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Thermal Modulation of Superconducting Inductors

IP.com Disclosure Number: IPCOM000041872D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Ketchen, MB: AUTHOR

Abstract

Increasing the superconducting penetration depth, by sandwiching a heater (normal metal film) between a superconducting stripline and its ground plane, increases the inductance per unit length and permits thermal adjustment or modulation of the inductance. The inductance per unit length (neglecting fringing) of a superconducting stripline over the groundplane is given by: where 1 is the width of the line, t is the separation between the groundplane and the line, g1 is the superconducting penetration depth of the groundplane, and g2 is the penetration depth of the stripline. (The superconductors are assumed to be thick compared to g1 and g2.) If the temperature is increased, the energy gaps to the stripline and groundplane decrease, leading to an increase in the penetration depths and an increase in L.

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Thermal Modulation of Superconducting Inductors

Increasing the superconducting penetration depth, by sandwiching a heater (normal metal film) between a superconducting stripline and its ground plane, increases the inductance per unit length and permits thermal adjustment or modulation of the inductance. The inductance per unit length (neglecting fringing) of a superconducting stripline over the groundplane is given by: where 1 is the width of the line, t is the separation between the groundplane and the line, g1 is the superconducting penetration depth of the groundplane, and g2 is the penetration depth of the stripline. (The superconductors are assumed to be thick compared to g1 and g2.) If the temperature is increased, the energy gaps to the stripline and groundplane decrease, leading to an increase in the penetration depths and an increase in L. A number of applications for a variable inductor have been suggested, such as adjustable delay lines, tunable Josephson oscillators, phase shifters, etc. Sketches of the adjustable inductor are shown in Figs. 1a and 1b (plan view and cross section, respectively). A heater 1 in the form of a thin normal-metal film is interposed between the stripline 2 and insulated groundplane 3. As current is passed through heater l, the temperature of both groundplane 3 and stripline 2 increases. This decreases the energy gaps of both superconductors, leading to an increase in g1 and g2, and a corresponding increase in L. A circuit di...