Showing papers in "Ultrasonics in 1998"
TL;DR: In this paper, the authors present a review of the studies of the propagation of the waves and their sensitivity to defects which have been conducted in order to provide a sound scientific basis for the method.
Abstract: The detection of corrosion in insulated pipes is of major importance to the oil and chemical industries. Current methods involving point-by-point inspection are expensive because of the need to remove the insulation. An alternative method which is being developed at Imperial College is to propagate guided waves in the walls of the pipes, and to look for reflections from defects. The test configuration is essentially pulse-echo; the insulation is removed at just one location on a pipe and the signals are then transmitted and received using a single transducer unit. The technique is currently undergoing field trials. This paper presents a review of the studies of the propagation of the waves and their sensitivity to defects which have been conducted in order to provide a sound scientific basis for the method. Issues of importance were the selection of the optimum guided wave modes and the establishment of relationships between the defect size and the strength of wave reflection. Analytical and numerical studies were conducted in parallel with an extensive experimental programme.
TL;DR: In this article, the second-order acousto-elastic coefficient (SOC) was measured in a variety of materials including plastics, metals, composites and adhesives.
Abstract: The ultimate strength of most structural materials is mainly limited by the presence of microscopic imperfections serving as nuclei of the fracture process. Since these nuclei are considerably shorter than the acoustic wavelength at the frequencies normally used in ultrasonic nondestructive evaluation (NDE), linear acoustic characteristics are not sufficiently sensitive to this kind of microscopic degradation of the material's integrity. On the other hand, even very small imperfections can produce very significant excess nonlinearity which can be orders of magnitude higher than the intrinsic nonlinearity of the intact material. The excess nonlinearity is produced mainly by the strong local nonlinearity of microcracks whose opening is smaller than the particle displacement. Parametric modulation via crack-closure significantly increases the stress-dependence of fatigued materials. A special experimental technique was introduced to measure the second-order acousto-elastic coefficient in a great variety of materials including plastics, metals, composites and adhesives. Experimental results are presented to illustrate that the nonlinear acoustic parameters are earlier and more sensitive indicators of fatigue damage than their linear counterparts.
TL;DR: The results of experimental investigation of acoustic non-linear phenomena on contact boundaries are presented in this article, where simulation experiments demonstrated a threshold nonlinear distortion due to "clapping" and "kissing" mechanisms, multiple bifurcations and chaos development for contact vibrations.
Abstract: The results of experimental investigation of acoustic non-linear phenomena on contact boundaries are presented. Simulation experiments demonstrated a threshold non-linear distortion due to ‘clapping’ and ‘kissing’ mechanisms, multiple bifurcations and chaos development for contact vibrations. Hertzian contact non-linearity was shown to increase with the decrease in contact load and to be predominated by a ‘clapping’ mechanism in a mixed mode of vibrations. Ultrasonic waves propagating on contact interfaces exhibited extremely efficient non-linear properties, unconventional higher harmonics ratio and non-linear waveform distortion. Non-linear sound reflection was accompanied by spectrum inversion, rectification and contact radiation broadening effects. Several modes of non-linear non-destructive evaluation (NDE) were proposed and shown to detect small fractured defects ‘invisible’ by linear NDE techniques.
TL;DR: A comparison of the usability of different wave types is presented in this article, where planar technologies are used for fabrication of the acoustic-wave devices, which will be given of gas sensors, biochemical sensors in liquids, viscosity and density sensing and highvoltage sensing.
Abstract: In the past two decades, acoustic-wave devices have gained enormous interest for sensor applications. The delay line device, where a transmitting and a receiving interdigital transducer are realized on a (piezoelectric) substrate is the most common structure used. The sensitive part is the surface between the two transducers. By placing the device in the feedback loop of an amplifier, an acoustic-wave oscillator is formed with properties such as inherent high sensitivity, high resolution, high stability and a frequency output signal which is easy to process. A very interesting development is the large amount of wave types now available for sensor applications. Sensors have been published using Rayleigh waves, Lamb waves, Love waves, acoustic plate modes, and surface transverse waves (STW). Each of these wave types have their special advantages and disadvantages with respect to sensitivity, stability, usability in liquids or gases, and fabrication complexity. For the fabrication of the acoustic-wave devices, planar technologies are used, which will be discussed in the paper. Examples will be given of gas sensors, biochemical sensors in liquids, viscosity and density sensing and high-voltage sensing. A comparison of the usability of the different wave types will be presented.
TL;DR: A description is given of its various scientific and engineering applications, including the study of wave dispersion in structures, global and long-range inspection of steel pipes and tubes, condition monitoring of machinery such as combustion engines, and onboard sensing of crash events for vehicle safety system operations.
Abstract: The magnetostrictive sensor (MsS) is a type of transducer which can generate and detect time-varying stresses or strains in ferromagnetic materials. In this paper, a general description is first given of the physical principles of the MsS. sensor configuration and instrumentation, and operating characteristics and capabilities. Then a description is given of its various scientific and engineering applications, including the study of wave dispersion in structures, global and long-range inspection of steel pipes and tubes, condition monitoring of machinery such as combustion engines, and onboard sensing of crash events for vehicle safety system operations.
TL;DR: In this paper, the Lamb wave propagation in large plates and its use in internal defect detection have been studied and the Lamb modes which are most efficient for detecting different types of internal defects are identified.
Abstract: In this paper, Lamb wave propagation in large plates and its use in internal defect detection have been studied. The Lamb modes which are most efficient for detecting different types of internal defects are identified. Stress fields inside the plate for different Lamb modes are computed. From these stress plots one can conclude which Lamb mode should be efficient for detecting which type of material defect. Theoretical predictions are experimentally verified.
TL;DR: In this article, the authors present a model and subsequent solution to a boundary value problem that can evaluate the source influence as a function of the comb transducer design parameters, along with an insight into future directions.
Abstract: A countless number of guided wave modes at particular frequencies could be selected for a particular NDE problem, each point producing special sensitivities by way of wave structure across the thickness of the component being studied and also specific penetration powers as a result of interface and surface displacement values and subsequent energy leakage into neighboring media. The mode and frequency choice has a strong influence on NDE and flaw detection, classification and sizing potential as well as an ability to propagate guided waves over long distances, despite the presence of coatings and other surrounding media. The approach to mode and frequency selection is therefore crucial, which can ultimately be based on theoretical and/or experimental means. One aspect of a theoretical approach beyond dispersion curve analysis includes theory of elasticity computations of displacement distributions across a structure. Focus can be on achieving in-plane or out-of-plane optimal values on a surface or at a specific location inside a structure in an attempt at flaw analysis or improved penetration power. From an experimental point of view, an angle beam transducer at a specific angle can be used to achieve a particular phase velocity value. Unfortunately, the presence of a phase velocity spectrum due to a transducer source influence, size and velocity pattern, as well as the frequency spectrum itself, often limits the ability to specifically achieve the particular mode and frequency of choice. Multiple modes can be obtained. An alternate transducer choice to the angle beam transducer can be a multiple element array or comb based on various design choices of element size, spacing and pulsing schedules to produce specific modes and frequencies. The purpose of this paper is to present a model and subsequent solution to a boundary value problem that can evaluate the source influence as a function of the comb transducer design parameters. Advantages of the comb transducer, the mathematical model and analysis, and sample experimental results are all presented in the paper along with an insight into future directions.
TL;DR: The aim of the project partially presented here is the development and validation of an example of a Doppler test object fulfilling the requirements of the IEC 1685, and very precise recipes have been developed for the composition and preparation of both TMM and BMF.
Abstract: Doppler test objects are used to characterise Doppler systems, both stand-alone systems and the Doppler part of so-called duplex scanners. The aim of the project partially presented here is the development and validation of an example of a Doppler test object fulfilling the requirements of the IEC 1685. The project has been carried out by nine partners of five European countries and has been funded by the European Commission. The flow Doppler test object is composed of: tissue mimicking material (TMM), blood mimicking fluid (BMF), tube (embedded in the TMM and carrying the BMF), tank, flow system, including a pump and a flow meter. In the normative part of the IEC 1685, requirements are given for the values of acoustical parameters of TMM and BMF such as sound velocity, attenuation and backscattering. For BMF, requirements are given also for values of density and viscosity. In an informative (but not compulsory) annex, a description is given of a flow test object meeting these requirements as an example. This 'example test object' developed during the project is composed of TMM based on agar and including SiC-and Al2O3-powders, BMF based on nylon particles suspended in water and glycerine, and a tube of c-flex, a silicon copolymer. Two tube sizes are used: 4.0 mm ID and 8.0 mm ID. During the project, very precise recipes have been developed for the composition and preparation of both TMM and BMF. Based on these recipes and a description of the construction in a design five flow test objects have been constructed in the laboratories of five participants. The test objects have been compared by measurements of the physical parameters and by Doppler measurements of the five test objects with the same Doppler system. The measurements have been carried out by five observers. Inter-test object and inter-observer variabilities are determined, yielding information about usefulness of the parameters. © 1998 Elsevier Science B.V. Chemicals/CAS: Agar, 9002-18-0; Aluminum Oxide, 1344-28-1; Biocompatible Materials; C-Flex, 104521-01-9; Glycerol, 56-81-5; Nylons; Polyethylenes; Polystyrenes; Silicon, 7440-21-3
TL;DR: By applying these methods, it has become possible to take the AE signal from the rotating tools and in terms of AE signal processing for identifying the machining processes, application of the artificial neural network will be introduced.
Abstract: This paper deals with the application of the acoustic emission (AE) sensor for monitoring the cutting process with single-point as well as multipoint cutting tools and the grinding process. Some trials to take full advantage of the AE sensor for tool condition monitoring will be conducted relating to the sensor mounting and the signal processing. As a practical solution for the AE sensor mounting, for example, the coolant stream is successfully used as a medium for transmitting the AE wave in the case of milling process monitoring, and for grinding process monitoring, the sensor is mounted in the grinding wheel with other necessary devices so that the AE signal can be transmitted to the outside of the wheel by radio. By applying these methods, it has become possible to take the AE signal from the rotating tools. In terms of AE signal processing for identifying the machining processes, application of the artificial neural network will be introduced.
TL;DR: In this paper, a machining process with the superimposing of ultrasonics is considered and the accumulated experimental results are explained theoretically in the framework of rheological models.
Abstract: The machining process with the superimposing of ultrasonics is considered. The accumulated experimental results are explained theoretically in the framework of rheological models. It is confirmed that under the influence of high frequency vibration, the phenomenological transformation of elasto-plasticity into visco-plasticity and fluidization of dry friction occurs. The dynamic characteristics of transformed machining processes are obtained. They include the dependence of reduced cutting forces on the material and vibration parameters. It is shown that excitation of the vibro-impact mode of tool-workpiece interaction is the most effective way of using ultrasonic influence on dynamical characteristics of machining. The dynamics of an ultrasonic cutting machine under technological load is investigated. The nonlinear amplitude response of the vibrating tool in the process of cutting is obtained. The theoretical results are confirmed by experiments. The method of stabilization of resonant ultrasonic excitation is described. The advantages of ultrasonic cutting and possible ways of using it are discussed.
TL;DR: Harmonic imaging is a new contrast-specific imaging modality, which utilizes the nonlinear properties of some agents in an attempt to alleviate current limitations of ultrasound contrast studies.
Abstract: Within the last decade safe and practical ultrasound contrast agents have been introduced. Most of these are based on gas-filled microbubbles, which markedly enhance Doppler signals and, in some cases, also gray-scale images. The clinical improvements expected from ultrasound contrast is reviewed. Tissue-specific contrast agents constitute another area of potential clinical significance. One particular agent is taken up by the reticulo-endothelial system and produces so-called acoustic emission signals when imaged. An introduction to the unique clinical applications of acoustic emission is given. Harmonic imaging is a new contrast-specific imaging modality, which utilizes the nonlinear properties of some agents in an attempt to alleviate current limitations of ultrasound contrast studies. Examples of harmonic images are presented.
TL;DR: In this article, it is shown that the kissing bonds can be effectively detected by some leaky Lamb mode, and the theoretical and experimental results are presented to show that using the Lamb waves is an effective way of detecting kissing bonds.
Abstract: Closed cracks under compressive normal stresses are difficult to detect by the conventional ultrasonic techniques. When the crack surfaces stay in very close contact with each other then the bond between the two surfaces of the crack is called a ‘kissing bond’. This is a very dangerous bond. Catastrophic failures can result if the system is subjected to crack opening normal stresses or shear stresses. When the crack surfaces are smooth then kissing bonds cannot transmit shear stress very well but can carry compressive normal stress, these bonds are called ‘slip bonds’. Conventional P-wave scans (C-scan or A-scan) are based on the assumptions that P-waves are reflected by the defective interface. However, an interface subjected to a large compressive stress cannot reflect P-waves effectively, hence these bonds remain invisible to the conventional P-wave based C-scan or A-scan techniques. In this paper it is shown that the kissing bonds can be effectively detected by some leaky Lamb mode. Theoretical and experimental results are presented to show that using the Lamb waves is an effective way of detecting kissing bonds.
TL;DR: In this article, the influence of element width on the ultrasonic beam steering properties was investigated and the beam directivity patterns were analyzed and used as the criteria for determining optimal transducer design parameters.
Abstract: Certain characteristics of linear phased arrays were studied by investigating the influence of element width on the ultrasonic beam steering properties. The beam directivity patterns were analyzed and used as the criteria for determining optimal transducer design parameters. An approximate value of the critical interelement spacing, whilst squelching undesirable grating lobes, was obtained analytically using a Taylor's series expansion. The effect of element size on the pressure in the steering direction was also studied. This work showed that the influence of element size on steering characteristics is marginal and a simple solution for discrete point sources can be used as a very close approximation to that of phased arrays. It was recommended to use the largest possible element width to produce the highest pressure while suppressing the grating lobe amplitude.
TL;DR: In this paper, a film shot at 500 frames s −1 shows the acoustic stable and transient cavitation activity in a stationary field at 28 kHz frequency, where stable cavities are simply bubbles that oscillate, often non-linearly, around some equilibrium size during many cycles of acoustic pressure.
Abstract: Electricite de France is involved in understanding the complex physical mechanism induced by power ultrasounds in the bulk of a liquid. The propagation of a ultrasound wave (from 20 to 800 kHz) through a liquid initiates a little-known phenomenon called acoustic cavitation. A film shot at 500 frames s −1 shows the acoustic stable and transient cavitation activity in a stationary field at 28 kHz frequency. Stable cavities are simply bubbles that oscillate, often non-linearly, around some equilibrium size during many cycles of acoustic pressure. They are collected at pressure nodes and give rise to large bubble clouds. Transient cavities exist for less than one cycle. Cavities expand rapidly, often to many times their original size. They then collapse violently, generally breaking up into many smaller bubbles. These bubbles are gathered into a small cloud which grows to up to 10 times the emergence size during 15 ms. They move from arising locations at pressure antinodes to pressure nodes at velocity around 50 cm s −1 . Such high-speed photographs can help to better understand acoustic cavitation phenomena.
TL;DR: In this paper, the authors reviewed the phenomena involved in the creation of electric signals by ultrasound in aqueous solutions of electrolytes with special reference to the acousto-electric interaction signal resulting from the local, periodic conductivity changes produced by the propagation of a pressure wave.
Abstract: The paper reviews the phenomena involved in the creation of electric signals by ultrasound in aqueous solutions of electrolytes with special reference to the acousto-electric interaction signal resulting from the local, periodic conductivity changes produced by the propagation of a pressure wave. The effects can be sorted into three groups: the molarity changes due the bulk compressibility of the medium, the changes in ionic mobility, and the changes in the dissociation equilibrium of partially dissociated ionic species. A equation is derived for the relative conductivity changes against pressure. For totally dissociated electrolytes, the coefficient is near 1 × 10−9Pa−1 and the influence of the ionic species is low. The bulk compressibility is responsible for about 47% of the conductivity changes, the effect of pressure on the ionic mobility for about 18%, and the effect of the temperature changes due to the adiabaticity of the compression on ionic mobility for about 35%. Further investigations of these phenomena include the assessment of their dependency upon the applied ultrasound frequency and the study of possible biological effects.
TL;DR: In this paper, the authors used linear acoustic equations and fluid dynamics equations to predict acoustic cavitation fields in a cylindrical sonoreactor at 28 and 500 kHz and showed good agreement with both theory and calculations.
Abstract: Sonochemistry, or chemistry under ultrasound, has increased in interest in the past few years. Electricite de France is involved in scaling up this new technology to industrial plants. The propagation of a power ultrasound wave (from 20 to 800 kHz) through a liquid initiates a little-known phenomenon called acoustic cavitation. Inceptions and germs grow into bubbles which collapse, possibly giving rise to extreme conditions of temperature and pressure (assessed to be up to 10 000 K and 500 atm). These conditions initiate and greatly enhance chemical reactions. Thus, it is important to know where bubbles are and how intense cavitation is, depending on geometric and acoustic factors. Then, mathematical modelling may help to predict acoustic cavitation fields. Two computations, the first one based on linear acoustic equations and the second one based on fluid dynamics equations, are presented. Calculated pressure fields are obtained in the case of a cylindrical sonoreactor at 28 and 500 kHz. The comparison with experimental observations and measurements shows good agreement with both theory and calculations.
TL;DR: Ordered band formation was preserved by the laminar flow in the expansion chamber, although bands that formed very close to the wall were dissipated downstream, and the microscopy chamber provided evidence of significant lateral particle concentration within bands in the pressure nodal planes.
Abstract: Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been constructed. The chambers were driven at frequencies over the range 0.66-12.2 MHz. The behaviour of 2 microns diameter latex microparticles and 5 microns diameter yeast in the chambers has been elucidated. One (flow) chamber had a downstream laminar flow expansion section to facilitate observation of concentrated particle bands formed in the ultrasonic field. A second (microscopy) chamber allowed direct observation of band formation in the field and their characterisation by confocal scanning laser microscopy. Clear band formation occurs when the chamber pathlength is a multiple of half wavelengths at the driving frequency, so that the chamber rather than the transducer resonance has the most influence on band formation in this system. Band formation occurred in half-wavelength steps from a position one quarter of a wavelength off the transducer to a band at a similar distance from the reflector. Ordered band formation was preserved by the laminar flow in the expansion chamber, although bands that formed very close to the wall were dissipated downstream. The microscopy chamber provided evidence of significant lateral particle concentration within bands in the pressure nodal planes. The approaches described will be applicable to the manipulation of smaller particles in narrower chambers at higher ultrasonic frequencies.
TL;DR: In this article, the authors examined the rate of free radical production of the MTS system under different conditions of temperature, pressure and ultrasound amplitude using the terephtalate dosimeter.
Abstract: The use of manothermosonication (MTS), a combined treatment of heat and ultrasound (20 kHz frequency) under moderate pressure, has been recently proposed as an alternative to conventional heat treatment of liquid foods. The efficiency of MTS has been proved on several enzymes of interest in food industry. One of the MTS enzyme inactivation mechanisms proposed is the interaction of free radicals produced by water sonolysis with some amino acid residues. In this paper we examine the rate of free radical production of the MTS system under different conditions of temperature, pressure and ultrasound amplitude using the terephtalate dosimeter. The ultrasound amplitude was varied between 20 and 145 μm at two different temperatures and pressures ( 70 ° C 200 kPa and 130 ° C 500 kPa ). In both cases, free radical production rate increases linearly with increasing ultrasound amplitude. The pressure effects on free radical production was studied under two different conditions at 117 μm: 70 °C and 130 °C. At 70 °C an increase of hydrostatic pressure results in an increase in free radical production rate, whereas increasing hydrostatic pressure at 130 °C had a negligible effect on free radical production rate. Temperature effects were studied between 30 and 140 °C at 117 μm ultrasound amplitude. Results show that increasing temperature results in a decrease in hydroxyl radical rate production.
TL;DR: An algorithm to detect grey level transitions with multiple scales of resolution to improve edge detection and localisation in ultrasound images of the prostate is investigated, illustrating an edge detection method suitable as pre-processing step in interpretation of medical images.
Abstract: Objective: We investigated an algorithm to detect grey level transitions with multiple scales of resolution to improve edge detection and localisation in ultrasound images of the prostate. Introduction: We had developed a non-analytical operator for prostate contour determination implemented with minimum and maximum filters to identify and locate edges. We implemented a technique for improved determination of boundary parts in prostatic ultrasound images by adjusting the edge detection parameter to signal information. Methods: First the influence of prefilter settings and edge detection parameters is investigated in a test image and a real ultrasound image. Then, local standard deviation is used to identify more or fewer homogeneous regions that are filtered with course resolution, while areas with larger deviation indicate that grey level transitions occur, which should be preserved using smaller filter sizes to improve edge localisation. Results: Analysis of images with different filter sizes indicated that areas are merged for increasing filter sizes: less pronounced edges disappear or displace for larger filters. Two scales of resolution lead to an improved localisation of edges when smaller filter sizes are used in areas with an increased local standard deviation. Conclusions: This paper illustrates an edge detection method suitable as pre-processing step in interpretation of medical images. By adapting input parameters to signal information, object recognition can be applied in images from different imaging modalities. Also, disadvantages are discussed, resulting in a new application combining a localisation algorithm to find the initial contour and a delineation algorithm to improve the outlining of the resulting contour.
TL;DR: In this article, the phase velocity and attenuation of Lamb modes are measured and compared with numerical predictions, and it is shown that the air-coupled transducers can be used for NDT applications of materials.
Abstract: Electrostatic, air-coupled, ultrasonic transducers are used to generate and detect Lamb waves in viscoelastic, isotropic or anisotropic solid plates. The phase velocity and the attenuation of Lamb modes are measured and compared with numerical predictions. These results show that the air-coupled transducers can be used for NDT applications of materials.
TL;DR: In this article, a micro particle trapping system based on the opposite phases ultrasonic traveling waves is proposed, which is carried out by polystyrene spheres and some characteristics of the method, such as size of the micro particles trapped inside the flow and phase error between two ultrasonic waves, are discussed.
Abstract: When two ultrasonic transducers are placed side by side and are driven by continuous signals with opposite phases, an acoustic black spot with zero acoustic power is produced just in front of the boundary of the two ultrasonic transducers, regardless of the wave propagation distance. By this effect, the acoustic radiation field can be modulated spatially. The modulated acoustic field applies the acoustic radiation force to small objects, such as micro particles, in the direction perpendicular to the ultrasonic wave propagation direction. If the small objects flow into the acoustic field by the surrounding fluid flow, they are trapped inside the acoustic black spot. In this paper, a micro particle trapping system, which is based on the opposite phases ultrasonic traveling waves, is proposed. Some characteristics of the method, such as size of the micro particles trapped inside the flow and phase error between two ultrasonic waves, are discussed. The basic experiment is carried out by polystyrene spheres.
TL;DR: In this article, an ultrasonically energized polishing process, suitable for the polishing of complex dies and moulds has been successfully developed and patented, which is based upon the combination of the two "non-traditional" techniques of abrasive flow machining and ultrasonic machining.
Abstract: Dies and moulds used in the fabrication of metal, glass and plastic products require a high quality surface finish in terms of both appearance and integrity. Current manual polishing methods of surface finishing are time consuming and expensive. Consequently, a reduction in operator input and processing time has the potential to significantly reduce the cost of the finished mould. An ultrasonically energised polishing process, suitable for the polishing of complex dies and moulds has been successfully developed and patented. The process is based upon the combination of the two ‘non-traditional’ techniques of abrasive flow machining and ultrasonic machining. It has proved to be capable of improving surface finishes by factors of up to 10:1. This paper describes the development of the process and reports results achieved.
TL;DR: In this paper, the kinetic equation of evaporation and condensation of water vapour at the bubble wall is calculated numerically in order to investigate the non-equilibrium effect of nonequilibrium effects.
Abstract: The kinetic equation of evaporation and condensation of water vapour at the bubble wall is calculated numerically in order to investigate the non-equilibrium effect of evaporation and condensation. The liquid temperature at the bubble wall is also calculated as a function of time by estimating the heat flux at the bubble wall. Calculations are performed under a single-bubble sonoluminescence condition. It is clarified that the partial pressure of water vapour is identical to the saturated vapour pressure except at bubble collapse. At a strong collapse, the partial pressure of water vapour differs an order from the saturated vapour pressure of the heated liquid layer at the bubble wall. It is also clarified that most of all the vapour molecules (H 2 O) undergo chemical reactions at the strong collapse.
TL;DR: In this paper, the influence of the technological parameters on the surface hardening of metals by ultrasonically accelerated small balls was evaluated, and the experimental results showed that the ultrasonic impact treatment of steel might be used in industrial scale.
Abstract: The influence of the technological parameters on the surface hardening of metals by ultrasonically accelerated small balls was evaluated. It was demonstrated that the impact force grows with the increase of the amplitude and frequency of ultrasonic vibrations, density of material and size of balls and decreases with the increase of the distance between irradiator and sample. The experimental results showed that the ultrasonic impact treatment of steel might be used in industrial scale. The general advantages of the ultrasonic treatment are very short treatment time and the ability to treat all shapes with a simple apparatus.
TL;DR: In this paper, the authors measured the acoustic properties of the contrast agent and compared them with those of the myocardium, showing that the difference between scattering of the Myocardium and scattering of intravenously injected Albunex is too slight to be visible on an echographic image.
Abstract: The goal standard of contrast echocardiography is the absolute measure of myocardial perfusion using a contrast agent. Actually, several contrast agents are developed. All these agents show left ventricular opacification after intravenous injection. However, none of these agents shows an acceptable enhancement of the myocardium yet using conventional imaging techniques. The explanation of this phenomenon should be easy by measuring the acoustic characteristics of the contrast agent and then making a comparison of these characteristics with those of the myocardium. In this study we present definitions of standard acoustic parameters of ultrasound contrast agent, the backscatter coefficient B s and the scattering-to-attenuation ratio STAR. Afterwards, considering an intravenous injection of the contrast agent, and taking into account the effects of lung filtering and cardiac pressure, the standard properties of contrast agents are determined in different sites: right ventricle (before lung passage), left ventricle (after lung passage and taking into account the pressure effect) and in the coronary system. Calculations showed that the acoustic properties are considerably influenced by these two effects: lung filtering and cardiac pressure. Comparison of these properties with the tissue properties (myocardium) is then performed. This determines the contribution of the contrast agent to the enhancement of the tissue visualization. The simulations are performed on Albunex microspheres. The results reveal that the difference between scattering of the myocardium and scattering of intravenously injected Albunex is too slight to be visible on an echographic image.
TL;DR: In this article, a new technique called material characterization by resonance acoustic spectroscopy (MCRAS) is introduced for the evaluation of the elastic constants of isotropic rods and wires, compared to the traditional time-of-flight measurement technique.
Abstract: Examples of the applications of resonance acoustic spectroscopy (RAS) for the purposes of nondestructive evaluation (NDE) and on-line monitoring of the properties of various cylindrical components are presented in this paper. The mathematical equations for the scattering of a plane acoustic wave from isotropic and transversely isotropic cylinders and isotropic clad rods are reviewed. A new technique called material characterization by resonance acoustic spectroscopy (MCRAS), for the evaluation of the elastic constants of isotropic rods and wires, is introduced. This new technique is compared to the traditional time-of-flight measurement technique. Possible applications of RAS in NDE and on-line monitoring of clad rods are demonstrated using practical examples. The possibility of using RAS for evaluation of axial and transverse properties of fiber-reinforced composite wires and rods, which are transversely isotropic in nature, is discussed. The results indicate that RAS can be used as a tool for NDE and on-line monitoring of various properties of cylindrically-shaped components.
TL;DR: In this paper, a SiGMA (simplified Green's function for moment tensor analysis) code is developed to determine moment tensors components in ultrasonic waveforms to determine time-of-flight information.
Abstract: Elastic waves in the ultrasonic frequency range are extensively applied to nondestructive evaluation (NDE) of defects in concrete. One is the passive technique known as acoustic emission (AE), by which generation of a new crack can be detected. The other is ultrasonic testing (UT), where elastic waves are driven and configuration of an existing crack is estimated from diffraction. The theoretical treatment of both techniques is clarified. For AE, a procedure to determine moment tensor components is developed as a SiGMA (simplified Green's function for moment tensor analysis) code. A technique for reading the first motions in this analysis is also applied to the UT waveforms to determine time-of-flight information. The waveform analysis of UT signals is carried out to estimate defects in a reinforced concrete (RC) column in service. Because the moment tensor analysis of AE could locate cracks, classify crack types, and determine crack orientations, the procedure is applied to clarify fracture mechanisms of notehed beams.
TL;DR: In this paper, the authors reported measurements of diffusivities and absorption in other materials, particularly in metallic polycrystals, as well as measurements of modal densities for the high-frequency regime.
Abstract: Open celled foamed aluminum typically consists of an irregular frame of solid struts with typical lengths of the order of millimeters and thicknesses of a fraction of a millimeter. Total aluminum volume fractions are of the order of 10%. Quoted values of static modulus and mass density allow one to infer long wavelength (much greater than strut length) ultrasonic wave speeds. These predictions are compared with the velocities observed in 100 kHz transient signals. At higher frequencies, where wavelengths are comparable with strut lengths, ultrasound can be transported only diffusively. Wave speeds are unmeasurable and of little meaning anyway. We therefore also report on ultrasonic measurements appropriate for the high-frequency regime. These include diffusivity, absorption and modal density. Recent literature has reported measurements of diffusivities and absorption in other materials, particularly in metallic polycrystals. Measurements of modal densities are new.
TL;DR: In this article, a laser impact of short time duration is used to create a point source of Lamb waves and the detected waves are then remitted, but in time reverse order, according to this reemission, they obtain an axial hyperfocusing effect whose maximum is localized at the initial laser generation point.
Abstract: Lamb waves are particularly useful in the non-destructive testing domain of guided structures. However, they have the drawback to be dispersive and multimodal. These two characteristics make their processing particularly delicate during measurements. With a time reversal mirror (TRM), realized with an array of 32 transducers coupled to a Lucite wedge and where each transducer is associated to an appropriate individual electronic, we demonstrate that the time reversal process allows to compensate the problems linked to these two characteristics. In the set of experiments presented in this paper, we use a laser impact of short time duration to create a point source of Lamb waves. Using the TRM, detected waves are then remitted, but in time reverse order. According to this re-emission, we obtain an axial hyperfocusing effect whose maximum is localized at the initial laser generation point. This hyperfocusing effect generated by the time recompression is tested on different plates of various thickness and geometry. Experimental results are then compared to a numerical bidimensional scalar model.
TL;DR: Three-dimensional ultrasound imaging techniques that are capable of acquiring B-mode, colour Doppler and power Dopplers images of the vasculature are developed by using a conventional ultrasound system to acquire a series of two-dimensional images and then mathematically reconstructing them into a single three-dimensional image, which may then be viewed interactively on an inexpensive desktop computer.
Abstract: With conventional ultrasonography, the diagnostician must view a series of two-dimensional images in order to form a mental impression of the three-dimensional anatomy, an efficient and time consuming practice prone to operator variability, which may cause variable or even incorrect diagnoses. Also, a conventional two-dimensional ultrasound image represents a thin slice of the patients anatomy at a single location and orientation, which is difficult to reproduce at a later time. These factors make conventional ultrasonography non-optimal for prospective or follow-up studies. Our efforts have focused on overcoming these deficiencies by developing three-dimensional ultrasound imaging techniques that are capable of acquiring B-mode, colour Doppler and power Doppler images of the vasculature, by using a conventional ultrasound system to acquire a series of two-dimensional images and then mathematically reconstructing them into a single three-dimensional image, which may then be viewed interactively on an inexpensive desktop computer. We report here on two approaches: (1) free-hand scanning, in which a magnetic positioning device is attached to the ultrasound transducer to record the position and orientation of each two-dimensional image needed for the three-dimensional image reconstruction; and (2) mechanical scanning, in which a motor-driven assembly is used to translate the transducer linearly across the neck, yielding a set of uniformly-spaced parallel two-dimensional images.