Ultrasonic Nondestructive Testing Research Articles

Laser generated Ultrasound System (LUS) and its application for the Non-Destructive Testing of metallic components

One of the investigation areas regarding the Ultrasonic Non-Destructive Test (UT-NDT) is the development of non-contact technologies like Air-Coupled UT, EMAT or UT generated by Laser. These technologies show several interesting advantages like no couplant needed or their application to the inspection of components with complex geometries and extreme surface conditions (temperature, roughness, radiation…). In the Laser Ultrasonics Techniques (LUS), ultrasound is generated by a pulsed laser that produces a thermal expansion of the surface where it impacts and generates vibrations at ultrasonic frequencies. These vibrations can travel through the inside of the material and its surface; and they are reflected, refracted or diffracted in the defects or discontinuities of the material. The disturbances generated by the interaction of the vibration with the defects are detected in another point of the material using a secondary detection system. Tecnatom is working with LUS technology since 2010, acquiring, installing and optimizing a laboratory system for its implementation in the inspection of metallic materials (aluminum, carbon steel and stainless steel). During this time, several works have been carried out to determine the scope of the technology as: initial study for the characterization of the waves generated by the laser; studies in test blocks without discontinuities to determine the experimental conditions in which ultrasonic disturbances are generated in thermo-elastic and ablative regime; simulations and microstructural studies of the pieces to determine both the structural state and the residual stresses caused by the incidence of the laser; inspection of blocks with artificial reflectors, both superficial and embedded, and set-up techniques to increase the amplitude of the detected signal; optimization of the detection system through the combination of technologies and identification of safety criteria, use and improvement of the system for validation use in industrial environments. In this work, Tecnatom presents the main conclusions of the development carried out to determine the capacities and limitations of the techniques based on Laser Ultrasonics for its application in Non-Destructive Testing for the inspection of metallic components.

AI-based Model to Estimate the Flaws from Ultrasonic NDT Data

This study explores an artificial intelligence (AI) approach for assessing the geometrical features of flaws in nondestructive testing (NDT) using ultrasonic oscillograms. A validated numerical model, generated through acoustic finite element analysis (FEA), produced ultrasonic signals. The AI model was trained on 525, validated on 113, and tested on 112 oscillograms from models with varied flaw characteristics. Training inputs were parameters derived from ultrasonic signals, and the network's performance was evaluated by comparing its outputs for flaw location, length, and angle with desired values. Statistical analysis, including Root Mean Square Error (RMSE) and Efficiency (E), indicated promising results, suggesting the potential of the proposed AI-based method for estimating flaw geometrical features in ultrasonic NDT.

Quantitative Measurement and Evaluation of High-Resolution Ultrasonic Sound Fields using a Novel Automated Ultrasonic Immersion Scanner

Ultrasonic probes are an integral part of the automated ultrasonic non-destructive testing and evaluation (NDT&E) systems to detect and size the defects in a wide range of structural materials in production lines. A complete quantitative assessment of the performance characteristics of an application-specific UT probe is needed to be evaluated on the basis of the international standard DIN EN ISO 22232-2. This requirement of full assessment not only improves the quality assurance of the manufactured probes by evaluating the acceptance criteria but also provides the useful technical information to the end-user to optimize the automated ultrasonic testing on-site. In addition, the evaluation of probe characteristics should be carried periodically throughout their service life. In this work, we developed a novel high-precision ultrasonic immersion scanner to evaluate the full ultrasonic probe characteristics which include the squint angle measurement in three different reference planes (XY, XZ, and YZ), RF-signal and its frequency spectrum at water-steel interface, focal distance, focal range, focal width, focal length and also the angle of beam divergence in different planes of the sound field distribution. In the newly developed UT immersion scanner, for the first time, we successfully integrated the high-precision Hexapod with six axes to achieve a few micrometer (~15 µm) spatial-resolution in the measured sound field patterns and a good angular resolution (~0.05°) in the squint angle measurement. In addition, we used a verified UT instrument in accordance with the standard DIN EN ISO 22232-1 to obtain more accurate amplitude values (±0.5 dB) while scanning a test block. The automated scanning, data acquisition, evaluation, visualization and the automated test report generation are carried based on the standard DIN EN ISO 22232-2. The measured sound beam characteristics of both focused and non-focused application-specific ultrasonic probes with center frequencies ranging from 0.2 - 15 MHz using the pulse-echo technique on a 3 mm half-ball steel reflector are presented. In addition, the measured sound beams of an application-specific 5 MHz multi-element transmit-receive (TR) probe using the 3 mm flat-bottomed-hole (FBH) reflector in a steel reference plate are discussed. Finally, the quantitative analysis of the measured sound field results and the acceptance criteria in accordance with DIN EN ISO 22232-2 are discussed.

Influence of cement and water content on the multifaceted capabilities of a self-sensing cement-based geocomposite: a comprehensive analysis

This study investigates the synergistic effects of cement, water, and hybrid carbon nanotubes/graphene nanoplatelets (CNT/GNP) concentrations on the mechanical, microstructural, durability, and piezoresistive properties of self-sensing cementitious geocomposites. Varied concentrations of cement (8% to 18%), water (8% to 16%), and CNT/GNP (0.1% to 0.34%, 1:1) were incorporated into cementitious stabilized sand (CSS). Mechanical characterization involved compression and flexural tests, while microstructural analysis utilized dry density, apparent porosity, water absorption, and non-destructive ultrasonic testing, alongside TGA, SEM, EDS, and x-ray diffraction analyses. The durability of the composite was also assessed against 180 Freeze-thaw cycles. Moreover, the piezoresistive behavior of the nano-reinforced CSS was analyzed during cyclic flexural and compressive loading using the four-probe method. The optimal carbon nanomaterials (CNM) content was found to depend on the water and cement ratios. Generally, elevating the water content led to a rise in the CNM optimal concentration, primarily attributed to improved dispersion and adequate water for the cement hydration process. The maximum increments in flexural and compressive strengths, compared to plain CSS, were significant, reaching up to approximately 30% for flexural strength and 41% for compressive strength, for the specimen containing 18% cement, 12% water, and 0.17% CNM. This improvement was attributed to the nanoparticles’ pore-filling function, acceleration of hydration, regulation of free water, and facilitation of crack-bridging mechanisms in the geocomposite. Further decreases in cement and water content adversely impacted the piezoresistive performance of the composite. Notably, specimens containing 8% cement (across all water content variations) and 10% cement (with 8% and 12% water content) showed a lack of piezoresistive responses. In contrast, specimens containing 14% and 18% cement displayed substantial sensitivity, evidenced by elevated gauge factors, under loading conditions.

Nondestructive quantification of internal raster path for additively manufactured components via ultrasonic testing.

This work investigates the viability of discerning the raster pattern of additively manufactured components using high frequency ultrasonic nondestructive testing. Test coupons were fabricated from poly cyclohexylenedimethylene terephthalate glycol using the fused filament fabrication process, in which layers were deposited at various predetermined raster angles. Each printed part was scanned using spherically focused, high-resolution, ultrasonic transducers of various peak frequencies between 7.5 and 15MHz. From the captured waveform data, images are extracted to observe the raster pattern in a layer-by-layer manner, with the results from the 10MHz element yielding the best performance. An in-house MATLAB script was developed to analyze the transducer signal to investigate C-scan images at various depths throughout the component. From the resulting C-scan images, one can consistently identify the proper raster orientation within 2°-4° in each of the first 10 deposited layers, with the accuracy decreasing as a function of depth into the component. Due to signal attenuation, there is insufficient data at depths beyond the 11th and 12th layer, to properly analyze the present data sets accurately. Validation was performed using X-ray computed tomography scans to demonstrate the accuracy of the ultrasonic inspection method.

Three-dimensional reconstruction of transverse hole defect in plate based on TOFD inspection

ABSTRACT In this paper, aluminium plate specimens with circular transverse hole defect was prepared, and the specimen was subjected to ultrasonic non-destructive testing using the TOFD (Time-of-Flight Diffraction) inspection method. Simultaneously, addressing the issue of three-dimensional reconstruction of defect within the field of ultrasonic non-destructive testing, a method combining the least squares approach and volumetric rendering was proposed to process the B-scan images obtained from TOFD inspection. This method was used to reconstruct the three-dimensional shape of transverse hole defect. The result shows that processing defect information acquired through TOFD inspection using the integrated approach of least squares and volumetric rendering leads to clear three-dimensional reconstruction images. This research offers an efficient method for the three-dimensional visualisation of transverse hole defect in plate.

Mechanical properties of recycled aggregate concrete containing brick particles

To investigate the mechanical properties of recycled aggregate concrete containing brick particles(RACB), compressive strength tests were conducted on RACBs with different water cement ratios and recycled fine aggregate substitution rates. The changes in compressive strength, elastic modulus, and peak strain of RACB with recycled fine aggregate substitution rates were analyzed, and a stress–strain equation was established. A damage model was established using ultrasonic nondestructive testing technology to reveal the damage mechanism of RACB. Results show that the basic mechanical properties of RACB reach the best when the replacement rate of recycled fine aggregate (r) is 30%. The model parameter a of the stress–strain curve equation is consistent with the change rule of elastic modulus with r. The model parameter b has a quadratic function relationship with r, reflecting the brittleness of RACB. The initial damage of RACB is relatively large, and the cracks penetrate the recycled coarse aggregate, and lead to specimen failure.

Air-coupled transducer tilted C-scan for delamination introduced during the manufacturing process in CFRP plates

ABSTRACT Carbon fibre reinforced polymers (CFRPs) have gained attention as viable substitutes for conventional metals and alloys in weight-sensitive applications like aerospace, primarily because of their outstanding strength-to-weight characteristics. Nevertheless, these materials are susceptible to intricate and challenging-to-anticipate sub-surface impairments, such as delamination after certain impacts. Non-destructive ultrasonic testing (NDT) is a widely employed technique for examining workpieces’ properties. Nonetheless, conventional ultrasonic testing faces significant constraints due to the necessity of physically coupling ultrasonic transducers to the test medium, typically involving substances like liquid and gel, which could cause unnecessary corrosion and pollution on composite materials. This study proposed a tilted non-contact C-scan detection on carbon composite plates with internal delamination based on air-coupled transducers (ACT). By introducing a tilted C-scan method, the subtle pre-fabricated internal impurities can be detected.

Ultrasonic non-destructive inspection method for glass fibre reinforcement polymer (GFRP) hull plates considering design and construction characteristics

The design and construction characteristics, including glass fibre weight fraction ( Gc), number of single-ply layers, fabric combination, and fabrication quality, of glass fibre reinforcement polymer (GFRP) hull plates affect ultrasound propagation characteristics, such as ultrasonic velocity and attenuation, thereby influencing the accuracy of ultrasonic non-destructive test results. Therefore, this study is to propose a method to decrease the ultrasonic test errors of GFRP hull plate by using statistical method. The GFRP specimens with Gc of approximately 30–50 wt%, thicknesses of approximately 5–20 mm, and different fabric combinations were prepared using the hand lay-up method, considering the general design–construction characteristics. Further, an ultrasonic velocity decision method for ultrasonic inspection was proposed considering the GFRP hull design-construction characteristics, such as Gc and number of single-ply layers of hull plate by multiple linear regression method. The results show that the proposed method can reduce the thickness measurement error from approximately 20%–30% to 1%–2%, compared to an existing ultrasonic inspection method, only considering the Gc effect on ultrasonic velocity, which indicates that the proposed test method is suitable for practical applications.

Mechanical properties of solid waste-based composite cementitious system enhanced by CO2 modification

Utilizing CO2 to modify solid waste and produce high-performance cementitious material is a promising strategy. In this study, circulating fluidized bed fly ash (CFBFA), calcium carbide slag (CS) and flue gas desulphurization gypsum (FGDG) were prepared by mixing CO2 to produce cementitious materials. The impacts of CO2 on mechanical properties and carbonation reaction mechanism of composite materials were investigated. The results shown that the microstructure and mechanical properties of the gelling materials were improved by CO2 modification. When the CO2 mass transfer conditions as followed: CO2 flow rate was 1.5 L/min, stirring rate at 600 r/min, and stirring time at 20 min, compressive strength of modified material was 22 % higher than that of the non-CO2 modified material. Additionally, the density increased by 3.2 %, and porosity was reduced by 34.1 %. Among them, TG/DTG analysis found that the highest effective fixed CO2 rate was 11.1 %. The ultrasonic nondestructive testing also shown that the structure of the CO2-modified cementitious material was significantly better than that of the CFBFA-CS-FGDG composite cementitious system, and the ultrasonic loss rate was reduced by 9.4 %. Therefore, the use of CO2 to modify the composite system was of great significance for the realization of CO2 storage and the improvement of the properties of composite materials. One interesting future possibility is solid waste-based grouting materials production at energy plants: CFBFA, CS and FGDG can be used to capture CO2 from flue gases, thus improving the strength of produced grouting materials.

Ultrasonic resonance evaluation method for deep interfacial debonding defects of multilayer adhesive bonded materials

Abstract Multilayer adhesive bonded structures/materials (MABS) are widely used as structural components, especially in the field of aerospace. However, for MABS workpieces, the facts that the weak echo of the deep interfacial debonding defects (DB) caused by the large acoustic attenuation coefficient of each layer and this echo, which generally aliases with the excitation wave and the backwall echo of the surface layer, pose a great challenge for the conventional longitudinal wave ultrasonic nondestructive testing methods. In this work, an ultrasonic resonance evaluation method for deep interfacial DBs of MABS is proposed based on the ultrasonic resonance theory and the aliasing effect of ultrasonic waves in MABS. Theoretical and simulation analysis show that the optimal inspection frequency for II-interfacial DBs is 500 kHz when the shell thickness is 1.5 mm and the ethylene propylene diene monomer (EPDM) thickness is 1.5 mm, and the optimal inspection frequency is 250 kHz when the shell thickness is 1.5 or 2.0 mm and the EPDM thickness is 2.0 mm. Verification experiments show that the presence of a DB in the II-interface causes a resonance effect, and in the same inspection configuration, the larger the defect size, the more pronounced this effect is. This resonance effect manifests itself as an increase in the amplitude and an increase in the vibration time of the A-scan signal as well as a pronounced change in the frequency of the received ultrasonic wave. In addition, the increase in the excitation voltage further highlights the ultrasonic resonance effect. Four imaging methods – the integrations of the signal and the signal envelope curve, the maximum amplitude of the fast Fourier transform (FFT) of the signal, and the signal energy – were used for C-scan imaging of ultrasonic resonance evaluation of MABS’s deep interfacial DBs and all these methods can clearly show the sizes and locations of the artificial defects and internal natural defect. The normalized C-scan imaging method proposed in this study can further highlight the weak changes in the signals in the C-scan image. The research results of this study have laid a solid theoretical and practical foundation for the ultrasonic resonance evaluation of MABS.

Implementing expansion force-based early warning in LiFePO4 batteries with various states of charge under thermal abuse scenarios

The characteristics of thermal runaway in batteries exhibit significant differences depending on their states of charge (SOCs), posing considerable challenges in accurate and timely warning for thermal runaway accidents. This paper conducts an experimental investigation into the external expansion force, voltage, and temperature behaviours of batteries under different SOCs under thermal abuse scenarios. The expansion force signal was found first to exhibit abnormal characteristics (with an indicator value of 5 N/s), offering an earlier warning signal >642 s prior to thermal runaway, when the battery back temperature is merely approximately 318.15 K. To analyse the main causes of abnormal expansion, ultrasonic nondestructive tests were performed and suggested that a higher SOC intensify the side reactions and cause gas generation inside batteries. Notably, compared to normal-charged batteries (0% ≤ SOC ≤ 100%), over-charged batteries (SOC > 100%) are more sensitive to expansion force than normal-charged batteries. Furthermore, compared with voltage and temperature signals, the early warning time of the expansion force rises with the increase in the SOC of an overcharged battery, in contrast to normal-charged batteries. Finally, a novel hazard classification safety warning strategy for battery failure is effectively proposed. These novel findings hold substantial practical implications for creating more accurate early warning systems for battery thermal runaway, enhancing the safe and reliable operation of battery systems.

Ultrasonic Non-Destructive Testing on Fast-Charging Lithium-Ion Battery’s Capacity Fading

Fast charging technology provides a solution to the issue of charging time for power supplies with long life requirements. However, it will shorten the charging period while also hastening the power battery’s capacity degradation, reducing its service life. The ultrasonic inspection technique has been widely used for the internal structure detection and reaction process characterisation of lithium-ion batteries because of its nondestructive testing properties. This paper presents a method for monitoring the capacity attenuation of a fast-charging battery by calculating the ultrasonic attenuation coefficient α. The experimental findings indicate that the battery’s capacity is more vulnerable to lithium plating during high-rate charging. The parameter α can be employed to illustrate the energy dissipation characteristics of sound as it propagates through the electrode. Moreover, the inhomogeneous ageing of battery electrode material is observed and quantified based on the differences in acoustic signals, which provides new insights into battery health management and uneven ageing assessment.

Early detection of steel tube welded joint failure using SPC-I nonlinear ultrasonic technique

Welding is a commonly used method for joining two or more parts together in steel construction. Various defects in weld regions such as cracks, pores, and slag inclusion can be present from the beginning, generated during the welding process, or can be developed while in service. Such defects are the weak spots that degrade the structure’s quality and can lead to structural failures. Therefore, early detection of these defects in welded joints, before visible cracks appear, is very important. Using appropriate ultrasonic non-destructive testing and evaluation (NDT&E) techniques, one can detect these defects and take remedial actions to prevent catastrophic structural failures. Guided acoustic wave-based techniques have been proven to be effective for damage detection in steel pipes and rods. Several studies have previously attempted to detect damage in steel tubes using guided ultrasonic waves. Unlike earlier attempts which mostly focused on conventional linear ultrasonic techniques, a relatively new nonlinear ultrasonic technique called sideband peak count-index (SPC-I) is carried out in this research. For this investigation, cast steel components and round hollow structural sections are welded together, and a four-point bending test is conducted under fatigue loading. The welded joints are continuously monitored in real time using strain gages and lead zirconate titanate (PZT) transducers. The PZT transducers are used to generate and receive guided acoustic waves. The signal is propagated through the specimen in a single-sided transmission mode setup. The strain gage readings and the nonlinear ultrasonic parameter, the SPC-I values, are monitored simultaneously. The results obtained from the nonlinear ultrasonic NDT&E measurements are compared with the data obtained from the strain gages to determine the robustness and reliability of the SPC-I technique for monitoring welded joints. This investigation also shows the potential effectiveness of the nonlinear ultrasonic parameter SPC-I for early detection of weld failure.

Study on freeze-thaw deterioration model of new-to-old concrete based on pore surface fractal characteristics

New-to-old concrete (NTOC) structures are widely used in engineering practice, the adhesive interface as a weak part is easily damaged under freeze-thaw environment. At present, most of NTOC deterioration models are grounded in the empirical summary of experiment data. In this paper, the bonding and durability of NTOC adhesive interface under different freeze-thaw cycles were investigated by splitting tensile test and ultrasonic nondestructive test, and the pore distribution characteristics of adhesive interface were obtained by mercury intrusion porosimetry. Based on the S-N equation and the constitutive relationship of damaged concrete, the phenomenological freeze-thaw damage model of NTOC was established. According to the fractal analysis of the effective bearing area of the pores, the freeze-thaw deterioration model of NTOC adhesive interface was further established, which was named PDM model. The splitting tensile strength (macroscopic mechanical properties) and ultrasonic wave velocity (microscopic defects) of the concrete repaired by four kinds of alkali activated slag-fly ash were used to verify PDM model. The results showed that PDM model could reflect the change of bonding properties and the defects of NTOC adhesive interface under freeze-thaw conditions. The microscopic pore evolution characteristics reflected the macroscopic mechanical properties. With a restricted number of monitoring sites, the PDM model could n forecast the changing trend of the whole freeze-thaw degradation process of NTOC.

Robust transport and topological valley refraction of fundamental symmetric lamb waves in perforated phononic crystal plates

Lamb waves can be divided into antisymmetric Lamb waves (type A) and symmetric Lamb waves (type S), which are widely used in health monitoring of engineering structures and nondestructive evaluation of materials. However, due to the fact that each mode of Lamb wave has the setting group velocity in a certain bandwidth range, it is easy to cause the aliasing of multi-mode Lamb waves, partly limiting the application scenarios of Lamb wave. In this paper, a hexagonal lattice meta-structure is designed and the zero-order symmetric (S0) Lamb wave in a finite thickness plate is successfully separated. By breaking the spatial C 3v symmetry, a valley topological phononic crystal (PnC) plate for the pure S0 mode is constructed, and its robust topological transports are demonstrated. Firstly, the valley topological phase transition of S0 mode is realized by changing the angle of scatterer in PnC plate and the valley edge state of S0 mode is obtained. Furthermore, by introducing structural mismatch, it is verified that the edge state of S0 mode is robust to various bends and defect. Finally, by changing the material property of the terminal, the valley refraction with different directionality is realized. The results offer a route to individually study the symmetric modes of Lamb waves, and have potential application prospects in rapid and accurate ultrasonic nondestructive testing based on Lamb waves.

Special Issue on Ultrasonic Modeling for Non-Destructive Testing

This Special Issue of Applied Sciences focuses on advancing modeling methods for the ultrasonic Non-destructive Testing (NDT) of materials [...]

A Novel Nondestructive Testing Probe Using AlN-Based Piezoelectric Micromachined Ultrasonic Transducers (PMUTs).

Ultrasonic nondestructive testing (NDT) usually utilizes conventional bulk piezoelectric transducers as transceivers. However, the complicated preparation and assembly process of bulk piezoelectric ceramics limits the development of NDT probes toward miniaturization and high frequency. In this paper, a 4.4 mm × 4.4 mm aluminum nitride (AlN) piezoelectric micromachined ultrasonic transducer (PMUT) array is designed, fabricated, characterized, and packaged for ultrasonic pulse-echo NDT of solids for the first time. The PMUT array is prepared based on the cavity silicon-on-insulator (CSOI) process and packaged using polyurethane (PU) material with acoustic properties similar to water. The fabricated PMUT array resonates at 2.183 MHz in air and at around 1.25 MHz after PU encapsulation. The bandwidth of the packaged PMUT receiver (244 kHz) is wider than that of a bulk piezoelectric transducer (179 kHz), which is good for axis resolution improvement. In this work, a hybrid ultrasonic NDT probe is designed using two packaged PMUT receivers and one 1.25 MHz bulk transmitter. The bulk transmitter radiates an ultrasonic wave into the sample, and the defect echo is received by two PMUT receivers. The 2D position of the defect could be figured out by time-of-flight (TOF) difference, and a 30 mm × 65 mm detection area is acquired. This work demonstrates the feasibility of applying AlN PMUTs to ultrasonic NDT of solids and paves the way toward a miniaturized NDT probe using AlN PMUT technology.

Quantitative ultrasonic imaging of weave structure in textile composites

Textile composites owe their desirable mechanical properties to the intricate fabric architecture. However, manufacturing deviations can influence these attributes, significantly affecting their mechanical performance. Thus, ensuring the quality and structural integrity of fabric architectures has become pivotal, leading to the advancement of ultrasonic non-destructive testing techniques. However, existing techniques, primarily tailored for unidirectional laminates, often struggle with weave pattern extraction, given the complex features of fabric laminates. To address this gap, a pulse-echo ultrasound coupled to a 2D analytic-signal analysis is proposed. The 2D analytic-signal methodology autonomously discerns the complex ultrasound features from fabric laminates, streamlining weave pattern analysis. The study showcases ply-by-ply reconstruction of local weave patterns of fabric laminates with nominal layups of [#(0/90)]8 and [#(+45/−45)#(0/90)]5s, respectively. The efficacy of the methodology is ascertained through quantitative metrics, highlighting its innovative potential for through-depth extraction of local weave patterns in a swift and automated manner.

Wide-bandwidth immersion ultrasound transducer made of Mn:PIMNT single crystal/epoxy 1–3 composite

The sensitivity and bandwidth of immersion ultrasound transducer directly determine the echo signal intensity and axial resolution of the immersion ultrasonic testing (IUT) equipment. The active piezoelectric material, which is the core part of the transducer, usually operates in a thickness-stretching vibrational mode. Hence, it is necessary for piezoelectric materials to possess high piezoelectric performance. In this work, a relaxor-based ferroelectric Mn:PIMNT single crystal with excellent electromechanical performance (d33=1220 pC/N, g33=37.87×10−3 Vm/N, and k33=90%) was used to fabricate a crystal/epoxy 1–3 composite transducer. The crystal-based transducer has a center frequency of 3 MHz. The −6 dB bandwidth is 111.4%, and the insertion loss is −25.2 dB, which are much better than PZT-5 H 1–3 composite transducer (74.5% and −32.9 dB). Additionally, the imaging test reveals that the 1–3 composite transducer made of Mn:PIMNT single crystal exhibits better axial resolution, which shows a good application prospect in the field of ultrasonic nondestructive testing.