Temperature Dispersion of Complex Piezoelectric Modulus of Wood

Abstract

Experimental technique for determining the ratio of piezoelectric polarization to the applied sinusoidal stress as well as the phase angle between them is described. The real and imaginary components of the complex piezoelectric modulus d=d'-j d'' were determined for a few kinds of wood in a temperature range from -170°C to +150°C at a frequency of 20 c/s. In the vacuum dried specimen, d' gradually increased with temperature and the polarization lagged behind the stress. In the specimen including moisture, the piezoelectric moduli showed troughs at the room temperature range with the rise of temperature and the phase or the polarization led beyond the stress. The maximum of d'' at about -100°C was ascribed to the sum of viscoelastic loss and dielectric loss. The minimum of d'' at room temperature was accounted for by the dielectric loss due to the leakage current by moisture surrounding the piezoelectric cellulose crystallites. A simple model for explaining the piezoelectric dispersion is proposed.