Fusion of multi-view ultrasonic data for increased detection performance in non-destructive evaluation.

State-of-the-art ultrasonic non-destructive evaluation (NDE) uses an array to rapidly generate multiple, information-rich views at each test position on a safety-critical component. However, the information for detecting potential defects is dispersed across views, and a typical inspection may involve thousands of test positions. Interpretation requires painstaking analysis by a skilled operator.

Location Specific Temperature Compensation of Guided Wave Signals in Structural Health Monitoring.

In guided wave structural health monitoring, defects are typically detected by identifying high residuals obtained through the baseline subtraction method, where an earlier measurement is subtracted from the "current" signal. Unfortunately, varying environmental and operational conditions (EOCs), such as temperature, also produce signal changes and hence, potentially, high residuals. While the majority of the temperature compensation methods that have been developed target the changed wave speed induced by varying temperature, a number of other effects are not addressed, such as the changes in attenuation, the relative amplitudes of different modes excited by the transducer, and the transducer frequency response.

Scattering of the Fundamental Shear Guided Wave From a Surface-Breaking Crack in Plate-Like Structures.

Cracks in critical sections of steel structures pose a major safety concern in many industries. Existing high-frequency ultrasonic techniques offer high detection sensitivity to cracks but have poor inspection volume coverage, limiting their practical use for monitoring large areas of structures. Low-frequency guided waves have relatively high inspection area coverage and are currently used in pipeline monitoring for corrosion defects but face challenges in detecting critical cracks that often cause over an order of magnitude lower cross-sectional area loss.

Investigation of ultrasonic backscatter using three-dimensional finite element simulations.

Theoretical models are commonly used to describe ultrasonic backscattering in polycrystalline materials. However, although a full multiple scattering formalism has been derived, due to the difficulty in evaluation, currently only the single and double scattering effects have been evaluated. Three-dimensional finite element (3D FE) models have recently been demonstrated to be capable of predicting ultrasonic attenuation in polycrystalline materials and thereby show great potential in overcoming this limitation.

Interaction Between SH Guided Waves and Tilted Surface-Breaking Cracks in Plates.

The interaction between SH guided waves and simple defects is well understood and documented, and the SH and related torsional guided waves are commonly used in inspection. However, tilted and branching cracks, for which vertical notches are a poor approximation, are found in some environments, particularly when pipes are buried in alkaline soils. This paper studies the interaction between SH guided waves and tilted, surface-breaking cracks, investigating the effect of the tilt and depth of the defect.

Relative Ability of Wedge-Coupled Piezoelectric and Meander Coil EMAT Probes to Generate Single-Mode Lamb Waves.

Ultrasonic guided waves are used extensively when checking for defects in petrochemical and other industries and are mostly generated using piezoelectric transducers on an angled wedge or electromagnetic acoustic transducers (EMATs) in different configurations. Low-frequency inspection allows for long-distance propagation, but it is best suited for detecting relatively large defects, while at higher frequencies, the presence of multiple wave modes limit defect detectability, so achieving practical single Lamb mode excitation via careful transduction is very beneficial. This paper investigates the relative ability of angled piezoelectric and meander coil EMAT probes to produce single-mode transduction in the medium (~1-5 MHz-mm) and high (>5 MHz-mm) frequency-thickness regions of the dispersion curves.

Efficient generation of receiver operating characteristics for the evaluation of damage detection in practical structural health monitoring applications.

Permanently installed guided wave monitoring systems are attractive for monitoring large structures. By frequently interrogating the test structure over a long period of time, such systems have the potential to detect defects much earlier than with conventional one-off inspection, and reduce the time and labour cost involved. However, for the systems to be accepted under real operational conditions, their damage detection performance needs to be evaluated in these practical settings.

The scattering of torsional guided waves from Gaussian rough surfaces in pipework.

In older sections of industrial pipework there are often regions of general corrosion that typically have a Gaussian thickness distribution. During guided wave inspection this corrosion causes an increase in the background noise and a significant attenuation of the inspection wave. These effects are investigated in this paper through finite element modelling of the interaction of torsional guided waves with rough surfaces in pipes.

Cardiac Magnetic Resonance Imaging Versus Transthoracic Echocardiography for Prediction of Outcomes in Chronic Aortic or Mitral Regurgitation.

In subjects with aortic regurgitation (AR) or mitral regurgitation (MR), transthoracic echocardiography (TTE) is recommended for surveillance. Few prospective studies have directly compared the ability of TTE and cardiac magnetic resonance (CMR) to predict clinical outcomes in AR and MR. We hypothesized that, given its higher reproducibility, CMR would predict the need for valve surgery or heart failure (HF) hospitalization better than TTE.

Investigation of guided wave propagation in pipes fully and partially embedded in concrete.

The application of long-range guided-wave testing to pipes embedded in concrete results in unpredictable test-ranges. The influence of the circumferential extent of the embedding-concrete around a steel pipe on the guided wave propagation is investigated. An analytical model is used to study the axisymmetric fully embedded pipe case, while explicit finite-element and semi-analytical finite-element simulations are utilised to investigate a partially embedded pipe.

Feasibility and Reliability of Grain Noise Suppression in Monitoring of Highly Scattering Materials.

A feasibility study on grain noise suppression using baseline subtraction is presented in this paper. Monitoring is usually done with permanently installed transducers but this is not always possible; here instead monitoring is conducted by carrying out repeat C-scans and the feasibility of grain noise suppression by subtracting A-scans extracted from the C-scans is investigated. The success of this technique depends on the ability to reproduce the same conditions for each scan, including a consistent stand-off, angle, and lateral position of the transducer relative to the testpiece.

Excitation of Single-Mode Lamb Waves at High-Frequency-Thickness Products.

Guided wave inspection is used extensively in petrochemical plants to check for defects such as corrosion. Long-range low-frequency inspection can be used to detect relatively large defects, while higher frequency inspection provides improved sensitivity to small defects, but the presence of multiple dispersive modes makes it difficult to implement. This paper investigates the possibility of exciting a single-mode Lamb wave with low dispersion at a frequency thickness of around 20 MHz-mm.

Quantitating aortic regurgitation by cardiovascular magnetic resonance: significant variations due to slice location and breath holding.

Objectives: Compare variability in flow measurements by phase contrast MRI, performed at different locations in the aorta and pulmonary artery (PA) using breath-held (BH) and free-breathing (FB) sequences.

Methods: Fifty-seven patients with valvular heart disease, confirmed by echocardiography, were scanned using BH technique at 3 locations in the ascending aorta (SOV = sinus of Valsalva, STJ = sinotubular junction, ASC = ascending aorta at level of right pulmonary artery) and 2 locations in PA. Single FB measurement was obtained at STJ for aorta.

Mode selection for corrosion detection in pipes and vessels via guided wave tomography.

Guided wave tomography offers a method to accurately quantify wall thickness losses in pipes and vessels caused by corrosion, using ultrasonic waves transmitted over distances of approximately 1 to 2 m, and measured by an array of transducers. These measurements are then used to reconstruct a map of wall thickness throughout the inspected region. To achieve accurate estimations of remnant wall thickness, it is vital that a suitable Lamb mode is chosen.

Prospective comparison of valve regurgitation quantitation by cardiac magnetic resonance imaging and transthoracic echocardiography.

Background: Both transthoracic echocardiography (TTE) and cardiac magnetic resonance (CMR) imaging allow quantification of chronic aortic regurgitation (AR) and mitral regurgitation (MR). We hypothesized that CMR measurement of regurgitant volume (RVol) is more reproducible than TTE.

Methods And Results: TTE and CMR performed on the same day in 57 prospectively enrolled adults (31 with AR, 26 with MR) were measured by 2 independent physicians.

Study and comparison of different EMAT configurations for SH wave inspection.

Guided wave inspection has proven to be a very effective method for the rapid inspection of large structures. The fundamental shear horizontal (SH) wave mode in plates and the torsional mode in pipe-like structures are especially useful because of their non-dispersive character. Guided waves can be generated by either piezoelectric transducers or electro- magnetic acoustic transducers (EMATs), and EMATs can be based on either the Lorentz force or magnetostriction.

The reflection of guided waves from simple supports in pipes.

Successful ultrasonic guided wave detection of flaws at support locations relies on the ability to distinguish between the reflection produced by a simple support on an undamaged pipe and the reflection produced by pipe flaws. Consequently, it is essential to know how the reflections produced by simple supports behave; very little work has so far been reported on this subject. Through finite element simulations and experiments, this study develops a systematic understanding of how ultrasonic guided waves propagating along a pipe, in particular the T(0, 1) mode, interact with simple supports.

High-temperature (>500°c) wall thickness monitoring using dry-coupled ultrasonic waveguide transducers.

Conventional ultrasonic transducers cannot withstand high temperatures for two main reasons: the piezoelectric elements within them depolarize, and differential thermal expansion of the different materials within a transducer causes them to fail. In this paper, the design of a high-temperature ultrasonic thickness gauge that bypasses these problems is described. The system uses a waveguide to isolate the vulnerable transducer and piezoelectric elements from the high-temperature measurement zone.

Quantitative modeling of the transduction of electromagnetic acoustic transducers operating on ferromagnetic media.

The noncontact nature of electromagnetic acoustic transducers (EMATs) offers a series of advantages over traditional piezoelectric transducers, but these features are counter-balanced by their relatively low signal-to-noise ratio and their strong dependence on material properties such as electric conductivity, magnetic permeability, and magnetostriction. The implication is that full exploitation of EMATs needs detailed modeling of their operation. A finite element model, accounting for the main transduction mechanisms, has been developed to allow the optimization of the transducers.

The aorta wall of patients presenting to the emergency department with acute myocardial infarction by cardiac magnetic resonance.

Background: Inflammation has been shown to be a major component in the pathophysiology of acute coronary syndrome (ACS). In patients presenting with acute myocardial infarction (AMI), a critical component of the ACS spectrum, multiple coronary arteries are involved during this inflammatory process. In addition to the coronary vasculature, the inflammatory cascade has also been shown to affect the carotid arteries and possibly the aorta.

Guided wave diffraction tomography within the born approximation.

Detection and sizing of corrosion in pipelines and pressure vessels over large, partially accessible areas is of growing interest in the petrochemical industry. Low-frequency guided wave diffraction tomography is a potentially attractive technique to rapidly evaluate the thickness of large sections of partially accessible structures. Finite element simulations of a 64-element circular array on a plate show that when the scattering mechanism of the object to be reconstructed satisfies the Born approximation, the reconstruction of the thickness is accurate.

Evaluation of the damage detection capability of a sparse-array guided-wave SHM system applied to a complex structure under varying thermal conditions.

A sparse-array structural health monitoring (SHM) system based on guided waves was applied to the door of a commercial shipping container. The door comprised a corrugated steel panel approximately 2.4 m by 2.

Detection of myocardial damage in patients with sarcoidosis.

Background: In patients with sarcoidosis, sudden death is a leading cause of mortality, which may represent unrecognized cardiac involvement. Delayed-enhancement cardiovascular magnetic resonance (DE-CMR) can detect minute amounts of myocardial damage. We sought to compare DE-CMR with standard clinical evaluation for the identification of cardiac involvement.