Defect Detection Sensitivity Research Articles

Comparing the diagnostic efficacy of intraoral radiography and cone beam computed tomography volume registration in the detection of mandibular alveolar bone defects

The aim of this study was to (1) compare bone loss detection accuracy with intraoral radiography and registered cone beam computed tomography (CBCT); (2) assess repeatability with both modalities; (3) determine factors affecting defect detection; and (4) determine the effect of buccolingual bone thickness on defect detection. Six observers viewed intraoral radiographs and CBCT scans before and after the defect to determine defect presence and extent. Receiver operating characteristic (ROC), sensitivity, specificity, logistic regression, odds ratio, intraclass correlation coefficient, and weighted kappa were used. CBCT and intraoral radiography mean ROC area under the curve values were not statistically different (0.90 vs 0.81; P = .06). CBCT had higher sensitivity compared with intraoral radiography (0.85 vs 0.63; P = .01) but similar specificity (0.91 vs 0.84; P = .45). Bone thickness, imaging modality, and observer had significant effects on defect detection (P < .001). Odds ratios for CBCT vs intraoral radiography were 2.29 for diagnostic accuracy and 1.52 for buccolingual bone thickness. There was moderate interobserver agreement for detection of defects and substantial intraobserver agreement for measurement of extent. CBCT showed equivalent diagnostic efficacy and specificity for defect detection and higher sensitivity compared with intraoral radiography. CBCT increases the odds of accurate defect assessment more than 2-fold compared with intraoral radiography. The odds of bone loss detection increase by approximately 50% per millimeter of buccolingual alveolar bone loss.

High sensitivity detection of ultrasonic signal for nondestructive inspection using pulse compression method

Semiconductor parts are currently being stacked and miniaturized, and as device structures become more complicated, nondestructive inspections are increasingly needed for improving yield and securing reliability. Scanning acoustic microscopy (SAM) is used to detect delamination and voids. However, when the frequency of the ultrasonic probe is increased to improve the spatial resolution, conventional SAM cannot detect defects in deep parts because ultrasonic attenuation increases. In this research, we developed high sensitivity detection technique of ultrasonic signal using a pulse compression method, examined a modulation method, and designed the waveform of the transmitted signal to achieve high defect detection sensitivity. Conventional and developed detection techniques of ultrasonic signal were applied to a 3-layer stacked specimen, and their ultrasonic images, noise reduction effect, and defect detection sensitivity were compared.

Enhanced ability of defect detection using high voltage time-domain resonance analysis and impedance spectrum

Impedance spectroscopy is a well-established method for detecting mechanical defects in materials and structures activated by piezoelectric resonance. However, the detection sensitivity is not always satisfactory for very small defects, such as those that are of great importance for high-field insulation. In this study, an enhanced defect detection method is developed to solve this problem. A high-voltage (1 kV) time-domain resonance analysis is used in combination with conventional impedance spectrum analysis. The resonant frequencies and damping factors of the characteristic high-voltage piezoelectric resonances are extracted from time-domain data, and the damping factors are found to be more sensitive to the defect geometry. The results suggest that the time-domain method used here may have potential for applications where a high sensitivity of defect detection is required.

Low Frequency Eddy Current Testing of Insulators and Composites

Eddy current testing (ECT), a non-destructive testing method widely used to evaluate defects within conductive materials, is explored in this study as it applies to insulators and non-uniformly conductive materials. Previous work has shown that at high frequencies, differences in electric permittivity can be detected with ECT. In this study, a new design of an ECT sensor that employs two resonance-tuned coils is evaluated. Results show that material inconsistencies in insulators are detectable due to spatial variations in permittivity and magnetic permeability, and that detection is possible at lower frequencies than previously demonstrated. In addition to determining signal dependence on individual electromagnetic parameters, sensitivity for defect detection in a carbon fiber-reinforced polymer (CFRP) composite is qualitatively determined. Although low signal-to-noise ratio is observed with a small-diameter coil, by increasing the coil diameter, the signal to noise ratio is increased while preserving adequate spatial resolution to detect defects in the sample. This study expands on previous studies of the application of ECT to insulators, and demonstrates that defect detection is possible in CFRPs.

Periodic Pulsed Thermography for Inner Defects Detection of Lead-Steel Bonded Structure

Multilayer materials with metal-metal bonded structure have been widely applied in aviation, aerospace, and nuclear industry. Disbond is prone to exist in lead-steel bonded structure, which degrades the load capacity and mechanical behaviors. Thermography nondestructive testing is a potential candidate for sub-layer defect detection. However, lead-steel bonded structure is unbearable when undertaken with over-heating of instantaneous temperature, which will lead to subsequent damage or generation of more unpredictable disbond. In addition, detection sensitivity of the deeper defects requires to be enhanced. In this paper, the mathematical derivation and the implementation of the periodic pulsed thermography have been established for detecting inner defects of lead-steel structure. This has been especially conducted for detecting small and deep defects that require high energy to increase detectability. Validation of the proposed method has been undertaken on both inductive thermography and optical thermography. The obtained results have demonstrated that periodic pulsed thermography is highly efficient for deep inner defect inspection of metal-metal bonded structure.

FISTA Algorithm for Radiography Images Enhancement with Background Blurring Removal

ABSTRACTTesting and detecting potential defects in works of art is usually required to cause minimal or no damage; industrial Radiography Testing (RT) is often the method of choice provided the images are of the required high quality and yield high defect detection sensitivity. Various digital image processing methods can be employed to achieve improved image quality and information extraction as required. The level and nature of the noise in the RT images is usually unknown. In addition to the different noises, the image quality is degraded by the blurring effect. In this study, a modified form of the Fast Iterative Shrinkage-Thresholding Algorithm (FISTA) with quadratic regularization strategy was developed and applied to remove the blurring. The output of the application of the method to number RT images of five art objects was evaluated by industrial radiography and antiquities experts. It was confirmed that the applied method was efficient and improved image quality and defect detection.

Diagnostic Performance and Repeatability of a Novel Game-Based Visual Field Test for Children.

To demonstrate utility of a game-based test ("Caspar's Castle") for the detection of visual field defects in children. A validity and reliability study was carried out at Manchester Royal Eye Hospital Pediatric Ophthalmology Outpatients Department. We recruited 108 children with no eye pathology (aged 4-12 years) and examined a single eye with the Caspar's Castle system using either normal thresholds or thresholds artificially adapted to recreate defects to assess diagnostic utility. Number of peripheral stimuli missed was used to determine sensitivity and specificity of artificial defect detection and to plot receiver-operator characteristic curves. A further 21 children (aged 4-16 years) with pathology were recruited and Caspar's fields compared qualitatively with established field testing. A total of 106 of the Caspar's Castle examinations were able to be performed twice and repeatability was determined through coefficient of repeatability and Bland-Altman chart. In diagnostic testing using children with no eye pathology, 45 children completed a test using normal thresholds and 43 with tests using artificial defects. Area under receiver-operator characteristic curves for artificial defect detection was 0.895. Of the 21 children with pathology, seven had completed standard Humphreys field testing and Caspar's Castle fields corresponded with each of these by expert opinion. Coefficient of repeatability for number of points missed across all cohorts of children (106 patients) was 6.9 (95% confidence interval: 6.16-8.07). The Caspar's Castle system of assessing visual fields using novel game-based strategies demonstrates encouraging levels of sensitivity, specificity, and reliability. It could help address current difficulties in perimetry in young children.

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. The significance of errors are illustrated and a 3D cross correlation is used which enables the same lateral position to be located within successive C-scans. The experimental results show that a noise reduction of around 15 dB is obtained after baseline subtraction, which will significantly improve the defect detection sensitivity. In practice however, successive C-scans may be conducted at different temperatures and with different transducers of similar specifications but a varying frequency response. Compensation techniques to reduce the impact of such variations are then presented and their effectiveness is verified experimentally. It is shown that it is feasible to obtain an overall improvement of around 10 dB in the signal to noise ratio via baseline subtraction, where a temperature difference of up to 10 ^circ C and a peak frequency shift of as much as ±250 kHz from a baseline value of around 7 MHz can be tolerated. However, this improvement was obtained in laboratory conditions with no changes to the surface of the specimen due to oxidation or corrosion. It is shown that differences in temperature and transducer frequency response are more difficult to compensate for than changes in test geometry and position.

Magnetic field shielding technique for pulsed remote field eddy current inspection of planar conductors

Pulsed remote field eddy current (PRFEC) can be used for detection of deeply buried flaws in non-magnetic flat plates. However, detection sensitivity for buried defect is low due to the great depth and the weak detecting signal. To improve the defect detection sensitivity, the PRFEC probe is optimized with the magnetic field shielding techniques in this work. On one hand, the exciting coil with shielding structure can focus the indirect magnetic field to penetrate through the plate. On the other hand, the detecting coil and the region between these two coils with shielding material can block and minimize the magnetic field energy diffusion along the direct coupling path. In order to investigate the shielding technique which blocks the direct coupling magnetic field, simulation studies using finite element method (FEM) has been first conducted, where three different PRFEC probes have been simulated and compared. Both detection abilities to defects in different directions and to thickness variation have been analyzed by using the second probe with shielding structure. The conclusions derived from the simulation study have been validated through experimental studies. Both simulation and experimental studies have indicated that the shielding technique can improve the detection sensitivity of subsurface defects.

Impact of tool design on defect detection sensitivity in extreme ultraviolet actinic blank inspection

We discuss the impact of various tool design perspectives on defect detection sensitivity for dark-field-based extreme ultraviolet (EUV) actinic blank inspection. We consider the impact of pixel size, EUV source type, and photon collection efficiency on critical defect signal-to-noise ratio (SNR) performance. The results show that as the pixel size approaches the target defect image size, defect SNR increases, and that pixel size also determines the dominant noise source in the inspection system. Moreover, the choice of the EUV source affects the optimal numerical aperture (NA) and illumination settings. For plasma-discharged sources, more photons provided by larger partial coherent illumination can improve the defect SNR, while coherent illumination is needed to get a higher defect SNR for synchrotron-based source. In the end, we show that simply increasing the photon collection efficiency by using high-NA optics or increasing the source power cannot always improve the defect SNR. In a speckle-noise dominated situation, larger outer NA includes more noise than defect signal, thus resulting in a lower SNR. The impact of source power also saturates at a certain level as the system becomes speckle-noise limited compared to photon-noise limited.

Scattering of torsional flexural guided waves from circular holes and crack-like defects in hollow cylinders

A study on the scattering of torsional flexural guided waves from circular holes and crack-like defects in hollow cylinders is carried out through finite element simulation and laboratory experiment. Two types of defects: circular holes and crack-like defects with varying orientation angles are studied. Results show that the reflection coefficients for flexural modes with different helix angles of propagation detecting a crack-like defect vary greatly, while for a circular hole the reflection coefficients for different flexural modes are similar. It is observed that there exists a specific flexural mode that shows the maximum reflection coefficient for a crack-like defect. The scattering properties can be utilized to classify defects as circular hole and crack-like, the range of the orientation angle of a crack-like defect can also be predicted. The detection sensitivity for oblique crack-like defects is significantly improved by using flexural modes that propagate at a helix angle with respect to the pipe axis. A flexural mode sweeping technique is proposed for classifying and characterizing defects in hollow cylinders. The proposed classification and characterization method is validated by laboratory experiments. Pipeline inspection using flexural guided waves can be supplemental to current inspection using only axisymmetric waves in order to improve the probability of an accurate and reliable inspection process.

Impact of noise sources and optical design on defect detection sensitivity in extreme ultraviolet actinic pattern inspection tool

We discuss the impact of various noise sources and the optical design in bright field extreme ultraviolet (EUV) actinic inspection of mask features for defects in the patterned absorber. It is shown that an optimum pixel size is needed to maximize the defect signal-to-noise ratio (SNR) to balance the trade-off in increasing signal strength with shot noise from defect signal and the background pattern intensity (mask layout image) and speckle noise from the mask blank roughness. Moreover, we consider defocus showing that the EUV mask phase effect has an asymmetric impact on pattern defect SNR’s through-focus behavior. The impact of defocus limits inspection performance based on defect SNR. Using critical defect sizes in a case study, we show the defect SNR performance of the limiting case and discuss the possibility of utilizing a nominal defocus in the inspection system to leverage the phase effect of EUV mask absorber to improve the defect SNR. A 50% improvement in defect SNR is shown to be possible by introducing a −50 nm nominal defocus into the bright field inspection system.

Defect detection of pipes using Lyapunov dimension of Duffing oscillator based on ultrasonic guided waves

This study proposes a novel small defect detection approach for steel pipes using the Lyapunov dimension (D) of the Duffing chaotic system based on ultrasonic guided waves. In this paper, inspection model is constructed by inputting the measured guided wave signal into the Duffing equation as the external turbulent driving force term and thenDis calculated. The properties of the Duffing system's noise immunity are first demonstrated theoretically based on the Lyapunov exponents. By comparingDof the Duffing inspection system between the conditions of the inputted pure noise and the guided wave signal, the amplitude of the periodic force (F), the important parameter of the Duffing inspection system, could be determined. The values of other parameters of the Duffing inspection system are subsequently determined according to the numerical investigation. Furthermore, a time-moving window function is constructed to scan along the measured signal to locate the defect. And the small defect echo signal polluted by the noise is illustrated to prove the availability of the proposed method. Both numerical and experimental results show that the proposed approach can be used to improve the sensitivity of small defect detection and locate the small defect in pipes.

Study of extreme ultraviolet lithography patterned mask inspection tool for half-pitch 11-nm node defect detection performance

Extreme ultraviolet lithography (EUVL) patterned mask defect detection is one of the major issues to overcome for realization of EUVL-based device fabrication. We have designed projection electron microscope (PEM) optics that have been integrated into a new inspection system called EBEYE-V30 (“Model EBEYE” is EBARA’s model code), and the PEM system performs well in half-pitch (hp) 16-nm node EUVL patterned mask inspection applications. We also discuss the extendibility of this system to 11-nm node defect detection. The progress made in the performance of the PEM optics is not simply about producing an image sensor with higher resolution but is also about improvement of the image processing to enhance the defect signal. A high-speed image sensor, a high-speed image-processing circuit, and a bright and stable electron source are necessary for hp 11-nm defect inspection. We describe the experimental results for EUVL patterned mask inspection using the above system for the hp 11-nm node. Programmed hp 11-nm defects (equivalent to 44 nm on the mask) are used for defect detection sensitivity evaluation. Defects as small as 16 nm on the mask could be detected using the current PEM system configuration.

Effect of Spectral Reshaping on Frequency Modulated Thermal Wave Imaging for Non-destructive Testing and Evaluation of Steel Material

Infrared thermographic techniques show their potential usage for non-destructive testing and evaluation of various materials due to their inherent capabilities such as whole field, non-contact, qualitative and quantitative to detect surface and sub-surface anomalies. This contribution introduces a novel data analysis scheme by spectral reshaping of linear frequency modulated temperature profile captured over a mild steel specimen. Time and frequency domain based processing methods are adopted on the generated temporal thermal data to reveal the hidden defects. Obtained results show the potential capabilities of spectral reshaping based on Gaussian windowed chirp with enhanced resolution and sensitivity for sub-surface defect detection.

Effect of Pipe Bend Configuration on Guided Waves-Based Defects Detection: An Experimental Study

Ultrasonic guided waves is one of the most effective nondestructive testing techniques, which has been successfully applied for damage detection and evaluation of piping components. However, research about defects detection for pipelines with multiple bends is still limited. In this paper, effect of pipe bend arrangement on guided waves-based defect detection is investigated by experimental method, in which different configurations including space-Z type, U type, and plane-Z type are considered, respectively. Finite element (FE) simulation is used to explore the propagation behaviors of axisymmetric L (0, 2) mode in different bend configurations. On this basis, the detection sensitivity for different crack locations is experimentally investigated. Simulation and experiment results reveal that feature of guided waves propagation across the first and the second bend is totally different, and the defect detection sensitivity in the second bend is different from that in the first bend.

Extreme ultraviolet lithography patterned mask defect detection performance evaluation toward 16- to 11-nm half-pitch generation

High-sensitivity and low-noise extreme ultraviolet (EUV) mask pattern defect detection is one of the major issues remaining to be addressed in device fabrication using extreme ultraviolet lithography (EUVL). We have designed a projection electron microscopy (PEM) system, which has proven to be quite promising for half-pitch (hp) 16-nm node to hp 11-nm node mask inspection. The PEM system was integrated into a pattern inspection system for defect detection sensitivity evaluation. To improve the performance of hp 16-nm patterned mask defect detection toward hp 11-nm EUVL patterned mask, defect detection signal characteristics, which depend on hp 64-nm pattern image intensity deviation on EUVL mask, were studied. Image adjustment effect of the captured images for die-to-die defect detection was evaluated before the start of the defect detection image-processing sequence. Image correction of intrafield intensity unevenness and L/S pattern image contrast deviation suppresses the generation of false defects. Captured images of extrusion and intrusion defects in hp 64-nm L/S patterns were used for detection. Applying the image correction for defect detection, 12-nm sized intrusion defect, which was smaller than our target size for hp 16-nm defect detection requirements, was identified without false defects.

Nondestructive Evaluation of Friction Stir-Welded Aluminum Alloy to Coated Steel Sheet Lap Joint

Dissimilar lap joints of aluminum sheet (AA 6061) of 2 mm thickness and zinc-coated steel sheet of 1 mm thickness were produced by friction stir welding with different combinations of rotational speed and travel speed. Ultrasonic C- and B-scanning, and radiography have been used in a complementary manner for detection of volumetric (cavity and flash) and planar (de bond) defects as the defects are in micron level. Advanced ultrasonic C-scanning did not provide any idea about the defects, whereas B-scanning cross-sectional image showed an exclusive overview of the micron-level defects. A digital x-ray radiography methodology is proposed for quality assessment of the dissimilar welds which provide three-fold increase in signal-to-noise ratio with improved defect detection sensitivity. The present study clearly shows that the weld tool rotational speed and travel speed have a decisive role on the quality of the joints obtained by the friction stir welding process. The suitability of the proposed NDE techniques to evaluate the joint integrity of dissimilar FSW joints is thus established.

Artwork Inspection by Shearography with Adapted Loading

Methods for the investigation of the surface as well as methods to find subsurface and structure weakening defects are of special interest in the field of art conservation. Shearography is a self-referencing interferometric technique that was proven to be useful for the robust detection of various defects under practical conditions. In the past the investigation of artwork using shearography was mainly done by thermal loading. But other loading techniques, like pressure, vibration and humidity change can be applied with advantage. In this paper we investigate the influence of different loading types and mechanisms on the sensitivity of defect detection on artwork considering their possible impact on the intact part of the artwork. At different samples we will show that a kind of mechanic loading provides a suitable method to detect delaminations and cracks without damaging the paintings. For other typical defects like holes, or trapped air other types of loading like the thermal one is more suitable.

High frequency guided ultrasonic waves for hidden fatigue crack growth monitoring in multi-layer model aerospace structures

Especially for ageing aircraft the development of fatigue cracks at fastener holes due to stress concentration and varying loading conditions constitutes a significant maintenance problem. High frequency guided waves offer a potential compromise between the capabilities of local bulk ultrasonic measurements with proven defect detection sensitivity and the large area coverage of lower frequency guided ultrasonic waves. High frequency guided waves have energy distributed through all layers of the specimen thickness, allowing in principle hidden (2nd layer) fatigue damage monitoring. For the integration into structural health monitoring systems the sensitivity for the detection of hidden fatigue damage in inaccessible locations of the multi-layered components from a stand-off distance has to be ascertained. The multi-layered model structure investigated consists of two aluminium plate-strips with an epoxy sealant layer. During cyclic loading fatigue crack growth at a fastener hole was monitored. Specific guided wave modes (combination of fundamental A0 and S0 Lamb modes) were selectively excited above the cut-off frequencies of higher modes using a standard ultrasonic wedge transducer. Non-contact laser measurements close to the defect were performed to qualify the influence of a fatigue crack in one aluminium layer on the guided wave scattering. Fatigue crack growth monitoring using laser interferometry showed good sensitivity and repeatability for the reliable detection of small, quarter-elliptical cracks. Standard ultrasonic pulse-echo equipment was employed to monitor hidden fatigue damage from a stand-off distance without access to the damaged specimen layer. Sufficient sensitivity for the detection of fatigue cracks located in the inaccessible aluminium layer was verified, allowing in principle practical in situ ultrasonic monitoring of fatigue crack growth.