Properties of Piezoelectric Voltage Considering Microscopic Structure of Wood Cell Walls

Elastic calculations were performed for analyzing the elastic strain field in a cell wall and the cellulose microfibril (CMF) when the wood specimen having an inclined grain is subjected to a uniaxial load. Shear strain and shear stress generated in a cell wall and the CMF were finally predicted. In the present case, it is hypothesized that elastic constants E1, E2, G12, and ν21 in Eqs. (6) can be calculated from the simple mixture rule. If we consider that shear strain γ12 in Eq. (10) and γ'12 in Eq. (15) cause the generation of piezoelectric voltage in the CMF, measured piezoelectric voltage must be proportional to the superposition of those shear strains over all tracheid in the wood specimen. Assuming that a wood specimen could be represented by the multi-tracheid model as shown in Fig. 7, we derived the formulas (23) to (26) which should be proportional to piezoelectric voltage generated in the wood specimen having an inclined grain. Based on those ideas, we could explain the experimental result that a plot of the piezoelectric voltage versus the grain angle of the wood specimen gave a convex curve with a peak at 45 degrees.