Patch Transducer Research Articles

A Flexible Film Magnetostrictive Patch Transducer for Nondispersive Shear Horizontal Wave Testing

A Flexible Film Magnetostrictive Patch Transducer for Nondispersive Shear Horizontal Wave Testing

Coil-Only High-Frequency Lamb Wave Generation in Nickel Sheets

This study presents a novel, coil-only magnetostrictive ultrasonic detection method that operates effectively without permanent magnets, introducing a simpler alternative to conventional designs. The system configuration is streamlined, consisting of a single meander coil, an excitation source, and a nickel sheet, with both the bias magnetic field and ultrasonic excitation achieved by a composite excitation containing both DC and AC components. This design offers significant advantages, enabling high-frequency Lamb wave generation in nickel sheets for ultrasonic detection while reducing device complexity. Experimental validation demonstrated that an S0-mode Lamb wave at a frequency of 2.625 MHz could be effectively excited in a 0.2 mm nickel sheet using a double-layer meander coil. The experimentally measured wave velocity was 4.9946 m/s, with a deviation of only 0.4985% from the theoretical value, confirming the accuracy of the method. Additionally, this work provides a theoretical basis for future development of flexible MEMS-based magnetostrictive ultrasonic transducers, expanding the potential for miniaturized magnetostrictive patch transducers.

Efficient layerwise multiphysics spectral element model for delaminated composite strips with PWAS transducers

Efficient structural element-based models are essential for fast simulations of wave propagation in composite structures for model-based and physics-informed data-driven structural health monitoring. This article introduces the first efficient multiphysics time-domain spectral structural element for wave propagation analysis of beam and panel-type composite structures with piezoelectric transducers (patch or full layers) containing delaminations. A general framework is presented to model multiple delaminations and transducer patches located arbitrarily. The intact host and patch transducer-bonded laminates and sub-laminates between delaminations are modelled separately using an electromechanically coupled efficient layerwise zigzag theory (ZIGT) for kinematics and a piecewise quadratic variation for the electric potential across piezoelectric layers. The high-order spectral element (SE) features a virtual electric node to model equipotential surfaces of piezoelectric transducers apart from the usual physical nodes having mechanical and internal electric degrees of freedom. A hybrid point-least squares continuity approach is employed to maintain continuity at the intersections of delaminated sub-laminates or the patch-bonded laminate with the host laminate. The model’s performance in capturing electroelastic waves’ interaction with delamination is examined with reference to the conventional finite element (FE) solution based on the ZIGT, continuum-based FE solutions, and the SE solution based on a non-layerwise version of the laminate theory. Finally, the model is used to examine the impact of interfacial location and size of delaminations on wave propagation behaviour.

Best reconstruction frequency for time-reversal process of Lamb waves and its determination from a single measurement

This article presents a theoretical framework for the concept of the best reconstruction frequency (BRF) of Lamb waves in elastic plates and its significance in the context of structural health monitoring (SHM). The time-reversal process (TRP) of Lamb waves has been widely explored for baseline-free damage detection in thin-walled structures. Previous studies have indicated that the accuracy of damage detection can be significantly improved by exciting Lamb waves at a frequency where the time-reversibility in the undamaged state is maximum within a desired frequency range. This frequency, termed the BRF, has been determined phenomenologically in prior research but lacked a rigorous theoretical foundation. In this study, the BRF is derived as the frequency at which the amplitude dispersion of the main mode of the reconstructed signal after the TRP is minimized. Accordingly, a method is put forth to determine this frequency from a single measurement using a broadband excitation eliminating the need to compute the similarity between the reconstructed and input waveforms at different excitation frequencies. The developed theory is validated with experiments conducted on an aluminium plate with Lamb waves generated and sensed by surface-bonded piezoelectric patch transducers. Notably, the study establishes that the BRF is a system property specific to a given transducer-plate-adhesive system and is independent of the distance between transducers. This characteristic makes it suitable for identifying damage locations when employing multiple sensing paths. The findings constitute an important milestone in understanding the TRP of Lamb waves and developing robust SHM technologies based on it.

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 %.

Non-Invasive Plant Root Tomography Through Optimized Sonar Array Transducer Antenna Design Using Genetic Swarm Metaheuristic

Plant root imaging is crucial for progress in various domains such as plant breeding and crop optimization. Traditionally, root tomography involves invasive methods that disrupt plant systems and yield non-reproducible results. As a result, non-invasive techniques, particularly electrical tomography, have gained significant attention. Despite the advantages, these techniques have limitations in terms of radiation efficiency and directivity due to suboptimal antenna design. This paper presents a comprehensive simulation on antenna design optimization focusing on dimensions, spacing, and integration of advanced algorithms. A micropatch transducer antenna was engineered for an existing in-silico plant root setup operating within a 3–5 MHz frequency range. The optimized dimensions of the antenna are 109.32 mm × 140.67 mm × 2.55 mm, and it resonates effectively within a frequency range of 3.1–5.68 MHz. Using scalar minimization techniques, patch transducers were interconnected into an antenna array with an optimized 3 mm spacing. Utilizing multi-objective optimization algorithm based on sperm fertilization procedure and shuffled frog leaping algorithm, optimal frequencies were obtained at 3,989,796.88 Hz and 3,989,951.83 Hz, respectively. Validated using CADFEKO software, the proposed antenna design demonstrated distinctive voltage distribution, superior directivity of 9.24 dBi, gain of 9.15 dBi, and 98.6% radiation efficiency when compared to the existing silicon-based root tomography antenna setups.

Mode-entangled resonance for lamb waves in a plate

We report a novel resonance phenomenon called the mode-entangled resonance. It can occur at a specific frequency in a plate carrying both symmetric and antisymmetric Lamb wave modes. We show that at this resonance, a symmetric or antisymmetric Lamb wave can be fully transmitted with its mode preserved from one plate to another through a matching plate geometrically misaligned with the two base plates. This phenomenon appears to be counter-intuitive because both symmetric and antisymmetric waves are generally formed in the reflected and transmitted wave fields when the misaligned plate is used as a matching plate. Our analysis shows that if both symmetric and antisymmetric Lamb wave modes at the resonance are entangled in the misaligned matching plate to satisfy the established phase matching condition, the matching plate fully transmits any wave mode across the two base plates. The discovered phenomenon is related to the classical Fabry-Perot resonance (FPR), but FPR is only applicable for single-mode transmission through a matching plate aligned with two base plates. Numerical and experimental results were presented to validate the discovered mode-entangled resonance phenomenon. Furthermore, we show that the discovered phenomenon can be used for super-amplification of the amplitude of the antisymmetric Lamb wave when it is excited by plate-surface-mounted patch transducers.

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.

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.

Efficacy and Damage Diagnosis of Reinforced Concrete Columns and Joints Strengthened with FRP Ropes Using Piezoelectric Transducers.

Recent research has indicated that the implantation of a network of piezoelectric transducer patches in element regions of potential damage development, such as the beam-column joint (BCJ) area, substantially increases the efficacy and accuracy of the structural health monitoring (SHM) methods to identify damage level, providing a reliable diagnosis. The use of piezoelectric lead zirconate titanate (PZT) transducers for the examination of the efficiency of an innovative strengthening technique of reinforced concrete (RC) columns and BCJs is presented and commented on. Two real-scale RC BCJ subassemblages were constructed for this investigation. The columns and the joint panel of the second subassemblage were externally strengthened with carbon fiber-reinforced polymer (C-FRP) ropes. To examine the efficiency of this strengthening technique we used the following transducers: (a) PZT sensors on the ropes and the concrete; (b) tSring linear variable displacement transducers (SLVDTs), diagonally installed on the BCJ, to measure the shear deformations of the BCJ panel; (c) Strain gauges on the internal steel bars. From the experimental results, it became apparent that the PZT transducers successfully diagnosed the loading step at which the primary damage occurred in the first BCJ subassemblage and the damage state of the strengthened BCJ during the loading procedure. Further, data acquired from the diagonal SLVDTs and the strain gauges provided insight into the damage state of the two tested specimens at each step of the loading procedure and confirmed the diagnosis provided by the PZT transducers. Furthermore, data acquired by the PZT transducers, SLVDTs and strain gauges proved the effectiveness of the applied strengthening technique with C-FRP ropes externally mounted on the column and the conjunction area of the examined BCJ subassemblages.

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.

An efficient Lamb wave-based virtual refined time-reversal method for damage localization in plates using broadband measurements

This study proposes a modified virtual time-reversal (VTR) algorithm for baseline signal-free damage detection in plate-like structures. The physical actuation and sensing of Lamb waves are performed using a broadband Gaussian excitation instead of the conventional narrowband modulated tone burst excitations. The forward response and the reconstructed signal due to the time-reversal process for a narrowband input signal are then constructed virtually using the broadband transfer function. The method eliminates the possibility of numerical errors encountered in the conventional VTR method based on narrowband excitations. It is also more efficient than the traditional VTR algorithm because it can probe at multiple excitation frequencies using a single measurement for each sensing path. This modified VTR algorithm is employed in the recently developed refined time-reversal method (RTRM), which uses an extended signal length of the reconstructed signal for computing damage index (DI) and probes the structure at the best reconstruction frequency. The new method is termed the virtual refined time-reversal method (VRTRM). The DIs based on the VRTRM are used in the reconstruction algorithm for probabilistic inspection of defects to achieve baseline signal-free localization of damages. The efficacy of the proposed VRTRM for damage localization is experimentally verified with the established technique RTRM. Experiments are performed in an aluminium plate equipped with a network of surface-bonded piezoelectric patch transducers to illustrate the conventional VTR’s pitfalls and the modified VTR’s accuracy for a single mass damage scenario. The results show that the proposed VRTRM is as accurate as the established technique RTRM in estimating the reconstructed signals and localizing a block mass damage. Finally, the VRTRM is shown to localize in a dual damage scenario with excellent accuracy. In contrast, the conventional main mode-based VTR method fails to localize the damages with or without single-mode tuning.

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.