Pulse power generation from thermal quenching of magnetic materials

• US 5,301,362 A
• Filed: 05/06/1991
• Issued: 04/05/1994
• Est. Priority Date: 05/09/1990
• Status: Expired due to Fees

• Current Assignee: General Atomics, Inc.
• Original Assignee: General Atomics, Inc.
• Inventors: Ohkawa, Tihiro
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): GHEBRETINSAE, TEMESGHEN
• Application Number:
  US07/695,953
• Time in Patent Office: 1,065 Days
• Field of Search: 375/59, 455/98, 455/91, 342/450, 342/126
• US Class Current: 455/98
• CPC Class Codes: G01S 5/04 Position of source determined by a plurality of spaced direction-finders

Abstract

Generation of a high power rf pulse is achieved in a simple transmitting device that uses permanent magnet material(s) to store energy. Such energy is released through the thermal quenching of the magnetic material(s). Thermal quenching is accomplished, e.g., through an explosion. Such thermal quenching is facilitated in one embodiment by using a magnetic composite material comprising both magnetic particles and explosive particles. The rf pulse thus generated may be used for any desired purpose, e.g., tracking or research. The transmitting device includes a permanent magnet for establishing a constant magnetic flux for so long as the magnet retains its normal magnetic properties. The magnetic flux passes through a coil. Upon the thermal quenching of the magnetic material(s), the magnetic properties rapidly change, causing the magnetic flux to also rapidly change, thus inducing a high power electrical pulse in the coil. This high power electrical pulse may be used in a broad band spark transmitter or used to power a narrow band transmitter, causing the rf pulse to be generated. In one embodiment, the power of the electrical pulse is increased by charging a capacitor, followed by a very short discharge of the capacitor.

Claims

1. A single-pulse radio frequency (rf) generator comprising:

a permanent magnet having the general shape of a toroid, said permanent magnet having a magnetic flux density that circulates through said toroid;

a coil of at least one turn passing through a center of said toroid such that the magnetic flux density passes through said coil, said magnetic flux density having a constant value for so long as said permanent magnet remains unchanged, an electrical potential being developed across said coil only when said magnetic flux density changes;

transmitting means coupled to said coil for transmitting an rf pulse in response to a change in said magnetic flux density, said rf pulse being generated by the electrical potential developed across the coil when the magnetic flux density changes; and

means for thermally quenching said permanent magnet, thereby causing the magnetic flux density flowing through said coil to change, thereby causing said rf pulse to be generated.

2. The single-pulse rf generator as set forth in claim 1 wherein said means for thermally quenching said permanent magnet comprises an explosive material that explodes and generates intense heat.

3. The single-pulse rf generator as set forth in claim 2 wherein said explosive material is interspersed throughout said permanent magnet, said permanent magnet with said explosive material interspersed therein comprising a composite magnet/explosive.

4. The single-pulse rf generator as set forth in claim 3 further including detonator means for selectively detonating said explosive material within said composite magnet/explosive, whereby said thermal quenching of said magnetic material, and hence the generation of said rf pulse, may occur at a selected time.

5. The single-pulse rf generator as set forth in claim 3 wherein the ratio of the volume of said explosive material to the volume of said composite magnet/explosive comprises 0.2 to 0.8.

6. The single-pulse rf generator as set forth in claim 5 wherein said permanent magnet comprises NdFeB, and said explosive materials comprise a high explosive powder that does not oxidize NdFeB.

7. The single-pulse rf generator as set forth in claim 3 further including a casing around said toroid, said casing including means for preventing current flow therein that passes through the center of the toroid.

8. The single-pulse rf generator as set forth in claim 3 wherein said transmitting means coupled to said coil includes a transformer, said transformer including a magnetic core having first and second windings wrapped therearound, said first winding being coupled to the coil that loops through the center of said toroid, the thermal quenching of said composite magnetic/explosive inducing a first electrical potential in said first winding that causes a first current to flow, said first current causing a second magnetic flux density to flow in said magnetic core, said second magnetic flux inducing a second electrical potential in said second winding, said second electrical potential comprising an output signal from which said rf pulse is derived.

9. The single-pulse rf generator as set forth in claim 8 wherein the magnetic core of said transformer comprises a toroidal magnetic core, said toroidal magnetic core being physically spaced apart from said composite magnetic/explosive which is also in the shape of a toroid.

10. The single-pulse rf generator as set forth in claim 9 wherein said first winding comprises a single turn winding that passes through the center of the toroidal magnetic core and the center of the composite magnetic/explosive toroid, said second winding comprising a multi-turn winding that is wrapped around said toroidal magnetic core.

11. A method of generating an rf pulse upon the thermal quenching of magnetic material comprising the steps of:

(a) storing electromagnetic energy in magnetic material formed in the general shape of a toroid by establishing a constant magnetic flux that flows within said toroid;

(b) coupling a coil to said toroid so that said magnetic flux flows through said coil;

(c) thermally quenching the magnetic material by subjecting it to a temperature that exceeds the Curie point of the magnetic material, the stored electromagnetic energy being released from said magnetic material by said thermal quenching; and

(d) coupling a voltage induced in said coil when said magnetic flux changes as a result of said thermal quenching to an output terminal, said induced voltage including a portion of the electromagnetic energy that is released upon the thermal quenching of said magnetic material;

(e) generating an rf pulse using said induced voltage at said output terminal.

12. The method of generating an rf pulse as set forth in claim 11 wherein step (c) includes exploding said magnetic material.

13. The method of generating an rf pulse as set forth in claim 12 further including:

interspersing explosive particles through said magnetic material, thereby creating a composite magnetic material comprising part magnetic particles and part explosive particles; and

exploding said explosive particles.

14. The method of generating an rf pulse as set forth in claim 18 further including coupling a transformer to said coil and sensing said induced sensed voltage at a secondary winding of said transformer, said coupling including connecting a primary winding of said transformer to said coil, whereby a desired impedance match is obtained between said pulse generator and said coil.