木材の周期構造解析 I : 光学的フーリエ変換法による試み

Abstract

木材の組織構造と材質との具体的な関係を探るために, 木材をマクロからミクロまでの周期構造の集合物として捕らえ直すことを試みた。そしてこの周期構造を光学的なフーリエ変換法により検出するための基礎的な実験条件を検討した。ここで用いた光学的フーリエ変換法は, コヒーレントなHe-Ne レーザー光束と簡単な光学系からなり, フラウンホーファ回折現象を利用して木材の組織形態をフーリエ変換するものである。そして組織形態の周期性を二次元的なパワースペク卜ル像として出力する。木材の光学顕微鏡観察用標本や, 顕微鏡写真撮影フィルムをこの装置に入力することにより, 年輪の周期や細胞の寸法と配列, 細胞壁の厚さと方向性など, 木材の様々の形態と周期性を検出することができた。

Optical Fourier transformation was applied to analyze the periodicity of wood structure which may affect wood properties. An optical system for the Fourier transformation was constructed by a He-Ne laser source and several optical equipments by which very wide and uniform beam current can illuminate a material picture (Fig.2). Sections of wood specimen prepared for the light microscopy gave peculiar power spectrum (diffraction) patters having several striations and spots, although they were not so clear as those of X-ray (Fig.4). On these spectrums, "Fraunhofer diffractions of the single slit" reflecting many shapes on wood structure and "the diffraction of the multiple slits" reflecting various arrangements of these shapes are convoluted with each other (Fig.3). Therefore, modifications or disorganizations of the original picture of wood structure were designed in order to decode the convolution (Fig.5, 6) and these models were transformed by the same experimental condition with the original one. By the comparison between their spectrum patterns, many periodicities could be identified (Fig.4, 6).