JP2019021814A - EMI shielding device - Google Patents

Abstract

To provide an EMI shielding device capable of shielding electromagnetic waves only in a necessary area.SOLUTION: In an EMI shielding device 10, a plurality of coils 18 are arranged on a sheet body 16, and each of the coils 18 generates a cancellation magnetic field corresponding to leakage magnetic field when a current control circuit 36 of the coil causes a current set on the basis of a detection value of a magnetic detection sensor 46 to flow. As a result, the leakage magnetic field of a motor 12 is canceled by the cancellation magnetic field. Since each of the coil 18 is individually controlled by the corresponding current control circuit 36, it is possible to cancel the leakage magnetic field (shield the electromagnetic waves) only in a necessary region.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electromagnetic wave shielding device.

  Conventionally, high-frequency electromagnetic waves are shielded by surrounding an object with a metal material (conductor). An eddy current that cancels the electromagnetic wave is generated on the metal surface by the high-frequency electromagnetic wave that enters the metal surface, and the high-frequency current that is an eddy current flows concentrated on the conductor surface due to the skin effect, so the thickness of the metal material is small. In both cases, a sufficient shielding effect can be obtained.

  On the other hand, a low frequency electromagnetic wave produces only a small eddy current, and the shielding effect by the eddy current is small. Therefore, in order to shield low-frequency electromagnetic waves, a method of enclosing a space that needs to be shielded with a material having high magnetic permeability and bus-passing magnetic lines of force, or a method of weakening magnetic lines of force with a material having low magnetic permeability is generally employed. However, in order to secure a sufficient shielding effect by these methods, a shielding material having a large plate thickness is required, and there is a disadvantage that the weight increases.

  Alternatively, there is a method in which the electromagnetic wave generation source is moved away to obtain distance attenuation, but there are restrictions on the arrangement of devices and packaging.

  Electromagnetic wave shielding devices that absorb or reflect electromagnetic waves by methods different from these have been proposed. For example, in Patent Document 1, a plurality of coils and a dielectric container filled with gas are arranged on an antenna, and an electron cycloton resonance condition is established between the operating frequency of the antenna and a magnetic field generated by the coil. Such a configuration is proposed that adjusts the number of turns of the coil and the current value supplied by the power source, and absorbs or reflects electromagnetic waves coming from the outside using plasma.

JP-A-2015-173143

  The electromagnetic wave shielding device described in Patent Document 1 has a disadvantage in that the entire arrangement range of the coil on the antenna becomes the electromagnetic wave shielding range, so that it is not possible to shield the electromagnetic wave only in a necessary region of the coil arrangement range. It was.

  In view of the above facts, an object of the present invention is to provide an electromagnetic wave shielding device capable of shielding an electromagnetic wave only in a necessary region.

  The electromagnetic wave shielding device according to claim 1 is a sheet body, a plurality of coils arranged at equal intervals on the sheet body, a power source capable of supplying a current to each of the plurality of coils, and a magnetic field at each coil position. And a current control circuit for determining a current value to be passed through each of the coils to cancel the leakage magnetic field based on the output of each magnetic sensor and causing the current of the current value to flow through the coil. When the length of the coil is L, the coil pitch between adjacent coils is Lp, and the leakage magnetic field characteristic length is D, 0.4 ≦ L / Lp ≦ 0.6 and Lp ≦ D.

  In the electromagnetic wave shielding device according to claim 1, the sheet body is disposed in proximity to (a part of) the object to be electromagnetic wave shielded, and based on the magnetic field detected by each magnetic sensor at a plurality of coil positions formed on the sheet body. A current that cancels the magnetic field is supplied from the power source to each coil. Thereby, the magnetic field in the vicinity of the coil is canceled by the induced magnetic field generated by the current flowing through each coil.

In particular, when the length of the coils arranged at equal intervals on the sheet body is L and the pitch between adjacent coils is Lp, the current flows between the adjacent coils as L / Lp <0.4. Is too far away, the magnetic field between the coils is greatly reduced. On the other hand, if L / Lp> 0.6 and current is passed through the adjacent coils, the opposite magnetic field lines cancel each other and the magnetic field between the coils is greatly reduced. Therefore, by setting 0.4 ≦ L / Lp ≦ 0.6, it is possible to prevent the magnetic field between adjacent coils from greatly decreasing. Therefore, a canceling magnetic field according to the magnetic field distribution between the coils can be generated.
Here, the “coil length” refers to the length of the portion where adjacent coils face each other. If it is a polygon in plan view, it is the length of one side facing each other.

Further, since the pitch between the coils is made shorter than the leakage magnetic field characteristic length D, at least two coils can be arranged corresponding to the leakage magnetic field region, and a canceling magnetic field corresponding to the magnetic field distribution in the leakage magnetic field region is generated. be able to.
Here, the “leakage magnetic field characteristic length” is the maximum length in the leakage magnetic field region.

  Thereby, electromagnetic waves can be shielded more effectively.

  According to the first aspect of the present invention, it is possible to shield electromagnetic waves only in a necessary region.

It is the perspective view which showed the example by which the electromagnetic wave shielding apparatus which concerns on 1st Embodiment was applied to the motor. It is the typical top view showing the deployment state of the electromagnetic wave shielding device concerning a 1st embodiment. (A) is the surface figure which showed the structure of 1 coil part of the electromagnetic wave shielding apparatus which concerns on 1st Embodiment, (B) is the back view. It is a principal part expanded sectional view of 1 coil part of the electromagnetic wave shielding apparatus which concerns on 1st Embodiment. It is an end view of the motor concerning a 1st embodiment. It is a flowchart which shows coil current value determination control. It is a graph which shows the relationship between the detection signal DS detected with the magnetic detection sensor, and the calculation basic signal LS passed through the low-pass filter. It is a flowchart which shows coil current command value calculation control. It is a graph which shows the relationship between the value of the calculation basic signal LS memorize | stored in the map, and the coil electric current command value Ic. In the electromagnetic wave shielding apparatus according to the first embodiment, it is a schematic perspective view showing a state in which a canceling magnetic field is generated in some coils. It is a figure which shows the relationship of the magnetic force line which acts between adjacent coils, When (A) is coil length L / coil pitch Lp <0.4, (B) is 0.4 <= L / Lp <= 0.6. (C) is a diagram showing a case of 0.6 <L / Lp. It is a graph which shows the relationship between L / Lp and the magnetic field strength between adjacent coils. It is the typical top view which showed the expansion | deployment state of the electromagnetic wave shielding apparatus which concerns on 2nd Embodiment. It is the top view which showed the structure of 1 coil part of the electromagnetic wave shielding apparatus which concerns on 2nd Embodiment.

[First Embodiment]
An example in which the electromagnetic wave shielding device according to the first embodiment is applied to a motor will be described with reference to FIGS. The arrow A indicates the axial direction of the motor, the arrow C direction indicates the circumferential direction of the motor, the arrow X direction indicates the longitudinal direction of the electromagnetic shielding device in the deployed state, and the arrow Y direction indicates the short direction of the electromagnetic shielding device in the deployed state. .

(Constitution)
As shown in FIG. 1, the electromagnetic wave shielding device 10 includes a flexible sheet body 16 that covers a part of the outer peripheral surface of the housing 14 of the motor 12, and a plurality of matrix bodies formed on the surface of the sheet body 16. And a coil 18.

  A state where the sheet body 16 of the electromagnetic wave shielding device 10 is developed is schematically shown in FIG. In FIG. 2, the bus 30, supply lines 34 </ b> A and 34 </ b> B, a magnetic detection sensor 46, and the like formed on the back surface 16 </ b> B (see FIGS. 3B and 4) of the sheet body 16 are also provided on the front surface 16 </ b> A for convenience of explanation. Have been described.

  As shown in FIG. 1, four cooling holes 22 are formed on the end surface 20 of the housing 14 of the motor 12 at predetermined intervals in the circumferential direction.

  The sheet body 16 is formed in a rectangular shape, and a short direction perpendicular to the longitudinal direction at the end in the longitudinal direction (refer to the arrow X direction in FIG. 2, hereinafter sometimes referred to as “X direction”). (Refer to the arrow Y direction in FIG. 2. Hereinafter, it may be referred to as the “Y direction”.) A bus 30 extending along the line is formed. The bus 30 is connected to a DC power supply (hereinafter referred to as “power supply”) 31 via a power supply line 32, and a plurality of buses 30 extend in the X direction on the sheet body 16 in order to supply current to each coil 18. Are connected to the supply lines 34A and 34B. In the present embodiment, “plan view” means viewing from the thickness direction of the sheet body 16.

  A current control circuit 36 provided in each coil 18 is connected to the supply lines 34A and 34B. The current control circuit 36 controls the current of the current value calculated based on the detection value of the magnetic detection sensor 46 disposed on the back surface 16B of the sheet body 16 at the center position of each coil 18 in plan view to flow through the coil 18. Is what you do.

  The current control circuit 36 has a function of adjusting the amount of current flowing through the coil 18. Specifically, as shown in FIGS. 3 and 4, by switching the connection between supply lines 34A and 34B and a starting point 40 and an ending point 42 described later of the coil 18, the coil 18 is rotated clockwise in plan view, or It is configured to allow current to flow counterclockwise, and can be disconnected (current value 0). Further, the current amount can be controlled. 3B schematically shows a state where the supply line 34A and the start point 40, and the supply line 34B and the end point 42 are connected by the conductor portions 38A and 38B extending from the front surface 16A to the back surface 16B of the sheet body 16. It is shown.

  As shown in FIG. 3A, the coil 18 includes a first conductor portion 44 </ b> A that extends a certain distance in the Y direction from one end (hereinafter referred to as “starting point”) 40 connected to the conductor portion 38 </ b> A of the current control circuit 36. A second conductor 44B extending a distance L in the X direction from the end of the first conductor 44A, and a third conductor 44C extending a distance L in the Y direction from the end of the second conductor 44B. And a fourth conductor portion 44D extending from the end portion of the third conductor portion 44C to the other end (hereinafter referred to as “end point”) 42 by a constant distance in the X direction. That is, the coil 18 has a substantially square wiring pattern formed on the surface 16 </ b> A of the sheet body 16. In the present embodiment, the coil includes a wiring pattern that does not completely circulate in a plan view.

  As shown in FIGS. 2 and 3A, each coil 18 is formed in a substantially square shape having a length L of one side along the X direction and the Y direction.

  3A, 3B, and 4, a magnetic detection sensor 46 that detects a magnetic field is disposed on the back surface 16B side of the sheet body 16 at the center position of the coil 18 in plan view. Yes. The magnetic detection sensor 46 outputs a detection value (detection signal) of the magnetic field strength to the current control circuit 36 via the detection line 48. That is, the current control circuit 36 is configured to determine a current value to be passed through the coil 18 based on the detection value of the magnetic detection sensor 46 and to pass the current through the coil 18.

  The set of the coil 18, the current control circuit 36 disposed along with the coil 18, and the magnetic detection sensor 46 may be hereinafter referred to as a unit 49.

  Further, as shown in FIG. 2, a plurality of coils 18 are arranged on the surface 16 </ b> A of the sheet body 16 in a matrix along the X direction and the Y direction. In order to avoid the complexity of the drawing, only one row of coils 18 is provided with a reference symbol.

  As shown in FIG. 2, the length of one side (the second conductor portion 44B and the third conductor portion 44C) of each coil 18 is L, and the pitch of the coils 18 adjacent in the X direction and the Y direction is Lp. Yes.

  Here, L / Lp is set to 0.4 ≦ L / Lp ≦ 0.6.

  Further, if the circumferential length of the cooling hole 22 formed in the end surface 20 of the housing 14 of the motor 12 is the leakage magnetic field characteristic length D,

  Lp ≦ D.

  Here, the leakage magnetic field characteristic length D is the maximum length of the magnetic field region leaking from the housing 14 of the motor 12. For example, as shown in FIGS. 1 and 5, when the cooling hole 22 is formed in an arc shape in the housing 14 of the motor 12, it is the circumferential length of the hole 22, If the length is different on the inner side in the radial direction, it is the average value. Moreover, when the hole for cooling is not formed in the housing 14 of the motor 12 and the coil is arrange | positioned in a motor, the length which divided the outer periphery of the housing 14 by the number of coils corresponds.

(Function)
Next, the operation of the electromagnetic wave shielding device 10 formed in this way will be described.

  As shown in FIG. 1, the electromagnetic wave shielding device 10 covers a portion of the housing 14 of the motor 12 where a leakage magnetic field is desired to be shielded with a sheet body 16. For example, when the motor 12 is a drive motor for an electric vehicle, only the passenger compartment side of the outer peripheral surface of the housing 14 is covered.

  The current value determination control that flows through each coil 18 of the electromagnetic wave shielding device 10 that covers a part of the housing 14 of the motor 12 will be described with reference to FIGS. 6 and 7.

  A detection signal DS (see FIG. 7) is input from each magnetic detection sensor 46 to the current control circuit 36 of each unit 49 disposed on the sheet body 16 of the electromagnetic wave shielding device 10 via the detection line 48 (FIG. 6). , See step S10). The current control circuit 36 applies a low-pass filter to the detection signal DS to remove a high-frequency component, and generates a calculation basic signal LS (see FIG. 7) for calculating a coil current command value Ic described later (FIG. 6, step). (See S12). Next, the coil current command value calculation control is performed based on the calculation basic signal LS to calculate the coil current command value Ic (see step S14 in FIG. 6).

  Next, the coil current command value calculation control will be specifically described with reference to FIGS.

  In the current control circuit 36, it is determined whether or not the power supply 31 of the electromagnetic wave shielding device 10 is on (see step S20 in FIG. 8).

  When the electromagnetic shielding device 10 is not driven (N in FIG. 8, step S20), the value obtained by multiplying the calculated basic signal LS by the gain G (0 <G ≦ 1) is canceled and the target magnetic field strength Sc (Refer to FIG. 8, step S22).

  When the cancellation target magnetic field strength Sc exceeds the upper limit value Scmax and the lower limit value Scmin that may cause the electromagnetic wave shielding device 10 to overheat, the target magnetic field strength Sc is set to the upper limit value Scmax and the lower limit value Scmin, respectively. (Refer FIG. 8, step S24).

  Subsequently, the current control circuit 36 cancels the canceling magnetic field strength Sc based on a map in which the calibrated relationship between the canceling magnetic field strength Sc and the coil current command value Ic (see FIG. 9) is stored in advance. Is read out (see step S26 in FIG. 8).

  The current control circuit 36 connects the start point 40 and end point 42 of the coil 18 and the supply lines 34A and 34B so that the current value supplied to the coil 18 from the supply lines 34A and 34B becomes the coil current command value Ic. (Refer FIG. 8, step S28).

  As a result, the current of the coil 18A to 18F whose coil current command value Ic is not 0 is passed clockwise or counterclockwise in plan view. Accordingly, a canceling magnetic field corresponding to the leakage magnetic field is generated by the coils 18A to 18F, and the leakage magnetic field is canceled.

  Thus, after the first cancellation target magnetic field strength Sc after driving of the electromagnetic wave shielding device 10 is set (after the second time), the electromagnetic wave shielding device 10 is driven. Become. At this time, the cancellation target magnetic field strength Sc set for the first time is set as the previous cancellation target magnetic field strength Scold (see step S30 in FIG. 8).

  In the current control circuit 36, a value obtained by multiplying the calculation basic signal LS (corrected detection magnetic field strength) generated this time and the previous cancellation target magnetic field strength Scold by a gain G (0 <G ≦ 1) is obtained. A new cancellation target magnetic field strength Sc is set (see step S32 in FIG. 8).

  This is because, since the electromagnetic wave shielding device 10 has already been driven, the leakage magnetic field is canceled (reduced) by passing a current through the coil 18, so that the magnetic field strength of the cancellation target is the magnetic detection sensor. This is a measure for suppressing the influence of the fact that it is not accurately detected at 46.

  Thereafter, the coil current command value Ic is obtained in the same manner as the first time, and the current value supplied to the coil 18 from the supply lines 34A and 34B is controlled to become the coil current command value Ic (see steps S24 to S28 in FIG. 8). ).

  That is, as shown in FIG. 10, the coil current of the unit 49 (see FIG. 10, coils 18 </ b> A to 18 </ b> F) in which the leakage magnetic field is detected by the magnetic detection sensor 46 is applied to the coil current set by each current control circuit 36. The current of the command value Ic is flowed to form a canceling magnetic field, and the leakage magnetic field is canceled. In this way, since the canceling magnetic field can be generated by driving only the necessary range (coils 18A to 18F) of the electromagnetic wave shielding device 10 according to the range of the leakage magnetic field, the leakage magnetic field can be canceled efficiently. .

  The coil pitch Lp (see FIG. 2) in the X direction and the Y direction of the coils 18 arranged in a matrix on the sheet body 16 of the electromagnetic wave shielding device 10 and the X direction of the coil 18 formed in a substantially square shape in plan view and Since the ratio (L / Lp) to the coil length L in the Y direction (see FIG. 2) is 0.4 to 0.6, the magnetic field strength between adjacent coils is compared with the coil formation position. And does not drop significantly. Corresponding to the distribution of the magnetic field strength, the canceling magnetic field can be generated with high accuracy, and the leakage magnetic field can be canceled.

  That is, as shown in FIG. 11A, when the ratio (L / Lp) between the coil pitch Lp and the coil length L is less than 0.4, the adjacent coil 18J and the coil 18K are largely separated from each other. The density of magnetic lines of force formed in the third conductor portion 44C of the coil 18J and the first conductor portion 44A of the coil 18K is reduced (sparse) between the coils, and the magnetic field strength between the adjacent coils 18J and 18K is greatly reduced. To do.

  On the other hand, as shown in FIG. 11C, when the ratio (L / Lp) between the coil pitch Lp and the coil length L is larger than 0.6, the coil 18J and the coil 18K are too close to each other in the same direction ( For example, the direction of the current flowing through the third conductor portion 44C of the coil 18J and the direction of the current flowing through the first conductor portion 44A of the coil 18K are reversed by the current flowing counterclockwise. As a result, the magnetic lines of force formed by the current flowing through the third conductor portion 44C of the coil 18J and the magnetic lines of force formed by the current flowing through the first conductor portion 44A of the coil 18K cancel each other and cancel each other. , The magnetic field strength between 18K is greatly reduced.

  On the other hand, as shown in FIG. 11B, when the ratio (L / Lp) of the coil pitch Lp to the coil length L is formed to be 0.4 or more and 0.6 or less, the coil 18J The magnetic field formed in the third conductor portion 44C and the magnetic field formed in the first conductor portion 44A of the coil 18K are in the same direction between the coils 18J and 18K, and the magnetic field strength between the coils 18J and 18K is greatly reduced. Is suppressed.

  That is, as shown in FIG. 12, when the ratio (L / Lp) between the coil pitch Lp and the coil length L is set to 0.4 or more and 0.6 or less, the magnetic field strength between adjacent coils. Becomes the largest, and the decrease in the magnetic field strength between adjacent coils is most suppressed. Therefore, the leakage magnetic field can be effectively canceled between the coils.

  In addition, since the coil pitch Lp is set shorter than the leakage magnetic field characteristic length D, in this embodiment, the circumferential length D of the cooling hole 22 formed in the end surface 20 of the housing 14 of the motor 12, At least two coils 18 are arranged in the range of the circumferential length D of the hole 22 for use. As a result, a canceling magnetic field corresponding to the magnetic field distribution leaking from the cooling hole 22 can be generated with high accuracy. That is, the electromagnetic wave shielding device 10 can cancel the leakage magnetic field of the motor 12 with high accuracy within a desired range.

  Furthermore, since the electromagnetic wave shielding device 10 is formed on the flexible sheet body 16, it can be easily disposed along the surface of the housing 14 and the like of the motor 12. Thereby, the leakage magnetic field from the motor 12 can be canceled with higher accuracy.

  Moreover, since the electromagnetic wave shielding apparatus 10 controls the coil 18 of each unit 49 with the current control circuit 36 based on the detection value of the magnetic detection sensor 46 provided in each unit 49, the coil 18 in a necessary range. It is possible to cancel the leakage magnetic field by generating a canceling magnetic field by passing an electric current only through. That is, the leakage magnetic field can be canceled out efficiently.

  Further, since the electromagnetic wave shielding device 10 generates a canceling magnetic field by passing a current through each coil 18, not only a high frequency electromagnetic wave that can be shielded by an eddy current generated by covering the housing with a conductor but also a low frequency electromagnetic wave. It is possible to effectively shield against (leakage magnetic field). This is particularly effective when the housing 14 of the motor 12 is molded of resin or the like for weight reduction.

[Second Embodiment]
An electromagnetic wave shielding device according to the second embodiment will be described with reference to FIGS. 13 and 14. Note that the same components as those of the electromagnetic wave shielding apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. In FIGS. 13 and 14, the magnetic detection sensor 46 and the detection line 48 formed on the back side of the sheet body 16 are also shown on the front surface 16 </ b> A for convenience of explanation.

(Constitution)
As shown in FIG. 13, in the electromagnetic wave shielding device 50, a positive power line 52 connected to the power source 31 and a negative power line 54 are formed on the sheet body 16 in a honeycomb shape (a hexagonal continuous shape). Has been. The power supply lines 52 and 54 are formed slightly shifted in plan view. A first coil 56 and a second coil 58 having a circular shape in plan view are formed inside a hexagonal portion formed by the power supply lines 52 and 54. The first coil 56 and the second coil 58 are formed slightly shifted in plan view.

  As shown in FIG. 14, the first coil 56 is connected from the power supply line 52 to the start point 40 via the branch line 60 and the current control circuit 36A, and from the power supply line 54 to the end point via the branch line 62 and the current control circuit 36A. 42 is connected. Therefore, the first coil 56 is configured such that a current flows clockwise in plan view (see arrow P in FIG. 14).

  Similarly, as shown in FIG. 14, the second coil 58 is connected from the power line 52 to the start point 40 via the branch line 64 and the current control circuit 36B, and from the power line 54 to the branch line 66 and the current control circuit 36B. The end point 42 is connected via However, since the positional relationship between the start point 40 and the end point 42 with respect to the current control circuit 36B is opposite to that of the current control circuit 36A, a current is passed through the second coil 58 counterclockwise in plan view (see arrow Q in FIG. 14). is there.

  As shown in FIG. 14, the magnetic detection sensor 46 is disposed on the back surface 16 </ b> B of the sheet body 16 inside (substantially the center) of the first coil 56 and the second coil 58 in plan view. The magnetic detection sensor 46 is connected to current control circuits 36 </ b> A and 36 </ b> B of the first coil 56 and the second coil 58 via a detection line 48.

(Function)
The operation of the electromagnetic wave shielding device 50 formed in this way will be described.

  In the electromagnetic wave shielding device 50, the current control circuits 36A and 36B obtain the coil current command value Ic based on the detection signal of the magnetic detection sensor 46 in the same manner as in the first embodiment. When the coil current command value Ic is positive, a current of that value is supplied from the current control circuit 36A to the first coil 56 to generate a predetermined canceling magnetic field. On the other hand, when the coil current command value Ic is negative, only the current control circuit 36B passes the current of that value to the second coil 58, and generates a predetermined canceling magnetic field in the reverse direction.

  Thus, in the electromagnetic wave shielding device 50, the first coil 56 and the second coil 58 through which currents flow in opposite directions in a plan view are provided, so that a canceling magnetic field can be accurately applied in response to a change in the leakage magnetic field. Can be generated. That is, the leakage magnetic field from the motor 12 can be canceled with high accuracy.

  In addition, since the current is supplied to the first coil 56 and the second coil 58 through the power supply lines 52 and 54 having a honeycomb shape, a bus is not necessary.

Further, since the positive power supply line 52 and the negative power supply line 54 are of a honeycomb type, the structure of the sheet body 16 is reinforced.
In the present embodiment, as shown in FIG. 13, the adjacent “coil pitch Lp” indicates that the adjacent first coils 56 or the second coils in the direction in which the hexagons formed by the power supply lines 52 and 54 are adjacent to each other. It is the distance between 58. Further, the “coil length L” is the length of the opposing portions of the first coils 56 or the second coils 58 that are adjacent in the direction in which the hexagons are adjacent, that is, the length of the semicircular portion in plan view. is there.

(Other)
In the present embodiment, the sheet body 16 of the electromagnetic wave shielding apparatuses 10 and 50 is flexible. However, the present invention is not limited to this. That is, the sheet body 16 may be a rigid body.

  Moreover, in this embodiment, although the electromagnetic wave shielding apparatus 10 only covered a part of outer peripheral surface of the housing 14 of the motor 12, you may cover the whole periphery.

10, 50 Electromagnetic wave shielding device 16 Sheet body 18 Coil 31 DC power supply (power supply)
36 Current control circuit 36A Current control circuit 36B Current control circuit 46 Magnetic detection sensor (magnetic sensor)
56 First coil (coil)
58 Second coil (coil)
D Leakage magnetic field length L Coil length Lp Coil pitch

Claims (1)

A sheet body;
A plurality of coils arranged at equal intervals on the sheet body;
A power supply capable of supplying a current to each of the plurality of coils;
A magnetic sensor for detecting a magnetic field at each coil position;
A current control circuit for determining a current value to be passed through each of the coils in order to cancel the leakage magnetic field based on an output of each magnetic sensor;
When the length of the coil is L, the coil pitch between adjacent coils is Lp, and the leakage magnetic field characteristic length is D,
0.4 ≦ L / Lp ≦ 0.6
And Lp ≦ D
An electromagnetic shielding device.