Propagation Mechanism of Ultrasonic Waves in Porous Ceramics

In this paper, we present a probabilistic theory of propagation of ultrasonic waves in porous ceramics, and propose a new method of ultrasonic inspection for nondestructive pore characterization. The idea is based upon the arrival probability of ultrasonic rays. When incident rays impinge on a pore, they travel around the pore surface and increase the propagation time. We studied this process probabilistically, and found that the propagated waveforms can be expressed as Gaussian functions. The Gaussian waveform is determined by the porosity, pore size and pore shape. This new finding led to the following important laws. (1) The delay time of an ultrasonic wave passing through porous ceramics is proportional to the porosity. (2) The pulse width of the wave increases with increasing mean pore size. (3) The amplitude of the wave decreases with mean pore size. (4) The delay time and pulse width of the wave increase as the mean pore perimeter increases. Formulae for these relationships between ultrasonic and pore characteristics were derived, and an ultrasonic method for evaluating porosity and pore size was proposed.