. Basic methods for the calibration of sonar equipment. Chapter 2 OPERATION AND APPLICATION OF UNDERWATER SOUND DEVICES By Lvslif L. l-uldy CALiiiRAiioN work in under water sduihI is con- cerned primarily with devices which con\ ert elec- tric energy into acoustic energy (projectors) and, con- versely, those which convert the energy of a sound field into electric energy (hydrophones). Gencrically, these devices are known as electroacouslic transducers. To provide a suitable background for the detailed discussion of the problems invohed in caliljrating transducers, this chapter presents a brief
. Basic methods for the calibration of sonar equipment. Chapter 2 OPERATION AND APPLICATION OF UNDERWATER SOUND DEVICES By Lvslif L. l-uldy CALiiiRAiioN work in under water sduihI is con- cerned primarily with devices which con\ ert elec- tric energy into acoustic energy (projectors) and, con- versely, those which convert the energy of a sound field into electric energy (hydrophones). Gencrically, these devices are known as electroacouslic transducers. To provide a suitable background for the detailed discussion of the problems invohed in caliljrating transducers, this chapter presents a brief discussion of (1) the physical principles underlying the action of transducers, and (2) their uses. PRINCIPLES OF OPERATION OF TRANSDUCERS As ahead) noted, energy con\ersi()n is the finula- menlal pin pose of ' Most transducers can convert energy in either direction, thai is, ihey are re- \ersible. .According lo ihe naiiue of the [jhysical proc- ess used in the energy conxersion transducers may i)e classed luuler loin- general headings, namely electro- dynamic, electrostatic, piezoelectric, and magneto- striction. The principles in\ol\cd in each are dis- cussed here in a cpialitati\e manner. A more cjuantita- tive treatment is gi\en in Chapter 3. The simplest example of an electrodynamic trans- ducer is a mo\ing-ribbon instrument (Figure 1) which consists of a rectangular metallic strip or rii> boir suspended in a magnetic field. When the instru- ment is in a soinid field, there is generally a dilterence in pressure established between its front and back. Since the mass of the ribbon differs from that of the magnet, relative motion of the two results, inducing an electromotive force in the moving ribbon. Con- versely, if an alternating current flows through the suspended ribbon, the forces on it due to interaction of the current and the external magnetic field pro- duce vibration. This vibratory motion in turn creates a soimd field in the medium. Since the
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