TABLE OF CONTENTS While spherical and ring sources are omnidirectional in at least one plane, the piston-type transducer generally projects sound into one direction with a directionality that depends on its size compared to the wavelength. Large arrays of these transducers are used to project highly-directional, high intensity beams of sound into a particular area, as will be discussed in Chapter 5. Because they are well suited for large close-packed arrays, piston transducers are more commonly used than any other type in underwater acoustics. Moving coil and variable reluctance piston transducers are typically used in the frequency range below 600 Hz where piezoelectric or magnetostrictive transducers would be too long for most applications. However, mechanically leveraged piezoelectric X-spring piston transducers have been operated as low as 300 Hz and as high as 50 kHz. "Tonpilz" lumped mode transducers are typically operated in the range from 1 kHz to 50 kHz, sandwich type transmission line transducers cover the range from 10 kHz to 500 kHz; and piezoelectric plates, diced plates, or piezoelectric composites are used from about 50 kHz to beyond 2 MHz. The most common sonar projector is the Tonpilz and we begin the discussion of piston transducers with this design.
The Tonpilz transducer (see Figs. 1.11 and 1.12) takes its name from the German "sound mushroom," or "singing mushroom," [22] presumably because of a large piston head mass driven by a slender drive section which gives it the cross-sectional appearance of a mushroom. This concept...
