) devices; acoustic meta-surfaces (including meta-lens); beam steering
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Acoustics represent a key form of mechanical energy that is exerted everywhere in our world. It aid in sensing, actuating, and communicating, even in medical or industrial matters. With a broad operating spectrum, it is the most pivotal tool in various implementations, ranging from airborne applications to studies through different media, especially for needs beyond the physical limitations of other mechanisms (e.g., optical or electromagnetic waves). Alongside the progression of advanced transducer technology, more acoustic device alternatives have been optimized for conventional applications. In addition, consistent research efforts in the field of developing transducers enable rapid paradigmatic shifts in many emerging acoustic applications, which coherently accelerate the development of other peripheral technologies, such as thin-film materials used in acoustic transducers, circuits for acoustic devices, modules, algorithms, system integration, and even the integration of acoustic sensors into smart systems. In order to promote research efforts and advocate for continuous innovation in this field, in this Special Issue, the current state of the art in the field of ‘acoustic transducers and their applications’ will be presented, covering a wide range of related topics, including, but not limited to, the following:

  • New piezoelectric materials: ceramics, thin films, single crystals, polymers, composites, 2D materials, etc.;
  • Acoustic transducers: acoustic sensors and actuators, circuits for acoustic devices, modules, algorithms, and integrated systems;
  • Piezoelectric devices/acoustic transducers: fabrication, testing, characterization, design, modeling, simulation, manufacturing, 3D printing, packaging, and system integration;
  • Acoustic transducer applications: nondestructive testing, acoustic arrays for holograms and beam steering, acoustic ranging, acoustic lenses, meta-materials and meta-surfaces, energy harvesting, medical imaging, wearable sensors, biomedical applications, virtual reality/augmented reality, and other emerging applications for the metaverse.

Dr. Songsong Zhang
Dr. Liang Lou
Dr. Qiaozhen Zhang
Dr. Xing Haw Marvin Tan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2100 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • acoustic transducers and their design, simulation, testing, and characterization
  • piezoelectric MEMS device
  • thin-film piezoelectric materials and material properties
  • MEMS integration process
  • acoustic modules, algorithms, circuits, and systems
  • acoustic lenses and meta-surfaces
  • acoustic transducer arrays and their applications
  • implementation and usage of acoustic devices for various applications

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Related Special Issue

Published Papers (11 papers)

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Research

16 pages, 2281 KiB  
Article
Towards the Optimization of Apodized Resonators
by Ana Valenzuela-Pérez, Carlos Collado and Jordi Mateu
Micromachines 2025, 16(5), 511; https://doi.org/10.3390/mi16050511 - 27 Apr 2025
Viewed by 206
Abstract
Bulk Acoustic Wave (BAW) resonators are essential components in modern RF communication systems due to their high selectivity and quality factor. However, spurious resonances caused by Lamb wave mode propagation along the in-plane directions degrade the filter performance. Traditional Finite Element Method (FEM) [...] Read more.
Bulk Acoustic Wave (BAW) resonators are essential components in modern RF communication systems due to their high selectivity and quality factor. However, spurious resonances caused by Lamb wave mode propagation along the in-plane directions degrade the filter performance. Traditional Finite Element Method (FEM) simulations provide accurate modeling but are computationally expensive, especially for arbitrarily shaped resonators and solidly mounted resonators (SMRs), whose stack of materials is composed of many thin layers of different materials. To address this, we extend a previously published model (named the Quasi-3D model), which employs the Transmission Line Matrix (TLM) method, enabling efficient simulations of complex geometries with more precise meshing. The new approach allows us to simulate different geometries, and we will show several apodized geometries with the aim of minimizing the lateral modes. In addition, the proposed approach significantly reduces the computational cost while maintaining high accuracy, as validated by FEM comparisons and experimental measurements. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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13 pages, 15025 KiB  
Article
Design of Piezoelectric Ultrasonic Composite Vibration System for Precision Grinding
by Weiqing Huang, Kaijie Huang, Qunyou Zhong, Jialun Wu and Dawei An
Micromachines 2025, 16(4), 408; https://doi.org/10.3390/mi16040408 - 30 Mar 2025
Viewed by 348
Abstract
Due to the high hardness and brittleness of sapphire, traditional machining methods are prone to surface scratches and microcracks. As an advanced processing technique, ultrasonic machining can reduce damage to hard–brittle materials and improve surface quality. In this study, an integrated ultrasonic longitudinal–torsional [...] Read more.
Due to the high hardness and brittleness of sapphire, traditional machining methods are prone to surface scratches and microcracks. As an advanced processing technique, ultrasonic machining can reduce damage to hard–brittle materials and improve surface quality. In this study, an integrated ultrasonic longitudinal–torsional vibration system consisting of both a horn and a tool was designed. The resonant frequency and output amplitude of the horn were simulated and tested. The results indicated that the resonant frequency was 19.857 kHz, the longitudinal amplitude at the tool end was 4.2 µm, and the torsional amplitude was 1.8 µm. Experiments were then carried out to investigate the effects of various machining parameters on the reduction of sapphire surface roughness (Ra) and material removal rate (MRR). A comparative experiment was then conducted to evaluate the effects of ultrasonic longitudinal and longitudinal–torsional vibration on sapphire grinding. The ultrasonic longitudinal–torsional grinding experiments showed that the surface roughness of the sapphire workpiece was reduced from 960.6 nm to 82.6 nm, and the surface flatness was improved to 84.3 nm. Compared with longitudinal ultrasonic vibration, longitudinal torsional grinding reduced the surface roughness of sapphire workpieces by 48% and increased the surface flatness by 88.3%. The results of this study provide specific guidance for the longitudinal–torsional composite ultrasonic machining of hard–brittle materials. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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24 pages, 10912 KiB  
Article
Research on a High-Temperature Electromagnetic Ultrasonic Circumferential Guided Wave Sensor Based on Halbach Array
by Yuanxin Li, Jinjie Zhou, Jiabo Wen, Zehao Wang and Liu Li
Micromachines 2025, 16(4), 367; https://doi.org/10.3390/mi16040367 - 24 Mar 2025
Viewed by 349
Abstract
High-temperature pipelines, as core facilities in the fields of petrochemical and power, are constantly exposed to extreme working conditions ranging from 450 to 600 °C, facing risks of stress corrosion, creep damage, and other defects. Traditional shutdown inspections are time-consuming and costly. Meanwhile, [...] Read more.
High-temperature pipelines, as core facilities in the fields of petrochemical and power, are constantly exposed to extreme working conditions ranging from 450 to 600 °C, facing risks of stress corrosion, creep damage, and other defects. Traditional shutdown inspections are time-consuming and costly. Meanwhile, existing electromagnetic acoustic transducers (EMATs) are restricted by their high-temperature tolerance (≤500 °C) and short-term stability (effective working duration < 5 min). This paper proposes a high-frequency circumferential guided wave (CLamb wave) EMAT based on a Halbach permanent magnet array. Through magnetic circuit optimization (Halbach array) and multi-layer insulation design, it enables continuous and stable detection on the surface of 600 °C pipelines for 10 min. The simulations revealed that the Halbach array increased the magnetic flux density by 1.4 times and the total displacement amplitude by 2 times at a magnet’s large lift-off (9 mm). The experimental results show that the internal temperature of the sensor remained stable below 167 °C at 600 °C. It was capable of detecting the smallest defect of a φ3 mm half-hole (depth half of the wall thickness), with a signal attenuation rate of only 0.32%/min. The signal amplitude of Q235 pipelines under high-temperature short-term detection (<5 min) was 1.5 times higher than that at room temperature. However, material degradation under high temperature led to insufficient long-term stability. This study breaks through the bottleneck of long-term detection of high-temperature EMATs, providing a new scheme for efficient online detection of high-temperature pipelines. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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17 pages, 4346 KiB  
Article
Design and Fabrication of an Epoxy/Glass Microbeads-Based 1-3 Piezoelectric Composite
by Qiyun Liu, Jinjie Zhou, Ziliang Jia and Pengfei Zhou
Micromachines 2025, 16(4), 361; https://doi.org/10.3390/mi16040361 - 21 Mar 2025
Viewed by 342
Abstract
An epoxy/glass microbeads-based 1-3 piezoelectric composite is proposed, to enhance electromechanical conversion efficiency. Firstly, based on the series-parallel theory, the theoretical model is established. Secondly, the epoxy resin/glass microbeads-based 1-3 piezoelectric composite is simulated by finite element software. The effects of polymers with [...] Read more.
An epoxy/glass microbeads-based 1-3 piezoelectric composite is proposed, to enhance electromechanical conversion efficiency. Firstly, based on the series-parallel theory, the theoretical model is established. Secondly, the epoxy resin/glass microbeads-based 1-3 piezoelectric composite is simulated by finite element software. The effects of polymers with different acoustic impedances, the thicknesses of piezoelectric composites, and ceramic volume fractions are analyzed systematically. After parameter optimization, the epoxy/glass microbeads-based 1-3 piezoelectric composite is prepared. The experimental results agree well with the theoretical and simulation results. When the ceramic volume fraction is 60.0%, its electromechanical coupling factor is the largest, which is 0.714. Compared with the prepared traditional 1-3 piezoelectric composites with the same parameters, its electromechanical coupling factor is increased by 7.8%. Therefore, the epoxy/glass microbeads-based 1-3 piezoelectric composite can enhance the sensitivity and resolution of the transducers, which has potential advantages for improving the performance of transducers. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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13 pages, 4909 KiB  
Article
Design and Application of Uniaxially Sensitive Stress Sensor
by Kaituo Wu, Zixun Xiang, Xinbo Lu, Yichao Yan, Chunyang Wu, Tao Wang and Wanli Zhang
Micromachines 2025, 16(1), 94; https://doi.org/10.3390/mi16010094 - 15 Jan 2025
Viewed by 2534
Abstract
Current stress sensors for microsystems face integration challenges and complex signal decoding. This paper proposes a real-time uniaxially sensitive stress sensor. It is obtained by simple combinations of bar resistors using their sensitivity differences in different axes. With the aid of a Wheatstone [...] Read more.
Current stress sensors for microsystems face integration challenges and complex signal decoding. This paper proposes a real-time uniaxially sensitive stress sensor. It is obtained by simple combinations of bar resistors using their sensitivity differences in different axes. With the aid of a Wheatstone bridge, the sensor can measure the uniaxial stress magnitude by simple calibration of the stress against the output voltage and detect the bidirectional stress magnitude and direction in a micro-zone by simple rotation. The theoretical sensitivity obtained from simulation is 0.087 mV/V·MPa when the X-bridge is stressed in the X-direction under 1 V of excitation, and the test sensitivity of the X-bridge prepared in this paper is 0.1 mV/V·MPa. The design is structurally and procedurally simple, exhibits better temperature stability, and reduces interface requirements, making it suitable for the health monitoring of multi-chip microsystem chips. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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16 pages, 3741 KiB  
Article
Modeling and Characterization of Multilayer Piezoelectric Stacks via Dynamic Stiffness Method
by Wenxiang Ding, Zhaofeng Liang, Wei Zhao, Hongmei Zhong, Dan Chen, Maxime Bavencoffe and Marc Lethiecq
Micromachines 2025, 16(1), 20; https://doi.org/10.3390/mi16010020 - 26 Dec 2024
Viewed by 910
Abstract
Multilayer piezoelectric stacks, which are multiple layers of piezoelectric materials placed on top of each other, are widely used to achieve precise linear movement and high-force generation. In this paper, a dynamic stiffness (DS) method for the dynamic vibration analysis of multilayer piezoelectric [...] Read more.
Multilayer piezoelectric stacks, which are multiple layers of piezoelectric materials placed on top of each other, are widely used to achieve precise linear movement and high-force generation. In this paper, a dynamic stiffness (DS) method for the dynamic vibration analysis of multilayer piezoelectric stacks is presented. First, the general solutions for all physical quantities of the three vibration contributions (i.e., pure vibration, symmetrically coupled vibration, and anti-symmetrically coupled vibration) are derived from the governing equations of motion. Then, the DS matrices of each layer of the piezoelectric stack are obtained, and they are assembled to form a global DS matrix. The electrical impedances and the mode shapes of a piezoelectric stack consisting of two piezoelectric disks connected in series and in parallel are calculated using our method as well as by the finite element method. The comparison shows good agreement. Finally, the effect of the number of layers on the dynamic responses of piezoelectric stacks is investigated. The DS method developed here provides an efficient and accurate analytical tool for the parametric and optimization analysis of the coupled vibrations of multilayer piezoelectric structures. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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13 pages, 5261 KiB  
Article
A High-Performance Micro Differential Pressure Sensor
by Xutao Fan, Lei Wang and Songsong Zhang
Micromachines 2024, 15(11), 1396; https://doi.org/10.3390/mi15111396 - 20 Nov 2024
Cited by 2 | Viewed by 1081
Abstract
With the development of the micro electromechanical system (MEMS), which widely adopts micro differential pressure sensors (MDPSs), the demand for high-performance MDPSs had continuously increased. Pressure sensors realized using MEMS technology integrated with biomedical catheters are of significant importance in the detection and [...] Read more.
With the development of the micro electromechanical system (MEMS), which widely adopts micro differential pressure sensors (MDPSs), the demand for high-performance MDPSs had continuously increased. Pressure sensors realized using MEMS technology integrated with biomedical catheters are of significant importance in the detection and treatment of various biological diseases. Biomedical catheters used in low-Fr applications (1Fr = 0.33 mm outer diameter) require miniaturized sensors that do not compromise their performance. For instance, catheters (5Fr) used for central venous pressure (CVP) monitoring require the integration of high-performance sensors with total dimensions smaller than 1.65 mm along at least two directions (length, width, or height). In this paper, a silicon-on-insulator (SOI)-based MDPS was designed and fabricated for micro-pressure detection in the range of 0–1 kPa. The dimension of the sensor is only 1 mm × 1 mm × 0.4 mm, with a sensitivity of 3.401 mV/V/kPa at room temperature, nonlinearity of 0.376% FS (full scale), and an overall accuracy of 0.59% FS. The sensor operates normally when the temperature is even increased to 160 °C, and its temperature coefficient of zero output (TCO) and temperature coefficient of sensitivity (TCS) are 0.093% FS/°C and −0.144% FS/°C. The dimension and performance results of this MDPS demonstrate its potential to play a significant role in biomedical catheters. In addition, it is fabricated using an 8-inch MEMS process, which significantly reduces the cost. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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16 pages, 21094 KiB  
Article
Development of a Meander-Coil-Type Dual Magnetic Group Circumferential Magnetostrictive Guided Wave Transducer for Detecting Small Defects Hidden behind Support Structures
by Jinjie Zhou, Hang Zhang, Yuepeng Chen and Jitang Zhang
Micromachines 2024, 15(10), 1261; https://doi.org/10.3390/mi15101261 - 15 Oct 2024
Cited by 1 | Viewed by 1197
Abstract
In order to solve the problem that small defects hidden behind pipeline support parts are difficult to detect effectively in small spaces, such as offshore oil platforms, a meander-coil-type dual magnetic group circumferential magnetostrictive guided wave transducer is developed in this paper. The [...] Read more.
In order to solve the problem that small defects hidden behind pipeline support parts are difficult to detect effectively in small spaces, such as offshore oil platforms, a meander-coil-type dual magnetic group circumferential magnetostrictive guided wave transducer is developed in this paper. The transducer, which consists of a coil, two sets of permanent magnets, and a magnetostrictive patch, can excite a high-frequency circumferential shear horizontal (CSH) guided wave. The energy conversion efficiency of the MPT is optimized through magnetic field simulation and experiment, and the amplitude of the defect signal is enhanced 1.9 times. The experimental results show that the MPT developed in this paper can effectively excite and receive CSH2 mode guided waves with a center frequency of 1.6 MHz. Compared with the traditional PPM EMAT transducer, the excitation energy of the transducer is significantly enhanced, and the defects of the 2 mm round hole at the back of the support can be effectively detected. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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14 pages, 4550 KiB  
Article
Tunable Acoustic Tweezer System for Precise Three-Dimensional Particle Manipulation
by Jiyun Nan, Hiep Xuan Cao, Jong-Oh Park, Eunpyo Choi and Byungjeon Kang
Micromachines 2024, 15(10), 1240; https://doi.org/10.3390/mi15101240 - 8 Oct 2024
Cited by 1 | Viewed by 1556
Abstract
This study introduces a tunable acoustic tweezer system designed for precise three-dimensional particle trapping and manipulation. The system utilizes a dual-liquid-layer acoustic lens, which enables the dynamic control of the focal length through the adjustable curvature of a latex membrane. This tunability is [...] Read more.
This study introduces a tunable acoustic tweezer system designed for precise three-dimensional particle trapping and manipulation. The system utilizes a dual-liquid-layer acoustic lens, which enables the dynamic control of the focal length through the adjustable curvature of a latex membrane. This tunability is essential for generating the acoustic forces necessary for effective manipulation of particles, particularly along the direction of acoustic wave propagation (z-axis). Experiments conducted with spherical particles as small as 1.5 mm in diameter demonstrated the system’s capability for stable trapping and manipulation. Performance was rigorously evaluated through both z-axis and 3D manipulation tests. In the z-axis experiments, the system achieved a manipulation range of 33.4–53.4 mm, with a root-mean-square error and standard deviation of 0.044 ± 0.045 mm, which highlights its precision. Further, the 3D manipulation experiments showed that particles could be accurately guided along complex paths, including multilayer rectangular and helical trajectories, with minimal deviation. A visual feedback-based particle navigation system significantly enhanced positional accuracy, reducing errors relative to open-loop control. These results confirm that the tunable acoustic tweezer system is a robust tool for applications requiring precise control of particles with diameter of 1.5 mm in three-dimensional environments. Considering its ability to dynamically adjust the focal point and maintain stable trapping, this system is well suited for tasks demanding high precision, such as targeted particle delivery and other applications involving advanced material manipulation. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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14 pages, 3367 KiB  
Article
Piezoelectric Ultrasonic Local Resonant Ultra-Precision Grinding for Hard–Brittle Materials
by Dawei An, Jianghui Xian, Yi Zhang, Guoqiang Cheng, Yankai Huang, Zhongwei Liang and Weiqing Huang
Micromachines 2024, 15(10), 1216; https://doi.org/10.3390/mi15101216 - 29 Sep 2024
Cited by 1 | Viewed by 1430
Abstract
Hard–brittle materials are widely used in the optics, electronics, and aviation industries, but their high hardness and brittleness make it challenging for traditional processing methods to achieve high efficiency and superior surface quality. This study aims to investigate the application of ultrasonic local [...] Read more.
Hard–brittle materials are widely used in the optics, electronics, and aviation industries, but their high hardness and brittleness make it challenging for traditional processing methods to achieve high efficiency and superior surface quality. This study aims to investigate the application of ultrasonic local resonant grinding to sapphire to improve the efficiency and meet the requirements for the optical window in the surface roughness of the material. The resonant frequency of a piezoelectric ultrasonic vibration system and the vibration amplitude of a grinding head’s working face were simulated and tested, respectively. The results of ultrasonic grinding experiments showed that the local resonant system reduced the surface roughness parameter (Ra) of sapphire to 14 nm and improved its surface flatness to 44.2 nm, thus meeting the requirements for the ultra-precision grinding of sapphire. Compared with a conventional resonant system, the surface roughness of the sapphire ground with the local resonant system was reduced by 90.79%, its surface flatness was improved by 81.58%, and the material removal rate was increased by 31.35%. These experimental results showed that ultrasonic local resonant grinding has better effects than those of conventional ultrasonic grinding in improving surface quality and increasing the material removal rate. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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21 pages, 4988 KiB  
Article
An Adaptive Noise Reduction Method for High Temperature and Low Voltage Electromagnetic Detection Signals Based on SVMD Combined with ICEEMDAN
by Zhizeng Ge, Jinjie Zhou, Xingquan Shen, Xingjun Zhang and Caixia Qi
Micromachines 2024, 15(8), 977; https://doi.org/10.3390/mi15080977 - 30 Jul 2024
Viewed by 1241
Abstract
In view of the low signal-to-noise ratio (SNR) of shear wave electromagnetic acoustic transducers (EMAT) in the detection of high-temperature equipment, the use of low excitation voltage (LEV) further deteriorates the detection results, resulting in the echo signal containing defects being drowned in [...] Read more.
In view of the low signal-to-noise ratio (SNR) of shear wave electromagnetic acoustic transducers (EMAT) in the detection of high-temperature equipment, the use of low excitation voltage (LEV) further deteriorates the detection results, resulting in the echo signal containing defects being drowned in noise. For the extraction of the EMAT signal, an adaptive noise reduction method is proposed. Firstly, the minimum envelope entropy is taken as the fitness function for the Harris Hawks Optimizer (HHO), and the optimal successive variational mode decomposition (SVMD) balance parameter is searched by HHO adaptive iteration to decompose LEV EMAT signals at high temperatures. Then the filter is carried out according to the excitation center frequency and correlation coefficient threshold function. Then, improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) is used to decompose the filtered signal and combine the kurtosis factor to select the appropriate intrinsic mode functions. Finally, the signal is extracted by the Hilbert transform. In order to verify the effectiveness of the method, it is applied to the low-voltage detection of 40Cr from 25 °C to 700 °C. The results show that the method not only suppresses the background noise and clutter noise but also significantly improves the SNR of EMAT signals, and most importantly, it is able to detect and extract the 2 mm small defects from the echo signals. It has great application prospects and value in the LEV detection of high-temperature equipment. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications, 2nd Edition)
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