Acoustical method and system for measuring barrier membrane thickness and the correspondent area distribution using maximum transmission or maximum reflection coefficients

摘要

PCT No. PCT/US97/18221 Sec. 371 Date May 5, 1999 Sec. 102(e) Date May 5, 1999 PCT Filed Oct. 9, 1997 PCT Pub. No. WO98/16800 PCT Pub. Date Apr. 23, 1998The invention relates a method and a system for membrane thickness and the correspondent area distribution measurement based on the dependency of the acoustic intensity transmission coefficient upon the thickness of the insertion membrane and the proportion of the power of the transmitted acoustic plane waves to the area of the insertion membrane. The principle of the invention is that, when the acoustic wave travels in the acoustic medium and encounters an insertion membrane with different acoustic impedance, the intensity transmission coefficient T is related to the thickness d of the insertion membrane and the frequency f of the transmitting acoustic wave. As f sweeps, maximum T occurs at a set of frequency points corresponding to a certain thickness of the insertion membrane. By confining the sweeping frequency within a certain range, Tmax can only occur at one frequency point corresponding to a certain thickness of the insertion membrane. This frequency can be converted into the correspondent membrane thickness.