WO1996032655A1 - Rf squid gradiometer with resonant flux-focusing structure - Google Patents

Rf squid gradiometer with resonant flux-focusing structure Download PDF

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Publication number
WO1996032655A1
WO1996032655A1 PCT/DE1996/000636 DE9600636W WO9632655A1 WO 1996032655 A1 WO1996032655 A1 WO 1996032655A1 DE 9600636 W DE9600636 W DE 9600636W WO 9632655 A1 WO9632655 A1 WO 9632655A1
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Prior art keywords
squid
gradiometer
focusing structure
flux
loop
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PCT/DE1996/000636
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German (de)
French (fr)
Inventor
Erik Sodtke
Martin Gottschlich
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Forschungszentrum Jülich GmbH
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Publication of WO1996032655A1 publication Critical patent/WO1996032655A1/en

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01RMEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00Arrangements or instruments for measuring magnetic variables
    • G01R33/02Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/035Measuring direction or magnitude of magnetic fields or magnetic flux using superconductive devices
    • G01R33/0354SQUIDS
    • G01R33/0358SQUIDS coupling the flux to the SQUID

Definitions

  • the invention relates to an RF SQUID gradiometer with a SQUID loop containing at least one Josephson contact and acting as a gradiometer and a flux focusing structure made of superconducting material which acts as a high quality RF resonator.
  • HF-SQUID are highly sensitive sensors for measuring magnetic flux or spatial flow gradients.
  • sensors in thin-film technology are from EP 04 18 848 A2 in magnetometer form and from DE
  • 39 31 441 C2 known in the form of a gradiometer.
  • the magnetometer consist of a superconducting ring with an incorporated Josephson contact and a strip line coupled to this ring, which is designed as an X or ⁇ / 2 resonator at the operating frequency of the SQUID and with a high-frequency current of suitable amplitude and a frequency in the GHz range is fed.
  • the superconducting ring dampens the resonator as a function of the magnetic flux in the ring, as a result of which the voltage drop across the resonator changes.
  • the resulting amplitude or phase signal is used to read out the sensor. It is known that the intrinsic noise and thus the minimally resolvable magnetic flux are inversely proportional to the operating frequency of the Are SQUID. Furthermore, it is known that the magnetic flux-dependent voltage modulation at the RF resonator becomes greater, the lower the coupling constant k between the superconducting ring and resonator and the greater the quality Q of the resonator, the condition k ⁇ Q> 1 must be fulfilled.
  • HF-SQUID gradiometers In contrast to the version as a magnetometer, HF-SQUID gradiometers contain two superconducting loops, whose magnetic field-induced shielding currents flow through the Josephson contact in opposite directions, so that when the surfaces of the two superconducting rings are exact are the same, only a spatial field gradient leads to a net current through the contact.
  • sensors can be used to measure the gradient of magnetic fields which are superimposed by magnetic fields of greater field strength which do not vary at the location of the sensor and which would therefore not be measurable by magnetometers without additional shielding or interference field compensation.
  • the size limitation is removed by the strip line of the conventional HF-SQUID. In this way, the entire available substrate area can be used and a high field focus can be achieved in the SQUID loops.
  • the RF power is coupled to the resonator in one or two port operation in a known manner, for example via capacitively coupled RF lines or antennas. As a result, a superposition of several degenerate resonant modes at the fundamental frequency or the frequency of suitable upper modes is generally excited.
  • the resonated flux focusing structure is to be designed geometrically in such a way that a sufficient HF current flows through the Josephson contact.
  • the RF current amplitude determines the coupling constant k.
  • the frequency and RF current distribution the resonant modes can be modeled by field theoretical computer simulations.
  • resonance frequencies in the range 3 - 5 GHz for the fundamental oscillation can be found for an approximately 8 * 8 mm 2 large resonator on a 10 * 10 mm 2 large substrate realize. This ensures a sufficiently high frequency for the low-noise operation of the sensor.
  • the coupling k between the SQUID and the resonator can be coordinated by varying the coupling geometry and the resonator geometry.
  • 1 shows the schematic structure of the RF SQUID gradiometer according to the invention with the resonant flux-focusing surface made of superconducting material (1), the two SQUID loops (2a) and (2b), the Josephson contact (3) and the two RF coupling lines (4a) and (4b) for the case of a capacitive two-port coupling.
  • the setting of the RF current amplitude at the location of the Josephson contact can be done in different ways according to claims 2 and 3. If a superimposition of several degenerate modes is stimulated at the same time and these modes have different RF current amplitudes at the point of contact, the relative proportion of the modes and thus the RF current can be transmitted through an asymmetrical coupling of the RF power to the resonator the contact can be controlled. This can be done, for example, by shifting the coupling antennas (4a) and (4b) relative to one another. Furthermore, the current can be influenced via the contact by a targeted asymmetrical design of the resonator. This can be done, for example, by flattening two opposite corners of the resonator from FIG. 1. So fashionable The structure is schematically outlined in FIG. 2.
  • the quality can be achieved in the structure proposed according to the invention according to claim 4 by HF reflectors suitably arranged around the sensor increase.
  • the reflectors must be made of magnetically permeable or low-noise material.
  • the entire sensor can be encapsulated in an HF-tight envelope in order to completely prevent radiation losses.
  • an increase in the loaded quality by at least an order of magnitude or more is achieved.
  • a design of the resonator in stripline geometry also offers the possibility of realizing higher grades, which can increase by up to two orders of magnitude when using superconducting end plates, for example.
  • the sensor according to the invention accordingly offers the possibility of maximizing the output signal by specifically setting the coupling between the SQUID and the resonator and the loaded quality of the resonator.
  • the described advantages of the HF SQUID gradiometer according to claims 1 to 4 can also be used when the sensor is operated as a magnetometer.
  • the areas of the SQUID loops (2a) and (2b) should be chosen to be of different sizes.
  • an induced net current flows through the Josephson contact even in the case of a spatially non-varying magnetic field, since the magnetic flux in the two loops is not the same.
  • the sensor described can advantageously be used in an embodiment in high-temperature superconducting material at temperatures in the range of liquid nitrogen.
  • the advantages inherent in the HF-SQUID gradiometer, however, are also fully usable on the basis of low-temperature superconductors.
  • the maximum of the half-wave lies at the location of the Josephson contact (FIG. 4b).
  • the modes shown in FIGS. 3a and 4a are degenerate and therefore to be excited at the same time, so that an arbitrary ratio of the modes can be set by a suitable antenna arrangement.
  • the HF current via the Josphson contact can thus be set to the optimal value.

Abstract

The invention relates to a SQUID with a plurality of SQUID loops containing at least one common Josephson contact which act as a gradiometer and to a flux-focusing structure of superconducting material. This SQUID has such a flux-focusing structure which is constructed in such a way that it also acts as a tank resonant circuit. The fundamental resonant mode or one of the upper modes of the flux-focusing structure can be used here to couple the r.f. power to the gradiometer-SQUID loop. This provides a gradiometer with low inherent noise and a high magnetic field gradient sensitivity.

Description

B e s c h r e i b u n gDescription
HF-SQUID-Gradiometer mit resonanter Flußfokussierungs- strukturRF SQUID gradiometer with resonant flux focusing structure
Die Erfindung betrifft ein HF-SQUID-Gradiometer mit einer wenigstens einen Josephson-Kontakt enthaltender, als Gradiometer wirkender SQUID-Schleife und einer Flußfokussierungsstruktur aus supraleitendem Material, die als HF-Resonator hoher Güte wirkt.The invention relates to an RF SQUID gradiometer with a SQUID loop containing at least one Josephson contact and acting as a gradiometer and a flux focusing structure made of superconducting material which acts as a high quality RF resonator.
HF-SQUID sind hochempfindliche Sensoren für die Messung von magnetischem Fluß oder räumlichen Flußgradienten. Derartige Sensoren in Dünnschichttechnik sind aus EP 04 18 848 A2 in Magnetometerform und aus DEHF-SQUID are highly sensitive sensors for measuring magnetic flux or spatial flow gradients. Such sensors in thin-film technology are from EP 04 18 848 A2 in magnetometer form and from DE
39 31 441 C2 in Gradiometerform bekannt. Sie bestehen im Fall des Magnetometers aus einem supraleitenden Ring mit einem inkorporierten Josephson-Kontakt und einer an diesen Ring gekoppelten Streifenleitung, die als X- oder Λ/2-Resonator bei der Betriebsfrequenz des SQUID ausgebildet ist und mit einem Hochfrequenzstrom ge¬ eigneter Amplitude und einer Frequenz im GHz-Bereich gespeist wird. Der supraleitende Ring bedämpft den Re¬ sonator in Abhängigkeit vom magnetischen Fluß im Ring, wodurch sich der Spannungsabfall am Resonator ändert.39 31 441 C2 known in the form of a gradiometer. In the case of the magnetometer, they consist of a superconducting ring with an incorporated Josephson contact and a strip line coupled to this ring, which is designed as an X or Λ / 2 resonator at the operating frequency of the SQUID and with a high-frequency current of suitable amplitude and a frequency in the GHz range is fed. The superconducting ring dampens the resonator as a function of the magnetic flux in the ring, as a result of which the voltage drop across the resonator changes.
Das dabei enstehende Amplituden- oder Phasensignal wird zum Auslesen des Sensors verwendet. Es ist bekannt, daß das Eigenrauschen und damit der minimal auflösbare Mag¬ netfluß invers proportional zur Betriebsfrequenz des SQUID sind. Weiterhin ist bekannt, daß die magnetflu߬ abhängige Spannungsmodulation am HF-Resonator umso größer wird, je geringer die Kopplungskonstante k zwi¬ schen supraleitendem Ring und Resonator ist und umso größer die Güte Q des Resonators ist, wobei die Bedin- _) gung k^Q > 1 erfüllt sein muß.The resulting amplitude or phase signal is used to read out the sensor. It is known that the intrinsic noise and thus the minimally resolvable magnetic flux are inversely proportional to the operating frequency of the Are SQUID. Furthermore, it is known that the magnetic flux-dependent voltage modulation at the RF resonator becomes greater, the lower the coupling constant k between the superconducting ring and resonator and the greater the quality Q of the resonator, the condition k ^ Q> 1 must be fulfilled.
Für den rauscharmen Betrieb des Sensors ist es außerdem entscheidend, die Induktivität des supraleitenden Rin- ges auf Werte kleiner als ca. 200 pH zu begrenzen. Die damit verbundene kleine Fläche des Ringes erschwert die Einkopplung von zu messendem magnetischem Fluß in den Ring. Zur Verbesserung der Flußfokussierung können zu¬ sätzliche supraleitende Flächen in der Nähe des supra- leitenden Ringes plaziert werden (Y. Zhang et al., Su- percond. Sei. Technol. 7 (1994) 269-272). Bei herkömm¬ lichen HF-SQUID mit Resonatoren in der Form von Strei¬ fenleitern ist die Größe der Flußfokussierungsflachen jedoch durch die Ausdehnung des Resonators begrenzt, außerdem wird die Hochfrequenzstromverteilung im Reso¬ nator durch die zusätzlichen Flächen in der Nähe des supraleitenden Ringes ungünstig beeinflußt. Aufgrund der geringen Flußfokussierung der herkömmlichen HF- SQUID ist ihre Magnetfeldempfindlichkeit trotz geringen Eigenrauschen geringer als die von konventionellen Wechselstrom-Washer-SQUID, die im Frequenzbereich < 500 MHz arbeiten (Y. Zhang et al., IEEE Trans. Appl. Supercond. 3 (1993) 2465). Dies gilt auch entsprechend für die Magnetfeldgradientenauflösung herkömmlicher HF- SQUID-Gradio eter, wie sie aus DE 39 31 441 C2 bekannt sind. Im Unterschied zur Ausführung als Magnetometer enthalten HF-SQUID-Gradiometer zwei supraleitende Schleifen, deren magnetfeldinduzierte Abschirmströme den Josephson-Kontakt gegensinnig durchfließen, so daß, wenn die Flächen der beiden supraleitenden Ringe exakt gleich sind, nur ein räumlicher Feldgradient zu einem Nettostrom über den Kontakt führt. Derartige Sensoren können dazu verwendet werden, den Gradienten von Mag¬ netfeldern zu messen, die von am Ort des Sensors räu - lieh nicht variierenden Magnetfeldern größerer Feld¬ stärke überlagert sind und daher von Magnetometern ohne zusätzliche Abschirmung oder Störfeldkompensation nicht meßbar wären.For low-noise operation of the sensor, it is also crucial to limit the inductance of the superconducting ring to values less than approx. 200 pH. The associated small area of the ring makes it difficult to couple the magnetic flux to be measured into the ring. To improve the flow focusing, additional superconducting surfaces can be placed in the vicinity of the superconducting ring (Y. Zhang et al., Supercond. Sci. Technol. 7 (1994) 269-272). In conventional HF-SQUID with resonators in the form of strip conductors, however, the size of the flux focusing surfaces is limited by the expansion of the resonator, and the high-frequency current distribution in the resonator is adversely affected by the additional surfaces in the vicinity of the superconducting ring. Due to the low flux focus of the conventional HF-SQUID, its magnetic field sensitivity is lower than that of conventional AC washer SQUID, which operate in the frequency range <500 MHz (Y. Zhang et al., IEEE Trans. Appl. Supercond. 3 ( 1993) 2465). This also applies correspondingly to the magnetic field gradient resolution of conventional HF SQUID gradi eters, as are known from DE 39 31 441 C2. In contrast to the version as a magnetometer, HF-SQUID gradiometers contain two superconducting loops, whose magnetic field-induced shielding currents flow through the Josephson contact in opposite directions, so that when the surfaces of the two superconducting rings are exact are the same, only a spatial field gradient leads to a net current through the contact. Such sensors can be used to measure the gradient of magnetic fields which are superimposed by magnetic fields of greater field strength which do not vary at the location of the sensor and which would therefore not be measurable by magnetometers without additional shielding or interference field compensation.
Es ist daher Aufgabe der Erfindung, ein HF-SQUID-Gra¬ diometer zu schaffen, daß den Nachteil geringer Flußfo- kussierung beseitigt und somit gleichzeitig ein gerin¬ ges Eigenrauschen und eine hohe Magnetfeldgradienten¬ empfindlichkeit besitzt.It is therefore an object of the invention to provide an HF-SQUID graphite that eliminates the disadvantage of low flux focusing and thus at the same time has low intrinsic noise and high magnetic field gradient sensitivity.
Die Aufgabe wird erfindungsgemäß durch einen Sensor mit den Merkmalen des Anspruchs 1 gelöst.The object is achieved according to the invention by a sensor with the features of claim 1.
Durch die Integration von HF-Resonator und Flußfokus- sierungsstruktur in einer gemeinsamen supraleitendenBy integrating the RF resonator and the flux focusing structure in a common superconducting
Fläche wird die Größenbegrenzung durch den Streifenlei¬ ter der herkömmlichen HF-SQUID aufgehoben. So kann die gesamte zur Verfügung stehende Substratfläche ausge¬ nutzt und eine hohe Feldfokussierung in die SQUID- Schleifen erreicht werden. Die Ankopplung der HF-Lei¬ stung an den Resonator erfolgt im Ein- oder Zweitorbe¬ trieb in bekannter Weise z.B. über kapazitiv gekoppelte HF-Leitungen oder Antennen. Hierdurch wird im allgemei¬ nen eine Überlagerung mehrerer entarteter resonanter Moden bei der Grundfrequenz oder der Frequenz geeigne¬ ter Obermodi angeregt. Die resonarrte Flußfokussierungs- struktur ist dazu geometrisch so auszulegen, daß ein ausreichender HF-Strom über den Josephson-Kontakt fließt. Die HF-Stromamplitude bestimmt dabei die Kopp- lungskonstante k. Die Frequenz und HF-Stromverteilung der resonanten Modi kann durch feldtheoretische Com¬ putersimulationen modelliert werden. Auf gängigen Sub¬ straten für die Abscheidung von supraleitenden Schich¬ ten wie z.B Lanthanaluminat oder Saphir lassen sich für einen ca. 8*8 mm2 großen Resonator auf einem 10*10 mm2 großen Substrat Resonanzfrequenzen im Bereich 3 - 5 GHz für die Grundschwingung realisieren. Dadurch ist eine für den rauscharmen Betrieb des Sensors ausreichend hohe Frequenz gewährleistet.The size limitation is removed by the strip line of the conventional HF-SQUID. In this way, the entire available substrate area can be used and a high field focus can be achieved in the SQUID loops. The RF power is coupled to the resonator in one or two port operation in a known manner, for example via capacitively coupled RF lines or antennas. As a result, a superposition of several degenerate resonant modes at the fundamental frequency or the frequency of suitable upper modes is generally excited. For this purpose, the resonated flux focusing structure is to be designed geometrically in such a way that a sufficient HF current flows through the Josephson contact. The RF current amplitude determines the coupling constant k. The frequency and RF current distribution the resonant modes can be modeled by field theoretical computer simulations. On common substrates for the deposition of superconducting layers, such as lanthanum aluminate or sapphire, resonance frequencies in the range 3 - 5 GHz for the fundamental oscillation can be found for an approximately 8 * 8 mm 2 large resonator on a 10 * 10 mm 2 large substrate realize. This ensures a sufficiently high frequency for the low-noise operation of the sensor.
Durch Variation der Kopplungsgeometrie sowie der Reso¬ natorgeometrie kann die Kopplung k zwischen SQUID und Resonator abgestimmt werden. Fig. 1 zeigt den schemati¬ schen Aufbau des erfindungsgemäßen HF-SQUID-Gradiome- ters mit der resonanten flußfokussierenden Fläche aus supraleitendem Material (1) , den beiden SQUID-Schleifen (2a) und (2b), dem Josephson-Kontakt (3) und den beiden HF-Einkoppelleitungen (4a) und (4b) für den Fall einer kapazitiven Zweitorankopplung.The coupling k between the SQUID and the resonator can be coordinated by varying the coupling geometry and the resonator geometry. 1 shows the schematic structure of the RF SQUID gradiometer according to the invention with the resonant flux-focusing surface made of superconducting material (1), the two SQUID loops (2a) and (2b), the Josephson contact (3) and the two RF coupling lines (4a) and (4b) for the case of a capacitive two-port coupling.
Die Einstellung der HF-Stromamplitude am Ort des Jo- sephson-Kontaktes kann gemäß den Ansprüchen 2 und 3 auf verschiedene Weise geschehen. Wird eine Überlagerung mehrerer entarteter Modi gleichzeitig angeregt und ha- ben diese Modi unterschiedliche HF-Stromamplituden am Ort des Kontaktes, so kann durch eine asymmetrische Einkopplung der HF-Leistung an den Resonator der rela¬ tive Anteil der Modi und damit der HF-Strom über den Kontakt gesteuert werden. Dies kann z.B. durch eine Verschiebung der Einkoppelantennen (4a) und (4b) rela¬ tiv zueinander geschehen. Weiterhin kann durch eine ge¬ zielte asymmetrische Auslegung des Resonators der Strom über den Kontakt beeinflußt werden. Dies kann z.B. durch Abflachung zweier gegenüberliegender Ecken des Resonators aus Fig. 1 geschehen. Eine dergestalt modi- fizierte Struktur ist in Fig. 2 schematisch skizziert.The setting of the RF current amplitude at the location of the Josephson contact can be done in different ways according to claims 2 and 3. If a superimposition of several degenerate modes is stimulated at the same time and these modes have different RF current amplitudes at the point of contact, the relative proportion of the modes and thus the RF current can be transmitted through an asymmetrical coupling of the RF power to the resonator the contact can be controlled. This can be done, for example, by shifting the coupling antennas (4a) and (4b) relative to one another. Furthermore, the current can be influenced via the contact by a targeted asymmetrical design of the resonator. This can be done, for example, by flattening two opposite corners of the resonator from FIG. 1. So fashionable The structure is schematically outlined in FIG. 2.
Zur Verringerung der Strahlungsverluste aufgrund der räumlich ausgedehnten HF-Stromverteilung, wodurch die belastete Güte des Resonators in Mikrostreifengeometrie auf Q ~ 1000-2000 begrenzt wird, kann bei der erfindungsgemäß vorgeschlagenen Struktur gemäß Anspruch 4 durch geeignet um den Sensor herum angebrachte HF-Reflektoren die Güte erhöht werden. Die Reflektoren müssen aus magnetisch durchlässigem bzw. rauscharmen Material bestehen. Im Extremfall ist eine Kapselung des gesamten Sensors in einer HF-dichten Umhüllung möglich, um Strahlungsverluste ganz zu verhindern. In diesem Fall wird eine Steigerung der belasteten Güte um wenigstens eine Größenordnung oder mehr erreicht. Auch eine Ausführung des Resonators in Stripline-Geometrie bietet die Möglichkeit, höhere Güten zu realisieren, die bei Verwendung von supraleitenden Endplatten um beispielsweise bis zu zwei Größenordnungen ansteigen können.In order to reduce the radiation losses due to the spatially extensive HF current distribution, which limits the loaded quality of the resonator in microstrip geometry to Q ~ 1000-2000, the quality can be achieved in the structure proposed according to the invention according to claim 4 by HF reflectors suitably arranged around the sensor increase. The reflectors must be made of magnetically permeable or low-noise material. In an extreme case, the entire sensor can be encapsulated in an HF-tight envelope in order to completely prevent radiation losses. In this case an increase in the loaded quality by at least an order of magnitude or more is achieved. A design of the resonator in stripline geometry also offers the possibility of realizing higher grades, which can increase by up to two orders of magnitude when using superconducting end plates, for example.
Der erfindungsgemäße Sensor bietet demnach die Möglich¬ keit, durch gezielte Einstellung der Kopplung zwischen SQUID und Resonator sowie der belasteten Güte des Reso- nators das Ausgangssignal zu maximieren.The sensor according to the invention accordingly offers the possibility of maximizing the output signal by specifically setting the coupling between the SQUID and the resonator and the loaded quality of the resonator.
Die beschriebenen Vorteile des HF-SQUID-Gradiometers gemäß den Ansprüchen 1 bis 4 sind auch bei einem Be¬ trieb des Sensors als Magnetometer nutzbar. Hierfür sind die Flächen der SQUID-Schleifen (2a) und (2b) un¬ terschiedlich groß zu wählen. In diesem Fall fließt auch bei einem räumlich nicht variierendem Magnetfeld ein induzierter Nettostrom über den Josephson-Kontakt, da der magnetische Fluß in den beiden Schleifen nicht gleich groß ist. Gemäß Anspruch 6 kann der beschriebene Sensor bei einer Ausführung in hochtemperatursupraleitendem Material vorteilhaft bei Temperaturen im Bereich des flüssigen Stickstoffes eingesetzt werden. Die dem er indungsge¬ mäßen HF-SQUID-Gradiometer anhaftenden Vorteile sind aber auch auf der Basis von Tieftemperatursupraleitern voll nutzbar.The described advantages of the HF SQUID gradiometer according to claims 1 to 4 can also be used when the sensor is operated as a magnetometer. For this purpose, the areas of the SQUID loops (2a) and (2b) should be chosen to be of different sizes. In this case, an induced net current flows through the Josephson contact even in the case of a spatially non-varying magnetic field, since the magnetic flux in the two loops is not the same. According to claim 6, the sensor described can advantageously be used in an embodiment in high-temperature superconducting material at temperatures in the range of liquid nitrogen. The advantages inherent in the HF-SQUID gradiometer, however, are also fully usable on the basis of low-temperature superconductors.
AusführungsbeispielEmbodiment
1. Computersimuliert wurde die HF-Stromverteilung eines 8*8 mm2 großen HF-SQUID-Gradiometers mit zwei SQUID- Schleifen mit einer Fläche von je 100*200 μm im Grund- modus für eine kapazitive HF-Ankopplung in Mikrostrei- fengeometrie nach Fig. 1. Die Resonanzfrequenz auf einem 0,5 mm dicken Lanthanaluminatsubstrat liegt bei etwa 3,9 GHz. Die HF-Stromverteilung bei der Resonanz¬ frequenz ist in Fig. 3a dargestellt. Deutlich erkennbar ist die sich zwischen den Einkoppelstreifen im Resona¬ tor ausbildende Halbwelle und die Randüberhöhung des HF-Stromes. Die HF-Stromamplitude am Ort des Kontaktes ist vernachlässigbar klein (Fig. 3b).1. The RF current distribution of an 8 * 8 mm 2 RF SQUID gradiometer with two SQUID loops, each with an area of 100 * 200 μm in basic mode for a capacitive RF coupling in microstrip geometry according to Fig 1. The resonance frequency on a 0.5 mm thick lanthanum aluminate substrate is approximately 3.9 GHz. The HF current distribution at the resonance frequency is shown in FIG. 3a. The half wave that forms between the coupling strips in the resonator and the edge elevation of the HF current can be clearly seen. The RF current amplitude at the point of contact is negligible (Fig. 3b).
2. Bei um 90 Grad gegenüber Fig. 4a um den Resonator rotierten Antennen liegt das Maximum der Halbwelle am Ort des Josephson-Kontaktes (Fig. 4b). Die in Fig. 3a und 4a gezeigten Moden sind entartet und daher gleich¬ zeitig anzuregen, so daß durch eine geeignete Antennen- anordnung ein beliebiges Verhältnis der Moden einstell¬ bar ist. Der HF-Strom über den Josphson-Kontakt läßt sich somit auf den optimalen Wert einstellen.2. In the case of antennas rotated by 90 degrees in relation to FIG. 4a, the maximum of the half-wave lies at the location of the Josephson contact (FIG. 4b). The modes shown in FIGS. 3a and 4a are degenerate and therefore to be excited at the same time, so that an arbitrary ratio of the modes can be set by a suitable antenna arrangement. The HF current via the Josphson contact can thus be set to the optimal value.
3. Modifiert man den Resonator nach Fig. 3a durch eine Einkerbung an zwei gegenüberliegenden Ecken, erhält man die in Fig. 5a und 5b (Detail) dargestellte HF-Strom¬ verteilung. Die Einkerbung bewirkt eine Asymmetrie der Stromverteilung an den Innenkanten der SQUID-Schleifen, die zu einem höheren HF-Strom über den Josephson-Kon- takt führt. Gleichzeitig wird die reguläre Halbwellen- struktur gestört und der HF-Strom konzentriert sich an den Einkerbungen. Durch eine weniger starke Einkerbung ließe sich eine geringere Störung der Halbwelle errei¬ chen und somit der Strom über den Kontakt auf den ge- wünschten Wert einstellen. 3. If the resonator according to FIG. 3a is modified by a notch at two opposite corners, one obtains the HF current distribution shown in FIGS. 5a and 5b (detail). The indentation causes an asymmetry in the current distribution on the inner edges of the SQUID loops, which leads to a higher HF current via the Josephson contact. At the same time, the regular half-wave structure is disturbed and the HF current is concentrated at the notches. A less pronounced indentation would result in less interference in the half-wave and thus the current through the contact could be set to the desired value.

Claims

P a t e n t a n s p r ü c h e Patent claims
1. SQUID, insbesondere HF-SQUID, mit mehreren wenigstens einen gemeinsamen Josephson-Kontakt enthaltenden, als Gradiometer wirkenden SQUID- Schleifen und einer flächigen, supraleitenden Struktur zur Fokussierung des magnetischen Flusses in die SQUID-Schleife hinein, wobei die Flußfokussierungsstruktur lateral geometrisch so ausgebildet ist, daß sie gleichzeitig einen integrierten Tankschwingkreis bildet, wobei auf Grund der lateral geometrischen Ausbildung zum Betrieb des Tankschwingkreises der resonante Grundmodus oder einer von mehreren möglichen Obermodi, der in der Flußfokussierungsstruktur vorhandenen elektromagnetischen Schwingungen zur Ankopplung der HF-Leistung an die jeweilige Gradiometer-SQUID-Schleife genutzt wird.1. SQUID, in particular HF-SQUID, with a plurality of SQUID loops containing at least one common Josephson contact and acting as a gradiometer and a flat, superconducting structure for focusing the magnetic flux into the SQUID loop, the flux focusing structure being designed laterally geometrically in this way is that it simultaneously forms an integrated tank resonant circuit, the resonant basic mode or one of several possible upper modes, the electromagnetic vibrations present in the flow focusing structure for coupling the RF power to the respective gradiometer SQUID due to the lateral geometric configuration for operating the tank resonant circuit Loop is used.
2. SQUID nach Anspruch 1, d a d u r c h g e k e n n z e i c h n e t , daß mehrere resonante Moden der integrierten Flußfokussierungsstruktur zur gleichzeitige Anregung vorgesehen sind und zur Ankopplung der HF-Leistung an die Gradiometer-SQUID-Schleife genutzt werden. 2. SQUID according to claim 1, characterized in that several resonant modes of the integrated flux focusing structure are provided for simultaneous excitation and are used for coupling the RF power to the gradiometer SQUID loop.
3. SQUID nach Anspruch 1 oder 2, d a d u r c h g e k e n n z e i c h n e t , daß die HF-Stromverteilung der angeregten reso¬ nanten Mode oder Moden durch eine asymmetrische Geometrie der flußfokussierenden Struktur oder durch eine asymmetrische Ankopplung der externen HF-Leistung an das integrierte HF-SQUID gesteuert wird.3. SQUID according to claim 1 or 2, so that the HF current distribution of the excited resonant mode or modes is controlled by an asymmetrical geometry of the flow-focusing structure or by an asymmetrical coupling of the external HF power to the integrated HF SQUID.
4. SQUID nach Anspruch 1,2 oder 3, d a d u r c h g e k e n n z e i c h n e t , daß geeignet angebrachte HF-Reflektoren zur Steuerung der Güte des Resonators vorgesehen sind.4. SQUID according to claim 1, 2 or 3, so that suitable RF reflectors are provided to control the quality of the resonator.
5. SQUID nach Anspruch 1,2,3 oder 4 g e k e n n z e i c h n e t d u r c h unterschiedliche Lochgrößen der beiden einen gemeinsamen Josephson-Kontakt enthaltenden Schleifen des Gradiometer-SQUID.5. SQUID according to claim 1, 2, 3 or 4 g e k e n n z e i c h n e t d u r c h different hole sizes of the two loops of the gradiometer SQUID containing a common Josephson contact.
6. SQUID nach Anspruch 1,2,3,4 oder 5 g e k e n n z e i c h n e t d u r c h hochtemperatursupraleitendes Material zur Bildung der Schleife und der Flußfokussierungs-Struktur. 6. SQUID according to claim 1, 2, 3, 4 or 5 high-temperature superconducting material for forming the loop and the flux focusing structure.
PCT/DE1996/000636 1995-04-13 1996-04-09 Rf squid gradiometer with resonant flux-focusing structure WO1996032655A1 (en)

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Citations (3)

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GB2213267A (en) * 1987-12-05 1989-08-09 Stc Plc Hall effect magnetometer
EP0418848A2 (en) * 1989-09-21 1991-03-27 Forschungszentrum Jülich Gmbh Sensor for the measurement of magnetic flux
EP0481211A2 (en) * 1990-10-09 1992-04-22 International Business Machines Corporation Gradiometer having a magnetometer which cancels background magnetic field from other magnetometers

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Publication number Priority date Publication date Assignee Title
JP2749048B2 (en) * 1988-02-05 1998-05-13 株式会社日立製作所 Superconducting quantum interferometer
DE4119880C2 (en) * 1991-06-17 1993-12-23 Forschungszentrum Juelich Gmbh Circuit arrangement with SQUID for measuring magnetic flux
DE4319693A1 (en) * 1993-06-16 1994-12-22 Forschungszentrum Juelich Gmbh RF-SQUID with an integrated lambda microwave resonator as a highly sensitive magnetometer

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2213267A (en) * 1987-12-05 1989-08-09 Stc Plc Hall effect magnetometer
EP0418848A2 (en) * 1989-09-21 1991-03-27 Forschungszentrum Jülich Gmbh Sensor for the measurement of magnetic flux
EP0481211A2 (en) * 1990-10-09 1992-04-22 International Business Machines Corporation Gradiometer having a magnetometer which cancels background magnetic field from other magnetometers

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