Applied underwater acoustics

472

ANNOUNCEMENTSANDREVIEWS

Mr. Anstey described certain preliminary experiments with steam which showed the method had considerable promise and further reported that S. Wisotsky of the Submarine Signal Division of the Raytheon Co., using a valve to release a short pulse of steam, had managed to radiate sound at a level of 130 dB relative to I pbar at I m. The meeting was chaired throughout by Professor D. G. Tucker of the University of Birmingham and a total of 46 people attended. G. K. GAZEY

BOOK

REVIEWS

edited by H. D. Parbrook. London: Press Ltd. First printed 1967, Hard cover 10s. 6d.

TEACH YOURSELF BOOKS-ACOUSTICS,

Universities

The English

As the introduction states, this book will give the reader new to acoustics an insight and an understanding into the fascinating, extensive and interdisciplinary field of acoustics. In such a short text, and at the level the subject is treated, it must have been difficult to know which aspects of acoustics to mention and to what depths they should be discussed. Taken as a whole however, the balance of the treatment is good, although perhaps more detail could have been given on the community aspects of noise. There are five chapters dealing with “ Fundamental Concepts “, “ The Ear and Hearing-Psychoacoustics”, “ Environmental Acoustics “, “ Sound Reproduction-Electroacoustics” and “ Sonics ” (the industrial, research and medical applications of acoustics). One or two obviously unintentional factual and other textual errors appear and in parts the chapter dealing with the ear and hearing is unlikely to impress those who are already familiar with the subject. The lack of references and suggestions for further reading, and a somewhat incomplete index are noticeable omissions. Whilst it is obviously written more for the layman and the student new to the subject, than for readers of this journal, it is, however, a book whose existence should not pass unnoticed. C. G. RICE APPLIED UNDERWATER

Press, Commonwealth

ACOUSTICS, by D. G. Tucker

and International

Library.

and B. K. Gazey. London : Pergamon 27s. 6d.

Underwater acoustics was referred to as one of the important subjects neglected by British universities in the recent report of the working party set up by the Council for Scientific Policy to enquire into liaison between Universities and Government research establishments (Cmnd. 3222, March 1967). This criticism cannot be levelled at Birmingham University, where the Department of Electronic and Electrical Engineering provides a strong centre for teaching and research in underwater acoustics. The authors of this text book have based the contents on the courses given to the final-year undergraduates. The book is, therefore, concerned with the fundamentals of the subject. The layout of the textbook follows a special pattern. The initial 20% is devoted to the principles of underwater acoustic systems, including sonar, seismics and communications, and to an explanation of how the well-known concepts of bandwidth, noise and signal processing apply in underwater acoustics. This is followed by chapters, amounting to nearly 40% of the book, on the all-important subject of propagation of sound in water. This subject is dealt with generally from the point of view of propagation in an elastic medium and is followed up by a more detailed study of the anomalous propagation

ANNOUNCEMENTS AND REVIEWS

473

phenomena introduced by reflection at boundaries, and refraction in inhomogeneous media (i.e. the real sea). Then follows an excellent chapter on the fundamentals of acoustic transducer operation, including the necessary theoretical treatment. The book concludes with a chapter on the directivity of transducers and arrays. This covers the fundamentals and introduces ideas, such as superdirective arrays, which have been the subject of original research at Birmingham. The only criticism of this textbook, if there is one, is that it tends to play down, or ignore, certain other problems which are of fundamental importance in applications of underwater acoustics. These are reverberation, noise, and the reflecting properties of targets. Reverberation is a form of noise-limitation in many sonar systems and may arise from retro-reflection from irregular boundaries. Some theoretical treatment of these complex, but important, scattering processes should find a place in a fundamental textbook. Similarly, some forms of noise in real systems are of hydrodynamic origin, e.g. flow and cavitation noise, and a short chapter on this subject would have been an advantage, if only to bring home to the student that electrical and thermal noise limits are frequently not of major consequence in real systems. Target response is also of fundamental interest because it frequently involves a set of conditions where the size of the object is comparable with the wavelength of the sound. Also, as in fish, the question of resonant response arises. A chapter on this interesting subject would be rewarding. However, the textbook comprises lectures for undergraduates and this has obviously limited its scope. Nevertheless the subjects omitted are basic ones and it is hoped the authors will be tempted to include them in an enlarged edition of their textbook. The textbook ends with a number of specially chosen problems, and their solutions, which should prove valuable to the student wishing to test his expertise in the subject. Each chapter also provides up-to-date references for further study. The textbook is strongly recommended to all those wishing to make a start on the study of applied underwater acoustics. The authors are to be congratulated on having contributed a useful British textbook to this rather neglected field. J. TUNSTEAD