Quasi-real-time imaging using ultrasonic Fourier transform camera

This paper proposes an imaging method using ultrasound for objects which cannot be observed optically, such as objects in muddy water or in mist. The acoustic Fourier transform (AFT) is described, whereby the object information is Fourier-transformed using the ultrasound. A transmitter element and a number of receiver elements are placed on the transmitter-receiver plane. The object and the reference sound source are placed on the front side, so that they are located on a circle, with the distance between the object and the transmitter-receiver plane as the diameter. Then, the interference pattern between the reflected wave from the object and the reference wave contains the Fourier-transform information of the object on the receiver plane. The obtained interference pattern is fed into a computer. Executing the inverse transform using the fast Fourier transform (FFT) program, the image of the object is immediately reproduced. In the system proposed in this paper, the reference wave is constructed in the computer, instead of actually placing the reference source, and the reference wave is added electrically to the received signal. The object at an arbitrary distance can be imaged, by adjusting the curvature of the reference wave, based on the distance from the transmitter-receiver plane to the object measured by the pulse-echo method. The design parameters for the experimental system are determined by computer simulation, and an experimental system was constructed. The effectiveness of the proposed method was demonstrated by a computer simulation and a simple object reproduction experiment, which were conducted to examine the effectiveness of the proposed reproduction method. (C) 2001 Scripta Technica.