Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
1999-05-26
2001-10-09
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C505S846000
Reexamination Certificate
active
06300760
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an arrangement for coupling an rf-SQUID to a superconducting tank circuit and to a base plate, in which arrangement of the tank circuit and the rf-SQUID form a coplanar structure and the tank circuit has a slit.
2. The Prior Art
Various proposals have been pursued heretofore for coupling rf-SQUID magnetometers to superconducting tank circuits.
One possibility is to employ a lambda resonator, to which an rf-SQUID is coupled galvanically, whereby said rf-SQUID functions at the same time as a flux pickup loop. Such a SQUID magnetometer may have a tank frequency of 3 GHz.
The use of a lambda resonator, however, is problematic in that it has a quality of only a few 100, which represents a quite low quality in view of the fact that qualities of a few 1000 have already been obtained with lambda/2 resonators. Furthermore, the fact that it is necessary in view of the galvanic coupling to take into account also a parameter which is difficult to calculate, namely the high-frequency current distribution, leads to considerable problems as well. The high-frequency current distribution represents a quantity which is not easy to calculate or control by experimentation. Therefore, it is difficult to optimize the SQUID layout.
Another possibility is to produce planar LC-tank circuits from YBaCuO thin layers with high frequency and high quality. Such LC-tank circuits are operated in a flip-chip arrangement, with the rf-SQUID in washer-SQUID structure. The parasitic capacities occurring in this connection between the LC-tank circuit and the rf-SQUID reduce the quality of the LC-tank circuit and make the current distribution in the combined LC-tank circuit/washer-SQUID structure complicated.
The aforementioned arrangement has been described by this applicant in application 196 11 900.6, which is still unpublished. Said arrangement solves the problem of parasitic capacities. However, the problem continues to exist that the coplanar arranged rf-SQUID and tank circuit cannot be arranged in one plane with the base plate, and that the base plate, furthermore, represents a potential noise source that may limit the application of an rf-SQUID magnetometer.
SUMMARY OF THE INVENTION
Therefore, the problem of the present invention is to create an arrangement which eliminates the aforementioned problems when an rf-SQUID magnetometer is coupled to a superconducting tank circuit.
The problem is solved by providing a base configured as an outer loop which is coplanar to the rf-SQUID and to the tank circuit, and that it has a slit; and that the tank circuit has an inner loop in which the slit is embodied; and that the orientation of the slits of the inner loop and the outer loop relative to one another determines the resonance frequency f
r
.
The arrangement as defined by the invention relates to the possibility of advantageous, optimal coupling of an rf-SQUID to a tank circuit and to a base plate without the drawbacks outlined above. With the fully integrated arrangement comprising the rf-SQUID, the tank circuit and the base plate, and with the configuration or orientation of the slits in the rf-SQUID and in the base plate, it is possible to adjust the frequency of the tank circuit in a simple way depending on the geometry, which, therefore, offers an important advantage, for example when structuring a multi-channel SQUID system for medical applications. Furthermore, noise conditioned by the base plate can be suppressed.
In addition, the fully integrated arrangement permits simple estimation of the coupling between the rf-SQUID and the tank circuit.
It is advantageous that an adjustment of the slits relative to one another effects a change in the resonance frequency f
r
300≦MHz.
A further advantage is that a defined superconducting short-circuit is built-in between the rf-SQUID and the tank circuit because the resonance frequency of the resonance circuit increases with the decrease in dimension. Above a limit frequency of 1 GHz, however, the required SQUID electronics becomes very expensive and requires much expenditure. The resonance frequency is distinctly reduced by the defined superconducting short-circuit, so that it is possible in a very simple way to obtain through a simple change in the geometry discrete frequency ranges within a span of 600 MHz, and still resonance frequencies of up to 500 MHz with very small dimensions. Such discrete frequencies are a required precondition for realizing a multi-channel HTSL-SQUID system.
It is advantageous that a flow transformer is integrated in the arrangement in order to raise the magnetic field sensitivity of an rf-SQUID even further.
A further advantage consists on that the flow transformer comprises a coupling coil, which forms of current takes place, which exist in such an arrangement is short-circuited. Thereby, decoupling of two forms of current takes place, which exist in such an arrangement. The two types of current differ from each other with respect to their high and low frequencies. The parasitic contributions of the high-frequency current, which develop on the crossovers of the flow transformer, disappear due to the decoupling. In the decoupled state, only low-frequency current flows via the crossovers.
It is particularly advantageous if the short-circuit takes place on a defined position of the capacitor.
A further advantage consists in that the field direction of the insert loop opposes the field direction of the coupling coil. This amplifies the SQUID signal in this geometry.
REFERENCES:
patent: 0 441 281 (1991-08-01), None
Zhang Y et al: “Single Layer . . . ”, Applied Physics Letters, vol. 65, No. 26, Dec. 26, 1994, pp. 3380-3382.
Zhang Y et al: “High-Sensitivity Microwave . . . ”, Superconductor Science and Technology, vol. 7, No. 5, May 1, 1994, pp. 269-272.
Banzet Marko
Schubert Jurgen
Yi Huai-ren
Zander Willi
Zeng Xianghui
Collard & Roe P.C.
Forschungszentrum Julich GmbH
Patidar Jay
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