tailieunhanh - FUNDAMENTALS AND APPLICATIONS OF ULTRASONIC WAVES

This book grew out of a semester-long course on the principles and applications of ultrasonics for advanced undergraduate, graduate, and external students at Concordia University over the last 10 years. Some of the material has also come from a 4-hour short course, “Fundamentals of Ultrasonic Waves,” that the author has given at the annual IEEE International Ultrasonics Symposium for the last 3 years for newcomers to the field. In both cases, it was the author’s experience that despite the many excellent existing books on ultrasonics, none was entirely suitable for the context of either of these two courses | CRC Series in PURE and APPLIED PHYSICS Fundamentals and Applications of uMẽONIC J. David N. Cheeke 1 Ultrasonics An Overview Introduction Viewed from one perspective one can say that like life itself ultrasonics came from the sea. On land the five senses of living beings sight hearing touch smell and taste play complementary roles. Two of these sight and hearing are essential for long-range interaction while the other three have essentially short-range functionality. But things are different under water sight loses all meaning as a long-range capability as does indeed its technological counterpart radar. So by default sound waves carry out this long-range sensing under water. The most highly developed and intelligent forms of underwater life . whales and dolphins over a time scale of millions of years have perfected very sophisticated range-finding target identification and communication systems using ultrasound. On the technology front ultrasound also really started with the development of underwater transducers during World War I. Water is a natural medium for the effective transmission of acoustic waves over large distances and it is indeed for the case of transmission in opaque media that ultrasound comes into its own. We are more interested in ultrasound in this book as a branch of technology as opposed to its role in nature but a broad survey of its effects in both areas will be given in this chapter. Human efforts in underwater detection were spurred in 1912 by the sinking of RMS Titanic by collision with an iceberg. It was quickly demonstrated that the resolution for iceberg detection was improved at higher frequencies leading to a push toward the development of ultrasonics as opposed to audible waves. This led to the pioneering work of Langevin who is generally credited as the father of the field of ultrasonics. The immediate stimulus for his work was the submarine menace during World War I. The . and France set up a joint program for submarine .