scholarly journals A Model-Based Study of Transmit-Receive Longitudinal Arrays for Inspection of Subsurface Defects

2020 ◽  
Vol 3 (3) ◽  
Author(s):  
Ehsan Mohseni ◽  
Charles Macleod ◽  
Yashar Javadi ◽  
Randika K. W. Vithanage ◽  
Zhen Qiu ◽  
...  
Keyword(s):  
Surface Defects ◽  
Signal To Noise Ratio ◽  
Near Field ◽  
Target Material ◽  
Field Zone ◽  
Flat Bottom ◽  
Near Surface ◽  
Array Configuration ◽  
Surface Areas ◽  
Matrix Arrays

Abstract Dual matrix transmit-receive longitudinal (TRL) arrays have been shown to provide an improved signal to noise ratio in the near field zone which makes them the most suitable array configuration for the inspection of near-surface defects. This study aims to compare the performance of different configurations for transmit-receive longitudinal matrix arrays. For this purpose, four matrix configurations of 2 × 32, 4 × 16, 4 × 32, and 8 × 16 elements are investigated using EXTENDE CIVA modeling package. The array operating frequencies investigated are either 5 MHz or 10 MHz. The effect of different natural focal depths, arrays separation distances, dynamic electronic depth focusing, and electronic beam skewing for these TRL arrays are considered in models prepared in CIVA. The inspection of a series of flat bottom holes extended up to a few millimeters under the surface using the selected TRL configurations is also investigated in the study. It is found that the performance of focusing for near-surface areas is more efficient using the 4 × 16 and 8 × 16 elements configurations as compared with the others, and the signal amplitudes of the defects located deeper in the target material are almost independent of the configuration.

Detection of near-surface defects in rails combining Green's function retrieval of ultrasonic diffuse fields and sign coherence factor imaging

2020 ◽  
Vol 62 (4) ◽  
pp. 216-221
Author(s):  
Haiyan Zhang ◽  
Mintao Shao ◽  
Guopeng Fan ◽  
Hui Zhang ◽  
Wenfa Zhu
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Surface Defects ◽  
Signal To Noise Ratio ◽  
Near Surface ◽  
Coherence Factor ◽  
Array Transducer ◽  
Diffuse Fields ◽  
Ultrasonic Phased Array ◽  
Cross Correlations

A method combining Green's function retrieval theory and sign coherence factor (SCF) imaging is presented to detect near-surface defects in rails. The defects are close to the ultrasonic phased array and near-surface acoustic information of defects is obscured by the non-linear effects of the initial wave signal in directly acquired responses. To overcome this problem, cross-correlations of the diffuse field signals captured by the array transducer are performed to reconstruct the Green's function. SCF imaging is used to further improve the spatial resolution and signal-to-noise ratio (SNR) of near-surface defects in rails. Experiments are conducted on two rails containing two and four defects, respectively. The results show that these defects can be clearly identified when using the reconstructed Green's function. However, the images of near-surface defects are masked and cannot be distinguished when using directly captured signals and total focus imaging. The proposed method reduces the background noise and allows for effective imaging of near-surface defects in rails.

Effect of Three-Dimensional Near Surface Defects on Rolling and Sliding Contact Fatigue

1994 ◽  
Vol 116 (4) ◽  
pp. 841-848 ◽  
Author(s):  
M. Liu ◽  
T. N. Farris
Keyword(s):  
Stress Distribution ◽  
Fatigue Limit ◽  
Surface Defects ◽  
Near Field ◽  
Equivalent Stress ◽  
Three Dimensional ◽  
The Body ◽  
Sliding Contact ◽  
Element Formulation ◽  
Near Surface

The effect of three-dimensional defects such as voids and inclusions on the sliding contact subsurface stress distribution and fatigue limit is investigated. Three-dimensional finite-infinite boundary elements are utilized to model the body by discretizing its surface and the interface between the solid and the defect. The multidomain boundary element formulation is employed to accurately model the effect of the inclusion on the stress distribution. It is shown that the void has a greater near field effect on the stress distribution while the effect of a stiff inclusion applies over a larger distance. The critical stress points during a load passage are predicted based on a search of the maximum distortional strain energy. The stresses at the critical points are used for the fatigue limit pressure estimation by incorporating the equivalent stress concept with the Haigh diagram. The model predicts that a near surface spherical void of given size and depth reduces the maximum allowable fatigue limit design pressure by 75 percent while a stiff inclusion of the same size, shape, and location reduces it by 25 percent.

Improving imaging and repeatability on land using virtual source redatuming with shallow buried receivers

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. Q15-Q26 ◽  
Author(s):  
Dmitry Alexandrov ◽  
Andrey Bakulin ◽  
Roy Burnstad ◽  
Boris Kashtan
Keyword(s):  
Seismic Data ◽  
Near Field ◽  
Time Lapse ◽  
Elastic Model ◽  
Virtual Source ◽  
Field Zone ◽  
Near Surface ◽  
Actual Field ◽  
Different Sources

Time-lapse surface seismic monitoring typically suffers from different sources of nonrepeatability related to acquisition imperfections as well as due to complexity of the subsurface. Placing sources and receivers below the surface can improve seismic data repeatability. However, it is not always possible to bury a large number of sources, and therefore the next best option is monitoring with surface sources and buried sensors. We have discovered that redatuming of surface sources to the shallow buried receivers produced a reliable image of target reflectors despite the fact that receivers were placed in the near-field zone of the source. We redatumed data with the virtual source method using crosscorrelation of the measured wavefields. We found that redatuming also reduced nonrepeatability of seismic data associated with changes in acquisition geometry, variable source coupling, and daily/seasonal variations in the near surface. We developed these results with a synthetic case study using a realistic 1D elastic model with a free surface and acquisition geometry from an actual field experiment conducted in Saudi Arabia.

scholarly journals Detection and Localization of Defects in Monocrystalline Silicon Solar Cell

2010 ◽  
Vol 2010 ◽  
pp. 1-5 ◽  
Author(s):  
P. Tománek ◽  
P. Škarvada ◽  
R. Macků ◽  
L. Grmela
Keyword(s):  
Solar Cell ◽  
Surface Defects ◽  
Near Field ◽  
Electric Energy ◽  
Optical Methods ◽  
Reverse Bias Voltage ◽  
Field Methods ◽  
Near Surface ◽  
Surface Reflection ◽  
Detection And Localization

Near-surface defects in solar cell wafer have undesirable influence upon device properties, as its efficiency and lifetime. When reverse-bias voltage is applied to the wafer, a magnitude of electric signals from defects can be measured electronically, but the localization of defects is difficult using classical optical far-field methods. Therefore, the paper introduces a novel combination of electric and optical methods showing promise of being useful in detection and localization of defects with resolution of 250 nm using near-field nondestructive characterization techniques. The results of mapped topography, local surface reflection, and local light to electric energy conversion measurement in areas with small defects strongly support the development and further evaluation of the technique.

Specimen Preparation of Near Surface Ion Irradiated Samples

1985 ◽  
Vol 43 ◽  
pp. 170-171
Author(s):  
K. F. Russell ◽  
L. L. Horton
Keyword(s):  
Radiation Damage ◽  
Heavy Ions ◽  
Target Material ◽  
Metal Alloys ◽  
Specimen Surface ◽  
Specimen Preparation ◽  
Particle Accelerators ◽  
Near Surface ◽  
Graaff Accelerator ◽  
Van De Graaff

Beams of heavy ions from particle accelerators are used to produce radiation damage in metal alloys. The damaged layer extends several microns below the surface of the specimen with the maximum damage and depth dependent upon the energy of the ions, type of ions, and target material. Using 4 MeV heavy ions from a Van de Graaff accelerator causes peak damage approximately 1 μm below the specimen surface. To study this area, it is necessary to remove a thickness of approximately 1 μm of damaged metal from the surface (referred to as “sectioning“) and to electropolish this region to electron transparency from the unirradiated surface (referred to as “backthinning“). We have developed electropolishing techniques to obtain electron transparent regions at any depth below the surface of a standard TEM disk. These techniques may be applied wherever TEM information is needed at a specific subsurface position.

Electron Channelling Contrast Imaging of Dislocations

1990 ◽  
Vol 48 (1) ◽  
pp. 600-601
Author(s):  
J.T. Czernuszka ◽  
N.J. Long ◽  
P.B. Hirsch
Keyword(s):  
Field Emission ◽  
Secondary Electron ◽  
Surface Defects ◽  
Spot Size ◽  
Beam Divergence ◽  
Contrast Imaging ◽  
Scattered Electron ◽  
Near Surface ◽  
Filter System ◽  
Electron Channelling

In the 1970s there was considerable interest in the development of the electron channelling contrast imaging (ECCI) technique for imaging near surface defects in bulk (electron opaque) specimens. The predictions of the theories were realised experimentally by Morin et al., who used a field emission gun (FEG) operating at 40-50kV and an energy filter such that only electrons which had lost no more than a few 100V were detected. This paper presents the results of a set of preliminary experiments which show that an energy filter system is unneccessary to image and characterise the Burgers vectors of dislocations in bulk specimens. The examples in the paper indicatethe general versatility of the technique.A VG HB501 STEM with a FEG was operated at 100kV. A single tilt cartridge was used in the reflection position of the microscope. A retractable back-scattered electron detector was fitted into the secondary electron port and positioned to within a few millimetres of the specimen. The image was acquired using a Synoptics Synergy framestore and digital scan generator and subsequently processed using Semper 6. The beam divergence with the specimen in this position was 2.5 mrads with a spot size of approximately 4nm. Electron channelling patterns were used to orientate the sample.

Direct Plan View FIB Liftout for Near-Surface Defect Analysis in TEM

2013 ◽  
Author(s):  
Max L. Lifson ◽  
Carla M. Chapman ◽  
D. Philip Pokrinchak ◽  
Phyllis J. Campbell ◽  
Greg S. Chrisman ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Silicon Germanium ◽  
Focused Ion Beam ◽  
Surface Defects ◽  
Ion Beam ◽  
Misfit Dislocations ◽  
Tem Analysis ◽  
Plan View ◽  
Near Surface ◽  
Straightforward Method

Abstract Plan view TEM imaging is a powerful technique for failure analysis and semiconductor process characterization. Sample preparation for near-surface defects requires additional care, as the surface of the sample needs to be protected to avoid unintentionally induced damage. This paper demonstrates a straightforward method to create plan view samples in a dual beam focused ion beam (FIB) for TEM studies of near-surface defects, such as misfit dislocations in heteroepitaxial growths. Results show that misfit dislocations are easily imaged in bright-field TEM and STEM for silicon-germanium epitaxial growth. Since FIB tools are ubiquitous in semiconductor failure analysis labs today, the plan view method presented provides a quick to implement, fast, consistent, and straightforward method of generating samples for TEM analysis. While this technique has been optimized for near-surface defects, it can be used with any application requiring plan view TEM analysis.

scholarly journals Ultrasonic Imaging of Thick Carbon Fiber Reinforced Polymers through Pulse-Compression-Based Phased Array

2021 ◽  
Vol 11 (4) ◽  
pp. 1508
Author(s):  
Muhammad Khalid Rizwan ◽  
Stefano Laureti ◽  
Hubert Mooshofer ◽  
Matthias Goldammer ◽  
Marco Ricci
Keyword(s):  
Carbon Fiber ◽  
Pulse Compression ◽  
Phased Array ◽  
Signal To Noise Ratio ◽  
Near Field ◽  
Ultrasonic Imaging ◽  
Fiber Reinforced Polymers ◽  
Fiber Reinforced ◽  
Custom Made ◽  
Carbon Fiber Reinforced

The use of pulse-compression in ultrasonic non-destructive testing has assured, in various applications, a significant improvement in the signal-to-noise ratio. In this work, the technique is combined with linear phased array to improve the sensitivity and resolution in the ultrasonic imaging of highly attenuating and scattering materials. A series of tests were conducted on a 60 mm thick carbon fiber reinforced polymer benchmark sample with known defects using a custom-made pulse-compression-based phased array system. Sector scan and total focusing method images of the sample were obtained with the developed system and were compared with those reconstructed by using a commercial pulse-echo phased array system. While an almost identical sensitivity was found in the near field, the pulse-compression-based system surpassed the standard one in the far-field producing a more accurate imaging of the deepest defects and of the backwall of the sample.

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