CN101907693B - Method for quantitatively calibrating and eliminating crosstalk of SQUID (Superconducting Quantum Interference Device) planar three-shaft magnetometer - Google Patents

Abstract

The invention relates to a method for quantitatively calibrating and eliminating the crosstalk of a SQUID (Superconducting Quantum Interference Device) planar three-shaft magnetometer, which is characterized by testing the mutual inductance between a feedback coil and an SQUID adjacent to the feedback coil to quantitatively calibrate the crosstalk when the crosstalk of the planar three-shaft magnetometer exists between the feedback coil and the SQUID, thereby eliminating the crosstalk on the basis. The method comprises the following steps of: (1) preparing the SQUID planar three-shaft magnetometer; (2) quantitatively calibrating three-shaft crosstalk; and (3) analyzing and eliminating the crosstalk. The method is characterized in that the three-shaft magnetometer comprising a planar naked SQUID is used for replacing the traditional wire-wound magnetometer, and the mutual inductance is used as an index for calibrating the size of the crosstalk so that the crosstalk is eliminated. The method has the advantages that the SQUID planar magnetometer has high integration level so that the magnetic flux interference caused by line transmission is avoided, and the calibration and the elimination of the crosstalk ensure the optimized use of the SQUID planar magnetometer.

Description

SQUID plane three axis magnetometer crosstalk quantitatively calibrating and removing method

Technical field

The present invention relates to a kind of SQUID plane three axis magnetometer crosstalk quantitatively calibrating and removing method.

Background technology

Superconducting quantum interference device (Superconducting Quantum Interference Device, SQUID) be present the sensitiveest known magnetic flux transducer, be widely used in the detection [V.Pizzela et al, Supercond.Sci.Technol.14 (2001) R79-R114] of weak biological magnetic signal.

Weak magnetic signal and strong environmental magnetic field are the problems that the biological magnetic detection of SQUID must face.In order to suppress environmental magnetic field, the gradiometer technology is one of most popular method, and it can well suppress far-field noise, surveys nearly biological magnetic signal.Desirable gradiometer is zero to the response of uniform magnetic field, and owing to machinery in the winding process, make the reasons such as accurate, inevitably there is unbalancedness in gradiometer, has certain area of error.The area of error that brings in order to compensate the gradiometer unbalancedness, the most normal use is with reference to magnetometer, is equipped with three directions [D.Drung, IEEE Trans.Appl.Supercond.5 (1995) 2112-2117].Traditional three axis magnetometer is comprised of the magnetometer coil of three quadratures, is equipped with the SQUID device of three superconducting shieldings, realizes the detection of background magnetic field.The wire-wound magnetometer is because machinery, technique for coiling equal error, and there is certain deviation in three axle orthogonalities, and inevitably there is magnetic flux coupling in the transmission line between magnetometer coil and the SQUID, causes the design deviation theory of three axis magnetometer, affects compensation performance.

With respect to traditional magnetometer, the plane magnetometer is directly to adopt naked SQUID ring to carry out detection of magnetic field, the error of having avoided orthogonality that the wire-wound magnetometer brings and the coupling of transmission line magnetic flux to bring.Because naked SQUID device does not have superconducting shielding, there is mutual inductance between tickler and each SQUID ring, cause existing between three magnetometers and crosstalk.The space length that reduces SQUID tickler diameter and increase between the SQUID can affect by crosstalk reduction to a certain extent, but can't eliminate, so be badly in need of seeking qualitative assessment and the removing method that three axles are crosstalked.

Summary of the invention

The object of the present invention is to provide a kind of SQUID plane three axis magnetometer crosstalk quantitatively calibrating and removing method.Specifically, the present invention utilizes naked SQUID device to construct the plane three axis magnetometer, the crosstalking of plane three axis magnetometer is present between tickler and the adjacent S QUID mutual inductance between test tickler and SQUID can carry out to crosstalking quantitatively calibrating, crosstalk in this configuration basis elimination, thereby realize the quantitatively calibrating that three axles are crosstalked and eliminate analysis.

Three axis magnetometer crosstalk quantitatively calibrating and removing method in SQUID of the present invention plane comprises following steps:

(1) SQUID plane three axis magnetometer is prepared

Choose three good SQUID devices of work and construct three axis magnetometer assembly (seeing embodiment step 1).Whole three axis magnetometer and auxiliary lead Interface integration are on a reference test bar.

(2) the three axles quantitatively calibrating of crosstalking

Crosstalking between the three axis magnetometer demarcated by the mutual inductance between tickler and the SQUID.With the combination between tickler and SQUID, can be divided into inner mutual inductance and outside mutual inductance to mutual inductance.Inner mutual inductance mainly refers to the mutual inductance of single magnetometer tickler and SQUID ring.The low frequency test signal of input some strength is measured a fluxon Φ in the tickler ₀Corresponding output signal strength has

${\mathrm{\Φ}}_0=M_i\·\frac{V_{\mathrm{fi}}}{R_{\mathrm{fi}}}$ ${\mathrm{\ζ}}_i=\frac{V_{\mathrm{oi}}}{{\mathrm{\Φ}}_0}$

M wherein _iBe the inside mutual inductance of tickler and SQUID, V _FiBe test low frequency signal voltage strength, R _FiBe the feedback resistance in tickler transmission loop, ζ _iBe magnetic flux voltage transmission coefficient, V _OiBe SQUID sensing circuit latch voltage amplitude.By measuring, can be to M _iDemarcate, and can calculate ζ _i

Set the inner mutual inductance of three axis magnetometer and be respectively M _x, M _yAnd M _z, the magnetic flux voltage transmission coefficient is respectively ζ _x, ζ _yAnd ζ _z, have

$M_x=\frac{{\mathrm{\Φ}}_0{R}_{\mathrm{fx}}}{V_{\mathrm{fx}}}$ $M_y=\frac{{\mathrm{\Φ}}_0{R}_{\mathrm{fy}}}{V_{\mathrm{fy}}}$ $M_z=\frac{{\mathrm{\Φ}}_0{R}_{\mathrm{fz}}}{V_{\mathrm{fz}}}$ ${\mathrm{\ζ}}_x=\frac{V_{\mathrm{ox}}}{{\mathrm{\Φ}}_0}$ ${\mathrm{\ζ}}_y=\frac{V_{\mathrm{oy}}}{{\mathrm{\Φ}}_0}$ ${\mathrm{\ζ}}_z=\frac{V_{\mathrm{oz}}}{{\mathrm{\Φ}}_0}$

On the basis of demarcating inner mutual inductance, in tickler corresponding to i direction SQUID, input certain voltage signal V _Fi, regulate optimum Working and the locking of j direction SQUID, measure output voltage V _Oj, can be to the outside mutual inductance M between SQUID _IjDemarcate

${\mathrm{\ζ}}_j\·M_{\mathrm{ij}}\·\frac{V_{\mathrm{fi}}}{R_{\mathrm{fi}}}=V_{\mathrm{oj}}$

Demarcate successively the outside mutual inductance M that can calculate three between centers _Xy, M _Xz, M _Yx, M _Yz, M _ZxAnd M _Zy, these outside mutual inductances have reflected crosstalking between the three axis magnetometer.

(3) crosstalk analysis and elimination

In the situation of flux locked loop (Flux Looked Loop, FLL) locking, FLL is by tickler coupling magnetic flux Φ _fIn the SQUID ring with external magnetic field Φ _eOffset, to keep the circulation in the SQUID ring constant

Φ _e+Φ _f＝0

The magnetic flux of feedback is directly proportional with the FLL Voltage-output

${\mathrm{\Φ}}_f=M\·I_f=M\·\frac{V_o}{R_f}$

Wherein, M is SQUID and its tickler mutual inductance, R _fBe feedback resistance, V _oBe the FLL output voltage.The FLL output voltage is as follows with the linear relationship of outside magnetic flux

${\mathrm{\Φ}}_e=-M\·\frac{V_o}{R_f}$

Consider that three axis magnetometer works simultaneously, have

[Φ _e]+[Φ _f′]＝0

$\left[{{\mathrm{\Φ}}_f}^{\′}\right]=M^{\′}\·\left[I_f\right]=M^{\′}\·\frac{\left[V_o\right]}{R_f}$

$\left[{\mathrm{\Φ}}_e\right]=-M^{\′}\·\frac{\left[V_o\right]}{R_f}$

Wherein $\left[{\mathrm{\Φ}}_e\right]=\left[\begin{array}{c}{\mathrm{\Φ}}_{\mathrm{ex}}\\ {\mathrm{\Φ}}_{\mathrm{ey}}\\ {\mathrm{\Φ}}_{\mathrm{ez}}\end{array}\right];$ $\left[{{\mathrm{\Φ}}_f}^{\′}\right]=\left[\begin{array}{c}{{\mathrm{\Φ}}_{\mathrm{fx}}}^{\′}\\ {{\mathrm{\Φ}}_{\mathrm{fy}}}^{\′}\\ {{\mathrm{\Φ}}_{\mathrm{fz}}}^{\′}\end{array}\right];$ $M^{\′}=\left[\begin{array}{ccc}{M}_x& M_{\mathrm{xy}}& M_{\mathrm{xz}}\\ M_{\mathrm{yx}}& M_y& M_{\mathrm{yz}}\\ M_{\mathrm{zx}}& M_{\mathrm{zy}}& M_z\end{array}\right];$ $\left[I_f\right]=\left[\begin{array}{c}{I}_{\mathrm{fx}}\\ I_{\mathrm{fy}}\\ I_{\mathrm{fz}}\end{array}\right]$ $\left[V_o\right]=\left[\begin{array}{c}{V}_{\mathrm{ox}}\\ V_{\mathrm{oy}}\\ V_{\mathrm{oz}}\end{array}\right];$ $\left[R_f\right]=\left[\begin{array}{ccc}{R}_{\mathrm{fx}}& 0& 0\\ 0& R_{\mathrm{fy}}& 0\\ 0& 0& R_{\mathrm{fz}}\end{array}\right]$

For eliminating crosstalking that outside mutual inductance brings, the output of orthogonalizable SQUID three axles is revised the SQUID Voltage-output and is

$\left[{\mathrm{\Φ}}_e\right]=-M\·\frac{\left[V_o^{\′}\right]}{R_f}$

Wherein

Consider the consistance of outer magnetic flux, have

$M^{\′}\·\frac{\left[V_o\right]}{R_f}=M\·\frac{\left[V_o^{\′}\right]}{R_f}$

SQUID three axles after elimination is crosstalked are output as

$\frac{\left[V_o^{\′}\right]}{R_f}=M^{-1}{M}^{\′}\·\frac{\left[V_o\right]}{R_f}$

The use of SQUID plane three axis magnetometer is conducive to the system integration, demarcates and eliminates by crosstalking, and has guaranteed better orthogonality, solves the adverse effect of crosstalking and can bring to triaxiality.

This shows that advantage of the present invention is: planar S QUID magnetometer integrated level is high, the magnetic flux interference of having avoided the circuit transmission to bring, and the demarcation of crosstalking and elimination have guaranteed the optimization use of planar S QUID magnetometer.

Description of drawings

Fig. 1 is plane three axis magnetometer configuration: 1 is the SQUID device among the figure, and 2 is tickler, and 3 is the epoxy cube

Fig. 2 is inside mutual inductance and the outside mutual inductance synoptic diagram between single magnetometer tickler and SQUID

Fig. 3 is the inner mutual inductance of three between centers and outside mutual inductance synoptic diagram

Embodiment

1, with double faced adhesive tape three SQUID devices (1) are close to respectively on the mutually perpendicular three dimensions of epoxy cube (3), construct three axis magnetometer with this, whole device, lead-in wire and Interface integration are on a reference test bar;

2, reference test bar is placed cooled cryostat, three axis magnetometer works under the liquid helium temperature, tests at first respectively the inside mutual inductance M of each single magnetometer tickler (2) and SQUID ring (1) _i, utilize signal generator in the tickler in the low frequency test signal V of input some strength _fRegulate the parameter of sensing circuit, make flux locked loop FLL be operated in the best operating point of unlock state, adjust the intensity of tickler (2) input signal, symmetry is joined about making the FLL output signal, and the magnetic flux that this moment, SQUID surveyed is a fluxon Φ ₀, locking FLL, the output signal strength V of record corresponding frequencies _o, the inside mutual inductance M of calculating SQUID1 and tickler (2) _x, M _yAnd M _zInner mutual inductance is similar with measuring, regulate FLL duty and the locking of j direction SQUID, remove the extraneous input signal in the corresponding tickler of j direction SQUID, in the tickler of adjacent i direction SQUID, pass into the certain amplitude test signal, measure the output voltage of lock-out state j direction SQUID, calculate outside mutual inductance M _Ij, namely get M _Xy, M _Xz, M _Yx, M _Yz, M _ZxAnd M _Zy(seeing Fig. 2 and Fig. 3)

3, under general non-shielding environment, the output signal V of record SQUID plane three axis magnetometer lock-out state _o, utilizing crosstalks eliminates formula and eliminates interchannel crosstalking and eliminate crosstalking that mutual inductance brings, and realizes orthogonalization.

Claims (4)

1. SQUID plane three axis magnetometer quantitatively calibrating method of crosstalking, it is characterized in that utilizing naked SQUID device to construct the plane three axis magnetometer, the crosstalking of plane three axis magnetometer is present between tickler and the adjacent SQUID, test inside mutual inductance and outside mutual inductance between tickler and the SQUID, thereby carry out quantitatively calibrating to crosstalking;

Described quantitatively calibrating method may further comprise the steps:

(1) with double faced adhesive tape three SQUID devices (1) are close to respectively on the mutually perpendicular three dimensions of epoxy cube (3), construct three axis magnetometer with this, whole device, lead-in wire and Interface integration are on a reference test bar;

(2) reference test bar is placed cooled cryostat, three axis magnetometer works under the liquid helium temperature, tests at first respectively the inside mutual inductance M of each single magnetometer tickler (2) and SQUID ring (1) _i, utilize signal generator in the tickler in the low frequency test signal V of input some strength _fRegulate the parameter of sensing circuit, make flux locked loop FLL be operated in the best operating point of unlock state, adjust the intensity of tickler (2) input signal, symmetry is joined about making the FLL output signal, and the magnetic flux that this moment, SQUID surveyed is a fluxon Φ ₀, locking FLL, the output signal strength V of record corresponding frequencies _o, the inside mutual inductance M of calculating SQUID (1) and tickler (2) _x, M _yAnd M _zInner mutual inductance is similar with measuring, regulate FLL duty and the locking of j direction SQUID, remove the extraneous input signal in the corresponding tickler of j direction SQUID, in the tickler of adjacent i direction SQUID, pass into the certain amplitude test signal, measure the output voltage of lock-out state j direction SQUID, calculate outside mutual inductance M _Ij, namely get M _Xy, M _Xz, M _Yx, M _Yz, M _ZxAnd M _Zy

Described inner mutual inductance refers to the mutual inductance of single magnetometer tickler and SQUID ring; Calculate the magnetic flux voltage transmission coefficient by inner mutual inductance:

M in the formula _iBe the inside mutual inductance of tickler and SQUID, V _FiBe test low frequency signal voltage strength, R _FiBe the feedback resistance in tickler transmission loop, ζ _iBe magnetic flux voltage transmission coefficient, V _OiBe SQUID sensing circuit latch voltage amplitude; By measuring M _iDemarcate, thereby calculate ζ _i

On the basis of demarcating inner mutual inductance, in tickler corresponding to i direction SQUID, input certain voltage signal V _Fi, regulate optimum Working and the locking of j direction SQUID, measure output voltage V _Oj, can be to the outside mutual inductance M between SQUID _IjDemarcate

Demarcate successively the outside mutual inductance M that can calculate three between centers _Xy, M _Xz, M _Yx, M _Yz, M _ZxAnd M _Zy, the outside mutual inductance of six direction has reflected crosstalking between the three axis magnetometer.

2. by the quantitatively calibrating method of crosstalking claimed in claim 1, the lead-in wire that it is characterized in that three axle bias currents and tickler is selected the enameled wire of 0.1mm diameter, and multiple twin is drawn.

3. by the quantitatively calibrating method of crosstalking claimed in claim 1, it is characterized in that step 2 low frequency test signal frequency is 60Hz, intensity is according to test loop feedback resistance R _fAnd decide.

4. by the crosstalk eliminating method of the scaling method of crosstalking claimed in claim 1, it is characterized in that under non-shielding condition the output signal V of record SQUID plane three axis magnetometer steady state (SS) _o, utilize the elimination formula of crosstalking, eliminate interchannel crosstalking, realize orthogonalization; The step that comprises is:

1. in the situation of flux locked loop locking, FLL is by tickler coupling magnetic flux Φ _fIn the SQUID ring with external magnetic field Φ _eOffset, to keep the circulation in the SQUID ring constant

Φ _e+Φ _f＝0

The magnetic flux of feedback is directly proportional with the FLL Voltage-output

In the formula, M is SQUID and its tickler mutual inductance, R _fBe feedback resistance, V _oBe the FLL output voltage, the FLL output voltage is as follows with the linear relationship of outside magnetic flux

2. consider that three axis magnetometer works simultaneously, have

[Φ _e]+[Φ _f′]＝0

Wherein

Crosstalk the output of orthogonalization SQUID three axles for what eliminate that outside mutual inductance brings; Revising the SQUID Voltage-output is

Wherein

Consider the consistance of outer magnetic flux, then

3. SQUID three axles of eliminating after crosstalking are output as

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