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超音波計測に基づく花崗岩中の表面波伝搬特性に関する研究

A Study on the propagation characteristics of surface waves in a granite based on ultrasonic measurement

木本 和志*; 岡野 蒼*; 斎藤 隆泰*; 佐藤 忠信*; 松井 裕哉 

Kimoto, Kazushi*; Okano, Aoi*; Saito, Takayasu*; Sato, Tadanobu*; Matsui, Hiroya

本研究では、花崗岩試料を用いた超音波計測を行い、実測データから波数ベクトルが従う確率分布を推定した。花崗岩は数mm$$sim$$数cm程度の結晶粒から成る多結晶質体で、超音波はき裂や粒界で散乱を起こす。ここでは、圧電超音波探触子で花崗岩試料に表面波を励起し、その伝播挙動をレーザー振動計で可視化するとともに、波動場の位相と波数の構造を調べた。その結果、媒体の不均質性により波面が屈曲すること、波数ベクトルの確率密度分布は周波数に依存することなどが明らかとなった。

This study investigates the propagation characteristics of high frequency surface wave in a granite block by ultrasonic measurements. To this end, a surface wave field excited by a line-focus transducer is scanned finely over a rectangular aperture with a laser Doppler vibrometer. From the measured waveforms, the spatial distribution of Fourier phase is reconstructed, and the structure of the wave front system is investigated. Due to the heterogeneity of the granite, the wave fronts fluctuate spatially at a rate dependent on the ultrasonic frequency. The intensity of the fluctuation is then quantified as a local wavenumber vector. It was found as a result that the granite sample can be characterized by a random wave number whose probability density is frequency dependent, asymmetric and non-Gaussian having a finite support.

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