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Transcranial ultrasound therapy has become a non-invasive method for treating neurological and psychiatric disorders, and studies have further demonstrated that multi-target transcranial ultrasound therapy is a better solution. At present, multi-target transcranial ultrasound therapy in small animals can only be achieved by the multi-transducer or phased array. However, multiple transducers may cause spatial interference, and the phased array system is complicated, expensive, and especially unsuitable for small animals. This study is the first to design and fabricate a miniature acoustic holography lens for multi-target transcranial ultrasound therapy in rats. The acoustic holographic lens, working at a frequency of 1.0 MHz, with a size of 10.08 mm × 10.08 mm and a pixel resolution of 0.72 mm, was designed, optimized, and fabricated. The dual-focus transcranial ultrasound generated based on the lens was measured; the full width at half maximum (FWHM) of the focal spots in y-direction were 2.15 and 2.27 mm, respectively, and in z-direction were 2.3 and 2.36 mm, respectively. The focal length was 5.4 mm, and the distance between the two focuses was 5.6 mm, close to the desired values of 5.4 mm and 6.0 mm, respectively. Finally, the multiple-target blood-brain barrier opening in rats' bilateral secondary visual cortex (mediolateral area, V2ML) was demonstrated using the transcranial ultrasound therapy system based on the lens. These results demonstrate the good performance of the multi-target transcranial ultrasound therapy system for small animals, including high spatial resolution, small size, and low cost.

Objective. Exhaustion of Serotonin (5-hydroxytryptamine, 5-HT) is a typical cause of the depression disorder’s development and progression, including depression-like behaviors. Transcranial ultrasound stimulation (TUS) is an emerging non-invasive neuromodulation technique treating various neurodegenerative diseases. This study aims to investigate whether TUS ameliorates depression-like behaviors by restoring 5-HT levels. Methods. The depression model mice are established by chronic restraint stress (CRS). Ultrasound waves (FF = 1.1 MHz, PRF = 1000 Hz, TBD = 0.5 ms, SD = 1 s, ISI = 1 s, and DC = 50%) were delivered into the dorsal raphe nucleus (DRN) for 30 min per day for 2 weeks. Depression-like behavior changes are evaluated with the sucrose preference and tail suspension tests. Liquid chromatography–mass spectrometry is performed to quantitatively detect the concentration of 5-HT in the DRN to explore its potential mechanism. The effectiveness and safety of TUS were assessed by c-Fos immunofluorescence and hematoxylin and eosin (HE) staining, respectively. Results. Three weeks after CRS, 22 depressive mice models were screened by sucrose preference index (SPI). After 2 weeks of ultrasound stimulation of the DRN (DRN-TUS) in depressive mice, the SPI was increased (p = 0.1527) and the tail suspension immobility duration was significantly decreased (p = 0.0038) compared with the non-stimulated group. In addition, TUS significantly enhances the c-Fos (p = 0.05) positive cells’ expression and the 5-HT level (p = 0.0079) in the DRN. Importantly, HE staining shows no brain tissue damage. Conclusion. These results indicate that DRN-TUS has safely and effectively improved depression-like behaviors including anhedonia and hopelessness, potentially by reversing the depletion of 5-TH. Significance TUS may provide a new perspective on depression therapy, possibly through restoring monoamine levels.

Objective. Ultrasound neuromodulation has become an emerging method for the therapy of neurodegenerative and psychiatric diseases. The phased array ultrasonic transducer enables multi-target ultrasound neuromodulation in small animals, but the relatively large size and mass and the thick cables of the array limit the free movement of small animals. Furthermore, spatial interference may occur during multi-target ultrasound brain stimulation with multiple micro transducers. Approach. In this study, we developed a miniature power ultrasound transducer and used the virtual source time inversion method and 3D printing technology to design, optimize, and manufacture the acoustic holographic lens to construct a multi-target ultrasound neuromodulation system for free-moving mice. The feasibility of the system was verified by in vitro transcranial ultrasound field measurements, in vivo dual-target blood-brain barrier (BBB) opening experiments, and in vivo dual-target ultrasound neuromodulation experiments. Main results. The developed miniature transducer had a diameter of 4.0 mm, a center frequency of 1.1 MHz, and a weight of 1.25 g. The developed miniature acoustic holographic lens had a weight of 0.019 g to generate dual-focus transcranial ultrasound. The ultrasonic field measurements’ results showed that the bifocal’s horizontal distance was 3.0 mm, the −6 dB focal spot width in the x-direction was 2.5 and 2.25 mm, and 2.12 and 2.24 mm in the y-direction. Finally, the in vivo experimental results showed that the system could achieve dual-target BBB opening and ultrasound neuromodulation in freely-moving mice. Significance. The ultrasonic neuromodulation system based on a miniature single-element transducer and the miniature acoustic holographic lens could achieve dual-target neuromodulation in awake small animals, which is expected to be applied to the research of non-invasive dual-target ultrasonic treatment of brain diseases in awake small animals.

Selective laser melting (SLM) technology can rapidly form metal parts with complex geometry, but the internal microstructure and material properties are significantly different from those of traditionally manufactured parts, such as obvious anisotropy and inhomogeneity. This paper proposed a tri-mode ultrasonic system to nondestructively measure the anisotropic elastic constants of 316L stainless steel prepared by SLM. Firstly, the quantitative relationship between ultrasonic wave velocities and anisotropic elastic constants was derived for elliptical anisotropic materials. The anisotropic elastic constants and Thomsen anisotropic parameters can be determined by measuring four ultrasonic wave velocities V 11 , V 33 , V 12 , and V 13 . Therefore, a tri-mode ultrasonic transducer was designed and fabricated to build the elastic constant ultrasonic measurement system. Then, the elastic constants and Thomsen anisotropic parameters of SLM samples were measured, and the key process parameters’ influence was discussed. The standard static tensile test validated the result of the ultrasonic test, and the maximum relative error was 6.94%. This study will provide a novel nondestructive measurement method and system of anisotropic elastic constants to ensure internal quality and improve the additive manufacturing process.

Ultrasonic is one of the well-known methods for surface roughness measurement, but small roughness will only lead to a subtle variation of transmission or reflection. To explore sensitive techniques for surfaces with small roughness, nonlinear ultrasonic measurement in through-transmission and pulse-echo modes was proposed and studied based on an effective unit-cell finite element (FE) model. Higher harmonic generation in solids was realized by applying the Murnaghan hyperelastic material model. This FE model was verified by comparing the absolute value of the nonlinearity parameter with the analytical solution. Then, random surfaces with different roughness values ranging from 0 μm to 200 μm were repeatedly generated and studied in the two modes. The through-transmission mode is very suitable to measure the surfaces with roughness as small as 3% of the wavelength. The pulse-echo mode is sensitive and effective to measure the surface roughness ranging from 0.78% to 5.47% of the wavelength. This study offers a potential nondestructive testing and monitoring method for the interfaces or inner surfaces of the in-service structures.

The piezoelectric materials, such as ceramics, crystals, and films, have wide applications in the mechanical industry, medical imaging, electronic information, and ultrasonic devices, etc. Generally, adding oxide dopants, or introducing new solid solutions to form the morphotropic phase boundary of the piezoelectric materials were common strategies to enhance the electric properties. In recent decades, rare-earth elements doped piezoelectric materials have attracted much attention due to their multifunctional performances combining piezoelectric and photoluminescence properties, which has potential applications in ultrasonics, electronics, automatic control, machinery and optoelectronic fields. An overview of the recent investigations and perspectives on rare-earth doped piezoelectric ceramics, single crystals, and films were presented.

Elevator wire ropes with polymer cores hold and hoist heavy fluctuating loads in a corrosive environment. Such working condition causes metal fatigue, which together with abrasion around pulleys leads to progressive loss of the metallic cross section. This can be seen in the forms of a roughened and pitted surface of the ropes, reduction in diameter, and broken wires. Therefore, their deterioration must be monitored so that any unexpected damage or corrosion can be detected before it causes a fatal accident. Ultrasonic-guided wave-based inspection, which has proved its capability in nondestructive testing of platelike structures such as tubes and pipes, can monitor the cross section of wire ropes in their entire length from a single point. However, guided waves have drawn less attention for defect detection purposes in wire ropes. This article reports the condition monitoring of a steel wire rope from a hoisting elevator with broken wires as a result of corrosive environment and fatigue. Finite element analysis was conducted as a baseline to study guided wave propagation in wire ropes and plot dispersion curves. Guided wave propagation in wire ropes was experimentally investigated on a newly built cable stretching machine equipped with a load sensor under different amount of tensile loading. To expose the indication of broken wires, the recorded signals were analyzed by tailor-made continuous wavelet transform called tone burst wavelet.

Graphical abstract, Highlights • The influencing mechanism of ultrasound on the size of Cu nanoparticles is studied. • The mean size and size dispersion are significantly reduced ultrasound treatment. • A competition model between surface energy and ultrasonic force is proposed. • An exponential relation of between particle size and ultrasonic power is revealed. • Ultrasonic power and surface energy are keys to control the final particle size., Ultrasonic treatment is an effective method for size refinement and dispersion of nanomaterials during their synthesis process. However, the quantitative relationship between ultrasonic conditions and particle size in the synthesis of metal nanoparticles has not been fully revealed. In this study, Cu nanoparticles were synthesized via the wet-chemical redox method under ultrasonic treatment, and statistical analysis on the evolution of particle size distribution was carried out. It was found that the particle size decreased exponentially with increasing ultrasonic power. A quantitative model was then proposed to describe the influence of ultrasonic power on the size distribution of metal nanoparticles from the perspective of the competition between the surface energy and the ultrasonic force. A relational expression of Rc∝γ47P-37 was revealed, and it was proved to fit well with the experimental results. Our study provides new experimental basis and theoretical method for understanding the mechanism of ultrasonic-induced size refinement of metal nanoparticles.

The excellent performance of PMN–PT has received increasing attention and applications in high-frequency (>20 MHz) ultrasonic array transducers. However, due to its brittleness and low phase-transition temperature of PMN–PT, a decrease of piezoelectric properties in the fabrication of small-scale array elements is still an urgent problem and would substantially determine the performance of transducers. Here, in this study, ultrashort pulse laser technique is proposed to fabricate PMN–PT array transducers with outstanding performance. The effect of the laser parameters on domain structures has been studied systematically, and it was found that the ultrahigh piezoelectric properties of micro-sized elements still maintained after optimizing the laser parameters. A Fresnel array transducer with center frequency of 40.84 MHz and −6dB bandwidth as high as 122.28% was also designed and fabricated. This work demonstrates that it is feasible and promising to fabricate superior PMN–PT and other piezoelectric ultrasonic array transducers based on ultrashort pulse laser techniques.

A decrease of piezoelectric properties in the fabrication of ultra-small Pb(Mg1/3Nb2/3)–x%PbTiO3 (PMN–x%PT) for high-frequency (>20 MHz) ultrasonic array transducers remains an urgent problem. Here, PMN–31%PT with micron-sized kerfs and high piezoelectric performance was micromachined using a 355 nm laser. We studied the kerf profile as a function of laser parameters, revealing that micron-sized kerfs with designated profiles and fewer micro-cracks can be obtained by optimizing the laser parameters. The domain morphology of micromachined PMN–31%PT was thoroughly analyzed to validate the superior piezoelectric performance maintained near the kerfs. A high piezoresponse of the samples after micromachining was also successfully demonstrated by determining the effective piezoelectric coefficient (d33*~1200 pm/V). Our results are promising for fabricating superior PMN–31%PT and other piezoelectric high-frequency (>20 MHz) ultrasonic array transducers.

Defect inspection of braided carbon fiber reinforced polymer (CFRP) is very difficult due to its nonhomogeneity, anisotropy, and sensitivity to coupling agents. This paper presents a hybrid system for detecting microstructure and defects in braided CFRP that combines the advantages of laser-ultrasound and air-coupled ultrasonic testing . Through the finite element method, the ultrasonic field propagating on the braided CFRP was simulated during the laser-induced ultrasound, and the influences of laser parameters and surface braided structure were analyzed on the laser ultrasonic signal. This detection method based on air-coupled laser ultrasound can provide the near-surface microstructure characterization of the resin pockets and braided fiber bundles, and also can achieve both shallow and deep defect detection of CFRP sheets which is comparable to that of the contact-type high-frequency phased array with higher contrast and less distortion. These results indicate that it has the potential to develop a non-contact, high-resolution, and low-cost method for the detection and repairment of advanced composite materials.

Fiber Bragg gratings (FBGs) have being seen for a growing application in the field of structural health monitoring (SHM) because of their lightweight features. This letter introduces an adaptive SHM sensing system based on the ultrasonic guided wave (UGW) and FBG sensor technology. First, the capability of the proposed SHM sensing system used to detect UGW is demonstrated by the frequency detection of Rayleigh wave that is generated by the piezoelectric transducers with a function generator. Furthermore, a nanosecond pulse laser is utilized to generate Lamb wave on an aluminum plate, while the SHM sensing system is employed to detect the wave in a long distance. Finally, the SHM sensing system is used to locate the source of Rayleigh wave that is created by a pulsed laser. The experiment results show the proposed SHM sensing system is capable of localizing and monitoring the UGW by using four FBG cascaded on a loaded aluminum plate.

The excitation and propagation of an electromagnetic field is a very complex problem in Stratified conductive structures (SCS) because of their complicated physical properties. In single air-cored coil above multilayered conductive structures, the impedance of an eddy-current coil is calculated based on the electromagnetic field. This paper provides insight into eddy current models for stratified conductive structures using three types of analytical approaches, including Cheng’s matrix method, Truncated region eigenfunction expansion (TREE) method, and the innovative method based on the reflection and transmission theory of the electromagnetic waves. The analytical expressions of the three models are discussed and compared. Numerical simulation of an FEM model is performed, and the experimental results verify the developed models.

The anti-corrosive metal coatings on ferromagnetic tubes are the important components in power plants and need non-destructive evaluation (NDE) techniques to measure their thickness precisely. The objective of this research is to develop pulsed eddy current (PEC) technique for measuring the coating thickness accurately. PEC signals are investigated for the evaluation of coating thickness using a differential PEC probe, which consists of a driving coil and two pickup coils. The characteristics of PEC signals for coating thickness variations show that the related features, such as the time-to-peak and peak value, change linearly with thickness change. A new feature, called as time to the rising point, related to the propagation time of electromagnetic field in conductive metals is adopted for coating thickness measurement. These features can be used to inspect the coating thickness within the accuracy of 0.02 mm.

Non-linear interaction of waves with contact interfaces has been widely applied in non-destructive evaluation fields such as bonding quality evaluation, and the detection of closed microcracks and composite delamination. This paper proposes an absolute measurement of the ultrasonic non-linearity parameter using a piezoelectric detection method for two aluminum alloy blocks of different lengths. The results of a two-dimensional finite element method model verified by models for hard and soft contact interfaces, depending on the interface property, were compared with the measured non-linearity parameter. The measured values show good agreement with the modelled results, indicating good potential for measuring the non-linearity parameter at interfaces experimentally and numerically.

Rail health conditions are among the top concerns in the area of train safety. In this study, a fiber optic monitoring system is developed to achieve ultrasonic guided wave based rail crack detection. Although fiber Bragg grating (FBG) sensor is a wellknown suitable candidate for long-distance monitoring of rail, the sampling speed of commercially available optic spectrum analyzers limits their application to ultrasonic wave detection. A high-speed FBG interferometric interrogation module is developed, which constitutes the rail monitoring system in conjunction with an active wave generation module and a sensing network. To find appropriate excitation frequency and FBG dimension for ultrasonic guided wave generation and reception, dispersion analysis of rail, a waveguide with complex cross-section, is conducted to guide subsequent design of damage detection experiment. The system and the crack detection technique are then implemented on a long full-scale rail segment, by deploying PZT (lead zirconate titanate) actuator and FBG sensor in pitch-catch and pulse-echo configurations. Artificial cracks in different lengths are introduced to the rail. Frequency-domain analysis of the rail responses is used to identify the damageinduced discrimination after direct observation of time-domain signals. Power spectral density analysis of the purified signals, assisted by discrete wavelet filtering, leads to the graphic presentation of rail integrity.

A 3D model based on the finite element method (FEM) was built to simulate the infrared thermography (IRT) inspection process. Thermal contrast is an important parameter in IRT and was proven to be a function of defect parameters. Parametric studies were conducted on internal defects with different depths, thicknesses, and orientations. Thermal contrast evolution profiles with respect to the time of the defect and host material were obtained through numerical simulation. The thermal contrast decreased with defect depth and slightly increased with defect thickness. Different orientations of thin defects were detected with IRT, but doing so for thick defects was difficult. These thermal contrast variations with the defect depth, thickness, and orientation can help in optimizing the experimental process and interpretation of data from IRT.

A two-dimensional numerical model based on the finite element method was built to simulate the wave propagation phenomena that occur during the ultrasonic time of flight diffraction (TOFD) process. First, longitudinal-wave TOFD was simulated, and the numerical results agreed well with the theoretical results. Shear-wave TOFD was also investigated because shear waves have higher intensity and resolution. The shear wave propagation was studied using three models with different boundary conditions, and the tip-diffracted shear-tolongitudinal wave was extracted from the A-scan signal difference between the cracked and non-cracked specimens. This signal showed very good agreement between the geometrical and numerical arrival times. The results of this study not only provide better understanding of the diffraction phenomena in TOFD, but also prove the potential of shear-wave TOFD for practical application.

Impedance spectroscopy is a non-destructive evaluation (NDE) method first proposed and developed for evaluating TGO layers with compressive stress inside thermally degraded plasma-sprayed thermal barrier coatings (PS TBCs). A bode plot (phase angle (h) vs. frequency ( f )) was used to investigate the TGO layer on electrical responses. In our experimental study, the phase angle of Bode plots is sensitive for detecting TGO layers while applying compressive stress on thermal barrier coatings. It is difficult to detect TGO layers in samples isothermally aged for 100 hrs and 200 hrs without compressive stress, and substantial change of phase was observed these samples with compressive stress. Also, the frequency shift of the phase angle and change of the phase angle are observed in samples isothermally aged for more than 400 hrs.

This paper proposes an analytical approach that can describe the Pulsed Eddy Current Testing (PECT) of stratified conductive structures by a single air-coil used for detecting and sizing of metal loss due to interlayer corrosion. Specifically for a single air-cored coil above a multilayered conductive structure, the coil impendance response of the cylindrical eddy-current probe is calculated based on the truncated region eigenfunction expansion (TREE) method using the generalized matrix coefficients in series form. Analytical modeling of pulsed eddy current is developed using the Fourier series for multilayered conductive structures. A simulation study is carried out for demonstrating the capability of the proposed approach for sizing the metal loss in a two-layer specimen. Furthermore, the experiment is set up to confirm the simulating results of the analytical model for multilayered steels. Good agreement between the theoretical results and measured signals is observed.

Computed laminography (CL) is different from conventional computed tomography(CT) for its specialization in testing plate-type structures, such as integrated circuit boards (ICB), multilayer printing circuit boards (MPCB), and ball grid arrays (BGA). It adopts a different scanning way to successfully produce cross-sectional images of the plate-type objects, while the conventional CT cannot be used. According to the CL reconstruction algorithm, precise determination of the origin of the projection coordinate system is the first step during cone-beam CL scanning system calibration. But unfortunately, for the practical CL scanning system, it is impossible to measure the position of the X-ray focus projection by direct means. A new method to determine the X-ray focus projection coordinates with high accuracy is proposed. Firstly the angle between the central X-ray and the axis of rotation is set to zero by rotating the X-ray source and detector synchronously. Acquiring digital radiography (DR) images of several spherical objects at two geometrical magnification ratio positions in the cone X-ray beam, the two DR images are combined to one image, on the base of which image processing methods are employed to get the center points of each projection of the spherical object. And every two-positioned center points of the same spherical object determine a line, so all couples of projection centers of all the spherical objects construct a group of lines, mathematically an over-determined equation set. After solving the over-determined equation, the X-ray focus projection coordinates are finally obtained. The experimental results prove that the accuracy of this method can satisfy the requirements of the practical scanning system, meanwhile it is feasible to realize. (C) 2012 Published by Elsevier Ltd.

Visual inspection and assessment of the condition of metal structures are essential for safety. Pulse thermography produces visible infrared images, which have been widely applied to detect and characterize defects in structures and materials. When active thermography, a non-destructive testing tool, is applied, the necessity of considerable manual checking can be avoided. However, detecting an internal crack with active thermography remains difficult, since it is usually invisible in the collected sequence of infrared images, which makes the automatic detection of internal cracks even harder. In addition, the detection of an internal crack can be hindered by a complicated inspection environment. With the purpose of putting forward a robust and automatic visual inspection method, a computer vision-based thresholding method is proposed. In this paper, the image signals are a sequence of infrared images collected from the experimental setup with a thermal camera and two flash lamps as stimulus. The contrast of pixels in each frame is enhanced by the Canny operator and then reconstructed by a triple-threshold system. Two features, mean value in the time domain and maximal amplitude in the frequency domain, are extracted from the reconstructed signal to help distinguish the crack pixels from others. Finally, a binary image indicating the location of the internal crack is generated by a K-means clustering method. The proposed procedure has been applied to an iron pipe, which contains two internal cracks and surface abrasion. Some improvements have been made for the computer vision-based automatic crack detection methods. In the future, the proposed method can be applied to realize the automatic detection of internal cracks from many infrared images for the industry.