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Thickness Determination for a Two-Layered Composite of a Film and a Plate by Low-Frequency Ultrasound 被引量:9
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作者 毛捷 李明轩 王小民 《Chinese Physics Letters》 SCIE CAS CSCD 2007年第3期755-758,共4页
We present an ultrasonic method for determining the thickness of a composite consisting of a soft thin film attached to a hard plate substrate, by resonance spectra in the low frequency region, The interrogating waves... We present an ultrasonic method for determining the thickness of a composite consisting of a soft thin film attached to a hard plate substrate, by resonance spectra in the low frequency region, The interrogating waves can be incident only to the two-layered composite from the substrate side. The reflection spectra are obtained by FFT analysis of the compressive pulsed echoes from the composite, and the thicknesses of the film and the substrate are simultaneously inversed by the simulated annealing method from the resonant frequencies knowing other acoustical parameters in prior. The sensitivity of the method to individual thickness, its convergence and stability against experimental noises are studied, Experiment with interrogating wavelength 4 times larger than the film thickness in a sample of a polymer film (0.054mm) on an aluminium plate (6.24mm) verifies the validity of the method. The average relative errors in the measurement of the thicknesses of the film and the substrate are found to be -4.1% and -0.62%, respectively. 展开更多
关键词 THIN-VISCOELASTIC PLATE phase-velocity ELASTIC-MODULI ATTENUATION DENSITY SPECTROSCOPY
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Reflection and transmission coefficient approximation at weak-contrast interfaces for strong VTI media
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作者 Xingyao YIN Yaming YANG +1 位作者 Kai LIANG Kun LI 《Science China Earth Sciences》 SCIE EI CAS 2024年第12期3914-3938,共25页
Reflection and transmission(R/T)responses characterize the propagation and energy distribution of incident and reflected waves on both sides of an interface which is crucial for imaging,amplitude variation with offset... Reflection and transmission(R/T)responses characterize the propagation and energy distribution of incident and reflected waves on both sides of an interface which is crucial for imaging,amplitude variation with offset(AVO),and seismic inversion techniques.Subsurface media are typically characterized by anisotropy which can have a significant impact on the R/T response,even at small incident angles.Currently,anisotropic media problems including reflection,transmission,and inversion are generally discussed under a weak anisotropy assumption.However,this assumption is no longer valid in cases of large angles where anisotropy enhancement exacerbates the error of the conventional R/T coefficient approximation.An R/T coefficient approximation method for strong VTI media was proposed based on the assumption of weak-contrast of the media.In contrast to the conventional approach,which simplifies the phase velocity and polarization in an anisotropic background,the phase velocity and polarization at the weak-contrast interface of the elasticity and anisotropy parameters were approximated using a combination of the anisotropic background and perturbation terms.Specifically,a first-order approximation of the R/T coefficients for the VTI media characterized by elastic and anisotropic parameters was derived using Cramer's law to invert the anisotropic background matrix,avoiding the assumption of weak anisotropy.Subsequently,the exact solution of the Zoeppritz equations was used to correct the isotropic part,improving the accuracy of the R/T coefficients at interfaces with high-velocity contrast.Modeling tests on four classes of typical interfaces showed that the derived equations can be degraded to the Aki approximation in isotropic media,while exhibiting high accuracy in strong VTI media.Uncertainty analyses showed that a linear approximation that facilitates seismic inversion can be obtained by taking the S-to P-velocity ratio and anisotropy parameters in the coefficient terms a priori. 展开更多
关键词 Reflection and transmission coefficients Strong anisotropy VTI media Weak-contrast phase-velocity Polarization
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