Patent GB-637501-A (GB)
Title: Improvements in electroacoustic transducer
IPC: G01S1/72
Filed: 1945-01-10
Abstract: 637,501. Audible and like signalling apparatus. RAYTHEON MANUFACTURING CO. Jan. 10, 1945, No. 883. Convention date, May 3, 1940. [Class 118 (ii)] [Also in Group XXXIX] An electro-acoustic transducer comprises a circular or cylindrical radiating surface on which are mounted, side by side, a plurality of elongated magnetic vibrators having flexurally vibrating reed elements extending transversely therefrom and providing a magnetic gap between adjacent reeds containing a coil adapted to produce or receive electrical energy in the operation of the device. A diaphragm 1, Figs. 1 to 3, with radiating surface 2 and annular flange 3 is clamped by bolts 4 between a ring member 5 and a cup-shaped flanged cover 6, a gasket 7 forming a water-tight enclosure. A plurality of vibrators 8 are mounted on the back face of 1 by means of screws 9, preferably sunk into the face of 1 and the resulting holes filled by plugs 10 to provide a smooth radiating surface. A reed element 11, adapted to vibrate vertically by flexing, is formed,on each side at the upper end of the vibrators 8 and extends the whole length of the vibrator. The vibrators may be permanently magnetized but preferably are magnetized by D.C. energized coils 12 which are wound around every alternate vibrator and clamped between the rubber strips 33 and the diaphragm 1 by strips 34 fastened to the flange 3 by bolts 35. Coils 13, carrying the signal voltage, are constructed from insulated thin ribbon conductors wound edgewise and positioned in any suitable manner which avoids elasticity of mounting. The method described for this purpose comprises a pair of end plates 14, 15 mounted by screws 17 on the flange 3. A plate 19 having a plurality of non-magnetic ribs 20 is secured to the plates 14, 15 by the screws 18. The coil windings are connected to the ribs 20 and 21 where they are diminished in cross-section to a thickness equal to the width of the conductors in the coils. Conductors for making connections to the coils 12, 13 may be taken out through the liquid-tight stuffing tube 22. The supporting flange 3 is placed, as nearly as possible, in the plane of the vibrational mode which exists between the radiating surface 2 and the upper end of the vibrators 8. The ratio of the mass above this mode to that below is adjusted to produce the desired amplitude of vibration of the surface 2. For this purpose the plate 1 is made of considerable thickness but not greater than onequarter of the wavelength in the material at the signalling frequency. In a modification, Fig. 4 (not shown), flux leakage between adjacent vibrators, other than across the gap between the reeds, is partially suppressed by placing a number of bipolar permanent magnets opposite the vibrators so that the ends of the vibrators and their oppositely located members of the magnets are of like polarity. A modified construction, Figs. 5, 6, provides a cylindrical radiating surface on the inner face of which is mounted a plurality of elongated vibrating elements 44 mounted with their long dimensions parallel to the axis of the cylinder and projecting radially from the internal surface of the cylinder 41. The members 44 are similar to the vibrators 8, Figs. 1 to 3. The complete unit is made water-tight by means of the gaskets 58 ... 61 and the leads from the coils are brought out through the water-tight stuffing tube 62. The external surface of the cylinder 41 may be slotted between adjacent members 44, as shown at 63. In a further modification, Figs. 7, 8 (not shown), generally similar to that shown in Figs. 5, 6, the compressional wave radiation is directed towards the central axis of the unit, the vibrators being mounted on the external surface of the cylinder. The whole assembly is made water-tight around a centrally located pipe through which a liquid (to be subjected to the vibrations) may be conducted. The radiating surface may be slotted as in the previous modification.