CN102551711A - Method for measuring magnetic field by aid of superconducting quantum interference device and positioning current source of magnetic field - Google Patents

Abstract

The invention relates to a method for measuring a magnetic field by the aid of a superconducting quantum interference device and positioning a current source of the magnetic field. The method comprises following steps: 1) acquiring magnetic field signals on a small quantity of measuring points by the aid of the superconducting quantum interference device; 2) obtaining a magnetic field maximum value and a magnetic field minimum value at every moment according to the measured magnetic field signals; and 3) obtaining position and strength parameters of a magnetic field source after a computer processes the magnetic field maximum value and the magnetic field minimum value at every moment in the step 2). Compared with the prior art, the method has the advantages of simplicity, effectiveness, capability of greatly saving cost of hardware, and the like.

Description

Measure magnetic field and locate the method in field supply source with superconducting quantum interference device

Technical field

The present invention relates to the method for field supply source location, especially relate to superconducting quantum interference device and measure magnetic field and locate the method in field supply source.

Background technology

1970-1976 D.Cohen etc. has proposed under lab to use superconducting quantum interference device (superconducting quantum interference device first; SQUID) measure the cardiac magnetic field signal, and the method for locating an electric current dipole source.Over nearly 40 years, the research of magnetic field detection and source location causes the attention of various countries' height.Range of application constantly enlarges.In order to improve the precision of source location, the port number of measuring magnetic field with SQUID constantly increases, and this also causes equipment cost to increase.36-64 the passage SQUID synchro measure field signal that general commercial cardiac magnetic field measuring system need adopt 6X 6 to arrange, not only hardware system is complicated, and the computational methods and the software for calculation of Magnetic Field Source location inverse problem also face problems.Therefore, a kind ofly can carry out the accurate localized method in field supply source through a small amount of magnetic field measuring point and belong to new invention.

Summary of the invention

The object of the invention is exactly to provide method simple, efficient for the defective that overcomes above-mentioned prior art existence; And can save the hardware cost of magnetic field measurement system; Simplify related algorithm and software, obtain the measuring magnetic field and locate the method in field supply source of source location result accurately with superconducting quantum interference device.

The object of the invention can be realized through following technical scheme: measure magnetic field and locate the method in field supply source with superconducting quantum interference device; It is characterized in that this method may further comprise the steps: 1) utilize the field signal on a small amount of measuring point of superconducting quantum interference device collection; 2) obtain each magnetic field maximum and magnetic field minimum constantly according to the field signal that measures; 3) computer is to step 2) in each magnetic field maximum and magnetic field minimum constantly of trying to achieve obtain the position and the intensive parameter in field supply source after handling.

Whether counting that field signal need be measured in the described step 1) can be fixed to confirm according to the field supply source position, for the Magnetic Field Source of fixed-site, only needs two measurement points usually; If the source position periodically changes, then need gather the field signal on several adjacent test points, obtain maximum and the minimum of measuring magnetic field through interpolation.

Described step 1), step 2) in field signal comprise X-Y coordinate that each magnetic field value constantly is corresponding with this magnetic field value.

Described step 3) is specially:

31) at first utilize formula

$\mathrm{\θ}=\arcsin \left(\frac{\sqrt{6}}{3}\right)$

Obtain according to magnetic field maximum and minimizing coordinate

Value, maximum B in magnetic field on the measurement plane _Zmax(x ₁, y ₁) to magnetic field minimum B _Zmin(x, the angle of line D y) and measurement plane X axle does

32) then, with

value and step 2) in the magnetic field maximum of trying to achieve and minimum and their position coordinateses on measurement plane bring following formula into:

Obtain the depth d in field supply source;

33) utilize formula

$B_{z\max }=\frac{{\mathrm{\μ}}_{0}Q}{6\mathrm{\π}\sqrt{3}{d}^2}$

Obtain the coordinate (x in magnetic field intensity Q and field supply source ₀, y ₀), wherein, Q _xAnd Q _yBe the strength component of this field supply source at X and Y coordinate.

Described step 2) in, in the time can obtaining magnetic field maximum and magnetic field minima, just uses the minimum in this minima approximate substitution magnetic field, magnetic field according to field signal.

Described step 2) in, in the time can only trying to achieve maximum value of magnetic field and magnetic field minimum, just uses the maximum approximate substitution magnetic field maximum in this magnetic field according to field signal.

Because the present invention adopts above technical scheme; Promptly utilize the field signal on 2～8 measurement points of superconducting quantum interference device collection to carry out the field supply source location; So; Localization method is simple, effective, adopts 36 or 64 multichannel SQUID array detection methods to compare with prior art, can save hardware cost greatly.

Description of drawings

Fig. 1 is the sketch map that utilizes two field supply sources, field signal location on the SQUID measurement point;

Fig. 2 is the measuring point scattergram on the measurement plane.

Current dipole source of 1 expression among Fig. 1.

The specific embodiment

Below in conjunction with accompanying drawing 1 and specific embodiment the present invention is elaborated.

Embodiment

Two measurement points of A and B are arranged in the given coordinate system of Fig. 1.The position at the maximum place in A point expression magnetic field, B point expression minimizing position, magnetic field.The below of the measurement plane that the X-Y coordinate is formed, being positioned at the depth d place has a current dipole source that produces measured magnetic field.The angle of the line of measurement point A and this current dipole is θ on the measurement plane, and the angle of the line of A, B measurement point and X axle is

on the measurement plane

When measuring the source location in magnetic field with this method, ultimate principle is as shown in Figure 1.

Under Maxwell equation quasistatic approximation condition, according to the Biot-Savart law, the magnetic induction of a current dipole generation is in the space:

$B_z(x,y)=\frac{{\mathrm{\μ}}_0}{4\mathrm{\π}}\left(\frac{Q_x\left({y-y}_0\right)-Q_y\left({x-x}_0\right)}{{[{(x-x_0)}^2+{\left({y-y}_0\right)}^2+d^2]}^{3/2}}\right)---\left(1\right)$

Wherein, Q _xAnd Q _yBe the component of magnetic field intensity Q in X and Y direction.Generation is (x by the position coordinates in the current dipole source of measuring magnetic field ₀, y ₀, z ₀), the depth d in current dipole source=-z ₀

When the maximum of measuring magnetic field was equal with minimum, the depth d that produces the current dipole source in magnetic field can be calculated with formula

according to Fig. 1.Wherein, D is coordinate (x on the measurement plane ₁, y ₁) locate magnetic field maximum B _ZmaxAnd coordinate (x y) locates magnetic field minimum B _ZminBetween distance.Position (the x of this current source ₀, y ₀) can calculate with mid-point method.But, actual measurement to magnetic field often be not symmetrically distributed about measurement plane, and be non-linear relation between the parameter of the current source in magnetic field and generation magnetic field, when finding the solution this type of inverse problem, separate not unique.For this reason, we have proposed a kind of new source location method.

Fig. 1 has provided on the detection plane magnetic field maximum and the geometrical relationship of minimum and current source position on two measurement points:

Wherein,

$\mathrm{\θ}=\arcsin \left(\frac{\sqrt{6}}{3}\right)---\left(4\right)$

Magnetic field maximum B _ZmaxWith magnetic field minimum B _ZminCan obtain through measurements and calculations.On the measurement plane, measuring point (x ₁, y ₁) locate the magnetic field maximum of detected Z direction:

$B_{z\max }=\frac{{\mathrm{\μ}}_{0}Q}{6\mathrm{\π}\sqrt{3}{d}^2}---\left(8\right)$

Be positioned at (x, magnetic field minimum y):

Maximum B when known measurement magnetic field _ZmaxWith minimum B _ZminThe time, Q in formula (8) and (9) and d can be solved by these two equations.Thereby can obtain the current intensity component of current dipole on X and Y direction by (5), (6) and (7) formula, and calculate the plane coordinates of current source by (2) and (3) formula.When the maximum in magnetic field and minimum are not detected, can use detected maximum value of magnetic field and minima approximate substitution.

Implementation step is following:

1. two SQUID probes are aimed at respectively and can be detected magnetic field maximum B _ZmaxWith minimum B _ZminThe measuring position, and confirm the coordinate of these two measuring points on detection plane, i.e. (x ₁, y ₁) to locate be magnetic field maximum B _Zmax, (x y) is the magnetic field minimum B that measures _ZminThe position.

2. according to the minimizing coordinate (x in magnetic field; Y) and computing formula (5), angle

is obtained in (6)

3. will

Value and magnetic field maximum B _ZmaxAnd coordinate (x ₁, y ₁), magnetic field minimum B _ZminAnd coordinate (x y) brings formula (9) into and obtains the dipole depth d.

4. with formula (2), the X-Y coordinate (x of this current dipole is calculated in (3) ₀, y ₀).

5. calculate Q according to formula (8).

6. obtain Q according to formula (7) _xAnd Q _yComponent.

If there is not the time dependent situation of magnetic field peak value and valley, only need two measuring points just can accomplish the calculating of source location according to the method described above usually.Change if measure the peak value and the valley in magnetic field, can obtain the maximum and the minimum of field signal again through interpolation, carry out the current source CALCULATION OF PARAMETERS then through the signal value on the adjacent measuring point.The spacing of each measuring point can be 3.5-4cm.

When gathering field signal, as shown in Figure 2, rule of thumb confirm magnetic field maximum B earlier _ZmaxThe position at place, magnetic field minimum B _ZminThe right side of maximum normally, position in magnetic field, need rule of thumb search.After the peak value in magnetic field and the measuring position of valley are confirmed, the signal of synchronous detecting cardiac magnetic field on these two measuring points.

Claims (6)

1. measure magnetic field with superconducting quantum interference device and locate the method in field supply source, it is characterized in that this method may further comprise the steps:

1) utilizes field signal on a small amount of measuring point of superconducting quantum interference device collection;

2) obtain each magnetic field maximum and magnetic field minimum constantly according to the field signal that measures;

3) computer is to step 2) in after each magnetic field maximum constantly of trying to achieve and the processing of magnetic field minimum, obtain the position and the intensive parameter in field supply source.

2. according to claim 1ly measure magnetic field and locate the method in field supply source with superconducting quantum interference device; It is characterized in that; Whether counting that field signal need be measured in the described step 1) can come to confirm according to the fixed-site in field supply source; For the Magnetic Field Source of fixed-site, only need two measurement points usually; If the source position periodically changes, then need gather the field signal on several adjacent measurement points, obtain maximum and the minimum of measuring magnetic field through interpolation.

3. a small amount of superconducting quantum interference device measurement point of utilization according to claim 1 carries out the localized method of Magnetic Field Source, it is characterized in that described step 1) and step 2) in field signal comprise X-Y coordinate that each magnetic field value constantly is corresponding with this magnetic field value.

4. according to claim 1ly measure magnetic field and locate the method in field supply source, it is characterized in that described step 3) is specially with superconducting quantum interference device:

31) at first utilize formula

$\mathrm{\θ}=\arcsin \left(\frac{\sqrt{6}}{3}\right)$

Obtain according to magnetic field maximum and minimizing coordinate Value, maximum B in magnetic field on the measurement plane _Zmax(x ₁, y ₁) to magnetic field minimum B _Zmin(x, the angle of line D y) and measurement plane X axle does

32) then, with

value and step 2) in the magnetic field maximum of trying to achieve and minimum and their position coordinateses on measurement plane bring following formula into:

Obtain the depth d in field supply source;

33) utilize formula

$B_{z\max }=\frac{{\mathrm{\μ}}_{0}Q}{6\mathrm{\π}\sqrt{3}{d}^2}$

Obtain the coordinate (x in magnetic field intensity Q and field supply source ₀, y ₀), wherein, Q _xAnd Q _yBe the strength component of this field supply source at X and Y coordinate.

5. according to claim 1ly measure magnetic field and locate the method in field supply source with superconducting quantum interference device; It is characterized in that; Described step 2) in, in the time can obtaining magnetic field maximum and magnetic field minima, just uses the minimum in this minima approximate substitution magnetic field, magnetic field according to field signal.

6. according to claim 1ly measure magnetic field and locate the method in field supply source with superconducting quantum interference device; It is characterized in that; Described step 2) in, in the time can only trying to achieve maximum value of magnetic field and magnetic field minimum, just uses the maximum approximate substitution magnetic field maximum in this magnetic field according to field signal.

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