Magnetostrictive Patch Transducer Research Articles

Design of guided wave magnetostrictive patch transducer with vertical static bias magnetic field for pipe inspection

Compared with electromagnetic acoustic transducer (EMAT), magnetostrictive patch transducer (MPT) has higher energy conversion efficiency. MPT is often used to excite and receive long-distance ultrasonic guided waves for defect detection or structural health monitoring of large industrial equipment. In this work, a new design method of permanent magnet MPT using the vertical static bias magnetic field to excite shear horizontal (SH) guided waves is proposed. First, the mathematical model of exciting ultrasonic guided waves by a vertical static bias magnetic field MPT is established, and the equivalent surface stress in the magnetostrictive patch is calculated. It is shown that the vertical static bias magnetic field MPT can excite SH guided waves in plates. Then, the influence of static bias magnetic field intensity on the amplitude of guided wave signal is analyzed. Compared with other traditional MPTs, the amplitude of SH guided wave signal excited by the vertical static bias magnetic field MPT is increased. Finally, a periodic permanent magnet (PPM)-MPT with a central frequency of 120 kHz is designed. The proposed PPM-MPT improves the energy conversion efficiency compared to the circumferential alternating permanent magnet array type MPT. The PPM-MPT can detect defects in a steel pipe with a wall thickness of 3.5 mm and an inner diameter of 100 mm. The results show that the PPM-MPT designed in this paper successfully detects the through hole with a diameter of 2 mm, and the cross-section loss rate of the defect is about 0.6 %.

Soft magnetostrictive patches for guided wave ultrasonics using Wiedemann effect-based MPTs and EMATs

Magnetically soft and malleable magnetostrictive (MS) alloys are highly promising as low-cost solutions for high-efficiency generation of guided waves in industrial applications and a variety of magnetostrictive patch transducers (MPTs) have been described in the literature. This work focuses on understanding the mechanisms and behaviour of soft MPTs used in the Wiedemann effect geometry, generating shear horizontal (SH) guided waves using FeCo alloy patches. MPT operation is explored in relation to patch geometry, size, magnetic field directions and guided wave wavelength. MPTs are compared with electromagnetic acoustic transducers (EMATs) and EMATs are also placed on MS and copper foil patches bonded to large glass plates for some of the measurements. Periodic permanent magnet (PPM) array EMATs operating on MPTs bonded to ferritic steel samples produced significant enhancements in the generated wave amplitude and the detected signal amplitude when compared to directly generating on the steel substrate, which primarily operates through the Lorentz mechanism. This enhanced performance was investigated and was found to be due to the magnetic fringing fields at the magnet edges. Moreover, EMAT lift-off behaviour was significantly improved when an EMAT was placed above a magnetostrictive patch, with 50 mm lift-off between the EMAT and the patch demonstrated for SH wave generation at a 22 mm nominal wavelength at a 170 kHz excitation frequency on a glass plate sample.

A Flexible Film Magnetostrictive Patch Transducer for Non dispersive Shear Horizontal Wave Testing

A Flexible Film Magnetostrictive Patch Transducer for Non dispersive Shear Horizontal Wave Testing

Optimal design of transducers based on the Halbach arrays permanent magnet structure

ABSTRACT For enhancing the static magnetic field and reducing the size of torsional guided wave magnetostrictive patch transducer (MPT) with permanent magnets, a MPT with Halbach arrays is proposed. The structural parameters design of the MPT can be guided by finite element simulation. It is found that increasing the central angle of the radially magnetised magnets can increase the strength of the static magnetic field, and it can be adjusted through designing the radial size and lift-off distance of the magnets. The Halbach magnet arrays composed of circumferentially magnetised magnets with a circumferential size of 6 mm and radially magnetised magnets with a circumferential size of 4 mm are selected to experimentally compare with the alternating magnetised magnet arrays composed of magnets with a circumferential size of 10 mm. The results show that the static magnetic field strength can be increased by 54.7% using Halbach magnet arrays. The proposed MPT composed of the Halbach magnet arrays and a linear solenoid array can excite and receive T(0,1) guided wave. Compared with the alternating magnetised magnet array MPT, the guided wave signal amplitude is increased by about 70% generated and received by the MPT with the Halbach magnet arrays.

Torsional mode magnetostrictive patch transducer with TPSMs for liquid-filled pipes inspection

T (0,1) mode guided waves have no axial or radial vibration displacement. Therefore, the energy leakage is small in liquid-filled pipes, which is suitable for detecting the axial defects of the liquid-filled pipes. Fe–Co materials with high magnetostriction coefficient is fabricated. Its magnetic properties are tested. The size and distribution of static magnetic fields generated by different permanent magnets are verified by simulation. A new torsional mode guided wave magnetostrictive patch transducer with tile-shaped permanent magnets for defect detection of the liquid-filled pipes is proposed. The detection effect of the transducer on the liquid-filled pipes under different pressures is tested through experiments. The proposed transducer consists of four tile-shaped permanent magnets, eight triangular yokes, a coil, and two magnetostrictive patches. Four groups of tile permanent magnets are symmetrically distributed around the patch according to the polarity. Magnetic yokes are installed at both ends of each group of tile permanent magnets. The experiment verified that the magnetostrictive patch transducer realize the excitation and reception of guided wave signals in the magnetostrictive patches. The amplitude and signal-to-noise ratio of echo signals is improved. The position of pipe defects is determined according to the propagation time of guided wave. The influence of different pressures in the liquid-filled pipes on the amplitude of guided wave is verified.

Optimized Design of Torsional Guided wave Magnetostrictive Patch Transducer Based on Reversed Wiedemann Effect

Optimized Design of Torsional Guided wave Magnetostrictive Patch Transducer Based on Reversed Wiedemann Effect

Lowest remnant thickness estimation using Staircase Magnetostrictive Patch (ScaMP) Transducer

Wall thickness reduction, which typically results from corrosion, erosion, or operating conditions, is a significant challenge in many industries. In order to generate a broadband pure shear horizontal wave mode in plate structures, this paper proposes a magnetostrictive patch transducer called the Staircase Magnetostrictive Patch (ScaMP) Transducer. For ScaMP transduction, an optimised patch width offers a broadband frequency response is employed. The lowest remnant thickness of the sample was estimated using the wideband SH1 dispersive guided wave mode's cut-off property. The broad frequency excitation method enabled measurement over a range of wall thinning up to 80% of the nominal thickness with a single data acquisition. Experiments were carried out on an 8 mm nominal wall thickness aluminium plate with gouge defects to evaluate the proposed sensor's broad frequency response. The measurement of remnant thickness was estimated with a maximum error of 5.5%.

Defect Detection and Imaging in Composite Structures Using Magnetostrictive Patch Transducers

The use of thin magnetostrictive patches to generate and detect guided waves within the composite samples is investigated for defect detection. This approach has been implemented using SH0 shear horizontal guided waves in both CFRP and GFRP plates. A magnetostrictive patch transducer was able to generate SH0 waves with known directional characteristics. The synthetic aperture focusing technique (SAFT) was then used to reconstruct images of defects using multiple transmission and detection locations. The results for imaging defects in both types of material are presented.

Broadband torsional guided wave magnetostrictive patch transducer with circumferential alternating permanent magnet array for structural health monitoring

T(0,1) guided wave is non-dispersive and has been widely used in the long distance inspection and condition monitoring. Magnetostrictive patch transducer (MPT) is a new type of EMAT with high energy conversion efficiency, which can be used to generate and receive torsional guided waves in pipe samples. In this paper, a permanent magnet broadband torsional guided wave MPT composed of a linear coil EMAT array is proposed. The MPT was experimentally verified to be broadband and the bandwidth is 230.79 kHz when using a 5 mm wide linear coil. The wavelength corresponding to the center frequency of the transducer is about 0.6 times the width of the coil. Base on the design, through-hole defects with diameters of 3–6 mm in the 2-mm-thick aluminum plate were quantified by frequency sweeping detection, and the relative error is less than 7 %. Compared with the single-frequency guided wave signal reflected by through-hole defects, the variation pattern of the quantitative results using frequency sweeping can contribute to a more accurate prediction of the remaining service life of the test specimen.

Design method of unidirectional wideband SH guided wave phased array magnetostrictive patch transducer

The existing meander coil type SH guided wave electromagnetic acoustic transducer (EMAT) has a fixed center frequency and narrow bandwidth, which cannot quantify the defect size by continuous frequency scanning. Therefore, this study proposes an array of wideband unidirectional SH guided wave magnetostrictive patch transducer and its control method for excitation of unidirectional SH guided waves at random frequencies over a wide frequency range. A narrow magnetostrictive patch and a linear coil are used for each array element to increase the bandwidth of a single element. By controlling the excitation delay and initial phase of each array element separately, the direction of the SH guided wave can be controlled, and its wavelength can be changed without replacing the coil. In addition, a mathematical model of the array sources of finite width is developed to excite unidirectional SH guided waves at different frequencies. Based on this model, the effects of the number, width and distance of the array element on the frequency response characteristics of the transducer array are analyzed. The experiments show that: The proposed transducer array can excite unidirectional SH guided waves of random frequency over a wide frequency range. The amplitude of the guided wave signal on the suppressed side is almost 0, while the signal on the non-suppressed side is significantly increased, leading to a significant improvement in the energy conversion efficiency. The frequency range can be selected by designing the width and distance of array elements, and the experimentally measured frequency response characteristics of the transducer array are highly consistent with the trend of the mathematical model results.

Performance optimization of harmonized flexible printed coils of axial magnetized magnetostrictive patch transducers for pipeline inspection

Currently, different types of magnetostrictive patch transducers (MPT) utilizing high magnetostriction patches, such as iron-cobalt alloys attached to the tested samples, have been proved to be effective electromagnetic acoustic transducers (EMAT). In 2019, an innovative guided wave-based MPT called the harmonized flexible printed coil (HFPC) sensor, consisting of a harmonized flexible printed coil sheet and a magnetized iron-cobalt patch, was proposed to replace conventional MPT. The HFPC sensor exhibits better performance than conventional MPT by generating a uniform magnetic field and triggering stronger signals. On the basis of previous research, this paper reported a newly optimized multilayer HFPC sensor, which considers coil inductance, capacitance, and other related parameters in a fixed-voltage AC power supply environment, which is rarely done by most researchers before. The optimized HFPC parameters were obtained from simulation studies and verified by the experimental investigation, where the performance was improved by 1.68 times compared to the old HFPC-based MPT.

A Flexible Thin-Film Magnetostrictive Patch Guided-Wave Transducer for Structural Health Monitoring

Structural health monitoring (SHM) technology has attracted more and more attention in aerospace and energy industries as it may detect and monitor early degradation and damage in the structures and thus avoid life and financial loss. Guided wave (GW) based inspection is very useful for the SHM of thin-walled structures due to its capability for long-distance and wide-range inspection with high sensitivity. However, the lack of small and high-performance transducers seriously limits the development of GW-based SHM technology. In this paper, a thin-film magnetostrictive patch transducer (MPT) that can generate and receive single-mode and almost nondispersive GW is proposed. The new transducer is composed of an alloy patch and a double-layer flexible printed circuit (FPC). Firstly, the basic structure and principle of the proposed transducer are presented and analyzed. Compared with current single-mode GW transducers, the main advantages of the proposed transducer are lightweight, flexibility, and high transduction efficiency. Both the numerical simulation and experimental results validate that the new transducer has good performance in generating and receiving single and almost nondispersive S0 mode GW in an aluminum plate. It is very promising to be applied for the SHM in curved thin-walled structures.

Performance investigation on the balance of static and dynamic magnetic field strength of magnetostrictive patch transducer with different permanent magnets

Nowadays, a magnetostrictive patch transducer(MPT) utilizing the high magnetostriction patch such as iron-cobalt alloy attached to the tested specimen like pipes, tubes, and cables has attracted more attention from many scholars. A harmonized flexible printed coil magnetostrictive patch transducer (HFPC-MPT) was proposed in 2019 by the author's research group, and this high-performance MPT could generate a more even magnetostrictive force than before. However, that research was an MPT optimization from sensor circuit design perspective. From the perspective of the magnetic field, this type of sensor has not been explored yet to improve its performance. In this research, firstly, the author conducted numerical simulations to find the optimal balance range between the static and dynamic magnetic fields of HFPC-MPT. Secondly, some experiments have been designed to verify the simulation results. The simulation results have been validated and are in agreement with the experimental results. This research provided a deep insight into improving the performance of HFPC-MPT from the perspective of the static magnetic field, which is also beneficial to both industrial and academic areas.

Performance optimization of axial magnetized magnetostrictive patch transducer for transduction of L(0,2) ultrasonic guided wave for pipe inspection

Magnetostrictive patch transducers (MPT) are widely used in non-destructive testing for flexibility, reputability, and durability. Based on the theory of magnetostriction, we developed a method for the design and optimization of axial magnetized MPTs for the transduction of L(0,2) ultrasonic guided waves. To get the optimum static bias magnetic field, we conducted experiments with different magnetostrictive patch aspect ratios, which were based on the theory of demagnetization. Furthermore, we analyzed the variations in solenoid coil parameters with changes in the dynamic alternating magnetic field and induced voltage via simulations and experiments. An optimized MPT was obtained, with its performance improved by 2.79 times compared with those of transducers without magnetostrictive patch.

Performance Optimization of Axial Magnetized Magnetostrictive Patch Transducer for Transduction of L(0,2) Ultrasonic Guided Wave in Pipe Inspection

Performance Optimization of Axial Magnetized Magnetostrictive Patch Transducer for Transduction of L(0,2) Ultrasonic Guided Wave in Pipe Inspection

Bolt looseness detection using SH guided wave and wave energy transmission

Lap joints are commonly used in civil infrastructure and mechanical assembly structures. Detecting the connection status of bolts, particularly in the early stages of use, is critical for ensuring structural integrity. A shear horizontal (SH) guided wave-based bolt looseness detection method, excited by a magnetostrictive patch transducer (MPT), is presented in this paper. A normalised bolt-looseness index was proposed based on the wave energy transmission theory by analysing the signals received at the transducer for the transmitted wave passing through the actual contact area and the transducer for the direct incoming wave. Numerical and experimental studies were conducted on a lap joint with four bolts. The relationship between the and bolt loads was obtained, verifying the effectiveness of this method for detecting the extent of the bolt looseness under various bolt tightness states. The results also show that SH0 waves, excited by an MPT, have better detection capability than Lamb waves, when the surface of the lap joint is subjected to liquid medium such as water and professional paint for bridges.

Novel design of an effective pneumatic magnetostrictive patch transducer based on the ultrasonic guided wave for application of fast pipe health inspection

Pipelines are widely used to transport water, oil, and gas. Severe corrosion of pipes can cause leakage of natural gas and result in an explosion or even more severe disasters. Magnetostrictive sensors based on ultrasonic guided waves have been validated as feasible for non-destructive testing of pipes with advantages of long-range inspection, high signal to noise ratio, with high testing efficiency. Using a patch made from a highly magnetostrictive material dramatically enhances the performance of these sensors; however, mounting this patch of smart material on a pipe requires using strong epoxy glue. Plus, applying the glue on the pipe and waiting for it to dry is time-consuming. After completing the test, leaving the pipe’s smart material could be hazardous and initiate electrochemical corrosion. Thus, smart material must be removed after the test. Nonetheless, it is complicated to remove smart material from the pipe’s surface after the glue dries. Considering such complications, as a solution to this problem, in this paper, the novel design of the pneumatic magnetostrictive patch transducer (PMPT) is proposed that benefits from the advantages of the patch in the magnetostrictive sensor but also eliminates such drawbacks. The performance of PMPT was validated by theoretical analysis and experimental investigation. The flexible, fast feature and portable configuration of the proposed PMPT make it easy to be applied on in-service pipes in different diameters with corrosion surfaces or coating.

Multi-feature integration and machine learning for guided wave structural health monitoring: Application to switch rail foot

Switch rails are weak but essential components of high-speed railway systems that have urgent nondestructive testing requirements owing to aging and the associated potential for fatigue damage accumulation. This study presents a multi-feature integration and automatic classification algorithm for switch rail damage using guided wave monitoring signals. A combination of piezoelectric transducers and magnetostrictive patch transducers is adopted to improve the monitoring performance and meet actual monitoring requirements. Furthermore, multiple features extracted from various signal processing domains—such as the time domain, power spectrum domain, and time–frequency domain—are proposed and defined according to the structure and characteristics of the switch rail and guided wave to represent the complex nature of the damage. A damage index is defined to eliminate the influence of various environmental and operational conditions, signal power, and other factors. In addition, a feature selection method based on binary particle swarm optimization with a new fitness function is proposed to select the most damage-sensitive features and eliminate irrelevant and redundant features to improve the classification performance. Moreover, considering that the results are easily influenced by experts’ subjective judgment and experience, the least-squares support-vector machine is used to construct automatic classification models to reduce the probability of artificial incorrect diagnosis and improve the generalization ability to unknown environments. Finally, three types of experiments on the foot of a switch rail are presented to evaluate the proposed method. The results indicate that the proposed method is capable of identifying damage in challenging cases and is superior to conventional methods.

A model to predict the elastic field radiated by a magnetostrictive patch transducer into an omnidirectional waveguide

Magnetostrictive patch transducers (MPT) can be used as sources or sensors of elastic guided waves in non-destructive testing and structural health monitoring methods. A tool for simulating them is under development to help designing optimal MPT for a given application. It requires the prior accurate modelling of transduction phenomena involved in such patches and of the GW fields they generate. A MPT is made of a thin magnetostrictive strip under a static magnetic field, glued to the waveguide under examination and excited by an alternative current circulating in a coil. In the strip where they take place, transduction phenomena are similar to those generated by an electro-magnetic acoustic transducer (EMAT) in a ferromagnetic medium. They involve magnetostrictive strain, magnetization force and surface traction and Lorentz force (Clausse et al. 2017 J. Phys.: Conf. Ser. 797 102004), which can be transformed into equivalent surface stresses at the outer surface of the strip. A matrix model is developed to propagate the equivalent stresses from this outer surface to that of the waveguide. Once equivalent stress distributions are computed at this latter surface, a model (Barras et al. 2020 Ultrasonics 103 1060782) is used to predict the MPT radiation into the waveguide. Overall, the chaining of these models constitutes a semi-analytical multi-physics model for GW radiation by MPT of high computing efficiency.

Quantification of defects in an aluminum plate using direction-tunable shear horizontal wave imaging

The quantification of damage, in plates, pipes and such like structures, is one of the current research areas. In this study, to estimate the notch size, shape, and orientation was carried out experimentally based on fundamental shear horizontal mode, SH0 mode. Using least number of transmitters, the reconstruction algorithm for the probabilistic inspection of damage (RAPID) has been used to carry out fast and efficient investigation of scattered waves using SH0wave interaction with notch at various incident angles. An approach of ultrasonic guided waves and (RAPID) algorithm, using a direction-tunable shear-horizontal mode array magnetostrictive patch transducer (DT-SHMA-MPT), the notch in a thin aluminum plate is experimented. Firstly, the RAPID algorithm, based on SH0mode, is used here to quantitatively study a notch in a thin aluminium plate. Secondly, the imaging application using DT-SHMA-MPT is achieved. Experiments were conducted using an array of eight DT-SHMA-MPTs based on a pitch-catch mode to utilize the scattered waves at the notch. The results obtained through experiments reveal the effect of directionality of the scattered waves and have find out the optimal transducers configuration. The localization, quantification and orientation at the same time are obtained using only two or three transmitters. To improve the accuracy of imaging, a threshold value was selected. The presented approach can be used to detect, locate and image the surface defects in aluminum plate.