Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1995-12-15
1999-02-02
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Magnetometers
505846, 505160, 327527, G01R 33035, H01P 700
Patent
active
058670246
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national phase of PCT/DE94/00671 filed 15 Jun. 1994 and based, in turn, upon German national application P 43 19 693.4 filed 16 Jun. 1993 under the International Convention.
FIELD OF THE INVENTION
The invention relates to an rf-SQUID comprised of a superconductive ring formed with a Josephson element and including a superconductive microwave resonator coupled therewith and forming an electric resonant circuit.
BACKGROUND OF THE INVENTION
A SQUID is a sensor for measurement of magnetic flux. A SQUID is coupled with a flux transformer in the performance of measurement of a magnetic field, the flux transformer converting the magnetic field into a flux. A conventional flux transformer is comprised of a so-called pick-up coil for field-flux conversion and a coupling coil for further conduction of the flux to the SQUID. Such a construction is referred to as a SQUID magnetometer. A measure of the functional capability of a SQUID magnetometer is the field sensitivity. To operate a rf-SQUID-magnetometer, the latter is generally coupled to an electric resonant circuit, also called a tank circuit, into which a high-frequency current is fed at the resonance frequency of the tank circuit. The SQUID damps the tank circuit with a degree of damping dependent upon the magnetic flux through the superconductive ring. As a result there is a change in the voltage drop across the tank circuit which is used as a read-out for the SQUID.
From EP 04 18 848 A2, a LT.sub.c -RF-SQUID with an integrated microwave resonator is known. In this case the superconductive ring as well as the tank circuit are formed in one component. The tank circuit is comprised of a strip conductor. The electrical length of the strip conductor corresponds to a half microwave .lambda. of the operating frequency and thus forms a .lambda./2 microwave resonator. The strip resonator is capacitatively connected to the evaluation electronics.
To reliably set the resonator characteristics, the SQUID is arranged symmetrically relative to the strip conductor. This symmetry further allows the SQUID to be at a location of maximum current flux which ensures a sufficiently good coupling between resonator and SQUID. One such construction is fabricated from high temperature superconductive materials in accordance with Appl. Phys. Lett. 60(18), p. 2303, 1992.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an rf-SQUID magnetometer with improved field sensitivity and which can be fabricated from high temperature superconductive material.
This object is achieved with an rf-SQUID comprised of a superconductive ring having a Josephson element and with an electric resonant circuit coupled with the ring and forming a superconductive microwave resonator wherein the microwave resonator is formed as a closed superconductive conductor. The closed conductors can have optionally formed geometry. For example, the closed conductor can be realized in a ring-like or oval form. The structure is fabricatable from a single high-temperature superconductive layer. The SQUID ring and closed conductor can thus be formed from strip conductors.
Because of the closed conductor, this system for the first time provides a .lambda. resonator instead of .lambda./2 resonator. Such a resonator has not been used heretofore since it was not possible with the required closed conductor to effect the presumably required symmetrical coupling of the SQUID to the resonator.
The closed conductor in the present system functions however not only as a resonator but also as a pick-up coil. In comparison to the construction with the .lambda./2 resonator, the collection of the magnetic flux is significantly increased.
For the operation of the SQUID, the resonance frequency is supplied in known manner by a capacitive coupling which forms standing waves in the resonator. The standing waves can by initially selecting an optional length of the resonator develop as a result of testing or adjusting a resonance frequency. If one must ope
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Kornev et al. "Microwave-Frequency SQUID with a High-Q Dielectric Resonator" Radio Engineering & Eletronic Physics vol. 25, No. 12 Dec. 1980 pp. 122-128.
Dubno Herbert
Forschungszentrum Julich GmbH
Snow Walter E.
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