Ultrasonic characterization of frequency dependent attenuation properties of plaster boards

Plaster boards are heterogeneous materials with quite substantial degree of attenuation when exposed to ultrasonic waves. The attenuation properties are determined from the frequency shifts induced by the presence of scatterers within the material continuum. In this work, ultrasonic principle is used to estimate the frequency shifts in three different plaster boards-Cement board (CB), Glass Fiber Reinforced Gypsum (GRG) and Exterior Glass fiber Reinforced Gypsum (EGRG) - for the purpose of attenuation characterization. 49 signals, obtained via ultrasonic backscattered echo technique, were extracted from the samples of each material with contact mode Harisonic 2.25MHz transducer connected to the workstation. These signals are processed via time domain and optimized homomorphic analyses. Histograms of the time domain results indicate a general shift towards the low amplitudes and non-uniform shift magnitudes are observed in each sample and across the three materials. The skewness and standard deviation of the frequency shifts clearly show some fundamental differences in scattering and absorption nature of these materials. Downwards shifts in the centre frequencies compared to the steel reference material are equally significant. The mean center frequencies are found to be 2.3891, 2.2695 and 2.2102MHz for CB, GRG and EGRG respectively indicating lowest attenuation in CB. Also, attenuations are found to increase with increase in frequency within the limit of the transducer bandwidth of 2.0286 and 3.4402 MHz. Tests of repetitions confirm that the observed frequency changes are due to sample non-uniformity and not signal processing artifacts.