Kimihisa Miura

Calculation of Two-Dimensional Reflection Energy of SH Waves from a Gradient Inhomogeneous Layer. Stacking Approximation by New Rationalized Layer Elements.

In a previous paper, considering the reflection energy of SH waves from a gradient inhomogeneous layer, we offered a new rationalized layer element for a two-dimensional elastic analysis. We confirmed that the reflectance is exactly estimated using this new elements without any complexities. In this paper, we expanded this analysis to the case of a layer with an arbitrary distribution of the acoustic impedance. As an example, when the acoustic impedance and the phase velocity vary sinusoidally with the thickness, and the mass density is constant through the layer, the ressiting reflectance is in very close agreement with the exact value, and shows rapid convergence properties. Furthermore, it is shown that the existence of the maximum value of the acoustic impedance in the layer gives rise to the total rellection, even if the acoustic impedance values of the refected and transmitted side of the layer are equal.

Equivalent Homogeneous Layer Model to a Linear Inhomogeneous Layer System.

The backscatter of elastic waves from an inhomogeneous layer inserted between two homogeneous half spaces, was investigated by introducing the equivalent homogeneous layer model. It was observed that discontinuation of the acoustic impedance at the layer interfaces mainly affects the backscatter intensity. The continuous variation of impedance inside the inserted layer has little affect especially in the high-frequency domain. Consequently, the layer system can be approximated by a suitable homogeneous layer system. Development of a new equivalent homogeneous layer model is the main subject of this paper. The model introduced will simplify the evaluation of backscatter intensity of a gradient inhomogeneous material. The simple modeling method is discussed and the model is evaluated and compared with the results for impulsive reflecting energy calculated by the model and by the exact analysis.

Elastic Wave Reflection from a Gradient Inhomogeneous Layered Part.

Discussion of elastic wave backscatter from an inhomogeneous layered part of a composite is made with the computational results by using a special layer elements. The stacking of linear inhomogeneous layer element, say LILE, has been certified as an excellent model for the computation of a gradient inhomogeneous layer. Intensity curves of the backscatter calculated as a function of incident wave number are presented in a wide frequency range, and characteristic relations between the inhomogeneous structure and the backscatter intensity are discussed. The results show that some peaks appear on the curves. Study of the characteristic features provides us viable clues for computation to get the information on layering structure and spatial exponential decay of inhomogeneous material constants of composites.

Energy Reflection of Elastic Waves from an Inhomogeneous Layer.

Energy reflection of plane elastic waves impinging on an inhomogeneous elastic layer is investigated. The variation of acoustic impedance throughout the inhomogeneous layer is given as a linear function of thickness coordinate of the layer. Closed-form analytical solutions of the coefficient of energy reflection and transmission are obtained for the normal case to show fundamental but reliable results. The discontinuity of acoustic impedance at interfaces dominantly affects energy reflection. The effect is systematically explained from the variation in impedance. The special coefficients for the long wave limit coincide with the well-known results for a homogeneous elastic layer. The model presented here may be applicable to such materials as a transitional layer of deteriorated bonding interface or a layer of functionally gradient material.