JP2010118553A - Phase correction type active magnetic shield device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase correction type active magnetic shield device securely cancel a disturbing magnetic field of an AC magnetic field and a time-varying magnetic field by removing a residual magnetic field signal corresponding to a magnetic field remaining without being canceled because the disturbing magnetic field and a canceling magnetic field are not in phase with each other. <P>SOLUTION: A phase correction signal similar to the residual magnetic field signal is generated by a phase correction signal generating means 10 so as to remove the unnecessary residual magnetic field signal included in an output signal of a magnetic sensor S, and the phase correction signal and residual magnetic field signal are made to cancel each other through an adding/subtracting means 12, thereby removing the residual magnetic field signal. The phase correction signal generating means 10 includes a phase synchronizing means 17 for synchronization with the output signal phase of the magnetic sensor S and an amplitude adjusting means 18 with a polarity switching function for changing the phase of the phase correction signal in accordance with the output signal phase of the magnetic sensor S. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an active magnetic shield technology that cancels out the phase and amplitude of a cancellation magnetic field for canceling a disturbance magnetic field, which is an alternating magnetic field, in accordance with the phase and amplitude of the disturbance magnetic field.

  Magnetic non-destructive inspection of various material parts, various biomagnetic measurements, medical diagnostic equipment and extremely weak magnetic field measuring device used in systems for analyzing biological functions, immunodiagnostic system by magnetic response, precise measurement of pathogen testing system In fields where measurement is possible only in a magnetic field management space close to no magnetic field or a very stable magnetic field space, such as an electron microscope and an MRI apparatus, conventionally, the surroundings of equipment are surrounded by magnetic materials with high permeability such as silicon steel plates and permalloy. However, such a passive magnetic shield has a limit due to insufficient magnetic shielding effect.

  In contrast, the active magnetic shield technology cancels the disturbance magnetic field in the opposite direction to the disturbance magnetic field in the target space where the magnetic shield is to be applied, and cancels the disturbance magnetic field to form a magnetically stable magnetic field space. Technology. Here, since devices to be protected from the disturbance magnetic field are installed in the target space, the magnetic sensor installation space and the target space rarely overlap each other and are separated in most cases.

  For this reason, the magnetic sensor simultaneously detects the canceling magnetic field of the compensation coil in the space where the magnetic sensor is installed in addition to the sensor signal of the disturbance magnetic field to be canceled (hereinafter referred to as the disturbance magnetic field sensor signal). Is included as an unnecessary canceling magnetic field gradient sensor signal.

  This canceling magnetic field gradient sensor signal is one of the main causes of the deterioration of the active magnetic shield performance. Examples of typical prior arts that attempt to remove the cancellation magnetic field gradient sensor signal are disclosed in Patent Document 1 and Patent Document 2.

  This technique will be described with reference to the schematic configuration diagram shown in FIG. 5. In order to cancel the disturbance magnetic field in the target space T-Space, the disturbance magnetic field Bn is detected by the magnetic sensor S installed in the magnetic sensor installation space S-Space. The detected signal is amplified by the amplifier 21, and a static magnetic field offset such as a geomagnetic component is subtracted from the amplified signal by the subtraction circuit 22, and only the signal for the variable magnetic field is sent to the current output circuit 23.

  Then, the disturbance magnetic field canceling current output from the current output circuit 23 is shunted in the shunt 24. One of the diversion destinations is a compensation coil L1 that generates a magnetic field that cancels the disturbance magnetic field. The remaining one is a canceling coil L2 for generating a magnetic field gradient that cancels a part of the canceling magnetic field of the compensation coil L1 as an unnecessary magnetic field is applied to the magnetic sensor S.

  In this prior art, in order to cancel the canceling magnetic field gradient applied to the magnetic sensor S, a method of canceling the canceling magnetic field gradient applied to the magnetic sensor S by dividing the disturbance magnetic field canceling current to the canceling coil L2 wound around the magnetic sensor S is adopted. is doing.

JP-A-48-38972 (see FIG. 2) Japanese Patent No. 3406273 (see FIGS. 1 and 2)

  The range in which the above-mentioned conventional method can be effectively applied is limited to a DC magnetic field or a fluctuating magnetic field close to it. When the frequency of the disturbance magnetic field increases, an amplification phenomenon or an oscillation phenomenon occurs, and the active magnetic shield becomes impossible. The inherent defect was.

  The main reason is that there is a difference between the current phase flowing through the compensation coil L1 and the current phase flowing through the cancellation coil L2. In other words, there is a shift in the phase of the magnetic field generated in the coil L1 and the coil L2. If there is a phase shift, as the frequency of the disturbing magnetic field increases, the phase of the magnetic field generated in the coil L1 and the coil L2 initially cancels each other in the 0 phase and the π phase, and the phase gradually overlaps and amplifies. Finally, the negative feedback circuit system of the active magnetic shield oscillates, and the active magnetic shield device itself becomes a magnetic field noise generation source.

Here, if the circuit of the shunt 24 is simplified so that the inductances of the coils L1 and L2 are L ₁ and L ₂ and the resistance values of the resistors R1 and R2 are R ₁ and R ₂ , the shunt 24 is as shown in FIG. It can be expressed by the circuit of

FIG. 6 is a typical circuit diagram for explaining the phase shift. Assume that the AC cancellation current i output from the current output circuit 23 is shunted at the branch point P, and the voltage at the branch point P is expressed as e = EmSinωt
As a result, the currents i ₁ and i ₂ flowing through the coils L1 and L2 will be solved.

In the circuit of FIG.
e = EmSinωt = L ₁ (di ₁ / dt) + R ₁ i ₁ = L ₂ (di ₂ / dt) + R ₂ i ₂
The following differential equation holds.
When this is solved, each current i ₁ and i ₂ is i ₁ = Em / √ (R ₁ ² + ω ² L ₁ ² ) · Sin (ωt−Tan ⁻¹ ωL ₁ / R ₁ )
i ₂ = Em / √ (R ₂ ² + ω ² L ₂ ² ) · Sin (ωt−Tan ⁻¹ ωL ₂ / R ₂ )
It becomes.

The phase angle difference ΔΦ between i ₁ and i ₂ is expressed as ΔΦ = (− Tan ⁻¹ ωL ₁ / R ₁ ) − (− Tan ⁻¹ ωL ₂ / R ₂ ) (1)
It becomes. Then, if this phase angle difference ΔΦ is made zero, the AC magnetic field should be cancelled.

  The first term on the right side of Equation (1) is the phase delay in the compensation coil L1 and the resistor R1, and is an element that depends on the installation environment, and therefore is a fairly unique and fixed constant as a parameter.

  On the other hand, the second term on the right side is a phase delay due to the cancellation coils L2 and R2 wound around the adjustable magnetic sensor S. The inductance adjustment of the coil L2 wound around the magnetic sensor S is a parameter that is fixed in advance or semi-fixed and is not suitable for on-site adjustment because it requires considerably high accuracy and is complicated.

After all, the current i ₂ that cancels the unnecessary canceling magnetic field gradient applied to the magnetic sensor is adjusted by the simplest resistor R2.

However, the main purpose of the resistor R2, by adjusting the current i ₂ cancel flowing through the cancellation coils L2, resistors for adjusting the intensity of the cancellation magnetic field gradient, the resistance to the main adjusting the amplitude in other words. Therefore, simultaneous adjustment of the individual elements of phase adjustment and amplitude adjustment with only one resistive element means that two independent circuit parameters are adjusted with one element parameter, which is unrealistic. .

  In both the coils L1 and L2 through which the cancellation current flows, the inductances of the coils are different, and the resistance values of the DC resistors R1 and R2 including the wiring wires are also different. Therefore, the phase angle ΔΦ does not become zero unless the accidental conditions overlap. .

  In addition, in the method of magnetically canceling in the space where the magnetic sensor is arranged, as a secondary problem, because the number of wiring lines increases, electromagnetic induction noise is superimposed from the middle of the line, or the coil wound around the magnetic sensor itself Inductive noise may be superimposed.

  Method of adjusting the number of turns of the cancellation coil wound around the magnetic sensor, especially in the case of a 3-axis configuration, fine adjustment of the orthogonality with the magnetic detection part of the magnetic sensor itself, fine adjustment of the cancellation coil position and orthogonality of the cancellation coil, between each axis of the cancellation coil Technical problems such as magnetic field interference and electromagnetic induction noise are complicating on-site adjustment.

  When the AC magnetic field canceling frequency band is increased, these technical problems are practically an obstacle in the magnetic method in which a canceling coil is wound around a magnetic sensor to cancel the magnetic field.

  In short, the prior art is limited to the function of adjusting the strength of the magnetic field, and there is no means to positively adjust the phase most important when canceling the unnecessary alternating magnetic field applied to the magnetic sensor. The problem remains.

  In the present invention, in order to remove the residual magnetic field signal corresponding to the magnetic field that cannot be canceled because the phase of the disturbance magnetic field and the phase of the cancellation magnetic field do not coincide with each other, the DC disturbance magnetic field as well as the AC disturbance magnetic field is increased. An object of the present invention is to provide a phase correction type active magnetic shield device capable of canceling accurately and reliably.

  In order to solve the above-described problem, a phase correction type active magnetic shield device according to the first configuration of the present invention detects at least one compensation coil that generates a canceling magnetic field for canceling a disturbing magnetic field, and detects the disturbing magnetic field. At least one magnetic sensor, and at least one phase correction signal forming unit that forms and outputs a phase correction signal very similar to the residual magnetic field signal included in the output signal of the magnetic sensor, and the phase correction of the residual magnetic field signal It has an addition / subtraction means for canceling with a signal, and has at least one current output circuit for outputting a cancellation current to the compensation coil.

  In the first configuration of the present invention, a phase correction provided separately is provided in order to cancel the disturbance magnetic field with high accuracy and certainty by removing the residual magnetic field signal that is a cause of deterioration of the magnetic shield performance included in the output signal of the magnetic sensor. The signal forming means generates a phase correction signal very similar to the residual magnetic field signal, and both the residual magnetic field signal and the phase correction signal are canceled by the addition / subtraction means. Note that “very similar” means that the waveforms are very similar.

In the phase correction type active magnetic shield device according to the second configuration of the present invention, the phase correction signal forming means for forming the phase correction signal synchronizes the phase of the phase correction signal with the phase of the magnetic sensor output signal. And a phase synchronization unit for switching the phase correction signal in response to the phase of the magnetic sensor output signal and an amplitude adjustment unit with a polarity switching function.
With this second configuration, the phase correction signal forming means can be realized by a combination of existing methods.

The active magnetic shield device of the phase correction type according to the third configuration of the present invention has an axial component corresponding to each axis for canceling at least two axial components of the three orthogonal axes of the disturbance magnetic field. In a plurality of compensation coil configurations capable of generating a canceling magnetic field component, the canceling magnetic field components generated by the compensation coils of the respective axis components cancel each other's magnetic field component signals that affect the other axis magnetic sensors. A means for individually adjusting the polarity and amplitude of the phase correction signal for canceling the other-axis magnetic field component signal to the phase correction signal forming means, and outputting each phase as a phase correction signal for canceling the other-axis magnetic field component signal In addition, a means for adding and subtracting the phase correction signal for canceling the magnetic field component signal of the other axis from the other axis is added to the adding and subtracting means.
This third configuration makes it possible to cancel magnetic field components in the biaxial direction and the triaxial direction.

According to a fourth aspect of the present invention, there is provided a phase correction type active magnetic shield device, wherein one or all of the phase correction signal forming means and / or one or all of the addition / subtraction means and / or one of signal processing circuits. A part or the whole is constituted by software means.
According to the fourth configuration, in addition to using phase correction signal forming means, addition / subtraction means, and signal processing circuit, it is realized by computer software using a DSP (digital signal processor) or CPU (central processing unit). You can also.

  According to the present invention, in order to cancel an AC magnetic field with high accuracy and reliability, an electronic circuit method is used instead of a conventional method in which an unnecessary canceling magnetic field that adversely affects magnetic shield performance is canceled by a canceling coil wound around a magnetic sensor. As a result of solving the above, the disturbance magnetic field to be canceled has been expanded to a DC magnetic field, a variable magnetic field, and an AC magnetic field of several hundred Hz. In addition, the cancellation coil around the magnetic sensor has been eliminated, wiring work has been simplified, and the adjustment work efficiency has been greatly improved.

  Magnetic shield performance is improved by more than 10 times compared to the conventional method. Use of components that are concerned about inductive noise such as AC noise sources, long lead wires that receive electromagnetic induction, cord wiring, and coils that induce electromagnetic induction noise. Avoiding this, we succeeded in reducing the noise and stabilizing the target space T-Space to the performance close to the performance limit of the magnetic sensor.

  Since the present invention is a basic technique for canceling an alternating magnetic field, it is greatly useful for improving the performance of a conventional apparatus as a technique for expanding the frequency band of a known active magnetic shield technique.

  For example, Patent Document 1 {Japanese Patent Laid-Open No. 48-38972 (Japanese Patent Publication No. 51-38215)}, Patent Document 2 {Japanese Patent Laid-Open No. 2001-281131 (Japanese Patent No. 3406273)}, Japanese Patent Laid-Open No. 2002-94280. JP, 2002-232182, JP 2003-273565, JP 2005-44826, JP 2008-78529, etc. have already been disclosed. Incorporating organically, the upper limit of the frequency band where the disturbance magnetic field can be canceled is remarkably expanded, and the magnetic shielding performance can be dramatically improved.

  After all, the products and modification techniques produced by incorporating the phase correction technology of the present invention become an embodiment included in the present invention, so that it can be expected to be widely used as a useful technology in the magnetic shield industry.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a basic configuration diagram of Embodiment 1 of the present invention. In FIG. 1, reference numeral 11 denotes a compensation coil, which generates a canceling magnetic field Bc for canceling the disturbance magnetic field Bn. As the magnetic field characteristics of the coil, the magnetic field strength increases as the coil approaches the coil from the center, and the uniform magnetic field space is limited to the coil center.

  As a measure for ensuring a large uniform magnetic field space, the two coils are opposed to each other to form a Helmholtz coil type. In many cases, devices that are to be protected from a disturbance magnetic field are installed near the center of the Helmholtz coil. FIG. 1 illustrates a case of a Helmholtz type compensation coil, and T-Space indicates a target space in which the apparatus is installed.

  The magnetic sensor S that detects the disturbance magnetic field Bn is installed in a magnetic sensor installation space S-Space that is distant from the target space T-Space. The magnetic field in this space includes a canceling magnetic field generated from the compensation coil 11 in addition to the disturbance magnetic field. Since the magnetic field can be decomposed or synthesized as a vector, the canceling magnetic field in the magnetic sensor installation space is canceled by a canceling magnetic field gradient ΔBc (referred to as a magnetic field gradient in this specification) at a position away from the target space. Can be replaced with a synthesized magnetic field that is a ± magnetic field strength difference between the magnetic field strength at the center point of the target space and the magnetic field strength at the center point of the sensor installation space.

In the illustrated example of the first embodiment, the case where the cancellation magnetic field in the magnetic sensor installation space S-Space is weaker than the cancellation magnetic field in the target space T-Space is taken as an example.
In order to facilitate understanding of the direction of the magnetic field, in this example, the combined value of the cancellation magnetic field applied to the magnetic sensor S is expressed by Bc−ΔBc.

  Therefore, based on the direction of the disturbance magnetic field, the magnetic field detected by the magnetic sensor S includes the disturbance magnetic field Bn, the cancellation magnetic field -Bc in the target space T-Space, and the magnetic field gradient ΔBc away from the target space T-Space. The sum {Bn− (Bc−ΔBc)} is obtained, and the output signal of the magnetic sensor S includes the disturbance magnetic field sensor signal e (Bn), the canceling magnetic field sensor signal −e (Bc), and the canceling magnetic field gradient sensor signal e (ΔBc). The sum [e (Bn) − {e (Bc) −e (ΔBc)}].

Among these signals, the signal that degrades the magnetic shielding performance due to the magnetic sensor installation space S-Space being separated from the target space T-Space is the cancellation magnetic field gradient sensor signal e (ΔBc), which is removed. There is a need to.
This removal countermeasure was filed by the present applicant as an “AC magnetic field compatible active magnetic shield device” (Japanese Patent Application No. 2008-274819).

However, when canceling the AC disturbance magnetic field, it is necessary to consider the phase delay of the entire active magnetic shield system in addition to the cancellation magnetic field gradient sensor signal described above.
This phase lag occurs because it takes time from detection of an external magnetic field to generation of a cancellation magnetic field. That is, the degree of phase delay of the cancellation current depends on the time required for signal processing from the generation of the cancellation current from the disturbance magnetic field sensor signal in the output signal of the magnetic sensor to generation of the cancellation magnetic field.

In other words, it is difficult to completely cancel the disturbance magnetic field because of this phase delay θ, and the remaining magnetic field component that cannot be canceled due to phase synchronization mismatch remains as a residual magnetic field signal in the magnetic sensor output signal. . That is, in the residual magnetic field signal, the disturbance magnetic field sensor signal e (Bn) and the cancellation magnetic field sensor signal −e (Bc) cancel each other in the magnetic sensor output signal {disturbance magnetic field sensor signal + cancellation magnetic field sensor signal + cancellation magnetic field gradient sensor signal}. This corresponds to the residual voltage corresponding to the phase shift remaining when the operation is performed.
This residual voltage becomes a part of the cancellation current output from the current output circuit 50 and is sent to the compensation coil 11 to deteriorate the magnetic shield performance.

  The current output circuit 50 includes an addition / subtraction means 12 for adding / subtracting an input signal, a signal processing circuit 13 for adjusting the amplitude and phase of the output signal of the addition / subtraction means 12, and a power amplifier 14 for amplifying the output signal of the signal processing circuit. Consists of components. When the signal processing circuit 13 performs signal processing on the residual voltage remaining at the output of the addition / subtraction means 12, an addition / subtraction function is added to the signal processing circuit 13 as necessary.

  In the present invention, the residual magnetic field signal Δe (θ) existing as phase information before addition / subtraction output from the magnetic sensor S is output from the phase correction signal forming means 10 in the addition / subtraction means 12 of the current output circuit 50 described later. It is canceled by the phase correction signal −Δe (θ) of the inverted signal. If the addition / subtraction is not performed by the addition / subtraction means 12 due to the circuit configuration, the residual voltage remaining at the output of the addition / subtraction means 12 is replaced by the signal processing circuit 13 instead of the addition / subtraction means 12 as shown by the broken line in FIG. The inverted phase correction signal −Δe (θ) output from the phase correction signal forming means 10 is received and canceled.

  At the input section of the addition / subtraction means 12, both the residual magnetic field signal Δe (θ) in the output signal of the magnetic sensor and the phase correction signal −Δe (θ) which is the output signal of the phase correction signal forming means 10 are used as a resistance and an operational amplifier. Use addition operation to erase. Further, the addition / subtraction means 12 executes subtraction of DC components such as geomagnetism and addition / subtraction for adjustment of offset with respect to other magnetic sensor output signals.

The added and subtracted signals are further adjusted in amplitude and phase in the signal processing circuit 13 and then sent to the power amplifier 14. The power amplifier 14 amplifies the output signal of the signal processing circuit 13 and outputs a cancellation current i _cancel for canceling the disturbance magnetic field to one terminal of the compensation coil 11.

The terminal on the other end side of the compensation coil 11 is connected in series to a resistor R that is a component of the current-voltage conversion circuit 15 and is grounded via the resistor. Since the canceling current i _cancel is detected by being converted into a voltage between the resistance terminals by the current flowing through the resistor R, the resistor R operates as a current-voltage conversion element. Therefore, the output terminal of the current-voltage conversion circuit 15 is a check point for monitoring the cancellation current waveform, and can be used as a monitor terminal for monitoring the operating state of the active magnetic shield.

The cancellation current i _cancel flowing through the compensation coil 11 generates a cancellation magnetic field Bc, cancels the disturbance magnetic field Bn, and flows to the ground via the resistor R. The compensation coil 11 and the resistor R are connected in series. Therefore, there is no parallel circuit configuration as in the case of the shunt. As long as the stray capacitance of the compensation coil 11 does not become a problem, the current phases of the compensation coil 11 and the resistor R are the same phase. Since this case, the cancellation magnetic field in the phase made of cancellation currents i _cancel matching current i _cancel the phase cancellation, the phase of the terminal voltage of the resistor R, and the phase of the cancellation magnetic field Bc is generated by the compensation coil 11 the The relationship of phase is established.

It became clear that information having the same phase as the phase of the canceling magnetic field Bc can be extracted from the voltage across the resistor R by using such a circuit configuration.
However, the current-voltage conversion circuit 15 is a component to be selected for selecting whether to be mounted according to the degree of the influence of the canceling magnetic field Bc of the compensation coil 11 on the magnetic sensor S or for the monitor terminal. It is.

  The phase correction signal forming means 10 is connected between the magnetic sensor S and the adding / subtracting means 12, and its configuration is composed of each component of the buffer circuit 16, the phase synchronization means 17, and the amplitude adjusting means 18 with polarity switching function. Composed.

  In order to remove the residual magnetic field signal Δe (θ) present in the output of the magnetic sensor S, a specific role of the phase correction signal forming means 10 is an inversion that closely resembles the residual magnetic field signal Δe (θ) from the magnetic sensor output signal. It is to create and send a phase signal.

  As a procedure for that, first, the phase synchronization means 17 of the phase correction signal forming means 10 is configured by a low-pass filter capable of adjusting the phase, and a phase signal having the same phase or an inverted phase according to the phase of the magnetic sensor output signal is created. Thereafter, the amplitude and polarity of the phase signal are adjusted by the amplitude adjusting means 18 with a polarity switching function to complete a phase correction signal −Δe (θ) having an inverted phase very similar to the residual magnetic field signal Δe (θ).

  Then, a phase correction signal −Δe (θ) having an inversion phase very similar to the residual magnetic field signal Δe (θ) is sent to the addition / subtraction means 12 to cancel the residual magnetic field signal Δe (θ) of the magnetic sensor output.

The influence of the residual magnetic field signal on the canceling current i _cancel is thus prevented at the stage of the addition / subtraction means 12.

  Next, a specific example of the phase synchronization means 17 will be described. For example, when the magnetic sensor S is a magnetic oscillation type magnetic sensor, a fluxgate type magnetic sensor, or the like, the magnetoelectric conversion circuit (including an amplification circuit) is described. ) Is generally used.

  In this case, the approximate configuration of the phase synchronization means 17 that can be implemented most simply is a configuration using only a resistor. However, a primary low-pass filter (integrating circuit) is configured by the resistor and the capacitor, and the resistance value of this circuit is variable. Thus, the phase of the phase correction signal can be matched with the output phase of the magnetic sensor S.

  Since the phase adjustment of the phase correction signal in the phase synchronization means 17 is made to correspond to the residual magnetic field signal phase, a low-pass filter or an integration circuit is used for phase lag correction, and a high-pass filter or differentiation is used for phase advance correction. A circuit may be used. The cut-off frequency and the order of each filter are basically considered including the magnetic sensor S and the subsequent connection circuit. However, it is possible to make a similar approximation with a close order, and these are all in any circuit configuration. It belongs to the scope of the present invention.

  It should be noted that the connection processing order of each component and its element function in the current output circuit 50 and the phase correction signal forming means 10 described above is not necessarily limited to the order described above, and is limited within the scope of achieving the object of the present invention. It is not a thing. Further, since the phase synchronization means 17 can be realized by a combination of an inductor and a resistance filter, or any combination of elements such as an inductor, a capacitor, a resistance, and an operational amplifier, various circuits or means including all-pass filters based on these combinations are also included in the present invention. It is included in the means for realizing the purpose.

  Further, the polarity switching of the amplitude adjusting means 18 with the polarity switching function will be described. The direction of the canceling magnetic field is reversed in the positive and negative directions depending on the arrangement positional relationship between the compensation coil 11 and the magnetic sensor S, and the phase of the canceling magnetic field gradient sensor signal is also reversed in the positive and negative directions. Sometimes. For example, in the single compensation coil, the direction of the canceling magnetic field is opposite between the inner side and the outer side of the compensation coil frame, so that the phase of the canceling magnetic field gradient sensor signal is also inverted.

Even within the compensation coil frame, depending on the magnetic sensor arrangement position, the phase of the phase correction signal may be reversed due to the relationship between the canceling magnetic field gradient strength and the disturbance magnetic field strength. It is also possible to switch the phase of the correction signal. This polarity switching can also be performed by switching the connection between the inverting input terminal and the non-inverting input terminal of the operational amplifier of the adding / subtracting means 12.
In any case, it is necessary to know in advance the presence or absence of polarity reversal from the positional relationship between the compensation coil 11 and the magnetic sensor arrangement.

  As another implementation means, a part or whole of the phase correction signal forming means 10, a part or whole of the addition / subtraction means 12, and a part or whole of the signal processing circuit 13 can be executed by software means. In this case, an AD converter that converts an analog signal into a digital signal, a digital signal processing circuit including a DSP or a personal computer, a DA converter that converts the processed digital signal back into an analog signal, an I / O interface, The corresponding part is replaced by software for controlling the digital signal processing circuit. This software includes an input / output data interface control program and the like in addition to the main program for executing the idea of the present invention.

Even when the magnetic sensor installation space S-Space and the compensation coil 11 are in a positional relationship, the installation position of the magnetic sensor S is close to the compensation coil 11, so that the cancellation magnetic field is strongly applied to the magnetic sensor 11. The cancellation magnetic field gradient sensor signal removal method can be dealt with by the same method as described above.
However, the cancellation of the cancellation magnetic field gradient sensor signal by the cancellation magnetic field and the removal of the residual magnetic field signal Δe (θ) can be performed simultaneously by one phase correction signal forming means 10, but depending on the arrangement position of the magnetic sensor S. A certain degree of deterioration of the magnetic shield performance is inevitable. Rather, it is better to separately connect the phase correction signal forming means 10 in parallel and cancel it to use it for removing the magnetic field gradient sensor signal.

Based on the description of the above-described embodiment, an embodiment in which the removal of the cancellation magnetic field gradient sensor signal by the cancellation magnetic field and the removal of the residual magnetic field signal Δe (θ) are performed by separate phase correction signal forming units will be described. 2 as shown in FIG.
In the illustrated example of the second embodiment, the case where the cancellation magnetic field in the magnetic sensor installation space S-Space is stronger than the cancellation magnetic field in the target space T-Space is taken as an example.
In order to facilitate understanding of the direction of the magnetic field, in this example, the combined value of the canceling magnetic field applied to the magnetic sensor S is expressed by Bc + ΔBc.

  Therefore, if the direction of the disturbance magnetic field is used as a reference, the magnetic field detected by the magnetic sensor S is the disturbance magnetic field Bn, the cancellation magnetic field -Bc in the target space T-Space, and the magnetic field gradient component -ΔBc far from the target space T-Space. The output signal of the magnetic sensor S is the disturbance magnetic field sensor signal e (Bn), the canceling magnetic field sensor signal −e (Bc), and the canceling magnetic field gradient sensor signal −e (ΔBc). The sum {Bn− (Bc + ΔBc)} The sum [e (Bn) − {e (Bc) + e (ΔBc)}] is obtained.

  The difference from the first embodiment is that the phase correction signal forming means 10a is newly set to the current voltage in order to create the inverted phase signal e (ΔBc) for removing the canceling magnetic field gradient sensor signal −e (ΔBc). This is a point additionally connected between the conversion circuit 15 and the addition / subtraction means 12.

  The configuration of the phase correction signal forming means 10a is the same hardware configuration as the phase correction signal forming means 10, and a buffer circuit 16a for receiving phase information of the voltage-converted cancellation current, and a cancellation magnetic field sensor signal − from the output signal of the buffer circuit 16a. Phase synchronization means 17a for producing a phase signal having the same phase as that of e (Bc) or an inverted phase, and amplitude adjustment means with a polarity switching function for adjusting the polarity and amplitude of this phase signal and outputting it as a phase correction signal e (ΔBc) It is comprised from each component of 18a.

Then, the phase correction signal e (ΔBc) for removing the cancellation magnetic field gradient sensor signal output from the phase correction signal forming unit 10 a is input to the input unit of the addition / subtraction unit 12.
In this way, with each phase correction signal formed for different purposes by the separate phase correction signal forming means 10 and 10a, the cancellation magnetic field gradient sensor signal -e (ΔBc) and the residual magnetic field signal Δe ( θ) is removed by the addition / subtraction means 12.
Obviously, the roles of the phase correction signal forming means 10 and 10a can be exchanged and can be implemented by only one of the phase correction signal forming means.

  FIG. 3 shows various embodiments of the compensation coil 11. In the figure, the number of windings and connections of the compensation coil, the fixing material for rolling or fixing the compensation coil, the situation attached to the wall, and the pits embedded in the floor are omitted, and only the center line of the compensation coil winding frame In FIG. (A)-(c) is an example when a compensation coil is comprised by a single coil, (a) is a 1-axis structure, (b) is a 2-axis structure, (c) is a case of a 3-axis structure. In a plurality of axes, the respective axis components are orthogonal to each other.

As an example of a Helmholtz type configuration in which a uniform magnetic field region is widely secured, (d) shows a one-axis configuration, (e) shows a two-axis configuration, and (f) shows a three-axis configuration.
In the Helmholtz type, basically two single coils are made to face each other and the central axes of the coils are made to coincide with each other, but this is not necessarily limited to this, and the shape of the coil and the spacing between the two coils were also on-site. A modified arrangement may be used.

  In principle, the detection axis of the magnetic sensor S is held parallel to the central axis of each coil. Depending on the number of axial components of the compensation coil, the magnetic sensor S is properly used as a 1-axis magnetic sensor, 2-axis magnetic sensor, or 3-axis magnetic sensor. For example, a three-axis magnetic sensor may be used in a one-axis configuration. It is also possible to use three uniaxial magnetic sensors instead of the triaxial magnetic sensor and distribute them in the vicinity of the coil surface of each axis.

The signal processing of the magnetic sensor S is made independent for each axis component. Therefore, not only the current output circuit 50 and the phase correction signal forming means 10, but also the current-voltage conversion circuit 15 that is selectively mounted as necessary requires at least the number of axis components.
Depending on the shape and size of the compensation coil, in the case of a 2-axis configuration or a 3-axis configuration, the compensation coil may become congested, making it difficult to access to and from the target space T-Space inside the compensation coil.

  As countermeasures, examples of bypass wiring around the door are introduced in the Journal of Biomagnetic Society Vol.20 No.1 June 2007 (Photo 1 on page 130, Figure 1 on page 131). You can do it.

FIG. 4 is a circuit connection diagram in the case of a three-axis configuration of the compensation coil according to the third embodiment of the present invention. This configuration is an embodiment in which the first embodiment and the second embodiment are combined.
In FIG. 4, SX, SY, and SZ are magnetic sensors for each axis, using a triaxial magnetic sensor, or using a uniaxial magnetic sensor in a distributed manner in the vicinity of each compensation coil, or The three single-axis magnetic sensors are collectively used as a three-axis magnetic sensor, or are installed in any configuration.

  11X, 11Y, and 11Z are compensation coils for each axis, 50X, 50Y, and 50Z are current output circuits, RX, RY, and RZ are current-voltage conversion circuits for each axis, and 10X, 10Y, and 10Z each have at least one phase correction signal Forming means.

  When the compensation coils 11X, 11Y, and 11Z have a three-axis configuration orthogonal to each other as shown in FIG. 3 (f), a part of the cancellation magnetic field of each axis is a new problem. A magnetic field interference phenomenon occurs in which the magnetic sensors are applied to the magnetic sensors on the axes (two axes) and influence each other. That is, the X-axis canceling magnetic field component is applied to the Y-axis and Z-axis magnetic sensors SY and SZ, the Y-axis canceling magnetic field component is applied to the X- and Z-axis magnetic sensors SX and SZ, and the Z-axis canceling magnetic field component is set to X. Since this affects the magnetic sensors SX and SY on the axis and the Y axis, it is necessary to remove them.

  In order to solve this magnetic field interference, the X axis will be described as an example. In principle, a magnetic field (or magnetic field lines) created by a closed loop coil always forms a closed loop that is curved in all directions. In the magnetic sensor installation space S-Space covered by the magnetic field of the compensation coil 11X, it may be considered that there are components of the X-axis component, the Y-axis component, and the Z-axis component. Although the X-axis component of the own axis has been described in detail in the first embodiment, the same method can be applied to other axes.

  First, as a countermeasure for the Y axis, the magnetic field component that adversely affects the Y axis component due to the X axis cancellation magnetic field is canceled in the Y axis current output circuit 50Y. Therefore, in addition to the amplitude adjusting means for the own axis, the Y axis dedicated amplitude adjusting means and the Z axis dedicated amplitude adjusting means are added to the X axis phase correction signal forming means 10X. A phase correction signal is sent to the current output circuit 50Y in order to cancel out the magnetic field component that adversely affects the means. The amplitude and polarity of the phase correction signal are implemented by the Y axis dedicated amplitude adjusting means.

  In addition to the inverted phase correction signal receiving terminal for the own axis, a terminal for receiving the phase correction signal from the X axis and the Z axis is provided independently at the input part of the current output circuit 50Y, and the phase from the X axis as described above is provided. The correction signal is received from the X-axis terminal and removed by the addition / subtraction means of the current output circuit 50Y.

  Next, as a countermeasure for the Z-axis, the magnetic field component that adversely affects the Z-axis component due to the X-axis canceling magnetic field is similarly canceled by the Z-axis current output circuit 50Z. For this purpose, a phase correction signal is sent to the current output circuit 50Z in order to cancel out the adverse magnetic field component from the Z-axis dedicated amplitude adjusting means of the X-axis phase correction signal forming means 10X. The amplitude and polarity of the phase correction signal are implemented by the Z axis dedicated amplitude adjusting means.

  In addition to the inverted phase correction signal receiving terminal for the own axis, a terminal for receiving the phase correction signal from the X axis and the Y axis is provided independently at the input part of the current output circuit 50Z, and the phase from the X axis as described above is provided. The correction signal is received from the X-axis terminal and removed by the addition / subtraction means of the current output circuit 50Z.

  Hereinafter, the method for removing the magnetic field component that adversely affects the X-axis component and the Z-axis component by the Y-axis canceling magnetic field, and the method for removing the magnetic field component that adversely affects the X-axis component and the Y-axis component by the Z-axis canceling magnetic field are described above. Since it implements similarly to the case of, description is abbreviate | omitted.

  The switching SW in the figure may be negligible because the influence of the canceling magnetic field on the other axis may be neglected, particularly in an arrangement in which three uniaxial magnetic sensors are arranged in a distributed manner. The ON / OFF state is determined according to the degree of.

  Although the description related to the present invention has been described above, in adjustment work such as circuit constants, a magnetometer is placed in the target space T-Space and adjustment is performed so as to reduce the output value, magnetic field waveform, or FFT analysis value of the magnetometer. The method to do is simple. Furthermore, if a magnetometer is also placed in the magnetic sensor installation space S-Space, it is useful for monitoring the magnetic field state.

  The present invention relates to the field of magnetic precision non-destructive inspection of various material parts that can be measured only in a magnetic field management space close to no magnetic field, various magnetic field measurements, medical diagnostic equipment, and extremely weak magnetic fields used in systems for analyzing biological physiological functions. It can be widely used in the field of precision measurement of measuring devices, immunodiagnostic systems using magnetic responses, pathogen testing systems, and fields of electron microscopes and MRI devices.

It is a basic composition figure of Embodiment 1 of the present invention. It is a basic composition figure of Embodiment 2 of the present invention. It is explanatory drawing which shows various embodiment of the compensation coil in this invention. It is a circuit connection diagram at the time of the 3 axis | shaft structure of the compensation coil which concerns on Embodiment 3 of this invention. It is a schematic block diagram which shows the example of a prior art. It is a circuit diagram for demonstrating the phase shift in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS S Magnetic sensor 10, 10a Phase correction signal formation means 11 Compensation coil 12 Addition / subtraction means 13 Signal processing circuit 14 Power amplifier 15 Current voltage conversion circuit 16, 16a Buffer circuit 17, 17a Phase synchronization means 18, 18a Amplitude adjustment with polarity switching function Means 50 Current output circuit

Claims (4)

At least one compensation coil for generating a canceling magnetic field to cancel the disturbance magnetic field;
At least one magnetic sensor for detecting the disturbance magnetic field;
At least one phase correction signal forming means for forming and outputting a phase correction signal very similar to the residual magnetic field signal included in the output signal of the magnetic sensor;
A phase correction type active magnetic shield device comprising: addition / subtraction means for canceling the residual magnetic field signal with the phase correction signal, and at least one current output circuit for outputting a cancellation current to the compensation coil. The phase correction signal forming means for forming the phase correction signal is:
Phase synchronization means for synchronizing the phase of the phase correction signal with the phase of the magnetic sensor output signal;
2. The phase correction type active magnetic shield device according to claim 1, further comprising at least one amplitude adjusting means with polarity switching function for switching the phase of the phase correction signal in response to the phase of the magnetic sensor output signal. In a plurality of compensation coil configurations capable of generating a canceling magnetic field component of an axial component corresponding to each axis for canceling a magnetic field component of at least two axial components among three orthogonal axes of a disturbance magnetic field,
In order to cancel the other-axis magnetic field component signals that the canceling magnetic field components generated by the compensation coils of the respective axis components influence the other-axis magnetic sensors,
A means for individually adjusting the polarity and amplitude of the phase correction signal for canceling the other-axis magnetic field component signal to the phase correction signal forming means, and outputting each phase as a phase correction signal for canceling the other-axis magnetic field component signal Add
3. The phase correction type active magnetic shield according to claim 1, wherein means for adding and subtracting the addition / subtraction unit upon receiving a phase correction signal for canceling the other axis magnetic field component signal from the other axis is added to the addition / subtraction unit. apparatus.   2. A part or the whole of the phase correction signal forming means and / or a part or the whole of the adding / subtracting means and / or a part or the whole of a signal processing circuit are constituted by software means. The phase correction type active magnetic shield device according to claim 3.

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