Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 46 for “"Pulse-echo"”.
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The Study of Ultrasonic Pulse -Echo Subwavelength Defect Detection Mechanism
… and solved two research challenges in ultrasonic pulse-echo nondestructive evaluation through both experimental and numerical approaches. The spatial sampling study will provide quantitative engineering guideline for real-time on-line package inspection implementation. The subwavelength defect …
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Reconstruction of spatially varying sound speed distributions from pulse-echo data
… that sound speed tomography can be performed in pulse-echo mode by exploiting cross-correlations of post-beamformed data acquired from multiple steered plane wave excitations. Unlike traditional sound speed tomography setups, pulse-echo sound speed tomography only requires a single linear array …
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Acoustooptical techniques for ultrasonic materials evaluation: optical fiber interferometry and pulse-echo systems
… system are discussed. The second system is a pulse-echo transducer system that generates an electronically focusable ultrasonic field and detects the reflected field optically. The generating transducer consists of concentric ring electrodes etched on a single x-cut quartz crystal substrate …
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Cepstrum-based deconvolution techniques for ultrasonic pulse-echo imaging of flaws in composite laminates
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 1999.
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Spatiotemporal excitation sequence manipulation and processing for Doppler ultrasound and pulse-echo sound speed imaging applications
… to extend the maximum detectable velocity in pulsed-wave Doppler ultrasound. This is achieved by a reordering of the frames to minimize the relative phase difference between them while preserving spatial resolution that could be expected using a traditional sequence. The second application, …
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Inspection of Defects in the Seal Region of Flexible Food Packages Using the Ultrasonic Pulse -Echo Technique
In conclusion, techniques developed in this study will provide safety assurance of the flexible food packages and make these packages more financially competitive by reducing inspection costs.
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Evaluation of carbon fiber laminates via the use of pulse-echo ultrasound to quantify ply-stack orientation and manufacturing defects.
… within carbon fiber laminates via the use of pulse-echo ultrasound. The first scientific contribution of this work is a method to determine the number of lamina and orientation of each lamina for plain weave carbon fiber laminates. Current methods to verify the ply stack are destructive, …
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Ultrasound field measurement and modelling for non-destructive testing
… backing and matching of the transducer to the pulse generator together play a major role in the generation of the ultrasonic waves. Furthermore, the quantitative interpretation of pulse echo data obtained when such transducers are used in nondestructive evaluation (NDE) requires a complete …
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The use of ultrasonics for characterising fats and emulsions
… Ultrasonic measurements were made using either a pulse echo technique (1-10MHz), or a pulse echo interferometric technique (5-55MHz). The ultrasonic velocities of a series of 0-30% w/w glyceride/oil mixtures and some commercial fats were measured with varying temperature (0-70°C) at 1MHz. …
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A feasibility study of PVDF piezoelectric sensors to detect damage in adhesive joints
… been successfully used as NDT transducers in pulse-echo, through-transmission, and acousto-ultrasonic techniques to monitor curing, to detect porosity and crack propagation in different model joint geometries. The potential of using these techniques for practical bonded structures has then …
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High-resolution ultrasonic non-destructive testing
The use of ultra-short pulse wideband ultrasonic transducers in Non-Destructive-Testing (NDT) has been investigated both theoretically and experimentally. It is demonstrated that the resolution of pulse-echo NDT is affected by diffraction effects which also complicate the interpretation of echo …
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Study of atomic tunneling centers in the mixed crystal KBr1̳-̳x̳(CN)x̳ using dielectric echo techniques
… glassy, high-concentration regime, dielectric-echo measurements were made on five KBrl_x(CN)x crystals that had cyanide concentrations varying from 0.034 to 70%. These experiments were at a frequency of 0.79 GHz and in the temperature range 10 to 60 mK. Three-pulse echo experiments measured the …
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A Study of Atomic Tunneling Centers in the Mixed Crystal Potassium-Bromide(1-X)(cyanide)(x) Using Dielectric Echo Techniques
… glassy, high-concentration regime, dielectric-echo measurements were made on five KBr$\sb{1-x}$(CN)$\sb{x}$ crystals that had cyanide concentrations varying from 0.034 to 70%. These experiments were at a frequency of 0.79 GHz and in the temperature range 10 to 60 mK. Three-pulse echo …
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Circumferential propagation of acoustic pulses in partially-filled cylindrical shells
… the circumferential propagation of acoustic pulses in partially water-filled aluminum and stainless steel thin-walled cylindrical shells in the frequency x thickness (fd) region 0.64 MHz mm < fd < 0.96 MHz mm. In pulse-echo experiments, a multiplicity of periodic echoes were received when a …
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Design, Fabrication and Characterization of a Microfluidic Device for Ultrasound-based Cell Sorting
… analysis, flow continuity experiments, and pulse-echo testing. Results suggested that flow in the flow channel was continuous, and the transducer operated effectively.
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Preparation, microstructure and properties of silicon carbide-dysprosia composites
… properties were determined by the ultrasonic pulse echo technique. Flexure strengths were determined using four point bend testing. Fracture toughness was determined by both the three point, single-edge notched beam test and by the microindentation methods.
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Ultrasonic wave propagation in thick, layered composites containing degraded interfaces
… non-overlapping, distinct return signals in pulse-echo ultrasonic nondestructive evaluation. The effect of the interface contact quality on the reflection and transmission coefficients of degraded interfaces is observed in both the simulated and theoretical results.
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Experimental investigation of scattering from randomly rough elastic cylinders
… for the backscattered field for a laboratory pulse-echo environment: spherically spreading directional source and receiver with arbitrary beam patterns. Efficient numerical integration algorithms are developed to solve for the backscattered field from a specified surface profile. Experimental …
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Nondestructive Evaluation of Zirconium Phosphate Bonded Silicon Nitride Radomes
… 0.25" diameter, 15 MHz focused transducer with a pulse-echo configuration was clearly superior at detecting cracks, delaminations, impurities, voids and porosity variation. A method for determining local porosity via the longitudinal elastic wave velocity was developed and can be incorporated into …
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