Figure 1 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
Source publication
Nondestructive testing (NDT) is an essential method for assessing structural integrity in the oil and gas industry. Electromagnetic acoustic transducers (EMATs) have been extensively used to detect the wall-thickness reduction of plate-like structures, because they do not require direct contact. The pulse intervals of echoes are used to calculate t...
Contexts in source publication
Context 1
... Section 4, the parameters of equivalent elements are obtained by means of impedance-curve-fittings, followed by the verification of the equivalent circuit, using EMAT signals. Finally, the findings are summarized in Section 5. Figure 1 shows the configuration of the EMAT applied to thickness measurement. EMATs rely on the interaction of the magnetic-bias-field and the eddy currents to generate or receive elastic waves in the metallic structures [17][18][19]. ...
Context 2
... theoretical pulse waveform can be obtained by Equation (15), which can then be fitted to the corresponding signal. Figure 10 shows one of the fitting results: the selected signal is measured with a 153-turn receiving coil, and the coilbackplate gap is 1.5 mm. In terms of pulse width and amplitude decay-rate over multiple periods, the theoretically calculated and measured wave packets are in good agreement. ...
Context 3
... focus on the effect of spacing on decay rate and pulse width, only envelope decay curves are drawn. The pulsed signals were selected when l2 was 0.1 mm, 0.8 mm and 1.5 mm, followed by fitting to the corresponding theoretically calculated damping-ratio, as shown in Figure 11. It can be seen that the signalpulse width is consistent with the theoretical calculation, and the errors are less than 10%. ...
Context 4
... can be seen that the signalpulse width is consistent with the theoretical calculation, and the errors are less than 10%. Figure 12 shows the measured and calculated damped-oscillation angular-frequency of the selected pulsed wave-packets. It can be seen that the similarities between the results of the two different coils are good. ...
Context 5
... k is the coefficient of coupling between the receiving coil and the specimen, I is the eddy current in the specimen, and U is the output voltage of the receiving coil. Therefore, the selection of the backplate position needs to consider the damping coefficient, amplitude and frequency of the pulse, as shown in Figure 13. As the receiving coil-backplate gap increases, the influence of the backplate on the receiving coil diminishes, and the variation rate in all three parameters drops. ...
Similar publications
The paper considers non-destructive testing (NTDs) as a means to solve the flaw detection problems of magnetic products. It proposes a new probe-coil magnetic-field NDT, not requiring the pre-magnetization of the test object material, which is mandatory for all conventional magnetic flaw detection techniques. A new bifactor excitation of the fluxga...
Citations
... To address this problem, this article investigated the frequency response of the PPM-EMAT receiver with multilayer racetrack coils using an equivalent model. The equivalent model is an effective method to study the electrical characteristics of EMAT, which has been used in the relevant literature to improve the transducer's lift-off performance, excitation/reception efficiency [21][22][23][24], or impedance matching problems. However, these works only study ultrasonic body wave transducers, and unlike body waves, guided wave signals are multi-mode and multi-modal [21][22][23]. ...
... The equivalent model is an effective method to study the electrical characteristics of EMAT, which has been used in the relevant literature to improve the transducer's lift-off performance, excitation/reception efficiency [21][22][23][24], or impedance matching problems. However, these works only study ultrasonic body wave transducers, and unlike body waves, guided wave signals are multi-mode and multi-modal [21][22][23]. Seher M et al. studied the electrical characteristics of Lamb-guided wave EMAT. However, the coil of Lamb-guided wave EMAT is arranged around the magnet, and the coil impedance is less affected by the magnet [24]. ...
Period-permanent-magnet (PPM) electromagnetic acoustic transducer (EMAT) has been widely used in shear horizontal (SH) ultrasonic guided wave testing owing to its advantages, such as non-contact coupling, and convenient to excite SH waves. However, its poor transduction efficiency leads to weak signals and limits the lift-off performance. This article investigates how to improve the signal amplitude by adjusting the number of turns of the racetrack coil. The inductive coupling process of the PPM-EMAT receiver is first studied using the equivalent circuit method, and the corresponding equivalent model is obtained. Aiming at the effects of coil configurations, the equivalent impedance parameters of multilayer racetrack coils are analyzed by calculations and measurements. The proposed model can be used to predict the receiving frequency response of PPM-EMAT receivers with different coil structures, and it has been verified experimentally. It can be obtained that by choosing an appropriate coil configuration and matching resistance, the SH wave signal amplitude can be increased by 3 times.
... Not only their coil geometry, but also the distance from the coil to the magnet, as explored by Wu et al. [9]. The presence of a backplate between the transducer's components also affects its impedance, as exposed by Wang et al. [15]. Beyond the EMAT itself, the distance from it to a ferrous material, so-called lift-off, also affects the transducer's impedance [10], and so does the temperature [12]. ...
... Wu et al. [9] studied the effect of magnet-to-coil distance on the performance characteristics of EMATs, concluding that the magnet-to-coil distance affects the magnetic flux density and eddy current density at the medium's surface and that, for a specific EMAT, there is an optimal magnet-to-coil distance that maximized its conversion efficiency over a range of lift-off distances. Wang et al. [15] explored the effects that a copper backplate, positioned between the coil and magnet at various distances from the coil, can have on the EMAT impedance, the received pulse width, and the amplitude of thickness-measurement signals. An equivalent circuit model of the receiving coil-backplate structure was established and used to predict these effects. ...
... Zao et al. [12] explored the variation in EMAT impedance with different temperatures and developed an automatic solution, based on L-network impedance matching, to enhance signal amplitude. These works [9,10,12,15] explored the effects that one variable can have on EMAT performance; namely, the magnet-to-coil distance, the backplate distance, lift-off, and temperature. In contrast, Jian et al. [17] explored the effects of various variables on the EMAT impedance; namely, coil geometry and size, different materials samples, and various lift-off distances. ...
Ultrasonic waves generated and received by electromagnetic acoustic transducers (EMATs) are advantageous in non-destructive testing, mainly due to the ability to operate without physical contact with the medium under test. Nevertheless, they present a main drawback of less efficiency, which leads to a lower signal-to-noise ratio. To overcome this, the L-network impedance-matching network is often used in order to ensure maximum power transfer to the EMAT from the excitation electronics. There is a wide range of factors that affect an EMAT’s impedance, apart from the transducer itself; namely, the properties of the specimen material, temperature, and frequency. Therefore, to ensure optimal power transfer, the matching network’s configuration needs to be fine-tuned often. Therefore, the automation of the laborious process of manually adjusting the network is of great benefit to the use of EMAT transducers. In this work, a simplified one-parallel-element automatic matching network is proposed and its theoretical optimal value is derived. Next, an automatic matching network was designed and fabricated. Experiments were performed with two different EMATs at several frequencies obtaining good agreement with theoretical predictions. The automatic system was able to determine the best configuration for the one-element matching network and provided up to 5.6 dB gain, similar to a standard manual solution and considerably faster.
... Magnetostriction is the property of ferromagnetic materials to deform in the presence of an external magnetic field. Thus, in ferromagnetic materials, the energy conversion efficiency of an EMAT based on magnetostriction is higher compared to an EMAT based on the Lorentz force [10,11]. ...
Inspections of critical components must be expedited in the oil and gas industry. It is critical to overcome current Non-Destructive Testing (NDT) challenges to forecast future demand in difficult-to-reach areas. In the realm of robot manipulators, there are some modern robots with desirable qualities for building automated NDT systems that can meet the demanding specifications of the oil and gas sector. This work presents an autonomous inspection using a robotic arm with 5 degrees of freedom to evaluate the use of nondestructive inspection by electromagnetic acoustic transducer in plate metal to thickness measurement. The increased inspection speed, associated with the expected limits, for running the scan improve the visualization of the various thickness are presented. Resumo: As inspeções de componentes críticos devem ser aceleradas na indústria de petróleo e gás. É fundamental superar os desafios atuais dos Ensaios Não Destrutivos (NDT) para prever a demanda futura em áreas de difícil acesso. No campo dos robôs manipuladores, existem alguns robôs modernos com qualidades desejáveis para a construção de sistemas automatizados de END que podem atender às exigentes especificações do setor de petróleo e gás. Este trabalho apresenta uma inspeção autônoma utilizando um braço robótico com 5 graus de liberdade para avaliar o uso da inspeção não destrutiva por transdutor acústico eletromagnético em chapa metálica para medição de espessura. O aumento da velocidade de inspeção, associado aos limites esperados, para a execução do escaneamento melhoram a visualização das diversas espessuras apresentadas. Palavras-chave: braço robótico, avaliação ultrassônica, processamento de sinais.
... Wang et al. found that the position of the backplate affects the pulse width and amplitude of the thickness measurement signal. Reducing the gap between the coil and the backplate can reduce the pulse width by over 80%, while increasing the gap can increase the signal amplitude by over 300% [26]. ...
The safety of railway transportation is crucial to social and economic development. Therefore, real-time monitoring of the rail is particularly necessary. The current track circuit structure is complex and costly, posing challenges to monitoring broken tracks using alternative methods. As a non-contact detection technology with a lower environmental impact, electromagnetic ultrasonic transducers (EMATs) have become a concern. However, traditional EMATs have problems such as low conversion efficiency and complex modes, which can limit their effectiveness for long-distance monitoring. Therefore, this study introduces a novel dual-magnet phase-stacked EMAT (DMPS-EMAT) design comprising two magnets and a dual-layer winding coil arrangement. The magnets are positioned at a distance equal to the wavelength of the A0 wave from each other, while the center distance between the two sets of coils beneath the transducer is also equal to the wavelength. After analyzing the dispersion curves of the rail waist, it was determined that the optimal frequency for long-distance rail monitoring is 35 kHz. At this frequency, adjusting the relative positions of the two magnets and the coil directly underneath to be one A0 wavelength can effectively excite a constructive interference A0 wave in the rail waist. The simulation and experimental results show that DMPS-EMAT excited a single-mode A0 wave, resulting in a 1.35-times increase in amplitude.
... The main limitation of current Toneburst-based EMAT thickness measurement tems is their limited range, leading to reduced accuracy and stability beyond this sc As the thickness of the specimen decreases, it becomes difficult to accurately disting the time intervals between echoes in the time domain using TOF [24], which is mainly to the following two aspects: ...
... The main limitation of current Toneburst-based EMAT thickness measurement systems is their limited range, leading to reduced accuracy and stability beyond this scope. As the thickness of the specimen decreases, it becomes difficult to accurately distinguish the time intervals between echoes in the time domain using TOF [24], which is mainly due to the following two aspects: ...
Metal thickness measurements are essential in various industrial applications, yet current non-contact ultrasonic methods face limitations in range and accuracy, hindering the widespread adoption of electromagnetic ultrasonics. This study introduces a novel combined thickness measurement method employing fuzzy logic, with the aim of broadening the applicational scope of the EMAT. Leveraging minimal hardware, this method utilizes the short pulse time-of-flight (TOF) technique for initial thickness estimation, followed by secondary measurements guided by fuzzy logic principles. The integration of measurements from the resonance, short pulse echo, and linear frequency modulation echo extends the measurement range while enhancing accuracy. Rigorous experimental validation validates the method’s effectiveness, demonstrating a measurement range of 0.3–1000.0 mm with a median error within ±0.5 mm. Outperforming traditional methods like short pulse echoes, this approach holds significant industrial potential.
