The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform
Mircea Calomfirescu - One of the best experts on this subject based on the ideXlab platform.
-
theoretical and experimental studies of lamb wave propagation in attenuative composites
The 14th International Symposium on: Smart Structures and Materials & Nondestructive Evaluation and Health Monitoring, 2007Co-Authors: Mircea Calomfirescu, Axel S HerrmannAbstract:This paper presents a theoretical model for anisotropic wave Attenuation in composites. The model has been implemented in a software called FIBREWAVE in order to predict dispersion and Attenuation of S 0 , A 0 and SH 0 Lamb wave modes. The required input data are the complex stiffness matrix coefficients of the unidirectional plies of the laminate, which have been measured by a laser interferometry method. Complex stiffness data for an unidirectional CFRP laminates are moreover presented. Satisfactory agreement has been observed between predicted and experimental group velocities and wave Attenuations.
Guy Cloutier - One of the best experts on this subject based on the ideXlab platform.
-
a frequency shift method to measure shear wave Attenuation in soft tissues
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2017Co-Authors: Simon Bernard, Siavash Kazemirad, Guy CloutierAbstract:In vivo quantification of shear-wave Attenuation in soft tissues may help to better understand human tissue rheology and lead to new diagnostic strategies. Attenuation is difficult to measure in acoustic radiation force elastography because the shear-wave amplitude decreases due to a combination of diffraction and viscous Attenuation. Diffraction correction requires assuming a cylindrical wavefront and an isotropic propagation medium, which may not be the case in some applications. In this paper, the frequency-shift method, used in ultrasound imaging and seismology, was adapted for shear-wave Attenuation measurement in elastography. This method is not sensitive to diffraction effects. For a linear frequency dependence of the Attenuation, a closed-form relation was obtained between the decrease in the peak frequency of the gamma-distributed wave amplitude spectrum and the Attenuation coefficient of the propagation medium. The proposed method was tested against a plane-wave reference method in homogeneous agar–gelatin phantoms with 0%, 10%, and 20% oil concentrations, and hence different Attenuations of 0.117, 0.202, and 0.292 $\text {Np}\cdot \text {m}^{-1}$ /Hz, respectively. Applicability to biological tissues was demonstrated with two ex vivo porcine liver samples (0.79 and 1.35 $\text {Np} \,\cdot \, \text {m}^{-1}$ /Hz) and an in vivo human muscle, measured along (0.43 $\text {Np}\,\cdot \, \text {m}^{-1}$ /Hz) and across (1.77 $\text {Np}\cdot \text {m}^{-1}$ /Hz) the tissue fibers. In all cases, the data supported the assumptions of a gamma-distributed spectrum for the source and linear frequency Attenuation for the tissue. This method provides tissue Attenuation, which is relevant diagnostic information to model viscosity, in addition to shear-wave velocity used to assess elasticity. Data processing is simple and could be performed automatically in real time for clinical applications.
-
A Frequency-Shift Method to Measure Shear-Wave Attenuation in Soft Tissues
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2017Co-Authors: Simon Bernard, Siavash Kazemirad, Guy CloutierAbstract:In vivo quantification of shear-wave Attenuation in soft tissues may help to better understand human tissue rheology and lead to new diagnostic strategies. Attenuation is difficult to measure in acoustic radiation force elastography because the shear-wave amplitude decreases due to a combination of diffraction and viscous Attenuation. Diffraction correction requires assuming a cylindrical wavefront and an isotropic propagation medium, which may not be the case in some applications. In this paper, the frequency-shift method, used in ultrasound imaging and seismology, was adapted for shear-wave Attenuation measurement in elastography. This method is not sensitive to diffraction effects. For a linear frequency dependence of the Attenuation, a closed-form relation was obtained between the decrease in the peak frequency of the gamma-distributed wave amplitude spectrum and the Attenuation coefficient of the propagation medium. The proposed method was tested against a plane-wave reference method in homogeneous agar-gelatin phantoms with 0%, 10%, and 20% oil concentrations, and hence different Attenuations of 0.117, 0.202, and 0.292 Np · m-1/Hz, respectively. Applicability to biological tissues was demonstrated with two ex vivo porcine liver samples (0.79 and 1.35 Np · m-1/Hz) and an in vivo human muscle, measured along (0.43 Np · m-1/Hz) and across (1.77 Np · m-1/Hz) the tissue fibers. In all cases, the data supported the assumptions of a gamma-distributed spectrum for the source and linear frequency Attenuation for the tissue. This method provides tissue Attenuation, which is relevant diagnostic information to model viscosity, in addition to shear-wave velocity used to assess elasticity. Data processing is simple and could be performed automatically in real time for clinical applications.
Axel S Herrmann - One of the best experts on this subject based on the ideXlab platform.
-
theoretical and experimental studies of lamb wave propagation in attenuative composites
The 14th International Symposium on: Smart Structures and Materials & Nondestructive Evaluation and Health Monitoring, 2007Co-Authors: Mircea Calomfirescu, Axel S HerrmannAbstract:This paper presents a theoretical model for anisotropic wave Attenuation in composites. The model has been implemented in a software called FIBREWAVE in order to predict dispersion and Attenuation of S 0 , A 0 and SH 0 Lamb wave modes. The required input data are the complex stiffness matrix coefficients of the unidirectional plies of the laminate, which have been measured by a laser interferometry method. Complex stiffness data for an unidirectional CFRP laminates are moreover presented. Satisfactory agreement has been observed between predicted and experimental group velocities and wave Attenuations.
Jun Matsushima - One of the best experts on this subject based on the ideXlab platform.
-
seismic wave Attenuation in methane hydrate bearing sediments vertical seismic profiling data from the nankai trough exploratory well offshore tokai central japan
Journal of Geophysical Research, 2006Co-Authors: Jun MatsushimaAbstract:[1] Data from two vertical seismic profiles (VSPs) from the Nankai Trough exploratory well, offshore Tokai, central Japan, are used to estimate compressional Attenuation in methane hydrate (MH)-bearing sediments at seismic frequencies of 30-110 Hz. We compare spectral ratio and centroid frequency shift methods for measuring Attenuation. To isolate intrinsic Attenuation from total Attenuation, Attenuation is computed from multiples using one-dimensional synthetic VSP data from sonic and density logs. The use of two different measurement methods and two VSPs recorded at just 100 m separation provides an opportunity to validate the Attenuation measurements. No significant compressional Attenuation was observed in MH-bearing sediments at seismic frequencies. Macroscopically, the peaks of highest Attenuation in the seismic frequency range correspond to low-saturation gas zones. In contrast, high compressional Attenuation zones in the sonic frequency range (10-20 kHz) are affected by the presence of methane hydrates in the same well locations. Thus this study demonstrated the frequency dependence of Attenuation in MH-bearing sediments; MH-bearing sediments cause Attenuation in the sonic frequency range rather than the seismic frequency range.
John F. Federici - One of the best experts on this subject based on the ideXlab platform.
-
Comparison of Experimental and Theoretical Determined Terahertz Attenuation in Controlled Rain
Journal of Infrared Millimeter and Terahertz Waves, 2015Co-Authors: Jianjun Ma, Francis Vorrius, Lucas Lamb, Lothar Moeller, John F. FedericiAbstract:The effects of rain Attenuation on 0.1- to 1-THz frequencies are reported in this paper. The THz pulses propagate through a rain chamber over a 4-m distance and are measured by THz time-domain spectroscopy (THz-TDS). A rain chamber is designed to generate controllable and reproducible rain conditions with different intensities. Image analysis software is employed to characterize the distribution of generated raindrop sizes. Theoretical THz power Attenuations due to rain are calculated using Mie scattering theory and are compared with our measurements. Results show that both experimental and theoretical results are in very good agreement with each other.