Glen Wade - Böcker

How to produce images with sound has intrigued engineers and scientists for many years. Bats, whales and dolphins can easily get good mental images with acoustical energy, but humans have little natural ability for obtaining such images. The history of engineering and science, however, is an impressive demonstration that technological solutions can compensate, and then some, for deficiencies of nature in humans. Thus with the proper technology, we too can "see" with sound. Many methods involv­ ing ultrasonic energy can be employed to enable us to do so. Few of these methods are at all reminiscent of the acoustic systems employed by animals. Pulse-echo, phase-amplitude and amplitude-mapping approaches constitute the conceptual bases for three fundamentally different types of acoustic imaging systems and can be used for categorizing the systems. However, by now systems exist that combine the approaches in such sophisticated ways as to make an unambiguous categorization of some of the more complicated systems difficult or impossible. Among the instruments so far pro­ duced are mechanically-scanning focused instruments, chirped pulse-echo instruments, and instruments involving holography, tomography, parametric excitation, phase conju­ gation, neural networks, random phase transduction, finite element methods, Doppler frequency shifting, pseudo inversion, Bragg diffraction and reflection, and a host of other principles. The fifty-five chapters in this volume are selected from papers presented at the Eighteenth International Symposium on Acoustical Imaging which was held in Santa Barbara, California on September 18 - 20, 1989.

The latest progress in acoustical holography and related research areas, generally involving imaging by means of acoustic waves, was discussed and treated in depth at the Fourth International Symposium on Acoustical Holography, held in Santa Barbara, California on April 10-12, 1972. This volume contains the proceedings of that symposium. As the papers presented here indicate, a num­ ber of startling advances have been realized in the state-of-the-art since publication of Volume 3 of Acoustical Holography. Progress has been partic­ ularly impressive in the field of acoustical imag­ ing. The Fourth International Symposium represents something of alandmark conference in this respect. The scope of this volume is substantially broad­ er than the term "acoustical holography' usually implies and encompasses the whole area of visualiza­ tion, detection, and recording of sound fields whether with long wavelengths, microwaves, or with extrememly short sound wavelengths. The 37 sympo­ sium papers appear here each as aseparate chapter. In general, the work reported deals mainly with ex­ perimental and theoretical developments in the a­ bove areas. This work has significant practical potential use in terms of seismic sensing, under­ water imaging, non-destructive testing, real-time acoustic microscopy, and medical diagnosis.