Piezoelectricity of Wood

The direct and converse piezoelectric effects of wood have been studied. Assigning the z axis to the grain direction and the x and y axes to the radial and tangential direction of annual rings respectively, the piezoelectric effects corresponding to d 14 and d 25 were observed. When the shearing force is applied to the fibers in their oriented plane, the polarization occurs on the side planes of the fibers. The effect is symmetrical to the z axis, that is, the grain direction. The converse effects were observed by clamping together the wood specimen and a Rochelle salt crystal between metal frames, and measuring the output voltage of the Rochelle salt crystal when the alternating voltage at audio frequency is applied to the wood specimen. The value of the piezoelectric constants, - d 14 = d 25 , is in the order of 10 -9 and about one twentieth of d 11 of quartz. If we assume that the natural cellulose possesses the piezoelectricity in its crystalline state, that the cellulose micelle are oriented in only one direction namely z axis, in which the positive and negative direction of long axis of micelle are equally distributed and that micelle are arranged quite at random in the x y plane, the apparent piezoelectricity of wood are reasonably explained.