Page 497 



ECHO SOUNDING 



5273 



5273. Magnetostrictive Units 



The magnetostrictive units (see fig. 109) for the Veslekari are nickel cyhnders about 

 5 inches long, built up from a great number of laminations which are a few thousandths 

 of an inch thick. These laminations are annular in shape, the outer diameter being 

 4% inches and the inner diameter 3% inches. A toroidal coil B of 23 turns of insulated 

 wire is wound around the cylindrical stack in such a way that the nickel laminations are 

 in its field. The wires pass through holes close to the outer periphery of the cylinder, 

 in order that they may not interfere with the acoustic radiation from the outer surface 

 of the cylinder. The axes of these holes are paraUel to the axis of the cylinder (fig, 

 109). 



H — 



H 



SCALE IN INCHED 



Figure 109. — Magnetostrictive acoustic unit. A. Magnetostrictive element. B. Toroidal coil. C. Double walled cone reflector, 

 filled with sponge rubber. D. Water-filled tank. E. Hull plate. H-H. Draft line. 



The magnetostrictive units vibrate at a rate of 16000 cycles per second. The prin- 

 ciple of this vibration is explained in 5161B. The vibrating outer cylindrical surface 

 of the transmitting unit is the source of acoustic energy in this case, since only the 

 vibration in a radial direction is utilized. 



Surrounding the magnetostrictive cylinder is a spun-metal truncated cone C, which 

 acts as a reflector. It is double walled, the cavity being filled with sponge rubber. 

 The angle of slope of the cone is 45° so the energy radiated horizontally by the magneto- 

 strictive cylinder is reflected at 45° from the cone's inner surface and directed down- 

 ward parallel to its axis. In this way all the radiated energy from the cylinder is in 

 phase at the opening of the cone, and the greater part of the energy of radiation is con- 

 centrated within an angle of 30°. The magnetostrictive elements and their reflectors 

 are installed in a water-filled tank D fastened to the inside skin of the ship. The 

 acoustic energy of the transmitting unit passes through the ship's steel hull and is 

 directed toward the sea bottom. The dash line HH in figure 109 represents the effec- 

 tive draft level of the unit (see 5512). 



465382 — 44 33 



