Ultrasonic Displacement Research Articles

Concrete Crack Identification Using a UAV Incorporating Hybrid Image Processing.

Crack assessment is an essential process in the maintenance of concrete structures. In general, concrete cracks are inspected by manual visual observation of the surface, which is intrinsically subjective as it depends on the experience of inspectors. Further, it is time-consuming, expensive, and often unsafe when inaccessible structural members are to be assessed. Unmanned aerial vehicle (UAV) technologies combined with digital image processing have recently been applied to crack assessment to overcome the drawbacks of manual visual inspection. However, identification of crack information in terms of width and length has not been fully explored in the UAV-based applications, because of the absence of distance measurement and tailored image processing. This paper presents a crack identification strategy that combines hybrid image processing with UAV technology. Equipped with a camera, an ultrasonic displacement sensor, and a WiFi module, the system provides the image of cracks and the associated working distance from a target structure on demand. The obtained information is subsequently processed by hybrid image binarization to estimate the crack width accurately while minimizing the loss of the crack length information. The proposed system has shown to successfully measure cracks thicker than 0.1 mm with the maximum length estimation error of 7.3%.

Acoustic Radiation Force Impulse (ARFI)-Induced Peak Displacements Reflect Degree of Anisotropy in Transversely Isotropic Elastic Materials.

In transversely isotropic (TI) materials, mechanical properties (Young's modulus, shear modulus, and Poisson's ratio) are different along versus across the axis of symmetry (AoS). In this work, the feasibility of interrogating such directional mechanical property differences using acoustic radiation force impulse (ARFI) imaging is investigated. We herein test the hypotheses that 1) ARFI-induced peak displacements (PDs) vary with TI material orientations when an asymmetrical ARFI excitation point spread function (PSF) is used, but not when a symmetrical ARFI PSF is employed; and 2) the ratio of PDs induced with the long axis of an asymmetrical ARFI PSF oriented along versus across the material's AoS is related to the degree of anisotropy of the material. These hypotheses were tested in silico using finite element method (FEM) models and Field II. ARFI excitations had F/1.5, 3, 4, or 5 focal configurations, with the F/1.5 and F/5 cases having the most asymmetrical and symmetrical PSFs at the focal depth, respectively. These excitations were implemented for ARFI imaging in 52 different simulated TI materials with varying degrees of anisotropy, and the ratio of ARFI-induced PDs was calculated. The change in the ratio of PDs with respect to the anisotropy of the materials was highest for the F/1.5, indicating that PD was most strongly impacted by the material orientation when the ARFI excitation was the most asymmetrical. On the contrary, the ratio of PDs did not depend on the anisotropy of the material for the F/5 ARFI excitation, suggesting that PD did not depend on material orientation when the ARFI excitation was symmetrical. Finally, the ratio of PDs achieved using asymmetrical ARFI PSF reflected the degree of anisotropy in TI materials. These results support that symmetrical ARFI focal configurations are desirable when the orientation of the ARFI excitation to the AoS is not specifically known and measurement standardization is important, such as for longitudinal or cross-sectional studies of anisotropic organs. However, asymmetrical focal configurations are useful for exploiting anisotropy, which may be diagnostically relevant. Feasibility for future experimental implementation is demonstrated by simulating ultrasonic displacement tracking and by varying the ARF duration.

압전형 수신 기법을 이용한 초음파 절대변위진폭 측정

음향 비선형 파라미터는 입사시킨 기본주파수 성분의 변위 진폭 크기와 재료의 비선형성에 의하여 발생된 2차 고조파 성분의 변위 진폭 크기의 비로 정의된다. 본 연구에서는, 압전소자 방식을 이용한 초음파 절대변위진폭 측정의 타당성을 확인하고자, 이 기법을 통해 초음파가 입사된 SUS316 시편의 절대변위진폭을 측정하였다. 또한 비교를 위해, 레이저를 통한 패브리패럿 방식의 간섭계를 이용하여 동일 시편에 대한 절대변위진폭을 측정하였다. 두 가지 기법을 통한 실험 결과는 서로 잘 일치하는 경향을 보였으며, 특히 압전형 수신 기법의 경우 기존의 레이저 변위측정기법에 비하여 반복 측정의 안정성이 우수한 것으로 나타났다. 이 결과로부터 압전형 수신 기법은 기존 레이저 측정 기법에 비하여 과정이 복잡하지만, 미세변위를 더 안정적으로 측정할 수 있어 음향 비선형 파라미터의 측정에 유리할 것으로 기대된다. A nonlinear ultrasonic parameter is defined by the ratio of displacement amplitude of the fundamental frequency component to that of the second-order harmonic frequency component. In this study, the ultrasonic displacement amplitude of an SUS316 specimen was measured via a piezo-electric-based method to identify the validity of piezo-electric detection method. For comparison, the ultrasonic displacement was also determined via a laser-based Fabry-Pérot interferometer. The experimental results for both measurements were in good agreement. Additionally, the stability of the repeated test results from the piezo-electric method exceeded that of the laser-interferometric method. This result indicated that the piezo-electric detection method can be utilized to measure a nonlinear ultrasonic parameter due to its excellent stability although it involves a complicated process.

Effect of Slope Angle on Seismic Response of Unreinforced and Reinforced Soil Slopes in Shaking Table Tests

This paper studies the effect of slope angle on the seismic response of unreinforced and reinforced soil slopes through a series of laboratory shaking table tests. Slopes were constructed using clayey sand and geogrids were used for reinforcing the slopes. The slope angle varies from 45°, 60° and 75° in different tests and the quantity and location of reinforcement is varied in different tests. Acceleration of base shaking varies from 0.1 to 0.3 g in the model tests and the frequency of base shaking was 2–10 Hz in different tests. The slope is instrumented with ultrasonic displacement sensors and accelerometers at different elevations. The response of different slopes is compared in terms of the horizontal displacements of the slope and acceleration amplifications measured at different elevations. At all frequency levels and base acceleration conditions, unreinforced slopes showed higher acceleration amplifications and increased displacements with the increase in steepness It was also observed from the test results that increase in steepness of the slope has detrimental effects on both acceleration amplifications and displacement response of unreinforced as well as reinforced model soil slopes.

Two-dimensional analytic modeling of acoustic diffraction for ultrasonic beam steering by phased array transducers

Phased array ultrasonic transducers enable modulating the focal position of the acoustic waves, and this capability is utilized in many applications, such as medical imaging and non-destructive testing. This type of transducers also provides a mechanism to generate tilted wavefronts in acousto-optic deflectors to deflect laser beams for high precision advanced laser material processing. In this paper, a theoretical model is presented for the diffraction of ultrasonic waves emitted by several phased array transducers into an acousto-optic medium such as TeO2 crystal. A simple analytic expression is obtained for the distribution of the ultrasonic displacement field in the crystal. The model prediction is found to be in good agreement with the results of a numerical model that is based on a non-paraxial multi-Gaussian beam (NMGB) model.

Plural spectral frequency divisions for ultrasonic tissue displacement vector measurement.

For a human tissue displacement vector or strain tensor measurement, the plural spectral frequency division method (PSFDM) is presented. In this report, the effectiveness of the processing is demonstrated by performing the measurements on an agar phantom interrogated by wideband ultrasonic (US) single beam scanning and compounding of steered plane wave transmissions.

Development of Compact Flexible Displacement Sensors Using Ultrasonic Sensor for Wearable Actuators

In position control of wearable actuator such as a rubber artificial muscle, a compact flexible displacement sensor is much attractive and required. In this paper, two types of flexible displacement sensor using the ultrasonic sensor were introduced. One is a built-in displacement sensor for rubber artificial muscle. Another is a sensor that can measure the sliding displacement on a flexible tube for flexible robot. Both sensors use ultrasonic displacement sensors. The construction, operating principle and measuring performance of two sensors were also described.

Ultrasonic Lateral Displacement Sensor for Health Monitoring in Seismically Isolated Buildings.

An ultrasonic lateral displacement sensor utilizing air-coupled ultrasound transducers is proposed. The normally-distributed far field of an ultrasound transducer in a lateral direction is taken advantage of for measuring lateral displacement. The measurement system is composed of several air-coupled ultrasound transducers as a receiver and several transmitters. The transmitters are immobilized at a fixed point, whereas the receiver set-up is separately arranged on the opposite side. In order to improve measurement accuracy, a correction method that utilizes polynomial approximation is introduced. The difference between the corrected lateral displacement and the reference displacement is estimated to be 0.2 mm at maximum for the two transmitters system. A good responsiveness is demonstrated by conducting a dynamic response experiment. When five transmitters are arranged, their measurement range is easily extended up to ±60 mm with an accuracy of 0.7 mm. In both cases, the fluctuations to the measurement ranges show less than 1%. These results indicate that the developed sensor system is useful for measuring relative lateral displacement of a seismically isolated building in the field of structural health monitoring.

Seismic response of reduced-scale modular block and rigid faced reinforced walls through shaking table tests

This paper focuses on understanding the seismic response of geosynthetic reinforced retaining walls through shaking table tests on models of modular block and rigid faced reinforced retaining walls. Reduced-scale models of retaining walls reinforced with geogrid layers were constructed in a laminar box mounted on a uniaxial shaking table and subjected to various levels of sinusoidal base shaking. Models were instrumented with ultrasonic displacement sensors, earth pressure sensors and accelerometers. Effects of backfill density, number of reinforcement layers and reinforcement type on the performance of rigid faced and modular block walls were studied through different series of model tests. Performances of the walls were assessed in terms of face deformations, crest settlement and acceleration amplification at different elevations and compared. Modular block walls performed better than the rigid faced walls for the same level of base shaking because of the additional support derived by stacking the blocks with an offset. Type and quantity of reinforcement has significant effect on the seismic performance of both the types of walls. Displacements are more sensitive to relative density of the backfill and decrease with increasing relative density, the effect being more pronounced in case of unreinforced walls compared to the reinforced ones. Acceleration amplifications are not affected by the wall facing and inclusion of reinforcement.

Non-contact measurement of elastic modulus by using laser ultrasound

Non-contact measurement of elastic modulus is necessary for the in-line assessment of material in harsh environments such as high temperature. In this paper, a fully non-contact method to measure elastic modulus is proposed based on the laser ultrasonic technique (LUT) that uses a short-pulsed laser to generate ultrasound and the other laser coupled to an interferometer using a photorefractive crystal to detect the ultrasonic wave displacement. Basically, this method measures velocities of shear wave and longitudinal wave to obtain the elastic modulus. The uniqueness is that the velocity of shear wave is measured in the thermo-elastic regime first and then the velocity of longitudinal wave is measured in the ablation regime. This is because the strong mode of generated ultrasound is the shear wave in the thermo-elastic regime while the longitudinal wave in the ablation regime. Regime change can be achieved simply by switching the laser power, with no change in the measurement setup. In order to demonstrate the usefulness of the proposed method, the elastic modulus of aluminum casting alloy has been measured and the results were compared with a conventional contact method and a destructive tensile test. They showed good agreement with each other, which verified the usefulness of the proposed noncontact elastic modulus measurement method.

Noninvasive Imaging of Thermal Fields Induced in Soft Tissues In Vitro by Pulsed Focused Ultrasound Using Analysis of Echoes Displacement

Abstract Therapeutic and surgical applications of focused ultrasound require monitoring of local temperature rises induced inside tissues. From an economic and practical point of view ultrasonic imaging techniques seem to be the most suitable for the temperature control. This paper presents an implementation of the ultrasonic echoes displacement estimation technique for monitoring of local temperature rise in tissue during its heating by focused ultrasound The results of the estimation were compared to the temperature measured with thermocouple. The obtained results enable to evaluate the temperature fields induced in tissues by pulsed focused ultrasonic beams using non-invasive imaging ultrasound technique

611 免震建物のヘルスモニタリングのための超音波横変位センサ

An ultrasonic lateral displacement sensor utilizing air-coupled ultrasound transducers is proposed. The normally-distributed far field of an ultrasound transducer in a lateral direction is taken advantage of for measuring lateral displacement. The measurement system is composed of several air-coupled ultrasound transducers as a receiver and several transmitters. The transmitters are immobilized at a fixed point, whereas the receiver set-up is separately arranged on the opposite side. In order to improve measurement accuracy, a correction method that utilizes polynomial approximation is introduced. A good responsiveness is demonstrated by conducting a dynamic response experiment. When five transmitters are arranged, their measurement range is easily extended up to ±60 mm with an accuracy of 0.7 mm. The fluctuations to the measurement ranges show less than 1%. These results indicate that the developed sensor system is useful for measuring relative lateral displacement of a seismically isolated building in the field of structural health monitoring.

Evidence of guided acoustic waves propagating along a micrometric fiber

We propose a contactless optical method to determine the dispersion curves of guided acoustic modes propagating along a micrometric fiber. Subnanosecond laser pulses are used to generate guided acoustic waves, and an optical probe is used for measuring the ultrasonic displacements at the fiber surface. The test sample is an aluminum fiber of diameter 33 μm. The comparison between the experimental and theoretical dispersion curves is presented.

Research on Ultrasonic Propagation at the Contact Interface in Ultrasonic Machining

This paper analyzes the factors, which causes the no-linear of the ultrasonic in the processing system, and the reasons of the ultrasonic reflection and transmission at the contact interface according to the wave theory. In this paper, the ultrasonic displacement coefficient, the pressure reflection coefficient, the displacement transmission coefficient and the pressure transmission coefficient are deduced. The relation among the x-axis and included angle, the incident wave, reflected transmitted waves. The relationship between the preload of the piezoelectric ceramics and the ultrasonic propagation is established, and the best of the bolt preload is investigated. The experiment is done to verify the relationship between the amplitude-frequency characteristics and the ultrasonic transducer at different preload, which provides a reliable basis for the ultrasonic system design, installation and maintenance.

Shaking table studies on geosynthetic reinforced soil slopes

This paper describes shaking table model studies conducted on unreinforced and reinforced soil slopes. A computer controlled hydraulically driven single degree of freedom shake table was used in these tests. Model soil slopes were constructed using clayey sand (SC) in a laminar box. Two different slope angles were used in tests. Two different types of reinforcement, namely, a woven geotextile and a biaxial geogrid were used in the tests. The models were instrumented with ultrasonic displacement transducers and accelerometers at different locations. The slopes were subjected to horizontal base shaking of known acceleration and frequency and the displacement and acceleration were monitored for time increments. Comparison of displacement and acceleration of tests with different slope angles and with reinforcing layers of different stiffness values resulted in some important observations regarding the response of these soil slopes under seismic shaking conditions. Tensile stiffness of the reinforcement plays an important role in controlling the seismic deformations and the beneficial effects of reinforcement are more pronounced in flatter slopes. Acceleration amplifications did not alter with the inclusion of reinforcing layers in the model studies reported in this paper because of the dimensional limitations. Numerical modeling of the geosynthetic reinforced soil slopes subjected to base shaking is also presented and the models are verified with the experimental results.

Ultrasonic imaging for appearance of vertical slot by reverse time migration

The problem in traditional industrial ultrasonic imaging methods is the difficulty to obtain the appearance or the shape of defects inside solid materials although the methods have the ability to detect and determine the position and lateral dimensions. These special defects, like the vertical slot or crack, are typical examples. Based on the multi-element array ultrasonic technique, the numerical and experimental studies on reverse time migration (RTM) ultrasonic imaging for metalic materials are carried out. In this paper, the objects in detecting and imaging experiments are aluminum samples with slot intersecting the bottom or interior slot, which cannot be effectively detected by traditional ultrasonic methods. First the single component ultrasonic field for RTM imaging is studied to obtain RTM ultrasonic imaging results based on numerical simulation and experimental measurements using a multi-element array ultrasonic testing system. Then, the RTM imaging techniques based on multi-component ultrasonic displacement field detection and converted shear wave separation are further studied, and a new approach using a multi-component laser interferometer is proposed. Numerical simulation results verify that the multi-component RTM imaging reconstructive method can overcome the shortcomings of single component method, and obtain better image quality.

Performance investigation of an advanced tracked prime mover on the low bearing soil

This study has presented a performance investigation of an advanced tracked prime mover for the operation of agricultural goods and other operations on peat terrain. The maximum and continuous traction torque of the prime mover has been developed by designing an advanced controller for controlling the intelligent system. The prime mover’s mobility is studied with ultrasonic displacement sensor, torque transducer, National Instrument cRIO-9004 Compact-RIO Real-time Controller Unit (RCU), a National Instrument TPC 2106T Touch Panel Control (TPC), a Trimble AG132 GPS antenna and receiver unit, and a Dlink DIR-655 router. The fuzzy logic controller (FLC) has been equipped with the prime mover hydraulic system to increase the traction torque of the hydraulic motor when the prime mover’s sinkage is more than or equal to 70mm. The prime mover’s design demonstrates good potential in traversing peat terrain as the measured tractive effort was found to be 48% of the vehicle’s gross weight while the recommended tractive effort is in the range of 30–36% of the vehicle’s gross weight.

Ultrafast ellipsometric interferometry for direct detection of coherent phonon strain pulse profiles

We describe an ultrafast optical technique to quantitatively detect picosecond ultrasonic displacements of solid surfaces, thus giving access to the longitudinal strain pulse shape. Transient optical reflectance changes recorded at oblique optical incidence with a common-path interferometric configuration based on ultrafast ellipsometry monitor gigahertz coherent phonon pulses. We demonstrate for a tungsten film the quantitative extraction of the strain pulse shape free of distortions arising from the photoelastic effect, and analyze the results with the two-temperature model to obtain the value g≈3×1017  Wm−3 K−1 for the electron–phonon coupling constant. Analysis of the data also reveals a thermo-optic contribution.

Bayesian speckle tracking. Part II: biased ultrasound displacement estimation.

Ultrasonic displacement estimates have numerous clinical uses, including blood flow estimation, elastography, therapeutic guidance, and acoustic radiation force imaging (ARFI). These clinical tasks could be improved with better ultrasonic displacement estimates. Traditional ultrasonic displacement estimates are limited by the Cramer-Rao lower bound (CRLB). The CRLB can be surpassed using biased estimates. In this paper, a framework for biased estimation using Bayes' theorem is described. The Bayesian displacement estimation method is tested against simulations of several common types of motion: bulk, step, compression, and acoustic-radiation-force-induced motion. Bayesian estimation is also applied to in vivo ARFI of cardiac ablation lesions. The Bayesian estimators are compared with the unbiased estimator, normalized cross-correlation. As an example, the peak displacement of the simulated acoustic radiation force response is reported because this position results in the noisiest estimates. Estimates were made with a 1.5-λ kernel and 20 dB SNR on 100 data realizations. Estimates using normalized cross-correlation and the Bayes' estimator had mean-square errors of 17 and 7.6 μm², respectively, and contextualized by the true displacement magnitude, 10.9 μm. Biases for normalized cross-correlation and the Bayes' estimator are -0.12 and -0.28 μm, respectively. In vivo results show qualitative improvements. The results show that with small amounts of additional information, significantly improved performance can be realized.

Influence of initial time of laser ultrasonic on calculating its propagation velocity in a diamond anvil cell

Sound velocity is important to study the elastic behaviors of materials in high pressure physics and the accuracy acquisition of travel time for velocity calculation is very essential. Thermoelastic finite element models of ultrasonic displacement field induced by a subnanosecond pulsed laser in metal films with a diamond anvil cell are established and the processes of laser ultrasonic generation are analyzed in detail. By confirming the initial time, we improved the accuracy of calculating the longitudinal wave velocity in the aluminum and copper thin films. The formulas of delay time are obtained by a set of simulations, and the overall errors of modified longitudinal velocity are reduced by 10–60 times of the unmodified ones.