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At least 775 records · Page 43Linked to original sources

PubMed2004

On the influence of fatigue on ultrasonic polar scans of fiber reinforced composites.

Ultrasonic polar scans have already proved to be well-suited as a practical means of characterizing fiber reinforced composite plates. The method consists of registering the reflected or transmitted sound amplitude as a function of each possible angle of incidence. It is hence an amplitude measurement by which it differs from more common 'time of flight' measurements. Ultrasonic polar scans are actually a fingerprint of a composite laminate. One of the many promising applications of the ultrasonic polar scan is the monitoring of fiber reinforced composites in service. Especially the progress of fatigue damage can be monitored easily and nondestructively. This paper presents numerical simulations of the influence of fatigue on ultrasonic polar scans as well as some experimental results.

Journal Article↗

PubMed2004

Ultrasonically assisted turning of aviation materials: simulations and experimental study.

Ultrasonically assisted turning of modern aviation materials is conducted with ultrasonic vibration (frequency f approximately 20 kHz, amplitude a approximately 15 microm) superimposed on the cutting tool movement. An autoresonant control system is used to maintain the stable nonlinear resonant mode of vibration throughout the cutting process. Experimental comparison of roughness and roundness for workpieces machined conventionally and with the superimposed ultrasonic vibration, results of high-speed filming of the turning process and nanoindentation analyses of the microstructure of the machined material are presented. The suggested finite-element model provides numerical comparison between conventional and ultrasonic turning of Inconel 718 in terms of stress/strain state, cutting forces and contact conditions at the workpiece/tool interface.

Journal Article↗

PubMed2005

Study of low-frequency ultrasonic cavitation fields based on spectral analysis technique.

A kind of new spectral analysis method for analyzing ultrasonic cavitation fields is brought forward in this paper. This method extracts the line spectrum and the continuous spectrum from the cavitation noise spectrum respectively, then obtains estimations of the energy intensities of different cavitation components such as the stable cavitation and the transient cavitation through corresponding calculations. The method is also applied to investigate low-frequency ultrasonic cavitation fields and is compared with spectral level analysis method. The results show that this method can provide adequate information on the course of the cavitation process, give the delicate analysis on the transient cavitation and the stable cavitation, and help to gain an insight into the nonlinear process of cavitation fields. Moreover, it also shows that the criterion for characterization of cavitation intensity presented by Frohly through studying the high-frequency ultrasonic fields can be used to evaluate the low-frequency ultrasonic fields.

Journal Article↗

PubMed2006

Characterization of TiN coating layers using ultrasonic backward radiation.

Since ceramic layers coated on machinery components inevitably experience the changes in their properties it is necessary to evaluate the characteristics of ceramic coating layers nondestructively for the reliable use of coated components and the remaining life prediction. To address such a need, in the present study, the ultrasonic backward radiation technique is applied to examine the very thin TiN ceramic layers coated on AISI 1045 steel or austenitic 304 steel substrate. Specifically, the ultrasonic backward radiation profiles have been measured with variations in specimen preparation conditions such as coating layer thickness and sliding loading. In the experiments performed in the current study, the peak angle and the peak amplitude of ultrasonic backward radiation profile varied sensitively according to two specimen preparation conditions. In fact, this result demonstrates a high possibility of the ultrasonic backward radiation as an effective tool for the nondestructive characterization of the TiN ceramic coating layers even in such a thin regime.

Journal Article↗

PubMed2006

Location of multiple proximate flaws using perpendicular NDT ultrasonic arrays.

An improved method for ultrasonic location of multiple flaws using perpendicular ultrasonic arrays, working in near-field conditions, is presented. The method uses the pulse-echo technique and is based on the processing of the information acquired by both the elemental emitting transducers and their adjacent ones. This type of processing improves the performance of a previous method that sometimes presents limitations for the detection of multiples flaws. This new method is applied to a set of ultrasonic traces, obtained with an ultrasonic prototype specifically designed for testing this method, showing the improvement obtained in imaging results.

Journal Article↗

PubMed2006

Lift-off compensation for improved accuracy in ultrasonic lamb wave velocity measurements using electromagnetic acoustic transducers (EMATs).

The crystalline texture of a sheet metal strongly affects its formability, so having knowledge of this texture is of great industrial relevance. The texture of rolled sheet metals, such as aluminium and steel, may be determined by ultrasonic measurement of the velocity of the zero order symmetric (S(0)) Lamb wave as a function of angle to the rolling direction. Electromagnetic acoustic transducers (EMATs) may perform this measurement without contacting the sample, therefore reducing perturbation to the plate wave system, as they are electromagnetically coupled to the sheet. The EMAT system measurements are non-destructive and may be made in real time, therefore offering advantages over the conventional techniques such as X-ray and neutron diffraction. It has been noticed that in the two EMAT pitch-catch system, the apparent arrival times of the ultrasonic waves change with variation in lift-off (distance between sample and transducer) due to impedance and aperture effects. For precise and accurate texture parameters to be obtained, accurate absolute ultrasonic velocity measurement is required and hence lift-off must be compensated for. This is of particular importance to online inspection systems where constant lift-off may be difficult to maintain. The impedance behaviour of various coil geometries has been investigated as a function of lift-off and frequency and compared to the received ultrasonic signal and the drive current pulse profile. Theoretical models have been used to explain the observed behaviour, and hence a scheme has been proposed for the compensation of lift-off effects in real time.

Journal Article↗

PubMed2006

The range equation of the ultrasonic link in gas media.

The paper presents a few chosen issues concerning the conditions that must be met to render possible the effective use of ultrasonic waves in active and passive applications in various gas media. The basic parameters of the gas medium influencing the transmission of ultrasonic waves in this kind of medium were discussed. An analysis of the range equation of the ultrasonic coupler in the gas medium and the computer model of the link in the stationary medium conditions were presented. An equation for the level of power decrease in the link was formulated and the calculated and measured characteristics of the level of power decrease for a few ultrasonic transducers working in the band of 20-100 kHz were presented in graphs.

Journal Article↗

PubMed2006

Eight-channel ultrasonic device for non-invasive quality evaluation in packed milk.

An eight-channel ultrasonic detecting device for microbiological quality evaluation of packed liquid foods is presented in this paper. This device makes possible a non-invasive detection of the microbial growth in liquid foods with no need to open the carton-based packages where they are contained. Thermal and humidity stabilization are required inside the measuring chamber. The changes in the liquid media produced by the microorganism growth induce variations in the ultrasonic propagation parameters giving a non-invasive evidence of the developing contamination. For that purpose, the amplitude and time of flight of an ultrasonic 800kHz tone burst travelling through an UHT milk pack are analysed. Inoculated and sterile packs were tested to evaluate the performance of this new non-invasive ultrasonic microbiological quality sensor.

Animals↗

PubMed2006

Image-based sizing of surface-breaking cracks by SH-wave array ultrasonic testing.

This paper presents calibration-free crack sizing techniques based on ultrasonic imaging. The techniques are intended for 2D (line) surface-breaking cracks with the size of the incident wavelength or greater. The probing wave mode is the anti-plane shear wave (SH-wave). Two methods are employed for the ultrasonic imaging. One is a synthetic aperture focusing technique (SAFT) and the other is a computed time-reversal focusing technique (TRFT). In this paper, those methods are modified so that crack tips are located directly from measured A-scope waveforms without any calibration experiments. The results are shown as a peak in the ultrasonic image created by the respective methods. Reasonable accuracies of the proposed techniques are demonstrated first for the sizing of slits with known depths. The techniques are applied thereafter to the sizing of fatigue cracks. Since fatigue cracks may not be open without an external load, ultrasonic measurements are taken with and without external loads. The results of the imaging show that the depths of open cracks can be estimated accurately. It is also shown that crack opening (closing) behavior can be deduced by observing appearance (disappearance) of the peak in the images indicating the crack tip.

Algorithms↗

PubMed2004

The microscopic visualisation of the sonocrystallisation of ice using a novel ultrasonic cold stage.

This work reports dynamic video images of the influence of ultrasonic cavitation on the sonocrystallisation of ice at a microscopic level. This has been achieved through the construction of a unique ultrasonic system for an optical microscope. The system consists of (1). an ultrasonic cold stage, (2). a temperature control system, and (3). a microscope and imaging setup. This allows the temperature of a sample to be systematically controlled while it is subjected to simultaneous excitation with alternating pressures in the ultrasonic frequency range. Both the amplitude of excitation and the frequency can be varied. Experiments on ice crystals in pure water and sucrose solutions were conducted. Three distinct phenomena were observed. Firstly, there is a tendency for cavitation bubbles to form at the grain boundaries between ice crystals. Secondly, there is a progressive melting of ice by cavitation bubbles which appear to eat their way into the ice phase. Thirdly, the dendritic ice structures may fragment under the influence of ultrasound, thus increasing the number of nuclei which may subsequently grow (secondary nucleation). These observations form the basis of a significantly enhanced understanding and exploitation of the sonocrystallisation of ice.

Journal Article↗

PubMed2004

Continuous contact- and contamination-free ultrasonic emulsification-a useful tool for pharmaceutical development and production.

A novel concept was developed here for the continuous, contact- and contamination-free treatment of fluid mixtures with ultrasound. It is based on exciting a steel jacket with an ultrasonic transducer, which transmitted the sound waves via pressurised water to a glass tube installed inside the jacket. Thus, no metallic particles can be emitted into the sonicated fluid, which is a common problem when a sonotrode and a fluid are in direct contact. Moreover, contamination of the fluid from the environment can be avoided, making the novel ultrasonic flow-through cell highly suitable for aseptic production of pharmaceutical preparations. As a model system, vegetable oil-in-water emulsions, fed into the cell as coarse pre-emulsions, were studied. The mean droplet diameter was decreased by two orders of magnitude yielding Sauter diameters of 0.5 microm and below with good repeatability. Increasing the residence time in the ultrasonic field and the sonication power both decreased the emulsion mean diameter. Furthermore, the ultrasonic flow-through cell was found to be well suited for the production of nanoparticles of biodegradable polymers by the emulsion-solvent extraction/ evaporation method. Here, perfectly spherical particles of a volume mean diameter of less than 0.5 microm could be prepared. In conclusion, this novel technology offers a pharmaceutically interesting platform for nanodroplet and nanoparticle production and is well suited for aseptic continuous processing.

Chemical Fractionation↗

PubMed2006

Structural and functional changes in ultrasonicated bovine serum albumin solutions.

Effects of high-intensity ultrasonication on functional and structural properties of aqueous bovine serum albumin (BSA) solutions were investigated. The functional properties of BSA were altered by ultrasonication. Surface activity of BSA increased. Minimal changes were observed in the global structure of BSA but surface charge increased particularly at basic pH values (e.g. pH>9). While dynamic light scattering measurements indicated that the particle size increased up to 3.4 times after 90 min of sonication, no significant increase in the oligomeric state of BSA using blue native PAGE was observed. The amount of free sulfhydryl groups in BSA after 90 min of sonication decreased. The increased particle size and decreased number of free sylfhydryl groups may be attributed to formation of protein aggregates. Surface hydrophobicity increased and circular dichroism spectroscopy and FTIR analysis indicated changes in the secondary structure of BSA. We hypothesize that mechanical, thermal and chemical effects of ultrasonication resulted in structural changes in BSA that altered the functional properties of the macromolecule which may be attributed to the formation of an ultrasonically induced state that differs from a thermally, mechanically or solvent induced state.

Dose-Response Relationship, Radiation↗

PubMed1983

In vivo ultrasonic tissue characterization of human intracardiac masses.

Interactions between an ultrasonic signal and cardiac tissue have been used to characterize the histologic state of myocardium in vitro. To assess the utility of in vivo ultrasonic tissue characterization, stochastic analysis was applied to the digitized echocardiographic signals from 15 patients with 2-dimensional echocardiograms suggesting intracardiac masses. Ten subjects with echocardiograms suggesting mural thrombi underwent subsequent surgery or necropsy, which confirmed thrombi in 6 and revealed no thrombi (designated artifact) in 4. Five other patients had intracardiac tumors. The amplitudes within the digitized ultrasonic signals were displayed as histograms, which were described by a parameter k that represented the degree to which each histogram departed from a totally random probability density function. In 5 of 6 thrombi, k = 0, but in all 4 artifacts, k greater than 0. The sixth thrombus had k = 0.5 due to the specular effect of the interface between the thrombus' 2 lobes. All 5 tumors had k greater than 0. Ultrasonic tissue characterization using a stochastic analysis of backscatter can be performed in vivo and helps differentiate thrombus from artifact and tumor in the heart.

Blood Coagulation↗

PubMed1985

Predictive value, sensitivity, and specificity of ultrasonic targeted imaging for fetal anomalies in gravid women at high risk for birth defects.

In this report the predictive value of ultrasonic targeted imaging for fetal anomalies (TIFFA) is defined. Six hundred fifteen pregnant women at high risk for birth defects were scanned from January, 1980, to December, 1983. Follow-up evaluation was available on 569 fetuses. The pregnancies were classified into five groups according to the indications used for ultrasonic targeted imaging studies. The largest number of women were placed in group 1 and were referred because of a variety of abnormalities in previous or ongoing pregnancies. The women classified in the other four groups were examined because of maternal or fetal reasons related to specific craniospinal (29%), urinary (7.9%), gastrointestinal (6.7%), and skeletal (3.7%) defects. In our series the predictive values of abnormal and normal ultrasonic targeted imaging studies were 95% and 99%, respectively. A detailed breakdown of the accuracy of ultrasonic targeted imaging in relation to each anatomic category is presented; these data are useful in counseling gravid women with anomalous fetuses.

Congenital Abnormalities↗

PubMed2000

[Evaluation of the Ultracision ultrasonic dissector in thyroid surgery. Prospective randomized study].

STUDY OBJECTIVE: This prospective randomized study was designed to evaluate the efficacy, safety and cost of the ultrasonic hook in thyroid surgery, in comparison with conventional hemostasis. METHODS: Thirty-four consecutive euthyroid patients with multinodular goiter undergoing total thyroidectomy were randomly assigned to either group I, Ultracision or group II, conventional hemostasis. Preoperative, intraoperative and postoperative biochemical, clinical, surgical and economic variables were compared in each group. RESULTS: Use of the ultrasonic hook resulted in a significant reduction in operating time (70.7 +/- 18.3 versus 96.5 +/- 28.9 minutes), blood loss (74.5 +/- 50.9 g versus 134.6 +/- 108.42 g), and postoperative analgesic consumption (paracetamol (mg): 700 +/- 722 versus 1888 +/- 978), and may also reduce the incidence of transient hypoparathyroidism (5.8% versus 23.5%). The ultrasonic hook was no more expensive than conventional hemostasis, as long as a minimum of 15 patients shared the initial unit cost of the device. CONCLUSION: Although the use of the ultrasonic dissector does not allow a major cost-saving in total thyroidectomy, the essential advantages were a significant reduction of intraoperative blood loss, length of operating time and postoperative analgesic consumption.

Adult↗

PubMed2004

Limitations of implantable, miniature ultrasonic transducers to measure wall movement in the canine jejunum.

BACKGROUND: We used implantable miniature ultrasonic transducers to measure longitudinal distance, circumference, and wall thickness dynamically in vivo in canine jejunum. We hoped to differentiate circular from longitudinal smooth muscle contractions and to correlate physical measurements of change in distance within the jejunal wall with intraluminal manometry. MATERIALS AND METHODS: In acute experiments at the time of celiotomy, longitudinal distances, circumferences, and wall thickness were measured directly and by ultrasonic transducers sewn to serosa and mucosa. Measurements were obtained with the intestine empty and after distention with air, water, or semisolid slurry. In chronic in vivo experiments in conscious dogs with indwelling ultrasonic transducers and intraluminal manometers, sonometric dimensions were correlated with manometric recordings. In acute experiments, sonometric measurements were similar to direct measurements. In chronic experiments in vivo, smallest ultrasonometric measurements of circumferences of the jejunum correlated in a phase-locked temporal manner with both highest intraluminal pressures and greatest wall thickness. RESULTS: Longitudinal distances increased during decreases in circumference. Distances orad to the site maximal intraluminal pressure peaked at 0.58 +/- 0.04 s ( x +/- SEM) before, and those aborad to this point 0.42 +/- 0.04 s after attaining minimum circumferences. CONCLUSIONS: Ultrasonic crystals can monitor geometric changes in the bowel wall with certain limitations, especially when obtained in vivo. Contraction of circular and longitudinal muscles, although phase-locked, do not appear to occur exactly synchronously in canine jejunum.

Animals↗

PubMed2002

Modeling the propagation of ultrasonic waves in the interface region between two bonded elements.

An important task in nondestructive materials evaluation is the development of techniques to characterize the bond quality of adherent joints. Binding forces are nonlinear and cause a nonlinear modulation of transmitted and reflected ultrasonic waves. As a consequence, the higher harmonics generated by an insonified monochromatic wave give information about the adhesive bonds. The local binding forces in thin bonded interfaces can be obtained by the amplitudes of the ultrasonic waves of the insonified frequency and its higher harmonics as transmitted through the interface. Additional phase measurements may enable one to obtain the evaluation of the full hysteretic cycle of the interaction force. In order to gain a deeper understanding of the interface region and to improve the technique, numerical simulations of the ultrasonic wave propagation through specimens of two bonded elements can be used. A simple model based on the local interaction simulation approach (LISA) is described in this contribution, and a comparison between the results of the simulations and the experimental data is presented. Besides its intrinsic relevance for NDE, the problem considered in this paper may be very useful to analyze and test models for the simulation of ultrasonic wave propagation in nonclassical nonlinear mesoscopic elastic materials.

Journal Article↗

PubMed2002

Directivity pattern of neurosurgical endoscopic ultrasonic probes.

The objective of this paper is to present recent investigations in characteristics of the sound field generated by neurosurgical endoscopic ultrasonic probes (NEUPs) for minimally invasive surgery. The importance of this information has been investigated and discussed taking into account following facts: 1. According to the International Standard IEC 61847:1998 basic acoustical output characteristics of ultrasonic surgical equipment is declared for and measured in an acoustical free field. The standard generally treats the ultrasonic probe as an omnidirectional point source of the zero order (monopole source). 2. In real conditions, operations with NEUPs are performed within the acoustical near field. Having in mind that the cavitational and hydrodynamic effects are dominant, two theoretical boundary conditions can be present. The first one takes place when operations are performed near the "soft" acoustical boundary (tissue/air), and the second one is near the "rigid" acoustical boundary (tissue/bone). Reflections of sound waves from boundaries have influence on the characteristics of the ultrasonic probe (transducer) and on the sound field. In such cases spherical waves of the first and second order are generated. Directivity of sound sources takes shape in the far field and is easier to measure there. On the basis of measured directivity patterns, the influence of different operational conditions (immersion depth of the probe tip, boundary type, acoustical impedance of the medium etc.) on the radiated sound power and spatial distribution of the sound pressure can be estimated.

Endosonography↗