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The development of Structural Health Monitoring (SHM) systems and integration in our structures is a necessity. It has proven to provide a robust and low-cost solution for monitoring structural integrity and can predict the remaining life of our structures. One of the most important aspects of SHM systems is the design and implementation of sensor networks. This study proposes a new hybrid model for optimizing sensor placement on convex and non-convex structures. We propose a novel framework in which two detection mechanisms are considered: pitch-catch and pulse-echo to provide coverage for a given surface. These two mechanisms will complement each other to minimize the number of sensors used while maintaining a high coverage. This combination also allows for better coverage of the corners and regions in the proximity of geometrical discontinuity (such as holes and openings). The monitored area is discretized into a set of control points. For a control point to be covered, it should satisfy the user-defined coverage level which is the number of sensing paths crossing that point. These sensing paths are provided by two modes of communications (pitch-catch and pulse-echo) between the actuator-sensor pairs. The model, which is solved using a genetic algorithm (GA), provides flexibility by allowing the user to input different parameters such as the attenuation distance of the propagating waves and the sensing path limits of both coverage configurations that can be determined through experimentation. The efficiency of the proposed model is then demonstrated by simulating different geometrical shapes. Significant improvement in the coverage of the monitored area, reaching 34.6%, was achieved when compared to the coverage provided by some preliminary solutions such as uniformly placing the sensors on the plate under study. Also, the advantage of combining both configurations (pitch-catch and pulse-echo) in the same model was investigated. It was shown that the latter highly impacted the coverage in the blind zones (corners and edges) where a single configuration is not effective. Afterward, experimental validation was carried out to evaluate the model’s accuracy in damage localization within the optimized sensor networks. The results demonstrated the proficiency of the model developed in distributing the sensors on the tested specimens.

The multifunctional pulse equipment allowіng to use the method of amplitude-independent internal friction in the frequency range 7.5 to 232.5 MHz is described. Equipment gjves the possibility to investigate the peculiarities of the process of phonon-dislocation interaction in crystals, to carry out thermoactivation analysis of the process of dislocation of the dislocations about the stoppers under the action of temperature and elastic loading, to study processes of dislocation and mechanical relaxation in loaded samples in the quasi-elastic and plastic strain range.

The acoustic path has been analyzed when carrying out the acceptance pulse echo inspection of the rail head. The influence of the parameters of the employed piezoelectric transducers on the sensitivity distribution for the sounding circuit used in the existing installations has been assessed, and the true sensitivity of detecting “nonmetallic inclusion” type flaws has been evaluated.

Detecting the debonding defects in the composite/rubber/rubber bonding structure is very difficult because of the high attenuation and aliasing of the ultrasonic wave from the structure. In order t...

One of the main challenges of using laser ultrasonic techniques for non-destructive testing applications is the typically low signal-to-noise ratio of the laser ultrasonic signals. In the case of thick composite structures, this is even more problematic since composite materials have very strong sound attenuation. This article investigates the effects of laser beam size and profile to the amplitude of pulse-echo laser ultrasonic signals with the constraint that the peak energy density (fluence) must be kept constant under the thermal damage threshold of material like polymer matrix composites. Such constraint is very important for the non-destructive feature of non-destructive testing, yet in a number of the existing parameter studies of laser ultrasonics, it was not fully investigated. In this article, a series of A-scan and C-scan experiments on thick composite specimens shows that the amplitude of the direct waves and the reflected waves increases with the increase in laser beam size with constant peak energy density. This amplitude enhancement significantly improves the propagation depth, thereby optimizing the system for inspection of thick composite structures. The validity of experimental results is verified theoretically by solving the thermoelastic model of epicenter displacement using Laplace–Hankel transformation.

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.

Here, the feasibility of using nonimaging pulse-echo ultrasound as a method of noninvasively detecting a bolus in the proximal esophagus was demonstrated. To accomplish this, patient swallows were recorded on a clinical ultrasound device with research interface that allowed for collection of the pulse-echo data. These ultrasound data of the proximal esophagus were processed with a series of signal processing techniques in both the temporal and spectral domains, which revealed characteristic signatures that were unique for both liquid and food boluses compared to the normal collapsed esophageal state. Since substantial amounts of laryngopharyngeal reflux are gaseous in nature, future work will revolve around expanding the data set to include boluses of gaseous refluxate, a standardized methodology for capturing bolus events; developing automated detection tools for identifying laryngopharyngeal reflux for an extended duration; and assessing technology limitations due to user error.

Buildings, bridges, roads, and other structures need to be regularly maintained if they are to last. In general, if a defect is detected early, the cost of its remediation is typically much lower than if the structure is allowed to degrade for months or years. A key means of locating hidden defects are non-destructive testing methods. This paper describes measurements that compare three non-destructive methods applied to a concrete bridge and a laboratory specimen with artificial defects to simulate cavities. Three methods (infrared thermography, ground-penetrating radar and ultrasonic pulse echo) were used to measure the depth and size of cavities in the concrete panel. Furthermore, the measurements were made using two different brands of radar and two different thermal imaging cameras from the same manufacturer. Lastly, the NDT methods were compared across general performance criteria in terms of accuracy, testing practicality, and costs.

Although ultrasonic-based techniques are the most widely used ones for the assessment of pipeline integrity they have some limitations, and alternative methods show potential to overcome them, such as laser scanning techniques. This paper presents the results of an experimental evaluation of pulse-echo ultrasonic and laser scanning techniques for pipeline inspection using a metal specimen which represents a damaged pipeline. Both techniques were able to detect all the defects on the inner surface of the specimen, but the defect geometry was important to define the accuracy of each technique. For almost all the evaluated defects, the differences between the reference and the three-dimensional representations created from the experimental data showed that the ultrasonic technique presented errors with magnitude around 0.2 mm, which is in general half the error observed for the laser scanning technique. However, ultrasonic technique demanded 8 h for specimen inspection, while laser technique required only 10 min.

Acoustic nonlinear parameter β, was of great interest in tissue characterization in recent years. Nonlinear imaging methods have been reported to provide improved spatial and contrast resolution. We introduce a nonlinear imaging method derived from nonlinear wave equation based on Gaussian-form solution assumption, which can be applied in pulse-echo mode on diagnostic ultrasound. Through making the use of two pulse transmission, only nonlinear effects are reserved and other effects like scattering, diffraction and linear attenuation can be eliminated. For validation of this method a set of simulation results are generated with a nonlinear simulator. Simulated images also indicate that our method clearly describes the spatial distribution of B/A in the medium.

This article proposes a pulse-echo ultrasonic propagation imaging system that is capable of autonomous target recognition and scanning an area of a customizable shape for the non-destructive evaluation of structural defects. The proposed system employs through-the-thickness bulk waves for ultrasonic inspection, which is achieved by joining two laser beams: one each for the ultrasonic wave generation and sensing. Moreover, the system is capable of autonomously suggesting a suitable inspection area for a specimen placed in front of the scanning head. The scan area delimitation algorithm uses the specimen image and ascertains the specimen border by means of edge and contour detection operations, following which a scan area closely conforming to the specimen boundary is suggested. The system can scan an area of any arbitrary shape, thereby preventing any wasteful operations that may result from fixed shape (rectangular or square) scanning. A Q-switched laser is used for generating the aforementioned ultrasonic waves, while a laser Doppler vibrometer is used for sensing these signals. A dual-axis automated translation stage is applied for raster scanning of the specimen, and a data acquisition card is employed for taking measurements. A camera mounted on the scan head is used for imaging the specimen for the scan area detection. Graphical user interface software controls all the individual blocks of the system, while implementing the required image processing, scan area detection, signal acquisition, signal processing, and result display. The graphical user interface is created in C++ using the Qt framework. Moreover, Qt Widgets for Technical Applications is used for the result display, and the Open Source Computer Vision Library is employed for the implementation of basic image processing algorithms. Multi-threading is used for real-time updating of the scan results while the scanning is ongoing.

Based on the analysis of the results of acceptance and operational inspection of rails, we formulate tasks to improve procedures for ultrasonic acceptance inspection of rails. An algorithm developed by the authors for calculating the amplitude of the echo signal from an arbitrarily shaped planar reflector is described, and a piece of the design software based on it is verified. A theoretical and experimental analysis of the acoustic path is carried out for testing the rail on the lateral face of the head, and ways to improve the existing testing procedure are suggested.

The laser ultrasonic technique with a pulse-echo mode has been investigated to detect disbonds in a multi-layer bonded structure and a quantitative method has been proposed to evaluate the defect sizes. The simulations were carried out to analyze influences of spot sizes on the characteristics of laser ultrasonic reflected waves, the interaction of laser ultrasonic reflected waves with disbonds, and quantitative characterization on disbonds. A noncontact laser ultrasonic inspection system has been established to perform a series of experiments to verify the theoretical results. Laser ultrasonic C-scans based on reflected shear waves can clearly redraw appearances of disbonds in the adhesive bond. The proposed quantitative method can evaluate the sizes of disbonds within a reasonable error range. Moreover, the experimental data are in good agreement with the simulation results. Therefore, a combination of the laser ultrasonic pulse-echo mode and the proposed quantitative strategy is practical for accurate detection of disbonds in multi-layer bonded structures.

Non-destructive tests have been increasingly used in historic buildings not only for pre-restoration investigation but also as useful tools to evaluate the effectiveness of eventual interventions. These tests can complement and supplement destructive tests like laboratory analysis of extracted samples as long as a sound sampling plan has been put in place to commensurate with the pattern and extent of dilapidation and materials distribution. Common methods employed in projects in Singapore and Malaysia include the infrared thermography, ground penetrating radar, microwave moisture tomography and ultrasonic pulse echo tomography. The paper discusses about a selection of case studies, demonstrating the application of various techniques for the identification of hidden details, defects and deterioration, and moisture detection.

Composite structures are assertively used for new airframe designs and manufacturing in military aircrafts because of superior strength-to-weight ratios and fatigue resistance. Because the composites have different fatigue failure characteristics compared with metals, it is necessary to develop different approaches for the composite fatigue design and testing. In this study, we propose an in situ damage evaluation technology with high spatial resolution during full-scale fatigue testing of composite aircraft structures. For real composite structure development considering composite fatigue characteristics, full-scale fatigue and damage tolerance tests of the composite fuselage structure were conducted to evaluate the structural characteristics. In the meantime, the laser ultrasonic nondestructive inspection method, called an angular scan pulse-echo ultrasonic propagation imager, which is fully noncontact, real-time, and portable to position it in between the complex test rigs, is used to observe in situ damage growth of the composite. Finally, the verification procedure assisted by the angular scan pulse-echo ultrasonic propagation imager assures no growth of the initial impact damages after lifetime operation and proves the damage tolerance capability of the developed composite fuselage structure.

We consider the problem of nondestructive quality control of complex structured articles, in particular, hydroacoustic antennas. Those features in the structure of these products are determined that affect the choice of methods and means of such control. The possibility of using ultrasonic methods (in particular, the pulse echo method with immersion technique of acoustic contact) and means for monitoring the quality of hydroacoustic antennas have been investigated; means have been proposed to ensure the automation of control.

We present mathematical modeling of the process of determining the time coordinate of the moment of arrival of a pulse echo in the dual-frequency probing technique, as well as graphs of the involved measurement error versus the comparator’s discrimination threshold for different ratios of frequencies and distances and ratio of the frequencies of emitted pulses. Mathematical modeling has revealed limiting cases in which the measurement error increases and can reach 3–4%. Analysis of results has made it possible to identify additional requirements for the mathematical processing of received signals to keep the error within 1%.

This work presents a method to estimate average anisotropy in speed of sound of soft tissue using pulse-echo ultrasound. In particular, our setup includes a passive acoustic reflector located opposite to the ultrasound probe, with tissue in between. This enables the generation of strong reflections from which we measure their traveltimes. We use ray-based approaches to derive the forward problem that relates observed traveltimes with speed of sound anisotropy parameters. The accuracy of the forward modelling is verified using numerical wave propagation simulations. We finally show the occurrence of anisotropy in muscle tissue using in-vivo data.

We report on a dual-fiber ultrasound probe for pulse-echo imaging. For ultrasound generation, a fiber is coated with a highly absorptive overlay made of carbon nanotube composite at its distal end. Ultrasound waves with a peak-to-peak amplitude of over 2.5 MPa can be photothermally generated by injecting nanosecond laser pulses. The scattered ultrasound waves at the specimen are detected by a paired fiber-laser-based ultrasound sensor, by translating the pressure waves into the variation of lasing frequencies. The probe has a diameter of 2.5 mm and an ultrasound spectrum centered at 22 MHz, and 90% -6 dB bandwidth. Ex vivo ultrasound imaging of a biological tissue has been performed with axial and lateral resolutions at 150 and 62 μm, respectively, by linearly scanning the probe, detecting the scattered waves and then forming an image via back projection. The all-fiber ultrasound probe offers an alternative approach towards next-generation intravascular and gastroenterological endoscopes.

Low frequency ultrasounds in air are widely used for real-time applications in short-range communication systems and environmental monitoring, in both structured and unstructured environments. One of the parameters widely evaluated in pulse-echo ultrasonic measurements is the time of flight (TOF), which can be evaluated with an increased accuracy and complexity by using different techniques. Hereafter, a nonstandard cross-correlation method is investigated for TOF estimations. The procedure, based on the use of template signals, was implemented to improve the accuracy of recursive TOF evaluations. Tests have been carried out through a couple of 60 kHz custom-designed polyvinylidene fluoride (PVDF) hemicylindrical ultrasonic transducers. The experimental results were then compared with the standard threshold and cross-correlation techniques for method validation and characterization. An average improvement of 30% and 19%, in terms of standard error (SE), was observed. Moreover, the experimental results evidenced an enhancement in repeatability of about 10% in the use of a recursive positioning system.

After 100 years of theoretical treatment of speckle patterns from coherent illumination, there remain some open questions about the nature of ultrasound speckle from soft vascularized tissues. A recent hypothesis is that the fractal branching vasculature is responsible for the dominant echo pattern from organs such as the liver. In that case an analysis of cylindrical scattering structures arranged across a power law distribution of sizes is warranted. Using a simple model of echo strength and basic transformation rules from probability, we derive the first order statistics of speckle considering the amplitude, the intensity, and the natural log of amplitude. The results are given by long tailed distributions that have been studied in the statistics literature for other fields. Examples are given from simulations and animal studies, and the theoretical fit to these preliminary data support the overall framework as a plausible model for characterizing ultrasound speckle statistics., 26 pages, 8 figures

We report on a new small animal imaging platform for concomitant noninvasive mapping of the absorbed optical energy, acoustic reflectivity, speed of sound and acoustic attenuation in whole mice with submillimeter resolution. In vivo mouse imaging experiments revealed fine details on the organ parenchyma, vascularization, tissue reflectivity, density and stiffness. The newly developed synergistic multimodal combination offers unmatched capabilities for imaging diverse tissue properties and biomarkers with high resolution, penetration and contrast.

A Summary A pilot study on the use of P-EU to identify patients without osteoporosis and/or a subclinical vertebral fracture after a recently sustained non-vertebral fracture (NVF).Introduction Screening with portable devices at emergency departments or plaster rooms could be of interest to limit referrals for dual X-ray absorptiometry (DXA) and vertebral fracture assessment (VFA). We calculated the number of negative tests for osteoporosis and/or subclinical vertebral fractures (VFs) using pulse-echo ultrasonometry (P-UE) at different thresholds.Patients and methods In this cross-sectional study, 209 consecutive women of 50-70 years with a recent non-vertebral fracture (NVF) were studied at the Fracture Liaison Service (FLS) of one hospital. All women received DXA/VFA and P-EU (Bindex (R)) assessments. Various P-EU thresholds (based on the density index (DI, g/cm(2))) were analyzed to calculate the best balance between true negative (indeed no osteoporosis and/or subclinical VF) and false negative tests (osteoporosis and/or subclinical VF according to DXA/VFA).Results Eighty-three women had osteoporosis (40%) and 17 women at least one VF (8%). Applying the manufacturer's recommended P-EU threshold (DI 0.844 g/cm(2)) being their proposed cut-off for not having hip osteoporosis resulted in 77 negative tests (37%, 31% true negative and 6% false negative tests). A DI of 0.896 g/cm(2) resulted in 40 negative tests (19.3%) (38 true negative (18.3%) and 2 false negative tests (1.0%)).Conclusion The application of P-EU enables the identification of a substantial proportion of women with recent non-vertebral fractures at the FLS who would not need a DXA/VFA referral because they had no osteoporosis and/or subclinical vertebral fractures. The most conservative P-EU threshold resulted in 18.3% true negative tests verified by DXA/VFA against 1% false negative test results.

Background: Pulse-echo ultrasonography (PEUS) is a novel ultrasound method that measures the thickness of cortical bone at peripheral skeletal sites with a handheld device connected to a personal computer using proprietary software. Previous studies have shown a significant correlation between density index (DI), a PEUS-derived parameter, and bone mineral density (BMD) measured by dual-energy X-ray absorptiometry at the hip. DI thresholds that discriminate patients likely to have osteoporosis with 90% sensitivity and 90% specificity have been established in a population of Caucasian women in Finland and validated in a study of predominately Caucasian women in the state of Minnesota in the USA. The DI thresholds have not previously been evaluated in non-Caucasian populations. Methodology: This study aimed to determine whether previously established DI thresholds in Caucasian women require adjustment in Hispanic women. PEUS measurements at the proximal tibia and dual-energy X-ray absorptiometry BMD at the hip were evaluated in Caucasian and Hispanic women at a single investigative site in Albuquerque, New Mexico, USA. DI was calculated for each patient and compared with BMD. The performance of DI threshold values for these populations was compared. Results: The study enrolled 293 postmenopausal women (153 Caucasian, 140 Hispanic) with and without osteoporosis. The sensitivity and specificity for DI thresholds to distinguish women with total hip or femoral neck T-score ≤ -2.5 or > -2.5 was similar in Caucasians (sensitivity 80%, specificity 86%) and Hispanics (sensitivity 80%, specificity 91%). Conclusions: The findings of this study confirm the utility of previously established DI thresholds to identify women who are likely or unlikely to have osteoporosis and suggest that the same thresholds can be used for postmenopausal Caucasian and Hispanic women.

Tube/Pipe (TP) 304 stainless steel has been widely used in industry, but a change in its microstructures may endanger its service safety, and it is essential to evaluate its microstructural evolution. In this work, a pulse-echo nonlinear method is proposed to characterize the microstructural evolution of the TP304 stainless steel. The detailed pulse-echo nonlinear experimental process is presented, and it is shown that the absolute nonlinear parameter can be determined when the effect of attenuation is taken into account. The microstructural evolution of TP304 stainless steel is artificially controlled by annealing treatments before it is evaluated by using nonlinear ultrasonic method and metallographic method. The results show that the grain sizes increase as the annealing time increases, which leads to the performance degradation of the TP304 steel and an increase in the nonlinear parameters, with the reason discussed considering the variation in the microstructure. The present pulse-echo nonlinear method is easier to conduct than the traditional transmission-through method and the absolute nonlinear parameter can be determined for quantitative characterization. The variation in determined nonlinear parameters provides a reference to evaluate the microstructural evolution of TP304 stainless steel.

Recently, study of physical properties of the liquid mixtures, their nature and behavior with change in frequency, temperature or concentration has gained interest. In the present work, ultrasonic velocity and attenuation measurements have been carried out in the binary mixture of nitrobenzene and ethanol using pulse echo technique in the temperature range of 274.15K-308.15K maintaining the temperature of the sample with an accuracy of ±0.1°C. It is observed that the mixture of nitrobenzene and ethanol shows maximum absorption at 277.15K at 0.27 moles of Nitrobenzene in the binary mixture. Critical nature of the mixture revealed by ultrasonic absorption indicates the molecular interaction between two liquids and attributes due to the fluctuation in the concentration.

Composite patch bonding repair is widely applied to metal and composite aircraft repair owing to its light weight and high resistance to fatigue and corrosion. However, composite patch repairing is done by vacuum bag processing in general, and the process itself is susceptible to manufacturing defects. In addition, the composite repair patches require more frequent inspections owing to the difficulty of the damage prediction. In this paper, we propose pulse-echo laser ultrasonic correlation mapping for a rapid quality evaluation method of composite repair patching. This method uses a pulse-echo ultrasonic propagation imaging system as a tool for in-situ and full-field inspection, and an ultrasonic correlation mapping (UCM) method was developed for fast and straightforward defect visualization. Two composite patch repair specimens were tested, and then UCM results were compared with other results using existing visualization methods. We also tested a composite laminate plate to verify the applicability of UCM to general composite parts. The UCM results showed similar or better performance than current visualization methods in all cases. Test results showed that the proposed system is suitable for both in-process quality evaluation and in-service field inspection.