APERTURE SYNTHESIS OF TIME-LIMITED X-WAVES AND ANALYSIS OF THEIR PROPAGATION CHARACTERISTICS

The feasibility of exciting a localized X-wave pulse from a finite ape rture is addressed. Also, the possibility of using a finite-time excit ation of a dynamic aperture to generate a finite-energy approximation to an X-wave pulse is explored. The analysis is carried out by using a Gaussian time window to time limit the infinite X-wave initial excita tion. Huygens' construction is used to calculate the amplitude of the radiated wave field away from the finite-time source. The decay rate o f the peak of the X wave is compared to that of a quasi-monochromatic signal. It is shown that the finite-time X-wave propagates to much far ther distances without significant decay. Furthermore, the decay patte rn of the radiated X-wave pulse is derived for a source consisting of an array of concentric annular sections. The decay behavior of the rad iated pulse is similar to that of an X-wave launched from a finite-tim e aperture. This confirms the fact that time windowing the infinite en ergy X-wave excitation is a viable scheme for constructing finite aper tures. A discussion of the diffraction limit of the X-wave pulse is al so provided. (C) 1998 Acoustical Society of America.