Bispectral Passive Holographic Imaging System
A new ultrasonic and/or acoustical imaging system, which uses non-Gaussian random signals and cross- and auto-bispectral analysis is presented in this paper. It consists of a fixed point receiver on a hologram plane and a scanning receiver on the same plane. The non-Gaussian signals radiated from the object and detected by these receivers are analyzed. By calculating their cross- and autobispectra and taking the ratio between them the holographic information, that is the distribution of the amplitudes and phases of a certain wave length is derived from these results over the plane. The following points will be presented; i) principle, ii) theoretical developments, iii) computer simulations and the outline of a prototype of a practical system for the diagnosis of machine system at audio frequency region. Mechanical noises, such. as the noises from engines of a submarine, can be regarded as non-Gaussian signals and ambiguous noises surrounding circumstances, such as the ocean tide, may be regarded as Gaussian noises, so this method is especially effective when it is used under fairly large additive Gaussian noises. Because bispectrum of Gaussian noises vanishes completely they do not disturb the hologram when it is obtained by the bispectral analysis. Although the fundamental parts of this method have been submitted in various journals (Refs. 1, and 2), comprehensive discussions will be given in this article.
KeywordsOcean Tide Random Signal Power Spectral Analysis Point Noise Bispectral Analysis
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