Magnetic assemblies for minesweeping or ship degaussing

Details Magnetic assemblies for minesweeping or ship degaussing Magnetic assemblies for minesweeping or ship degaussing

1985-02-25

1987-06-30

Nelson, Peter A.

Ammunition and explosives

Mines

Counter measure

367 1, F42B 2242

Patent

active

046761683

DESCRIPTION:

BRIEF SUMMARY
DETAILED DESCRIPTION OF THE INVENTION

Many ships have degaussing systems built into their structures. These systems comprise electrical coils which can be energised so that they produce a magnetic field which is equal and opposite to that of the ship so that the magnetic field of the ship is neutralised. Some ships, though, do not have built-in degaussing measures and situations may arise where such ships have to pass through mined waters. Thus a system is required which will enable such ships to be degaussed temporarily to allow them to pass through the dangerous areas.
There are a number of conventional minesweeping methods. The most common are the systems where the required magnetic fields are produced by electrically pulsed loops towed behind a ship. The loop may either be a closed loop system consisting of a large area horizontal plane loop or an open loop system consisting of two or more electrodes with the electric currents driven through the sea water between them. Other methods include a simple dc electromagnet, with a fixed magnetic moment, towed from a helicopter, and a fixed magnetic moment permanent magnet towed behind a small ship for precursor magnetic sweeping.
The object of the present invention is to provide a versatile magnetic system which can be used with a fixed or varying magnetic moment so as to be suitable for use in ship degaussing and also minesweeping systems.
The magnet system must be capable of operating in three modes: requires.
The invention provides a magnet assembly which comprises a plurality of permanent magnets, each of which can be switched from one magnetisation saturation state (positive or negative) to the opposite magnetisation situration state, such that the overall magnetic moment of the assembly can be varied stepwise. Thus the magnet assembly will be referred to as a "variable permanent magnet". Such magnet assemblies would be particularly suitable for use in minesweeping and ship degaussing systems.
Each of the permanent magnets has a positive or negative magnetic moment depending on whether the material is positively or negatively saturated. Each magnet can then be switched from one saturation state to the other by driving the magnet into the opposite saturation state. Thus, if one permanent magnet is switched to its opposite saturation state, the overall magnetic moment of the system increases or decreases by the change in the magnetic moment of that permanent magnet.
The switching means for each permanent magnet preferably comprises a solenoid winding. Preferably a solenoid is wound around each permanent magnet and can produce a field which will force the permanent magnet into positive or negative saturation in dependence on the direction of the solenoid current. An electric pulse through the solenoid produces a magnetic field which drives the permanent magnet into saturation such that the magnet is switched from one saturation state to the opposite saturation state. Preferably there is a control circuit to connect each individual solenoid to a dc power source for sufficient time to achieve magnetic saturation.
Each permanent magnet preferably comprises a plurality of rods or cylinders. The rods or cylinders are of a permanent magnetic material and they may be arranged in a bundle.
The amount of magnetic material in the variable permanent magnet depends on the maximum total magnetic moment required. For a larger magnetic moment requirement more magnetic material must be used in the system.
As each permanent magnet bundle has its magnetic moment switched the overall magnetic moment alters stepwise. The size of the step depends on the size of the magnetic moment of the bundle, thus for a certain overall magnetic moment finer steps are achieved by using more bundles, each of less material, and coarser steps are achieved by using fewer bundles, each of more material.
Thus the amount of magnetic material in each bundle is determined by the overall magnetic moment and step size requirements and from this the number of rods or cylinders in each bundle can be dete

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patent: 3939753 (1976-02-01), Rosborough et al.
patent: 4220108 (1980-09-01), Burt
patent: 4535716 (1985-08-01), Hill

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