5aSP4. The use of the finite-amplitude method to measure the nonlinearity parameter B/A and the harmonic growth in some fluids.

Session: Friday Morning, December 6

Time: 9:45

Author: Aly H. A. Moustafa
Location: Faculty of Electron. Eng., Dept. of Commun., Menoufia Univ., Menouf, Egypt


The acoustic nonlinearity parameter B/A for water and for sugar solution, and the growth of the harmonic contents in a finite-amplitude signal propagating in these fluids are investigated experimentally. The apparatus used consists of a perspex cylinder containing the fluid and a 2.25-MHz transducer (source), separated by a variable distance from a 4.5-MHz transducer (receiver). As the separation distance is increased distortion builds up as expected and the second harmonic, in particular, could be clearly observed due to the high sensitivity of the receiver at this frequency. It was possible to catch and store the received pulse, after averaging it for a large number of transmissions, using a digital storage oscilloscope. The capture signal was then spectrally analyzed using MATLAB software. The results showed that the fundamental component was almost constant, while the second harmonic had a linearly increasing trend with the separation distance. The higher harmonics are negligibly small. The receiver was separately calibrated, and its measured sensitivity was used to convert the fundamental and the second harmonic voltages into pressures which were then used to calculate the value of B/A. The results agree relatively well with published values for water. For sugar solution, B/A was found to be less than that for water.

ASA 132nd meeting - Hawaii, December 1996