Acoustic Transducer Research Articles

Battery state characterization based on a contactless electromagnetic ultrasound testing method

Nondestructive ultrasonic detection technology has been increasingly applied to battery diagnostics. However, currently used ultrasonic transducers must be affixed to the tested battery very tightly through coupling agents, thereby lowering the test efficiency and convenience. In this paper, a contactless electromagnetic ultrasonic testing technology is proposed for characterizing the states of lithium-ion batteries. The relationship between the ultrasonic frequency and wave velocity is analyzed via a finite element model. Meanwhile, the influence of battery boundary characteristics on ultrasonic signals is investigated. Based on the propagation characteristics of ultrasonic guided waves in the battery, contactless electromagnetic acoustic transducers (EMATs) are designed and optimized. Three features, including the time of flight, signal amplitude, and energy integration, are extracted from the received signals to indicate the variation in battery state during charging and discharging cycles. Experimental results demonstrate that the ultrasonic guided wave features obtained from EMATs change consistently and regularly with the charging and discharging states of the battery. The proposed method can be used to analyze the aging of batteries and the inconsistency of electrolyte infiltration inside batteries, which is expected to improve the battery safety.

Acoustic Transmission Measurements for Extracting the Mechanical Properties of Complex 3D MEMS Transducers.

Recent publications on acoustic MEMS transducers present a new three-dimensional folded diaphragm that utilizes buried in-plane vibrating structures to increase the active area from a small chip volume. Characterization of the mechanical properties plays a key role in the development of new MEMS transducers, whereby established measurement methods are usually tailored to structures close to the sample surface. In order to access the lateral vibrations, extensive and destructive sample preparation is required. This work presents a new passive measurement technique that combines acoustic transmission measurements and lumped-element modelling. For diaphragms of different lengths, compliances between 0.08 × 10-15 and 1.04 × 10-15 m3/Pa are determined without using destructive or complex preparations. In particular, for lengths above 1000 µm, the results differ from numerical simulations by only 4% or less.

Contactless Single Cell Extraction from Monolayer Cell Culture Using A MEMS Acoustic Droplet Ejector.

To achieve a contactless and damage-less extraction of a single (or a few) human retinal pigment epithelial (RPE) cell(s) from a cell monolayer with acoustic droplet ejection. An acoustic droplet ejector based on a self-focusing acoustic transducer (SFAT) is designed, microfabricated, and placed on a precision movable stage that aligns it to the targeted cell(s) in a Petri dish. The device delivers 20.1 MHz focused ultrasound (FUS) with a focal diameter of 100 μm, which ejects droplets capable of extracting and transferring only the targeted cell(s) from a monolayer. The extraction and collection of 1-10 cells are successfully demonstrated. The number of ejected cells can be controlled by the FUS pulse width. As confirmed by fluorescence-based cell viability assays and re-culture experiments, the ejected cell(s) and remaining monolayer cells are intact without damage after cell ejection. Furthermore, real-time reverse transcription polymerase chain reaction (RT-PCR) tests for both housekeeping genes (GAPDH and β -actin) and RPE-specific genes (MITF, PEDF, and PMEL17) show no significant difference between the acoustically ejected cells and those collected manually with a micropipette. The proposed technology realizes a contactless, damage-free extraction of cells with high spatial resolution and precise control of the number of cells ejected, with a simple setup. This powerful technology not only enables efficient, high-precision cell extraction for quality check applications but also opens new avenues for other advanced biotechnologies such as bioprinting.

Hybrid multi-modal NDE sensing system for in-motion detection and localization of rolling contact fatigue damage in rails

This article presents a multi-modal hybrid-probe approach to nondestructive inspection of RCF cracks and damage in rails. A combination of electromagnetic (EM) and ultrasonic testing (UT) techniques are presented, which allows for complementary physics to be utilized to enhance detection and characterization of surface and sub-surface cracks in a non-contact manner at high speeds. A novel integrated design which combines the motion-induced eddy current (MIEC) effect and ultrasonic Rayleigh surface waves generated and detected using electromagnetic acoustic transducer (EMAT) is presented. The hybrid probe was tested at low speeds to demonstrate an increased damage localization capability. This was carried out using a data registration and fusion approach between the sensing modalities. Finally, the capability of MIEC effect at high-speeds is demonstrated. The results show that the hybrid probe has a high potential for in-motion, high-speed damage detection and characterization in the future.

Bottom Crack Detection with Real-Time Signal Amplitude Correction Using EMAT-PEC Composite Sensor.

During electromagnetic ultrasonic testing, it is difficult to recognize small-size bottom cracks by time of flight (ToF), and the lift-off fluctuation of the probe affects the accuracy and consistency of the inspection results. In order to overcome the difficulty, a novel composite sensor of an electromagnetic acoustic transducer (EMAT) and pulse eddy current (PEC) is designed. We use the amplitude of a bottom echo recorded by EMAT to identify the tiny bottom crack as well as the amplitude of PEC signals picked up by the integrated symmetric coils to measure the average lift-off of the probe in real time. Firstly, the effects of lift-off and bottom cracks on the amplitude of bottom echo are distinguished by combining the theoretical analysis and finite element method (FEM). And then an amplitude correction method based on the fusion of EMAT and PEC signals is proposed to reduce the impact of lift-off on the defect signal. The experimental results demonstrate that the designed composite sensor can effectively detect a bottom crack as small as 0.1 mm × 0.3 mm. The signal fusion method can accurately correct the amplitude of defect signals and the relative error is less than ±8%.

Underwater quantitative thickness mapping through marine growth for corrosion measurement using shear wave EMAT with high lift-off performance

Underwater inspection is important to ensure the safety, integrity and functionality of underwater structures. Although numerous conventional methods have been adopted for underwater inspection, successful application of most methods relies on the surface condition of the object, which, however, is typically covered by marine growth. Consequently, routine inspection requires thorough cleaning of marine growth, which is time-consuming and costly. Hence a method which can inspect objects without the need for extensive surface cleaning is necessary. Two methods have the potential to achieve this: pulse eddy current (PEC) and electromagnetic acoustic transducer (EMAT). PEC attains a significant lift-off distance, enabling inspection through marine growth. However, it suffers from high sensitivity to environmental conditions and low inspection accuracy due to ‘relative’ property which means its results are interpreted by comparing received signals to reference values. In contrast to PEC, EMAT provides ‘absolute’ measurements, ensuring precise results in the inspection. But it is limited by a small lift-off distance (<2∼3 mm), rendering it unsuitable for underwater applications with marine growth. Therefore, if the lift-off distance can be enhanced to a specific value, this method may offer a superior solution for underwater inspections. In this paper, a quantitative measurement method is proposed through employing a shear wave EMAT with high lift-off performance. A repelling configuration of magnets is introduced to achieve a significantly improved maximum effective lift-off distance of up to 5 mm in both air and seawater conditions with only 400 Vpp applied. This EMAT is then demonstrated to measure thickness through marine growth, showing excellent underwater performance in quantitative thickness mapping for corrosion inspection.

An Adaptive Noise Reduction Method for High Temperature and Low Voltage Electromagnetic Detection Signals Based on SVMD Combined with ICEEMDAN.

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.

Structural Optimization and Performance of a Low-Frequency Double-Shell Type-IV Flexural Hydroacoustic Transducer.

To amplify the displacement of the radiation shell, a double-shell type-IV curved hydroacoustic transducer was proposed. Through Ansys finite element simulation, the vibration modes of the transducer in different stages and the harmonic response characteristics in air and water were studied, and the bandwidth emission of the hydroacoustic transducer was achieved. By optimizing the size of each component, the resonant frequency of the transducer is 740 Hz, the maximum conductivity was 0.66 mS, and the maximum transmitting voltage response was 130 dB. According to the optimized parameters, a longitudinal acoustic transducer prototype was manufactured, and a physical test was conducted in an anechoic pool. The obtained resonant frequency was 750 Hz, the maximum conductivity was 0.44 mS, the maximum transmitting voltage response was 129.25 dB, and the maximum linear dimension was 250 mm, which match the simulated value of the virtual prototype and meet the expected requirements.

Robotic Arm-Aided Non-Destructive Testing Using Eletromagnetic Acoustic Transducers for Thickness Measurement in Industrial Applications

Robotic Arm-Aided Non-Destructive Testing Using Eletromagnetic Acoustic Transducers for Thickness Measurement in Industrial Applications

A novel method to fabricate curved piezoelectric composites with high piezoelectric phase volume fraction

Underwater acoustic transducer based on high piezoelectric phase volume fraction, large thickness, large area and curved piezoelectric composites (PC) possess wider beam width, higher source level and better directivity. However, the curved PC with large size is difficult to fabricate. The preparation of curved PC with large size and high piezoelectric phase volume fraction is even more tricky. The reported methods have risks of depolarization, deformation and poor periodicity and are not suitable for preparing PC with high piezoelectric phase volume fraction and large thickness. In this work, we proposed a novel fabrication method of the shaped-mold-assisted dice and fill technology. The 1–3 PC with high piezoelectric ceramic volume fraction of 80 %, thickness of 4.3 mm and area of 340 mm × 77 mm and the 2-2 PC with high piezoelectric ceramic volume fraction of 89.5 %, thickness of 5 mm and area of 262 mm × 20 mm were fabricated. The piezoelectric coefficient d33 and relative constant stress permittivity ε33T/ε0 of 1–3 and 2-2 PCs were comparable to piezoelectric phase itself. In addition, both 1–3 and 2-2 PCs exhibited a favorable performance consistency. This method solved the problem of limited cutting depth of thin blade, realizing PC with the structure of high piezoelectric phase volume fraction (＞ 70 %) and large thickness (＞ 3 mm) and eliminates the risk of depolarization, deformation and poor periodicity. This work enabled the potential for achieving large area, high piezoelectric phase volume and special-shaped PCs, which offers new ideas for designing innovative acoustic transducers and facilitates the progress of acoustic sensing technology.

Debonding inspection with an enhanced miniature EMAT based on multiple pulse echoes

The present paper proposes a non-contact ultrasonic testing method for the debonding inspection of metal-based composite structures, utilizing an improved electromagnetic acoustic transducer (EMAT). The enhanced EMAT incorporates a carbonyl iron powder coil backplate and a small butterfly coil to enhance the detecting ability for interfacial bonding. A two-dimensional finite element model is developed to quantify the effectiveness of the carbonyl iron powder coil backplate on increasing the eddy current density and the magnetic flux density in the specimen. An experimental setup was designed using the Ritec SNAP 5000 and the improved EMATs to examine an aluminium-epoxy resin composite structure. Ultrasonic C-scan images of the specimen's bonding interface were obtained from the experiment. Both simulation and experimental results show that carbonyl iron powder coil backplates can increase the efficiency of the EMATs. By investigating the influence of echo number on debonding detection, it was revealed that employing higher-order echoes and utilizing carbonyl iron powder as the coil backplate can enhance the debonding detection capability. The C-scan imaging results indicate that the utilization of high-order echoes enhances imaging quality, and the employment of high-quality miniaturized EMATs enhances the capability for quantitative analysis of debonding defects.

Derivation of Equivalent Material Coefficients of 2-2 Piezoelectric Single Crystal Composite.

Piezoelectric composites, which consist of piezoelectric materials and polymers, are widely employed in various applications such as underwater sonar transducers and medical diagnostic ultrasonic transducers. Acoustic transducers based on piezoelectric composites can have high sensitivity with broad bandwidth. In recent studies, it is demonstrated that 2-2 composites based on single crystals provide further increased sensitivity and wide bandwidth. In order to utilize a 2-2 composite in acoustic sensors, it is required to demonstrate the full material coefficients of the 2-2 composite. In this study, we investigated an analytic solution for determining equivalent material coefficients of a 2-2 composite. Impedance spectrums of the single-phase resonators with equivalent material coefficients and 2-2 composite resonators were compared by the finite element method in order to verify the analytic solutions. Furthermore, the equivalent material coefficients derived from the analytic solution were also verified by comparing the measured and the simulated impedance spectrums. The difference in resonance and anti-resonance frequencies between the measured and simulated impedance spectrums was around 0.5% and 1.2%. By utilizing the analytic solutions in this study, it is possible to accurately derive full equivalent material coefficients of a 2-2 composite, which are essential for the development of acoustic sensors.

Design of a Permanent Magnet Electromagnetic Acoustic Transducer (EMAT) for In-Situ Inspection of Metals at high Temperatures

In this proposed research, a permanent magnet longitudinal wave Electromagnetic Acoustic Transducer (EMAT) was designed for In-Situ inspection of metals at high temperatures. A permanent magnet EMAT generates Lorentz force inside metals by the interaction of magnetic fields and eddy currents. As temperature rises, various factors can influence the intensity of the Lorentz force, making it difficult to produce and detect ultrasonic waves. Thus, it is essential to optimize the sensor at ambient temperature before attempting to generate a reliable signal at elevated temperatures. The challenge highlighted has been addressed by optimizing the intensity of static field by varying the parameter like spacing between magnets that are being used. In order to minimize the effects of elevated temperatures, the sensor's stability has been enhanced by the implementation of efficient insulating measures. Furthermore, Finite Element (FE) simulations were conducted under on aluminium sample. These simulation results were then compared to experimental data to validate the efficiency of the designed sensor. Keywords: Permanent magnet, EMAT, Lorentz force, ultrasonic waves, high temperature, static magnetic field intensity.

Design of Staggered Halbach EMAT to Generate SH Guided Wave in Pipe Structures

This research investigates the application of Staggered Electromagnetic Acoustic Transducer (EMAT), mainly focusing on the beam steering capabilities of Shear Horizontal (SH) Guided Waves in pipe structures. As a specific case of EMAT, Staggered EMAT introduces a lateral movement in the magnet rows so that the wave propagation occurs at an angle. A three-dimensional model of double row Staggered Halbach EMAT is developed and a finite element analysis is carried out in an aluminium pipe with high radius to thickness ratio. To obtain better signal-to-noise ratio (SNR), the size of the magnets and the number of magnets in a row are optimized by studying multiple cases. For all the configurations, the in-plane surface displacement is studied keeping the wavelength of the transducer constant. The corresponding frequency is derived from the dispersion curve for SH0 wave mode. The results shows that there is significant increase in the amplitude of the in-plane surface displacement with the increase in magnet height and the number of magnets in a row, ultimately leading to the signal with higher amplitude and better SNR. The study then analyses Staggered Halbach EMATs where the second row of magnets is displaced by the maximum value of half of the wavelength. The interference between the waves generated from the two magnet rows resulted in the directivity change of the guided wave, thereby achieving the steering of the SH wave by the maximum value of 27°. The finding of this study shows the enhanced beam steering capabilities of Staggered EMATs, particularly in the field of pipeline monitoring and can lead to more precise and effective detection of structural defects. Keywords: Staggered Halbach EMAT, Beam Steering, SH Guided Wave, Pipeline Inspection

Development of a real-time ultrasonic monitoring tool for high-cycle thermal fatigue

Pipe networks within nuclear power plants (NPPs) are susceptible to high-cycle thermal fatigue (HCTF) failures especially in so-called mixing zones where fluids with different thermal and hydraulic properties interact. The 1998 incident at Civaux 1 NPP is a good example of such a failure and its potential consequences. Given the critical impact on safety of these NPP components, a non-invasive method for HCTF progression monitoring in real time is expected to be of great use. Previous ultrasonic monitoring work showed that it is possible to predict the through-thickness temperature distribution and its temporal evolution of a mild steel block to within ±2 °C, relative to a resistance temperature device. These predictions were achieved using time of flight measurements from an ultrasonic transducer placed on the accessible surface with the so-called inverse thermal model (ITM) to invert the data. However, experiments to date have been limited to slow (10 minute) thermal transients at low temperatures (T &lt; 100 °C). Given that HCTF is driven by thermal gradients, the ITM method seems promising to monitor its progression. In this work the performance of the ITM method was investigated under more realistic conditions: faster (1 minute) thermal transients at higher temperatures (≈ 250-300 °C). A special high temperature electromagnetic acoustic transducer (EMAT) and a fast acquisition and inversion methodology were created to collect the data. The measurement setup and the collected data will be presented in this paper.

Electromagnetic Acoustic Transducer and Method for Residual Stress Detection in Conducting Materials

Electromagnetic Acoustic Transducer and Method for Residual Stress Detection in Conducting Materials

SN-FSAT system for single sensor ultrasonic guided wave beam steering and damage detection

In wireless communications as well as in structural health monitoring (SHM) beam steering presents interesting advantages. In the former it plays an important role for data directivity, which is also a perk for energy efficiency and data security; for the latter, directional inspection through guided waves leads also to energy efficiency, arbitrary dedicated space scanning, multi-function operation through multiple beams and even to application of a base-line free inspection concept. Normally, to enable this simultaneous beam control and data communication in arbitrary spatial directions (2D) over a structure, a large array of transducers is required, arranged to a similarly complex hardware and software support system. In this work, we present a system based on a dedicated sensor node (SN) and frequency steerable acoustic transducer (FSAT) combination. The SN-FSAT system is charged of the adequate power and signal management for acquisition, transmission, processing and data evaluation, required to perform spatial scanning and damage detection, as well as direction focused wireless communication tasks. These were tested over an isotropic aluminum plate-like structure by means of a double symmetric beam, via differential actuation signals, or in a high directive beam in a single direction by means of a quadrature driving signals. The complete guided wave-based setup consists of three SN-FSAT pairs. As damage a pseudo fault of a small added mass with damping tacky tape was used. The results show that damage located in different positions around the FSATs can be detected without a baseline reference and multiple directional communication paths between the SN-FSAT network can be established.

Structural Design and Optimization of Low-Frequency High-Power Electromagnetic Transducer

Crucial equipment for marine engineering and research, high-power ultra-low frequency sound sources have become necessary with the rapid development of seabed resource exploration, marine environment monitoring, underwater remote target detection, and communication technology. The current ultra-low frequency sound source cannot meet the requirements of practical applications. In this paper, both the finite element method and equivalent circuit method are used to improve the electromagnetic acoustic transducer, focusing on solving the structural design of the functional parts of the transducer, as well as the mechanical, electrical, magnetic parametrization of the transducer and other key technologies. The structural parameters and material parameters in the transducer that affect the final performance response are obtained through the optimization of the genetic algorithm. The results show that the electromagnetic acoustic transducer studied in this paper can emit low-frequency sound waves below 50~Hz, and the maximum sound pressure level reaches 138~dB, which meets the requirements of general low-frequency high-power acoustic wave transducers in practical work.

Spatiotemporal energy regulation strategy for enhancing SNR and spatial resolution in the damage detection with SH0 waves

The fundamental shear horizontal (SH0) wave, which can be generated by electromagnetic acoustic transducers (EMATs), is widely used in the structural health monitoring fields owing to its non-dispersive nature and the ability to detect over long distances. However, current SH0 wave methods hardly achieve the excellent signal-to-noise ratio (SNR) of the echo signals and satisfactory spatial resolution to defects due to the co-restriction between them. To address these issues, a spatiotemporal energy regulation strategy (STERS) is proposed in this paper to optimize energy distribution in the temporal and spatial dimensions. First, spatiotemporal pulse compression technology (STPCT) is proposed to improve both SNR and spatial range resolution for defect detection. Second, a staggered dual-exciter employing two sets of excitation signals is designed to improve the spatial azimuth resolution. Besides, a double sidelobe suppression algorithm (DSSA) is proposed to suppress sidelobe issues arising from the application of STPCT, thereby further improving the performance of STPCT. Finally, multiple simulations and experiments are executed to demonstrate the advantages of the proposed damage detection system. Results show that our methods can achieve comprehensive improvement in SNR, spatial range resolution, spatial azimuth resolution, and sidelobe suppression ability.

Enhancing unilateral EMAT performance through topological optimization of Halbach permanent Magnet arrays

A novel unilaterally excited electromagnetic acoustic transducer (EMAT) is proposed as a solution to address the challenge of weak electromagnetic ultrasonic detection signals being susceptible to interference from clutter noise signals. EMAT employs Halbach permanent magnet array (HPMA) structure and a coil designed based on Huygens superposition principle. This design enables the generation and reception of highly directive Rayleigh surface waves in aluminum plates. To enhance the operational efficiency of EMAT while maintaining a high level of directivity for surface waves, a penalty function is implemented in COMSOL Multiphysics for the topological optimization of EMAT. The objective function in this optimization process is based on covariance (COV) of the magnetic induction intensity. The research results suggest that the homogeneity of the magnetic induction intensity within the coil region is enhanced by 50 % following topological optimization compared to the original design. The energy conversion efficiency of EMAT is enhanced by 5 times compared to traditional designs. The surface wave speed was determined to be 2631 m/s when measured at a frequency of 400 kHz. The value indicates a relative error of 6.37 % in comparison to the theoretical speed. The results indicate that EMAT has the capability to generate high-directional and pure Rayleigh waves.