ULTRASONIC CHARACTERIZATION OF FREQUENCY-DEPENDENT ATTENUATION IN PLASTER BOARDS

• Published in: ARPN journal of engineering and applied sciences 2012-05, Vol.7 (5), p.574-583
• Main Author: Asafa, Tesleem B
• Format: Article
• Language: English
• Subjects: Attenuation; Boards; Frequency shift; Gypsum; Plasters; Signal processing; Transducers; Ultrasonic attenuation
• ISSN: 1819-6608; 1819-6608

Plaster boards are heterogeneous materials with substantial degree of attenuation when ultrasonic waves pass through them. The attenuation properties are determined from the frequency shifts induced by the presence of scatterers within the material continuum. In this work, I used the principle of ultrasonic to estimate the frequency shifts in three different plaster boards which are: Cement Board (CB), Glass Fiber Reinforced Gypsum (GRG) and Exterior Glass fiber Reinforced Gypsum (EGRG). Few samples were obtained from these boards and each sample was partitioned into 49 grids from where signals were extracted with Harisonic 2.25MHz transducer operated in a contact mode. The signals were processed using time domain and homomorphic analyses. Histograms of the time domain analysis indicate a general shift towards low amplitudes with conspicuous non-uniformity in the shift magnitude. The skewness and standard deviation of the frequency shifts clearly show some fundamental differences in the nature of scattering and absorption in 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 which indicates that CB has the lowest attenuation. Also, attenuations are found to increase with increase in frequency within the range of the transducer bandwidth (2.0286 and 3.4402 MHz). Tests of repetitions confirm that the observed frequencies changes are due to the scatterers in the samples and not signal processing artifacts.