Patent GB-130050-A (GB)
Title: Improvements in Means for the Detection and Location of Metallic Bodies, particularly applicable to Detecting Submarines.
Inventor: BUSH VANNEVAR
IPC: G01V3/10
Filed: 1918-01-05
Abstract: 130,050. Bush, V. Jan. 5, 1918. Signalling proximity of vessels.-The proximity of metallic bodies, particularly submarines, is detected, and their approximate direction determined, by means of an electro-magnet 10 energized by alternating current, preferably from a generator of audio frequency, and a detecting-coil 11 situated outside the concentrated portion of the field. The magnet 10 is placed, for example, at the bow of the observing vessel V with its axis horizontal, and the coil 11 of toroidal form with its axis vertical, at the stern. Adjustment is made so that normally there is no current induced in the coil by the electro-magnet 10. After such adjustment, the distortion of the field of the electro-magnet due to eddy currents produced in a proximate metal body, such as a submarine S, gives rise to the production in the coil of induced currents of generator frequency, the presence of which is detected in any suitable way, as by means of a telephone receiver. The electro-magnet 10 is in circuit with a generator 13, the circuit being tuned to the generator frequency. The coil 11 is connected to an audion or other amplifier A, and the amplified current is passed through a telephone receiver 16. A resonator 38 of Helmholtz type may be mounted in front of the receiver 16, and the sound produced listened to through a stethoscope tube 42. The distance between receiver and resonator may be adjusted. For adjustment to eliminate induced current in the coil 11, under normal conditions, the coil is tilted about an horizontal axis until the sound heard is a minimum, in which position the coil is secured Further elimination is effected by imposing alternating current on the coil 11 in opposition to the current to be eliminated. As shown, crossed coils 32, 33 in parallel are connected through a transformer 29 with the electro-magnet circuit, and the crossed-coil circuits are adjusted to give an approximately circular resultant field in the coils 32, 33. Current of generator frequency is thereby induced in a coil 31, which can be adjusted angularly for phase-difference, and the current is superposed on the coil 11 through a potentiometer 36. To minimize disturbance due to small variations in the position of the coil 11 owing to vibrations of the vessel V, the coil 11 is provided with closed conductors 25. To enable the sound of generator frequency to be distinguished from sounds due to other causes, arrangement may be made to energize the electro-magnet intermittently, so that a correspondingly intermittent sound must be listened for. In this case. a rotary circuit-breaker I is provided, arranged to connect the generator 13 to the magnet 10 and to an equivalent load 18 alternately, so that the load on the generator is constant. The side of the vessel V to which the submarine lies may be determined by the use of additional coils 44 disposed with respect to the coil 11 as shown in Fig. 3. A switch is provided so that any one of the three coils may be connected to the telephone receiver at will. The current is stronger in that coil 44 which lies to the same side as the submarine. A circuit diagram for this three.coil arrangement is given, in which the coils 31, 32, 33 are omitted from the adjustment circuits.