WO2002086524A2 - VERFAHREN ZUM AUSLESEN VON MAGNETISCHEN FELDERN MIT EINEM dc SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE (dc-SQUID) SOWIE DAZU GEEIGNETE VORRICHTUNG - Google Patents
VERFAHREN ZUM AUSLESEN VON MAGNETISCHEN FELDERN MIT EINEM dc SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE (dc-SQUID) SOWIE DAZU GEEIGNETE VORRICHTUNG Download PDFInfo
- Publication number
- WO2002086524A2 WO2002086524A2 PCT/DE2002/001268 DE0201268W WO02086524A2 WO 2002086524 A2 WO2002086524 A2 WO 2002086524A2 DE 0201268 W DE0201268 W DE 0201268W WO 02086524 A2 WO02086524 A2 WO 02086524A2
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- squid
- current
- constant
- bias current
- transformer
- Prior art date
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R33/00—Arrangements or instruments for measuring magnetic variables
- G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
- G01R33/035—Measuring direction or magnitude of magnetic fields or magnetic flux using superconductive devices
- G01R33/0354—SQUIDS
Definitions
- the invention relates to a method and a device for reading magnetic fields with the aid of a de-SQUID.
- SQUIDs Superconducting quantum interference devices
- a dc-SQUID consists of a superconducting ring that is interrupted by two Josephson contacts. If a bias current I B is fed into the SQUID, a voltage drops across it. To measure magnetic fields, the external magnetic flux to be measured is coupled into a SQUID. The voltage drop across the SQUID is modulated by the coupled magnetic flux due to the quantum mechanical effects on the Josephson contacts. The voltage U ( ⁇ ) dropping at the SQUID is a periodic function of the magnetic flux ⁇ , the periodicity being determined by the flux quantum ⁇ 0 .
- a constant (de) current is fed into the SQUID, which is also described as a “de bias” current.
- the frequency of the AC voltage is also called the reversal frequency.
- the advantage of using ac bias current is that the 1 / f noise of the dc-SQUID can be significantly reduced.
- the reduction is a statistical effect, however, the higher the reversal frequency, the more effectively the l / f noise is suppressed.
- the additional noise can be explained as follows using FIG. 1.
- the SQUID When the SQUID is connected to an amplifier device (preamplifier), the SQUID is connected in parallel with an inductance (coupling transformer).
- the ac bias current I b impressed into this SQUID arrangement corresponds to a rectangular function, but the current I s through the SQUID does not.
- I s With each polarity reversal, I s receives an additional peak, which is generated by the inductance of the transformer.
- the additional noise is caused by the non-constant current I s .
- the ratios of t / T and A '/ A determine the amount of additional noise.
- t is the length of time that the non-constant current I s lasts
- T is the period of the alternating current (bias reversal current)
- a ' is the maximum value of the current (the height of the peak)
- A is the size of the constant ac bias current
- the object of the invention is achieved by a method with the entirety of the features of the main claim and by a device with the features of the auxiliary claim.
- Advantageous refinements of the method and of the device can be found in the dependent claims, which are dependent thereon.
- the method according to the invention for operating a dc-SQUID arrangement which comprises two Josephson contacts and a transformer coil connected in parallel, has the step that is essential to the invention that a non-constant ac bias current I b is fed into the SQUID arrangement.
- the non-constant ac bias current pens the current I c induced by the transformer such that the current I s flowing through the SQUID has a rectangular function.
- the current I s should have a rectangular function.
- the injected current I b is selected in a suitable manner so that the injected current I b and the current I c induced by the transformer compensate each other in such a way that a compensation of these two currents results in a rectangular function for the SQUID current I a .
- the current I b fed in has the following function:
- I R maximum flow of I b ;
- R N line resistance of the SQUID;
- the fed-in ac bias current has a reversal frequency of more than 10 kHz, in particular of more than 100 kHz.
- the high reversal frequency also has the advantage of a high bandwidth and thus enables the measurement of magnetic fields that change quickly over time with the highest sensitivity.
- the method has a dc-SQUID A and a coupling transformer B.
- the dc-SQUID is characterized by the line resistance R N.
- the primary winding of the transformer has inductance L.
- the non-constant current feed of the ac bias current takes place via a current source with a generator C, which supplies a square-wave voltage VI, a subtractor D, a capacitor C t and four resistors R lr R 2 , R t and R b .
- the voltage V b is converted into the current I by the resistor R b .
- the current of the dc-SQUID I s should have a rectangular function (see also FIG. 2). According to the Kirchhoff law, the following applies to the circuit shown in FIG. 2:
- a differential equation is set up to describe the relationships of the three currents after the polarity reversal.
- the desired bias current I b results from the solution of equation (4).
- the current I s thus remains constant immediately after each polarity reversal. This can advantageously drastically increase the reversal frequency.
- I b I R - 2I R xR N / (R N + R) xe "t / ⁇ (5)
- the first result means that only one parameter for all SQUIDs with different R N is set.
- the second result means that ⁇ is only dependent on the constant quantities L and R.
- FIG. 4 shows the advantageous embodiment of a device with which the method according to the invention is carried out. In addition to the dc-SQUID A and the read-out unit B, a possible circuit for the ac bias power supply is also entered in the figure.
- This circuit comprises a square-wave voltage generator C, four resistors Ri, R 2 , R t and R b , a capacitor C and a subtractor D.
- the ratio of R (series resistance of the coupling transformer B) to R N can be determined Set (line resistance of the dc-SQUID).
- the desired output voltage is generated by the subtractor D.
- the high-resistance resistor R b then converts the voltage into the ac bias current.
- the current I s remains constant immediately after each polarity reversal. This advantageously causes a very low noise even at reversible frequencies of the ac bias current of more than 10 kHz, in particular at more than 100 kHz.
Abstract
Description
Claims
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP02740234A EP1379887A2 (de) | 2001-04-19 | 2002-04-06 | VERFAHREN ZUM AUSLESEN VON MAGNETISCHEN FELDERN MIT EINEM i dc /i SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE ( i dc /i -SQUID) SOWIE DAZU GEEIGNETE VORRICHTUNG |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE2001119108 DE10119108A1 (de) | 2001-04-19 | 2001-04-19 | Verfahren zum Auslesen von magnetischen Feldern mit einem dc Superconducting quantum interference device (dc-SQUID) sowie dazu geeignete Vorrichtung |
DE10119108.1 | 2001-04-19 |
Publications (2)
Publication Number | Publication Date |
---|---|
WO2002086524A2 true WO2002086524A2 (de) | 2002-10-31 |
WO2002086524A3 WO2002086524A3 (de) | 2003-01-09 |
Family
ID=7681917
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/DE2002/001268 WO2002086524A2 (de) | 2001-04-19 | 2002-04-06 | VERFAHREN ZUM AUSLESEN VON MAGNETISCHEN FELDERN MIT EINEM dc SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE (dc-SQUID) SOWIE DAZU GEEIGNETE VORRICHTUNG |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP1379887A2 (de) |
DE (1) | DE10119108A1 (de) |
WO (1) | WO2002086524A2 (de) |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5469057A (en) * | 1994-03-08 | 1995-11-21 | University Of New Mexico | Method and apparatus for extending the dynamic range of DC-squid measurements using a flux tracking loop |
EP0846958A2 (de) * | 1996-12-06 | 1998-06-10 | Sumitomo Electric Industries, Limited | Spannungserhöhende Schaltung für magnetometrische Fühler |
WO1999054745A1 (de) * | 1998-04-22 | 1999-10-28 | Forschungszentrum Jülich GmbH | Messanordnung zur messung magnetischer flussänderungen sowie verfahren hierfür |
-
2001
- 2001-04-19 DE DE2001119108 patent/DE10119108A1/de not_active Withdrawn
-
2002
- 2002-04-06 EP EP02740234A patent/EP1379887A2/de not_active Withdrawn
- 2002-04-06 WO PCT/DE2002/001268 patent/WO2002086524A2/de not_active Application Discontinuation
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5469057A (en) * | 1994-03-08 | 1995-11-21 | University Of New Mexico | Method and apparatus for extending the dynamic range of DC-squid measurements using a flux tracking loop |
EP0846958A2 (de) * | 1996-12-06 | 1998-06-10 | Sumitomo Electric Industries, Limited | Spannungserhöhende Schaltung für magnetometrische Fühler |
WO1999054745A1 (de) * | 1998-04-22 | 1999-10-28 | Forschungszentrum Jülich GmbH | Messanordnung zur messung magnetischer flussänderungen sowie verfahren hierfür |
Non-Patent Citations (1)
Title |
---|
ZHANG Y ET AL: "Non-constant bias current for dc SQUID operation" PHYSICA C, NORTH-HOLLAND PUBLISHING, AMSTERDAM, NL, Bd. 368, Nr. 1-4, 1. M{rz 2002 (2002-03-01), Seiten 181-184, XP004336205 ISSN: 0921-4534 * |
Also Published As
Publication number | Publication date |
---|---|
EP1379887A2 (de) | 2004-01-14 |
WO2002086524A3 (de) | 2003-01-09 |
DE10119108A1 (de) | 2002-12-05 |
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