Patent GB-394994-A (GB)
Title: Improvements in and relating to magneto-striction transmitters and receivers for the transmission and reception of sound
IPC: B06B1/08
Filed: 1932-01-05
Abstract: 394,994. Sound receiving and transmitting devices. DRYSDALE, C. V., Research and Experiment Department, Admiralty, Whitehall, London, and SMITH, F. D., Admiralty Research Laboratory, Teddington, Middlesex. Jan. 5, 1932, No. 310. [Class 40 (iv).] A subaqueous magnetostrictive sound transmitter and/or receiver comprises one or more tubes of a material having a large factor of magnetostriction for small magnetic fields and free from initial strain or stress, such as nickel or nickel alloy, the walls of the tubes being as thin as possible consistent with the me. chanical strength necessary to withstand continuous longitudinal vibration so that the penetration of magnetic flux is as high as is practicable under these two opposing conditions, the tubes also being rigidly mounted in end loads so as to prevent any relative movement between the parts, the masses and dimensions of the end loads in conjunction with the dimensions and mass of each tube being such that with the tubes in resonant vibration by the application of the required periodic magnetization, the amount of damping applied to the vibrating system is such as to produce practical maximum conversion of electrical energy into sound energy. Fig. 1 (Prov.) shows a two-tube transmitter or receiver in which the tubes 1 are mounted in end loads 2, 4 of ferromagnetic material so that the whole forms a closed magnetic circuit. The load 2 is larger than load 4 and is recessed at 3, the masses of the loads being chosen so that a maximum output of sound energy is obtained. The ends of the tubes are expanded in the end loads, the tubes being formed with ridges 5 which are drawn tightly against the loads when the mouths of the tubes are expanded. Solenoidal windings 6 are provided to carry the requisite magnetizing currents whilst further closing of the alternating magnetic circuits may be effected by using a number of magnetic stampings or plates 7 secured by bolts 8 to the end loads. The complete oscillator vibrates longitudinally at a fundamental resonant mode of vibration, the end loads moving in opposite phase with a node therebetween but nearer the heavier end load. One of the end surfaces 9, 10, preferably the latter, constitutes the emitting surface. Fig. 2 (Comp.) shows a construction employing eight tubes 11 expanded in end loads 12 (only one of which is shown) of equal mass and both of which are in contact with the water, each load 12 being formed with an annular flexible edging 14 and outer cylindrical flange 15 which is secured in a reduced portion 16 of an outer metal casing 17. An insulating disc 18 is provided adjacent each end load, the discs being provided with holes to clear the tubes 11 and being connected together by bolts 19 and nuts 21. A central centring rod 23 passes through the discs and fits loosely in recesses 24 in the end loads, a thick rubber washer 25 being provided between each disc and end load. Locating pins 26 carried by the discs also engage recesses 27 in the end loads. Insulating tubes 28 surrounding the tubes 11 and fitted into recesses in the discs 18 are provided with a polarizing D.C. winding and an alternating or impulsive current winding, the D.C. windings being connected in series in such a way that a magnetic flux is established in all the tubes but in opposite directions in adjacent tubes and the A.C. windings are interconnected in a similar way. The end loads may be of ferromagnetic material so as to form a closed magnetic circuit with the tubes 11. The ends of the device may be left open so that the water has access to the interior of the tubes 11 and so carries away any generated heat' or the end loads may be provided with cover plates and the interior of the device filled with oil &c. One or more slots can also be provided between two continuous end portions of the tubes to reduce eddy current effect. Fig. 4 (Comp.) shows a further construction employing a single tube 11 consisting of end rings 11a joined by a number of bars 11b. Each ring 11a is rigidly mounted in an end load 12 closed by a plug 30 and provided with a flexible edging 14 and an outer flange 15 to which the casing 17 is fixed. A winding is wound solenoidally round the tube in such a way that the wire passes under and over the bars 11b outside and inside the cylinder alternatively. When this winding carries A.C. superimposed on a larger D.C., the bars are magnetized in the direction of their length but the flux runs in opposite directions in alternate bars. Alternatively the wire may be wound solenoidally along one leg and then solenoidally along the next leg and so on round the circumference. If desired, the various windings may be toroidal instead of solenoidal. Specifications 2578/82, [Class 40, Electric telegraphs &c.], 283,116, 291,521, [both in Class 40 (iv), Telephones &c.], 313,031, [Class 37, Electricity, Measuring . &c.], and 314,891, [Class 40 (iv), Telephones &c.], are referred to.