Guided-Wave Approach for Spectral Peaks Characterization of Impact-Echo Tests in Layered Systems

Although many imaging algorithms such as ellipse and hyperbola algorithm can roughly locate defects in large plate-like structures with sparse guided wave arrays, quantitative characterization of them is still a challenging problem, especially for those small defects known as subwavelength defects. Scattering signals of defects contain abundant information so that can be used to evaluate defects. A defects recognition method using the S-matrix (scattering matrix) was presented. S-matrices of hole and crack with S0 mode incident were experimentally measured. The results show that defects can be recognized from the morphology of 2D S-matrix chart. This method has great potential to achieve more specific parameters of small defects with sparse guided wave arrays.

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Characterization of Tissue Microstructure Scatterer Distribution with Spectral Correlation

Ultrasonic Imaging ◽

10.1177/016173469301500304 ◽

1993 ◽

Vol 15 (3) ◽

pp. 238-254 ◽

Cited By ~ 16

Author(s):

Tomy Varghese ◽

Kevin D. Donohue

Keyword(s):

Formation Process ◽

Biological Tissue ◽

Statistical Parameters ◽

Spectral Correlation ◽

Tissue Microstructure ◽

Power Spectral ◽

Spectral Peaks ◽

Ultrasound Signal

Characterization of tissue microstructure from the backscattered ultrasound signal using the spectral autocorrelation (SAC) function provides information about the scatterer distribution in biological tissue. This paper demonstrates SAC capabilities in characterizing periodicities in A-scans due to regularity in the scatterer distribution. The A-scan is modelled as a cyclostationary signal, where the statistical parameters of the signal vary in time with single or multiple periodicities. This periodicity manifests itself as spectral peaks both in the power spectral density (PSD) and in the SAC. Periodicity in the PSD will produce a well defined dominant peak in the cepstrum, which has been used to determine the scatterer spacing. The relationship between the scatterer spacing and the spacing of the spectral peaks is established using a stochastic model of the echo-formation process from biological tissue. The distribution of the scatterers within the microstructure is modelled using a Gamma function, which offers a flexible method of simulating parametric regularity in the scatterer spacing. Simulations of the tissue microstructure for lower orders of regularity indicate that the SAC components reveal information about the scatterer spacing that are not seen in the PSD and the cepstrum. The echo-formation process is tested by simulating microstructure of varying regularity and analyzing their effect on the SAC, PSD and cepstrum. Experimental validation of the simulation results are provided using in vivo scans of the breast and liver tissue that show the presence of significant spectral correlation components in the SAC.

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Raman Characterization of Protocrystalline Silicon Films

MRS Proceedings ◽

10.1557/proc-1153-a16-04 ◽

2009 ◽

Vol 1153 ◽

Cited By ~ 1

Author(s):

A. J. Syllaios ◽

S. K. Ajmera ◽

G. S. Tyber ◽

C. L. Littler ◽

R. E. Hollingworth

Keyword(s):

Substrate Temperature ◽

Dopant Concentration ◽

Hydrogen Dilution ◽

Spectral Peaks ◽

And Performance ◽

And Shifts ◽

P Type ◽

Hydrogenated Amorphous ◽

Raman Spectral

AbstractAn increasingly important application of thin film hydrogenated amorphous silicon (α-Si:H) is in infrared detection for microbolometer thermal imaging arrays. Such arrays consist of thin α-Si:H films that are integrated into a floating thermally isolated membrane structure. Among the α-Si:H material properties affecting the design and performance of microbolometers is the microstructure. In this work, Raman spectroscopy is used to study changes in the microstructure of protocrystalline p-type α-Si:H films grown by PECVD as substrate temperature, dopant concentration, and hydrogen dilution are varied. The films exhibit the four Raman spectral peaks corresponding to the TO, LO, LA, and TA modes. It is found that the TO Raman peak becomes increasingly well defined (decreasing line width and increasing intensity), and shifts towards the crystalline TO energy as substrate temperature is increased, H dilution of the reactants is increased, or as dopant concentration is decreased.

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Characterization of C/Enhanced SiC Composite During Creep-Rupture Tests Using an Ultrasonic Guided Wave Scan System

28th International Conference on Advanced Ceramics and Composites B: Ceramic Engineering and Science Proceedings, Volume 25, Issue 4 - Ceramic Engineering and Science Proceedings ◽

10.1002/9780470291191.ch41 ◽

2008 ◽

pp. 267-274 ◽

Cited By ~ 1

Author(s):

Don J. Roth ◽

Michael J. Verrilli ◽

Richard E. Martin ◽

Laura M. Cosgriff

Keyword(s):

Guided Wave ◽

Creep Rupture ◽

Ultrasonic Guided Wave

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Model-based nonlinear guided wave approach for nondestructive evaluation in solid media

The Journal of the Acoustical Society of America ◽

10.1121/1.4933845 ◽

2015 ◽

Vol 138 (3) ◽

pp. 1837-1837 ◽

Cited By ~ 1

Author(s):

Younho Cho ◽

Weibin Li

Keyword(s):

Nondestructive Evaluation ◽

Guided Wave ◽

Wave Approach ◽

Model Based ◽

Solid Media ◽

Nonlinear Guided Wave

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Design and Characterization of a Fourier Transform Micro-Spectrometer

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.74.211 ◽

2009 ◽

Vol 74 ◽

pp. 211-214 ◽

Cited By ~ 1

Author(s):

Shou Hua Wang ◽

Hong Bin Yu ◽

Fook Siong Chau ◽

X.S. Tang

Keyword(s):

Fourier Transform ◽

Optical Resolution ◽

Input Voltage ◽

Optical Path Difference ◽

Path Difference ◽

Optical Path ◽

Spectral Peaks ◽

Grating Interferometer ◽

Diode Pumped

In this paper, we present a Fourier Transform micro-spectrometer which works based on a lamellar grating interferometer. The spectrometer model is electrostatically driven by parallel plate actuators which change the optical path difference (OPD) between movable grating facets and fixed ones. With a 200V input voltage, a maximum OPD of 48.7μm is achieved. The spectrum of a combined light source of a diode-pumped solid-state (DPSS) laser (λ=532.0nm) and a laser diode (λ=637.2nm) is experimentally acquired to demonstrate the performance of the model. The reconstructed spectrum displays two separate spectral peaks at 530.5nm and 635.2nm and the corresponding full-width at half-maximum (FWHM) resolutions are 9.8nm and 12.8nm respectively, indicating good wavelength accuracy and optical resolution.

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Preparation and Characterization of the Active Layer for an Led Based on Oxidized Porous Silicon

MRS Proceedings ◽

10.1557/proc-452-687 ◽

1996 ◽

Vol 452 ◽

Cited By ~ 2

Author(s):

L. Tsybeskov ◽

K. D. Hiirschman ◽

L. F. Moore ◽

P. M. Fauchet ◽

P. D. J. Calcott

Keyword(s):

Porous Silicon ◽

Carrier Transport ◽

Strong Dependence ◽

Band Emission ◽

Annealing Conditions ◽

Near Ir ◽

Spectral Peaks ◽

Oxidized Porous Silicon ◽

Ir Emission

AbstractWe have studied the photoluminescence (PL) in oxidized porous silicon (PSi), prepared from anodized crystalline Si followed by annealing at temperatures ranging from 700 to 1000°C. It has been found that two PL bands with spectral peaks at 1.6 e V (near-IR band) and near 2 eV (red band) exist with a strong dependence on preparation (annealing) conditions. Recent experimental results show a correlation between the intensity of the near-IR band and the level of leakage current in the diode-like structure. The suppression of the near-IR emission results in improved carrier transport, and the enhancement of the red band emission maximizes the electroluminescence (EL) efficiency. The PL study of thermally oxidized PSi indicates different recombination mechanisms. The red PL band is associated with a mechanism similar to band-tail-recombination within the quasi-bandgap of Si nanograins, whereas the near infra-red PL is associated with recombination via defect centers. These mechanisms will be discussed.

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