### ASA 124th Meeting New Orleans 1992 October

## 4aSA2. On using dispersion characteristics to actively control transient
broadband signals.

**Emilios K. Dimitriadis
**

**
John J. McCoy
**

**
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*School of Eng., Catholic Univ. of America, Washington, DC 20064
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*
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Most current transient signal control techniques are based on system
identification and subsequent control of a discrete model. Estimation
uncertainties, and also modal coupling via excitation, control, or damping
determine the limits of successful control. The alternative suggested here, is
based on a priori obtaining the ``effective'' dispersion characteristics of a
chosen wave-propagation path. The dispersion induced by a complex waveguide may
be determined by measuring a broadband pulse at the intended control-sensor and
control-actuator locations. The technique of windowed Fourier transform is
employed to deduce the ``effective'' dispersion curve(s) for said path. In a
control situation, the sensed transient is computationally propagated in
time-frequency space to the control location. The controller subsequently
alters the time-frequency impedance characteristics of the control location to
optimally achieve the desired control objectives. Numerical experiments are
here described for two different beam structures. Laboratory experiments are
suggested and their implementation discussed. Finally, issues of structural
discontinuities, wave-mode conversion, and, very importantly, computational
speed requirements are addressed.