Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Superconductive type
Reexamination Certificate
1999-01-07
2001-02-06
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Superconductive type
C505S860000
Reexamination Certificate
active
06184765
ABSTRACT:
The present invention relates to the field of superconductors, i.e. materials which below a characteristic critical temperature exhibit no resistance to electrical current. More particularly, the present invention relates to superconducting materials exhibiting history-dependent magnetic permittivity, and to switch devices that incorporate such materials.
The maximum current-carrying capacity (or “critical current density”) of a superconducting material above which at a given temperature it becomes resistive to current flow is also a characteristic of the material. As distinguished from superconducting materials found to have ever higher critical temperatures and even higher critical current densities, the present invention utilizes superconducting materials characterized in that the critical current density can be either of two values, at a given temperature in a magnetic field of given strength. The discovery that the critical current density of such materials can be controllably and reversibly switched, and the discovery of how to achieve such controllability and reversible switching, are significant attributes of the present invention.
BRIEF SUMMARY OF THE INVENTION
One aspect of the present invention is a switch comprising
(A) a superconducting material whose field cooled and zero field cooled ac permittivities differ from each other, and whose field cooled and zero field cooled ac susceptibilities differ from each other, in a range of temperature below the superconducting transition temperature of the material;
(B) means for applying a static magnetic field to said material;
(C) means for controllably applying to said material an oscillating magnetic field of a magnitude effective to convert said material from a state exhibiting field cooled permittivity to a state exhibiting zero field cooled permittivity; and
(D) means for applying to said material a heat pulse effective to convert said material from a state exhibiting zero field cooled permittivity to a state exhibiting field cooled permittivity.
Another aspect of the present invention is a method of making a switch, comprising
(a) providing a superconducting material which exhibits field cooled and zero field cooled ac permittivities and ac susceptibilities which differ from each other in a range of temperature below the superconducting transition temperature of the material;
(b) providing a source of a static magnetic field acting on said material;
(c) providing means for controllably applying to said material an oscillating magnetic field of a magnitude effective to convert said material from a state exhibiting field cooled permittivity to a state exhibiting zero field cooled permittivity; and
(d) providing means for controllably applying to said material a heat pulse effective to convert said material from a state exhibiting zero field cooled permittivity to a state exhibiting field cooled permittivity.
Yet another aspect of the present invention is a method of increasing the critical current density of a superconducting material which exhibits field cooled and zero field cooled ac permittivities and ac susceptibilities which differ from each other in a range of temperature below the superconducting transition temperature of material, comprising applying to said material, while it is in a static magnetic field at a temperature in said range and while it is in a state exhibiting zero field cooled permittivity, a heat pulse effective to convert said material to a state exhibiting field cooled permittivity.
Another aspect of the present invention is a method of decreasing the critical current density of a superconducting material which exhibits field cooled and zero field cooled ac permittivities and ac susceptibilities which differ from each other in a range of temperature below the superconducting transition temperature of the material, comprising applying to said material, while it is in a static magnetic field at a temperature in said range and while it is in a state exhibiting field cooled permittivity, an oscillating magnetic field of a magnitude effective to convert said material to a state exhibiting zero field cooled permittivity.
REFERENCES:
patent: 4326188 (1982-04-01), Dahlberg
patent: 4419125 (1983-12-01), Charles et al.
patent: 4575927 (1986-03-01), Braginski et al.
patent: 5153803 (1992-10-01), Repeaux et al.
patent: 5323344 (1994-06-01), Katayama et al.
patent: 5679624 (1997-10-01), Das
patent: 5747425 (1998-05-01), Xin et al.
Banerjee Satyajit S.
Bhattacharya Sabyasachi
Grover Arun K.
Higgins Mark J.
Mishra Prashant K.
Donovan Lincoln
NEC Research Institute Inc.
Scully Scott Murphy & Presser
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