Nondestructive Testing Applications Research Articles

Luminescent and scintillating properties of Tb3+-doped fluoroxide glasses

Scintillator can convert ionizing radiation of high-energy ray or particle into ultraviolet/visible light, which is extensively employed for baggage screening and non-destructive testing applications. In this paper, transparent Tb3+-doped fluoroxide glass scintillators were fabricated successfully by melting quenching technique. Tb3+-doped fluoroxide glass possesses commendable luminescent properties. The optimal sample (SACNY-3Tb) has a high transmittance (87.6%@542 nm) and a suitable lifetime (2.24 ms). In addition, SACNY-3Tb has good scintillating properties. The X-ray excited luminescent intensity of SACNY-3Tb is 130% of that of Bi4Ge3O12, and 18 lp/mm of imaging resolution for X-ray can be obtained. In conclusion, the Tb3+-doped fluoroxide glass scintillator possesses potential for use within the application of steady-state X-ray detection.

Textured ferroelectric ceramics based 1–3 piezoelectric composite for photoacoustic imaging

The quality of ultrasound and photoacoustic imaging primarily depends on the performance of piezoelectric transducer elements, which is closely related to the acoustic and electrical properties of piezoelectric materials. With the increasing demand for high-performance, low-cost piezoelectric materials, a high-temperature-resistant <001>-textured ferroelectric ceramic Pb(In1/2Nb1/2)O3-Pb(Sc1/2Nb1/2)O3-PbTiO3 (PIN-PSN-PT) has been developed. In recent years, low-cost textured ceramic materials have exhibited high piezoelectric constants (d33) and large electromechanical coupling coefficients (kt). In this study, an ultrasonic transducer based on PIN-PSN-PT textured ceramic was successfully manufactured for the first time. The transducer has a center frequency of 4.7 MHz, −6 dB bandwidth of 60 %, effective kt of 0.76, and two-way insertion loss (IL) of −34 dB. Photoacoustic imaging experiments on carbon fiber-reinforced polymer (CFRP) were conducted to evaluate the sensitivity and imaging quality of the transducer. The results indicate that the use of PIN-PSN-PT textured ceramics holds great potential in developing acoustic sensors for photoacoustic non-destructive testing applications.

Novel fast full-wavefield modeling of air-coupled surface waves and its implications for non-contact pavement testing

We present a novel approach for deriving and modeling air-coupled surface waves with applications in non-contact non-destructive testing (NDT). It is based on the fast Fourier-Bessel series system in conjunction with the unconditionally stable dual-variable and position matrix method. Parametric studies, including sensitivity analysis, are conducted to assess the feasibility of using non-contact air-coupled measurements for pavement testing, focusing on Green's functions, time-domain waveforms, and experimental frequency-velocity spectra (FVS, i.e., the estimated Green's functions from acquired truncated wavefield). The predicted experimental FVS presented in this study are synthetic dispersion images, which are distinguished from the measured experimental FVS (i.e., measured dispersion images from multichannel analysis of surface wave (MASW) test). With the derived complete solution of air-coupled dynamic responses, we find that: (1) Striking similarities between the theoretical Green's functions of vertical displacement (on the pavement surface) and pressure (in the air), as well as in their corresponding experimental FVS. (2) The proposed accurate and efficient full-wave modeling of air-coupled surface waves avoids the need for good contact between geophones/accelerometers and pavement surface. This facilitates direct inversion of shear wave velocity profiles by fitting the predicted experimental FVS to the measured one. (3) Sensitivity analysis demonstrates no significant loss of information in the pressure measured in the air, supporting the feasibility of using non-contact measurement for non-destructive testing. These results suggest that non-contact air-coupled measurements hold great promise as a viable alternative to contact measurements in non-destructive testing.

On the use of phase laws for the Linear Sampling Method in an elastic waveguide. Application to nondestructive testing

This paper presents the use of phased array data as the input of the Linear Sampling Method for elastic waveguides. Indeed, this method enables the high frequency, hence high resolution, inspection of waveguides, which is of interest for example for nondestructive testing applications. However, the use of single emitter data, also known as Full Matrix Capture in the Non Destructive Testing (NDT) context, leads to poor signal to noise ratios as low amplitude signals are emitted and only a fraction of the energy reaches the potential defect. The use of phase laws, that is the simultaneous emission with multiple sensors, enables better signal to noise ratios. However, the drawback may be a loss on the conditioning of the method, which may lead to higher sensitivity to noise in the end. This paper shows how to choose the sensors and the phase laws to obtain a satisfactory imaging results. This is exemplified on experimental data acquired in a steel plate with a circular hole.

Reflection Measurement of the Scattering Mean Free Path at the Onset of Multiple Scattering.

Multiple scattering of waves presents challenges for imaging complex media but offers potential for their characterization. Its onset is actually governed by the scattering mean free path ℓ_{s} that provides crucial information on the medium microarchitecture. Here, we introduce a reflection matrix method designed to estimate this parameter from the time decay of the single scattering rate. Our method is first validated by an ultrasound experiment on a tissue-mimicking phantom before being applied invivo to a human liver. This Letter opens important perspectives for quantitative imaging of heterogeneous media with waves, whether it be for nondestructive testing, biomedical, or geophysical applications.

Friction-Induced Near-Infrared Emission and Its Mechanism.

Triboluminescence (TL) is an optical phenomenon in which light is emitted from the surface of a material when subjected to pressure or shear forces. Due to its potential applications in non-destructive testing, radiation sources, and spectroscopic probes, TL has garnered increasing attention over the past two decades. However, experimental observations in the infrared spectrum remain limited, and its emission mechanism has not yet been fully understood. In this study, significant emission in the near-infrared spectrum was experimentally observed from the tribo-pairs of Cr/YSZ and quartz/YSZ. The results indicate that the Tribo-Induced Near-Infrared Light Emission consists of three peaks, in which the 780 nm peak is related to the electronic transition between the 3d5/2 and 3d3/2 orbitals of Y3+ ions, while the 880 nm and 990 nm peaks can be attributed to hole centers and T-type centers in the intrinsic defects of YSZ, respectively. Additionally, experiments reveal that the Cr/YSZ tribo-pair exhibits a redshift of 11-18 nm at the 780 nm peak compared to the quartz/YSZ tribo-pair. To explain the cause of the redshift phenomenon, X-ray photoelectron spectroscopy and UV-Vis absorption spectroscopy were used to measure the energy level spacing between the 3d5/2 and 3d3/2 orbitals of Y3+ and the bandgap width of YSZ before and after friction, respectively. We found that the bandgap width of the doped YSZ decreases after friction, which is often accompanied by a reduction in the energy level spacing between the 3d5/2 and 3d3/2 orbitals of Y3+. The extent of the reduction in energy level spacing varies with different dopants, leading to the redshift phenomenon.

Sub-THz and THz Cherenkov radiation source with two-dimensional periodic surface lattice and multistage depressed collector

We present the theory, concept and design of an efficient, megawatt coherent Cherenkov radiation source based on a two-dimensional periodic surface lattice (2D-PSL) cavity combined with a novel energy recovery system for the generation of highly efficient (> 50%) single-frequency radiation. We demonstrate the scalability of the transverse dimension of the 2D-PSL cavity of the Cherenkov source and thus the potential for efficient, continuous-wave, high-power (> 1 MW) operation; fundamental to the eventual realization of clean, fusion energy. These new sources, with the capacity to operate in the 0.1-10THz range, hold strong promise to address the long-standing “Terahertz gap”. By combining a Cherenkov oscillator driven by a non-gyrating beam with an innovative four-stage depressed collector energy recovery system, the overall device efficiency can be increased to be competitive with gyrotrons in the requirements for heating and current drive in fusion plasma. In these Cherenkov devices, the frequency independence of the magnetic guide field enables advantageous frequency scaling without deployment constraints, making them especially attractive for high-impact applications in fusion science, turbulence diagnostics, non-destructive testing and biochemical spectroscopy. The novel energy recovery techniques presented in this paper have broad applicability to many electron-beam driven devices, bringing revolutionary potential to future THz source technologies.

A self-iterative learning with dual attention mechanism fusion method for pumpkin seed quality equipment

To perform fast and accurate classification of pumpkin seeds, three batches of pumpkin seed images were taken. A self-iterative learning large kernel attention-Squeeze and Excitation-Residual Network34 (LKA-SE-ResNet34) model was proposed by adding dual attention mechanism fusion of large kernal attention (LKA) mechanism and Squeeze and Excitation (SE) attention mechanism to each residual module of ResNet34 for recognizing pumpkin seeds. ResNet34 network model was chosen as the basic framework by comparing GoogleNet, AlexNet, EfficientNet, MobileNet, DenseNet, ResNet34 and Residual Network50 (ResNet50) deep learning network models. The comparation result showed that the top two models with the highest accuracy (Acc) are ResNet50 network model and ResNet34 network model among the compared models. The experimental results showed that the self-iterative learning LKA-SE-ResNet34 model outperformed the above-mentioned other network models in pumpkin seed recognition with an accuracy of 91.8%. To further validate the effectiveness of the proposed model for small sample size of data, two-sided images and deformed images of pumpkin seeds were collected and used, and the experimental results still proved that the proposed model had good generalization ability and accuracy, with the accuracies of 93.63% and 94.15% for two sides of pumpkin seeds as well as an accuracy of 99.03% for deformed pumpkin seeds. A set of seed sorting machine and an application (APP) for non-destructive testing of seeds were initially developed.

Generating sub-diffraction microwave needle beam for nondestructive testing by multifunctional transmissive metasurfaces

Sub-diffraction needle beams with high intensity, sub-diffraction focal size, and long depth of focus (DOF) have attracted many researchers’ attention. However, the traditional methods for needle beam generation typically require many devices, such as phase elements, amplitude filters, and lens, which leads to a complex and bulky system and unfavorable for their integration. To address these challenges, we use a single multifunctional transmissive metasurface to convert a linearly polarized plane wave into a needle beam in the microwave range. The guided wave inspired unit cells of the proposed metasurface is designed to simultaneously and independently modulate the polarization and phase of transmitted waves. By imposing the desired polarization and phase distributions on the metasurface, the proposed multifunctional transmissive metasurface can efficiently generate a needle beam with subdiffraction size and extended DOF at 10 GHz when it is illuminated by an x-polarized wave. The proposed metasurface is fabricated, and a sub-diffraction needle beam with good performance is obtained in our measurements. In addition, a proof-of-concept of a high-resolution nondestructive testing experiment based on our designed metasurface is accomplished. Our work is expected to have potential applications in nondestructive testing of materials and structures.

Tailoring the Microstructure and Porosity of Porous Piezoelectric Ceramics for Ultrasonic Transducer Application.

Porous piezoelectric ceramics and composites are advantageous for ultrasonic transducers due to their capability to decouple longitudinal and transverse modes, their improved voltage sensitivity, and their enhanced acoustic matching. However, the design and fabrication of porous piezoelectric ultrasonic transducers with excellent electromechanical properties are still challenging. In this work, porous lead zirconate titanate (PZT) ceramics with an aligned pore structure were prepared using the freeze-cast technique, and the effect of porous structure and porosity on the electromechanical parameters was investigated. The introduction of an aligned pore structure is beneficial to enhance the electromechanical properties and reduce the acoustic impedance. A high d33 (∼530 pC/N), a higher kt (∼0.676), and a lower acoustic impedance (∼10.4 MRalys) were achieved in the porous PZT ceramic with the porosity of 44 vol %. The effect of porosity and pore structure on the decoupling degree of vibration modes and ferroelectric polarization was considered to correct the homogeneous medium model, which can quantify the relationship between the kt and porosity of the porous structure. A demonstration of a piezoelectric ultrasonic transducer based on freeze-cast porous PZT ceramics was presented, which exhibits a -6 dB bandwidth of 52% and a theoretical axial resolution of 520 μm. This work therefore provides a potential alternative of piezoelectric ultrasonic transducers for nondestructive testing and imaging applications.

Evaluation of Physico-Static and Dynamic Elastic Properties of Eucalyptus pellita in Various Thinning Intensities

Acoustic velocity (AV) offers a non-destructive means of reliably measuring wood properties, presenting a valuable alternative to the traditional method known for its destructiveness, costliness, and time consumption. This technique is widely used in the timber industry to predict the bending strength of standing trees and logs. Hence, a study was conducted to assess the dynamic and static elastic properties of Eucalyptus pellita in various thinning intensities using the AV technique and laboratory testing. The selected 11-year-old E. pellita wood was obtained from thinning trials in Sabah Softwood Berhad, Brumas, Sabah. This investigation collected samples from three distinct thinning intensities (0%, 40%, and 60%). Dynamic modulus of elasticity (MOE), which relies on the time of flight (TOF) principle, was measured using an acoustic velocity approach, and physical and static testing was conducted according to standard ISO 13061. Results from this study show that thinning treatments significantly affect the physical and mechanical properties of E. pellita. The study also found that the static modulus of elasticity (MOE) value may be predicted using the acoustic velocity approach, with R2 = 0.46, R2 = 0.60, and R2 = 0.53 on standing trees, billets, and wood slabs, respectively. The application of non-destructive tests in forest plantations can help the foresters assess the wood properties efficiently, and specific parameters can be measured on a tree stand without falling the tree. Besides, thinning at a moderate intensity also helped to enhance the mechanical properties and dynamic MOE value of the E. pellita wood.

Debonding of piezoelectric transducers for residue-free ultrasonic non-destructive testing

ABSTRACT Components made of fibre-reinforced polymers (FRP) are prone to different types of damages such as delamination or matrix cracks, which can be critical for a component’s functionality. In classical ultrasonic nondestructive testing (NDT), lamb waves (LW) are frequently used to detect imperfections due to their favourable propagation characteristics over long distances. The LW are often excited by piezoelectric transducers, which are either bonded onto the component’s surface using comparatively stiff adhesives so to ensure loss-free LW coupling into the component or laminated directly into the FRP. In both cases the a priori nonseparable connection between the transducer and the substrate may itself be considered a defect when the component is put into service. In addition, laminating the transducers directly into the matrix is accompanied by both additional production effort and corresponding effects on thermomechanical component properties. To provide a cost-effective solution for NDT applications, the study focused on the development of a residue-free bonding concept for piezoelectric transducers. To this end, a total of three application approaches involving 14 commercially available adhesives and one dilatant material were investigated in different rounds of experimental testing. During the scientific campaign, the authors finally identified an adhesive that guarantees both lossless ultrasonic coupling and residue-free bonding, paving the way for much more process control and reusage of tested components for future NDT processes.

Eddy Currents Probe Design for NDT Applications: A Review.

Eddy current testing (ECT) is a crucial non-destructive testing (NDT) technique extensively used across various industries to detect surface and sub-surface defects in conductive materials. This review explores the latest advancements and methodologies in the design of eddy current probes, emphasizing their application in diverse industrial contexts such as aerospace, automotive, energy, and electronics. It explores the fundamental principles of ECT, examining how eddy currents interact with material defects to provide valuable insights into material integrity. The integration of numerical simulations, particularly through the Finite Element Method (FEM), has emerged as a transformative approach, enabling the precise modeling of electromagnetic interactions and optimizing probe configurations. Innovative probe designs, including multiple coil configurations, have significantly enhanced defect detection capabilities. Despite these advancements, challenges remain, particularly in calibration and sensitivity to environmental conditions. This comprehensive overview highlights the evolving landscape of ECT probe design, aiming to provide researchers and practitioners with a detailed understanding of current trends in this dynamic field.

Improvement of luminescence properties in Zn2.1Mg0.9Ta2O8:Cr3+ by the cation substitution and its application in biological nondestructive testing and night vision lighting.

Recently, it is of great significance to explore near-infrared (NIR) phosphor with more application prospects. In this work, a series of Zn2.1 Mg(0.9 - y)GaySnyTa(2 - y)O8:0.003Cr3+ NIR broadband phosphors with high quantum yields and high thermal stability are discovered by uniquely replacing [Mg2+-Ta5+] in Zn2.1Mg0.9Ta2O8 with [Ga3+-Sn4+]. Under 460 nm excitation, Zn2.1Mg0.85Ga0.05Sn0.05Ta1.95O8: 0.003Cr3+ depicts the 600-1100 nm broadband emission with a full-width at half maximum (FWHM) of 210 nm, and the quantum yields can reach 61.2%. Finally, the phosphor was mixed with epoxy resin and encapsulated in a 460 nm blue light emitting diode (LED) chip to convert the NIR LED by phosphor (NIR pc-LED), which was applied in the field of biological nondestructive testing and night vision lighting.

Robust elastic wave sensing system with disordered metasurface and deep learning

Elastic wave sensing is a crucial information acquisition technology with extensive applications in structural health monitoring, nondestructive testing, and other fields. However, traditional elastic wave sensing systems face challenges such as poor performance, high power consumption, and limited adaptability in complex environments. Here, a robust elastic wave sensing system integrating disordered metasurface and deep learning is demonstrated, enhancing the sensing performance in the environments with harsh noise or unknown signals. The scheme fully utilizes the complementary advantages of disordered metasurface and deep learning in physical encoding and intelligent decoding respectively. The meticulously designed disordered metasurface efficiently encodes elastic waves, and a single sensor acquires the encoding signals, enabling low-power information acquisition. The deep learning model performs adaptive and rapid intelligent decoding of the encoding signals, achieving efficient and robust information sensing while overcoming the sensing limitations of traditional compressed sensing in complex scenarios with low SNR and unknown signals. A series of experimental results demonstrate that, even under severe noise interference (known signal SNR≥−15dB, unknown signal SNR≥−7dB), the system can sense location information in elastic waves with a millisecond-level sensing speed and an accuracy above 90%. Furthermore, the successful application of the sensing system in vibration-tracking imaging and mechanical reading–writing further validates its practicability and robustness. This work may open up new avenues for the potential application of intelligent sensing in the fields of structural health monitoring, nondestructive testing, and human–machine interaction.

The numerical reconstruction methods for characterizing defects by full matrix data using an ultrasonic array

Abstract This study introduces ultrasonic imaging and inversion methods for the quantitative characterization of crack defects. The Total Focusing Method (TFM) is a high-precision ultrasonic imaging method, but it may produce length errors when used for large-angle defect detection. An SV transverse wave TFM method is introduced, significantly reducing length errors in a 60° crack to 8.31%. However, the ultrasonic image method is influenced by factors like array position, limiting its practicality. To overcome this limitation, the study proposes an inversion method using the subarray scattering coefficient matrix, which is more stable and less sensitive to array positioning. Comparative analysis with finite element simulations and experiments indicates optimal array positions associated with different methods. At these positions, both methods yield angular characterization errors for the 60° crack of less than 1%, validating the proposed techniques for non-destructive testing applications.

Strategy to optimize the broadband near-infrared emission based on Eu2+-doped sulfureted garnet phosphors toward emerging spectroscopy applications

Eu2+-doped near-infrared (NIR) emitting phosphors, known for their high efficiency, broadband emission and spectral tunability, have gained much attention. However, achieving efficient NIR emission based on Eu2+ remains a challenge due to the co-existence of Eu3+, especially in materials (i.e. garnets and apatites) containing trivalent lanthanide cations. In this study, a Eu2+ doped sulfureted NIR-emitting garnet phosphor Ca3(Sc, Eu)2Si3(O, S)12: Eu2+ is successfully designed and synthesized. Notably, a strategy for regulating the initial valence state of dopants is proposed by using prepared EuS instead of the conventional Eu2O3 as raw material, enhancing the NIR emission by 135 %. Moreover, a sulfuration strategy is further introduced to enhance the NIR-emitting intensity and internal quantum efficiency by 192 % and 167.8 %, and to improve thermal stability by 154 % at 120 °C. The luminescence origin of the unusual broadband NIR emission is re-examined through chemical unit co-substitution strategy by introducing [Al3+Hf4+] to replace [Sc3+Si4+] ion pairs. Meanwhile, the spectral regulation and the performance optimization mechanism are systematically discussed. Finally, a green light pumped NIR LED device with a photoelectric efficiency of 9.43 %@100 mA and output power of 22.74 mW@100 mA is fabricated, showing remarkable potential in nondestructive testing and biomedical imaging applications.

Air-coupled ultrasound using broadband shock waves from piezoelectric spark igniters

We used an optomechanical sensor to study the ultrasound generated by manually operated piezoelectric spark igniters. These low-energy sparks produce short-duration acoustic shock-wave pulses, with sub-microsecond rise times and frequency content extending well beyond 2 MHz in air. The same source–receiver combination was then used to demonstrate broadband characterization of solid (polymer and glass) plates in a simple setup, where single spark events yielded high signal-to-noise ratio data without the need for critical alignment. This setup also enabled us to estimate pressure excursions approaching 105 Pa at millimeter-scale distances from the spark. The results are in large part made possible by the small size, wide bandwidth, and high sensitivity of the optomechanical sensor and might be of interest for air-coupled ultrasound applications in nondestructive testing.

Terahertz super-resolution imaging with large depth of field enabled by the terajet of bilayer dielectric spheres.

Terahertz imaging has found extensive applications in non-destructive testing, security inspection, and other various fields. Intensive research on terahertz imaging systems has been executed to pursue high performance on imaging resolution and depth of field (DOF). However, the terahertz imaging systems with both high imaging resolution and large DOF have rarely been reported. In this paper, a mesoscopic-sized dielectric bilayer sphere-assisted super-resolution imaging method was proposed to simultaneously achieve enormously improved imaging resolution and extended DOF. Simulation analyses revealed that the ultrathin and long terajets were generated by the well-designed bilayer sphere. The THz super-resolution image for the samples can be captured by the point-by-point terajet scanning. The experimental results demonstrated that the best resolution reached up to 0.4λ, the DOF with super-resolution was up to 2λ, and the DOF with sub-wavelength resolution was up to 4λ. This method holds great potential for widespread application in terahertz imaging and detection, especially for curved or complex sample structures.

Broad bandwidth and excellent thermal stability in BiScO3-PbTiO3 high-temperature ultrasonic transducer for non-destructive testing

High-temperature ultrasonic transducer (HTUT) is essential for non-destructive testing (NDT) in harsh environments. In this paper, a HTUT based on BiScO3-PbTiO3 (BS-PT) piezoelectric ceramics was developed, and the effect of different backing layers on its bandwidth were analyzed. The HTUT demonstrates a broad bandwidth and excellent thermal stability with operation temperature up to 400 °C. By using a 10 mm thick porous alumina backing layer, the HTUT achieves a broad −6 dB bandwidth of 100 %, which is about 4 times superior to the transducer with an air backing layer. The center frequency (fc) of the HTUT remains stable with fluctuations of less than 10 % across the temperature range from room temperature to 400 °C. The HTUT successfully detected simulated defects in pulse-echo mode for NDT over 200 °C. This research not only advances high-temperature ultrasonic transducer technology but also expands the NDT applications in harsh environmental conditions.