Ultrasonic Imaging Technique Research Articles

Ultrasonic Imaging Technique of Spot Weld Structure for a High Strength Galvanized Steel Sheet

Abstract In this paper, ultrasonic C-scan imagery technique is applied to measure the nugget diameter and image the defects in a spot weld of a high strength galvanized steel sheet. In order to enhance the test precision, the ultrasonic C-scan image is divided into six characteristic color regions and the related A-scan signals are analyzed according to the structural characteristics of the high strength galvanized steel spot weld. The results indicate that the nugget diameter can be measured accurately, and the shape of inner defects of nugget is evaluated based on the C-scan image and the time domain analysis of A-scan signal. The method proposed in the research is not only a comprehensive and visualized method for spot welding evaluation, but also a kind of important auxiliary method for spot weld research since the inner structure of the spot weld can be investigated without devastating it.

Fractional derivative models for ultrasonic characterization of polymer and breast tissue viscoelasticity

The viscoelastic response of hydropolymers, which include glandular breast tissues, may be accurately characterized for some applications with as few as 3 rheological parameters by applying the Kelvin-Voigt fractional derivative (KVFD) modeling approach. We describe a technique for ultrasonic imaging of KVFD parameters in media undergoing unconfined, quasi-static, uniaxial compression. We analyze the KVFD parameter values in simulated and experimental echo data acquired from phantoms and show that the KVFD parameters may concisely characterize the viscoelastic properties of hydropolymers. We then interpret the KVFD parameter values for normal and cancerous breast tissues and hypothesize that this modeling approach may ultimately be applied to tumor differentiation.

High-resolution photoacoustic imaging with focused laser and ultrasonic beams

We report a photoacoustic imager that utilizes a focused laser beam in combination with a 20 MHz ultrasound focusing transducer to obtain micron-resolution tissue images over a long working distance. The imager is based on a ring transducer that combines ultrasonic and laser beams collinearly and confocally in a monolithic element. The combination of focused laser beam and short pulse irradiation led to significant improvement in lateral and axial resolutions compared to the pulse-echo ultrasonic imaging technique or photoacoustic imaging with an unfocused laser. Potential applications include clinical examination of the eye and characterization of thin and superficial tissues.

Development of adhesive bonds with reduced fracture strength as NDE benchmarks

A method for producing adhesively bonded aluminum joints with a predictable loss of fracture strength was developed and evaluated. The method uses an open-faced specimen geometry and a humid high-temperature environment to promote adhesive degradation. The rate of degradation was greatly increased over previous accelerated degradation schemes through the use of MgSO 4 as a contaminant. The contaminant was applied as an aerosol in a purpose-built duct having a controlled airflow. Specimens were prepared and subjected to accelerated aging under a variety of conditions and then fractured using a DCB loading jig. It was found that the contaminant surface concentration was a strong determinant of the fracture strength after hot-wet aging. Exposure to the hot-wet environment was shown to have little effect beyond an initial threshold. Standard ultrasonic imaging techniques were incapable of differentiating between fresh and hot-wet aged specimens, in spite of significant differences in the fracture strength. This is consistent with the hypothesis that the approach produced specimens that simulated the effects of environmental attack, since standard ultrasonic methods, such as those used in the present study, cannot detect such losses of fracture strength in the absence of any delamination between adhesive and adherend. FESEM and EDX analysis of the fracture surfaces showed residual aluminum, suggesting an intra-oxide locus of failure consistent with other accelerated degradation methods. The technique can be used to generate adhesive joint specimens to aid the development of ultrasonic methods capable of detecting the loss of fracture strength associated with environmental degradation.

Characterization of Reflector Types by Phase-Sensitive Ultrasonic Data Processing and Imaging

Ultrasonic and radar imaging techniques are limited in resolution by the wavelength in the material, yet information beyond those limits is hidden in complex frequency dependent reflection coefficients. The analysis of the phase of complex reflection coefficients together with the properties of imaging algorithms can help to characterize and to classify indications of defects in concrete buildings. This paper describes a method to extract phase information from measurements and SAFT reconstructed images. The influencing factors like material properties, transducer characteristics, and imaging algorithms based on Born or Physical Optics approximations are elaborated. Simulated and experimental results are briefly discussed.

Optimisation of electromagnetic stirring in continuously cast steel billets using ultrasonic C-scan imaging technique

The present paper presents the analysis of ultrasonic C-scan images obtained through an automatic computerised multiscan immersion system, to obtain optimum current and frequency of an electromagnetic stirrer (EMS), installed at Billet Caster-1 of LD Shop-1 of M/s Tata Steel Ltd, Jamshedpur. The purpose was to achieve minimum defects and maximum equiaxed zones in the continuously cast steel billets. The amplitudes and positional data were integrated and controlled by a PC based ultrasonic equipment. The defect size and area in C-scan image was calculated automatically by a labelling and clustering algorithm, which showed a good correlation to the condition of actual defects. One low carbon steel Grade-A and one high carbon Grade-A were selected for experimental trials. The experiments conducted with various current and frequency combinations revealed that in general, quality of continuously cast steel billets improved with increasing EMS current in both grades of steel considered in the present work. The most significant improvement was found at 280 A EMS current and frequency 3.5 Hz. Beyond this there was only a marginal improvement in the billet quality as well as equiaxed zone. Based on the experimental observations, it is recommended to operate EMS at 280 A current and EMS frequency at 3.5 Hz in the plant.

Dual‐frequency driving transducer for ultrasonic echography

We propose a novel ultrasonic imaging technique by transmitting ultrasonic pulse of dual‐frequency and receiving multifrequency echoes from the biological tissues. When the ultrasonic pulse of two frequencies is transmitted from a transducer, the secondary waves are generated during the nonlinear propagation through the biological media. A choice of f0 and 4f0 as the dual‐frequency results in the generation of 2f0, 3f0, and 5f0 components as the secondary waves. Multifrequency echoes are capable of improving the image quality by reducing the speckle noise. We have developed the following annular type transducer. The PZT disk of 7 mm in diameter is coaxially arranged in the PZT ring of 9 mm in inner diameter and 17 mm in outer diameter. The ring and circular transducers transmit the pulses of 2 and 8 MHz, respectively. It was confirmed that this transducer formed the ultrasonic beams of 4, 6, and 10 MHz as well as the beams of 2 and 8 MHz in degassed water. Then the experiments of imaging the agar‐gel phan...

Performance Evaluation of Ultrasonic Nakagami Image in Tissue Characterization

Conventional ultrasonic B-mode images qualitatively describe tissue structures but are unsuitable for quantitative analyses of scatterer properties. We have recently developed an ultrasonic parametric imaging technique based on the Nakagami statistical distribution that is able to quantify scatterer concentrations. The aim of the present study is to further explore both the behavior of a Nakagami image in characterizing different scatterer structures at different signal-to-noise ratios (SNRs) and the feasibility of Nakagami imaging using a general commercial ultrasound scanner for tissue examinations. Simulations, experiments on a tissue-mimicking phantom and in vitro measurements on a muscle tissue before and after microwave treatment were carried out. The SNR and contrast-to-noise ratio (CNR) were estimated to quantify image performance. The results demonstrate that a Nakagami image can differentiate different scatterer concentrations for single, hypoechoic and hyperechoic targets. Also, a Nakagami image, when combined with an ultrasound scanner, can complement the B-scan to characterize tissue and to identify the region of interest with a larger CNR. However, the noise effect can degrade the performance of a Nakagami image. When the signal SNR decreased to 15 dB in simulations and to 8 dB in experiments, the CNR of the hyperechoic Nakagami image decreased by 4% and 27%, respectively, and that of the hypoechoic one decreased by 42% and 80%, respectively. These results indicate that a Nakagami image behaves well in identifying regions with high scatterer concentrations but does not perform well when both the scatterer concentration and SNR are low.

Sampling phased array – a new technique for ultrasonic signal processing and imaging

Over the past 10 years, the improvement in the field of microelectronics and computer engineering has led to significant advances in ultrasonic signal processing and image construction techniques that are currently being applied to non-destructive material evaluation. A new phased array technique, called 'Sampling Phased Array', has been developed in the Fraunhofer Institute for Non-Destructive Testing [1] . It realises a unique approach of measurement and processing of ultrasonic signals. The sampling phased array principle makes use of the measurement of elementary waves generated by individual elements of a sensor array to reconstruct the composite phased array signal for any arbitrary angle or focus depth. The use of special signal processing and image reconstruction algorithms allows generating A-scans of several angles and/or sector-scans, which can be implemented in real time. With parallel computing structures, this principle is used for automatic testing systems at very high inspection speed. A comparative study was done with conventional phased array and the sampling phased array technique. The study shows that the signal characteristics in both techniques are equal. In addition, the sampling phased array technique is significantly beneficial in many aspects such as quality of information in specific cases, inspection speeds and adaptability to specific inspection tasks in comparison to conventional phased array. The development results, including relevant test methodology and equipment aspects, are presented in the current work, together with the benefits for industrial ultrasonic inspection.

Assessment of interface deformation and fracture in metal matrix composites under transverse loading conditions

The transverse properties of unidirectional metal matrix composites (MMCs) are dominated by the fiber/matrix interfacial properties, residual stresses and matrix mechanical response. In order to monitor and study, in situ, the failure of interfaces in titanium-based composites subjected to transverse loading conditions, an ultrasonic imaging technique has been developed. The interface was imaged ultrasonically and the change in ultrasonic amplitude with the transverse loading was monitored, indicating the sensitivity of the technique to fracture and deformation of interfaces. This change in amplitude has been explained in terms of the multiple reflection theory of ultrasonic waves. The multiple reflection theory enabled estimation of the interfacial deformation and debonding as a function of loading. The ultrasonic technique was also used in conjunction with finite element modeling in order to quantify the fiber/matrix interfacial transverse strength in situ in MMCs.

Introduction to the Special Issue on High Resolution Ultrasonic Imaging in Industrial, Material and Biomaterial Applications

This special issue introduces recent advances in high-resolution ultrasonic imaging techniques and their applications to industrial materials and biomaterials evaluation. Various papers with novel results and techniques, developed by leaders in this field and some research groups are presented.

Ultrasonic imaging in the liquid metals

In some nuclear reactors the core is intended to be cooled by means of liquid metal, for example, lead-bismuth eutectic alloy. For safety and licensing reasons, an imaging method of the interior of reactor has thus to be developed. The paper is devoted to development of ultrasonic imaging and measurement technique suitable for performance in the liquid Pb/Bi alloy.

Phase-coded multi-pulse technique for ultrasonic high-order harmonic imaging of biological tissues in vitro

Second or higher order harmonic imaging shows significant improvement in image clarity but is degraded by low signal–noise ratio (SNR) compared with fundamental imaging. This paper presents a phase-coded multi-pulse technique to provide the enhancement of SNR for the desired high-order harmonic ultrasonic imaging. In this technique, with N phase-coded pulses excitation, the received Nth harmonic signal is enhanced by 20 log10N dB compared with that in the single-pulse mode, whereas the fundamental and other order harmonic components are efficiently suppressed to reduce image confusion. The principle of this technique is theoretically discussed based on the theory of the finite amplitude sound waves, and examined by measurements of the axial and lateral beam profiles as well as the phase shift of the harmonics. In the experimental imaging for two biological tissue specimens, a plane piston source at 2 MHz is used to transmit a sequence of multiple pulses with equidistant phase shift. The second to fifth harmonic images are obtained using this technique with N = 2 to 5, and compared with the images obtained at the fundamental frequency. Results demonstrate that this technique of relying on higher order harmonics seems to provide a better resolution and contrast of ultrasonic images.

A forward model and conjugate gradient inversion technique for low-frequency ultrasonic imaging

Emerging methods of hyperthermia cancer treatment require noninvasive temperature monitoring, and ultrasonic techniques show promise in this regard. Various tomographic algorithms are available that reconstruct sound speed or contrast profiles, which can be related to temperature distribution. The requirement of a high enough frequency for adequate spatial resolution and a low enough frequency for adequate tissue penetration is a difficult compromise. In this study, the feasibility of using low frequency ultrasound for imaging and temperature monitoring was investigated. The transient probing wave field had a bandwidth spanning the frequency range 2.5-320.5 kHz. The results from a forward model which computed the propagation and scattering of low-frequency acoustic pressure and velocity wave fields were used to compare three imaging methods formulated within the Born approximation, representing two main types of reconstruction. The first uses Fourier techniques to reconstruct sound-speed profiles from projection or Radon data based on optical ray theory, seen as an asymptotical limit for comparison. The second uses backpropagation and conjugate gradient inversion methods based on acoustical wave theory. The results show that the accuracy in localization was 2.5 mm or better when using low frequencies and the conjugate gradient inversion scheme, which could be used for temperature monitoring.

Distorted Born Diffraction Tomography Applied to Inverting Ultrasonic Field Scattered by Noncircular Infinite Elastic Tube

This study focuses on the application of ultrasonic diffraction tomography to noncircular 2D-cylindrical objects immersed in an infinite fluid. The distorted Born iterative method used to solve the inverse scattering problem belongs to the class of algebraic reconstruction algorithms. This method was developed to increase the order of application of the Born approximation (in the case of weakly-contrasted media) to higher orders. This yields quantitative information about the scatterer, such as the speed of sound and the attenuation. Quantitative ultrasonic imaging techniques of this kind are of great potential value in fields such as medicine, underwater acoustics and nondestructive testing.

Sampling phased array a new technique for signal processing and ultrasonic imaging

Sampling phased array a new technique for signal processing and ultrasonic imaging

Differential ultrasonic imaging for the characterization of lesions induced by high intensity focused ultrasound

High intensity focused ultrasound (HIFU) is an effective technique for noninvasive local creating coagulative necrotic lesions in deep target volumes without damage to the overlaying or surrounding tissues. It is very important to detect and evaluate lesions generated by HIFU during treatment procedures. This study describes the development of several differential ultrasonic imaging techniques to characterize lesions based on estimation of relative changes in tissue properties derived from backscattered RF data. A single, spherical HIFU transducer was used to produce lesions in soft tissues. The RF signals were recorded as outputs from a modified diagnostic ultrasound system. After some preprocessing, the integrated backscatter values, which can be used as an indicator of the microstructure and backscattering property of tissues, were calculated before and after HIFU treatment. The differential integrated backscatter values were subsequently used to form images revealing the lesion areas. The differential attenuation imaging with the same RF data was also performed, which has been proposed by a few researchers. The results of the differential integrated backscatter imaging were compared with that of the differential attenuation imaging and the former method offers some advantages over the latter method. The two methods above are both based on spectrum analysis and would spend much computational time. Therefore, some simple digital differential imaging methods, including absolute difference (AD), sum absolute differences (SAD), and sum squared differences (SSD) algorithms, were also proposed to detect HIFU-induced lesions. However, these methods cannot provide the information of the degree of tissue damage. Experiments in vitro bovine muscle and liver validated the method of differential integrated backscatter imaging for the characterization of HIFU-induced lesions. And the AD, SAD, and SSD algorithms can be implemented in real-time during HIFU therapy to visualize the lesions.

Real time multicomponent echo particle image velocimetry technique for opaque flow imaging

This letter reports on a contrast-based ultrasonic particle imaging technique (echo PIV) for measuring multicomponent velocity vectors in opaque flows with excellent temporal (up to 0.5ms) and spatial (up to 0.4mm) resolution. Ultrasound contrast microbubbles are used as flow tracers, and digitally acquired rf data are converted into B-mode images for PIV analysis. Here, velocity fields from various flow patterns (including rotating and transient vortex flows) that are difficult to measure using other opaque flow methods such as ultrasound Doppler or magnetic resonance imaging are measured using echo PIV. This nonintrusive technique should be a promising addition to opaque flow diagnostics.

Three-dimensional ultrasound biomicroscopy, environmental and conventional scanning electron microscopy investigations of the human zonula ciliaris for numerical modelling of accommodation

Biomechanical modelling of the accommodation process is a useful tool for studying the mechanism of accommodation and presbyopia and can aid in the development of accommodative lens-replacing materials. Existing biomechanical models, however, use a very simplified zonula structure. The aim of this study was to use three-dimensional ultrasonic imaging and scanning electron microscopy to provide a more detailed, three-dimensional description of the structure of the human zonula to improve the modelling of accommodation. Five human eyes were examined without invasive manipulation using a custom-made three-dimensional ultrasonic imaging technique that allows scanning of features with a spatial resolution of 30 microm. Environmental and conventional scanning electron microscopy (SEM) provided information to complement the ultrasonic images for use in development of a more anatomically correct finite-element model of the zonula structures. These data along with the material properties of the ocular tissue structures were used to construct an advanced geometric model for finite-element simulation of the accommodation process. Images were obtained through three-dimensional ultrabiomicroscopy (3D-UBM) of anatomical features heretofore not directly imagable in their native state. Ciliary processes and zonula structures were clearly separated by both the 3D-UBM and the SEM methods. It was found that fibres inserting on the anterior and posterior lens capsule emerge anteriorly at the ciliary body. Fibres emerging near the pars plana insert on the lens and the ciliary body. No X-shaped crossing fibres were found. Modelling of the accommodation process with both the simple and the more complex geometric models produced refractive power changes comparable with in vivo findings. The 3D-UBM allowed examination of zonula structures in their native state with minimized preparation artefacts. While these data were incorporated into a complex and more anatomically correct finite-element simulation of intraocular features including lens, zonular system and ciliary body it was found that a simplified zonular model is sufficient for the numerical simulation of the accommodation process.

Confirming plant integrity by specialised NDE inspections

The UK power industry is going through a difficult period, trying to balance the demand for electricity with conforming to the new environmental regulations. Because of overcapacity, it is no longer an attractive proposition to build new power stations but, instead, it makes economic sense to keep older power stations running beyond their design life. Structural integrity is increasingly demanding greater accuracy and repeatability from NDE inspections; new equipment and technology has been developed predominantly based on ultrasonic and eddy current technology. The development of information technology has been crucial for the improvement of ultrasonic imaging techniques. Advanced specialist inspections including phased array, time-of-flight diffraction and advanced eddy current, have been developed for evaluation of steam pipework, generator end-rings, steam chests, blade roots, rotor bore and rotor discs and many other plant items. The latest phased array techniques bring considerable benefits to the inspection of complex geometries. Ultrasonic inspections on components with complex geometries can give rise to confusing signal patterns which influence the speed and integrity of inspections. Additionally, access restrictions often limit probe movement, further affecting test integrity. The development and utilisation of phased array ultrasonic hardware and analysis software, has enabled high-integrity high-speed scanning and imaging of complex components. 'Sweep Scanning' can be carried out from a static position allowing coverage where access is restricted; the data can then be stored for future interrogation if required. The phased array probe contains multiple elements, and scanning can be mechanical (probe movement), electronic (pulsed beam sweep), or a combination of both. Component drawings and geometries can be overlaid on the phased array images, enabling both inspection design and ease of analysis. Advantages are gained through scanning complex geometries quickly with high integrity. Focusing of the optimal inspection angle gives improved defect detection and electronic data storage enables an auditable inspection fingerprint. This paper concentrates on three main applications: phased array and time-of-flight diffraction applications, rotor bore applications and generator retaining ring (end-ring) applications.