### ASA 124th Meeting New Orleans 1992 October

## 4pSA10. Acoustic monitoring of beams by wavelet analysis.

**Peeter M. Akerberg
**

**
Ben H. Jansen
**

**
Pierre Y. Robin
**

**
**
*Dept. of Elec. Eng., Univ. of Houston, 4800 Calhoun Rd., Houston, TX
77204-4793
*

*
*
**Robert D. Finch
**

**
**
*University of Houston, Houston, TX 77204-4793
*

*
*
This talk proposes to use the discrete wavelet transform (DWT) of the
acoustic signal produced by a hammer impact, to examine the integrity of
metallic beams. The DWT is naturally adapted to transient signals and provides
better frequency resolution for low frequencies than Fourier transform-based
methods. Time-scale representations, such as the discrete wavelet transform,
are related to time-frequency representations, which provide a framework to
study variations of the signal frequency content over time. It has been found
that the rate at which the amplitudes of the resonant frequencies decay is an
important indicator of the integrity of metallic beams [Robin et al., J.
Acoust. Soc. Am. 91, 2359(A) (1992)]. The frequency-dependent decays have been
investigated more closely with the discrete wavelet transform. The decay
appears to ondulate, and the frequency of this ondulation is related to the
integrity of the beam. DWTs of actual vibration signals will be presented to
show that the ondulation in the decay rates of the resonant frequencies can be
used to differentiate between intact and slotted beams. [Work supported by NSF
Grant No. MSS-9024224.]