JP2012089714A - Electromagnetic shield housing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic shield housing capable of reducing the volume of an enclosure without reducing a quality factor a coil.SOLUTION: In an enclosure in which a winding type coil 50 is housed, an electromagnetic shield housing 100 that is a conductive shield plate surrounding the coil 50 includes: a bottom shield plate 10V, a right side shield plate 10R, a left side shield plate 10L, a front part shield plate 10F, and a rear part shield plate 10B in each of which a slit part 11 is provided so as to have the orthogonal direction with respect to a direction of current flowing into the coil 50 along the current direction at specific interval.

Description

  The present invention relates to an electromagnetic shielding housing in which a winding type coil is housed and provided with a shielding plate.

  An electromagnetic shielding casing that houses a main body of an electronic device in an outer casing having a shielding plate that shields electromagnetic waves is conventionally arranged in an external casing having ventilation holes, as described in Patent Document 1, for example. Is disclosed.

  Non-patent document 1 describes a rectangular waveguide management theory that explains the shielding effect of electromagnetic waves surrounded by a metal wall.

JP-A-5-72364

Clayton R. Paul, "Introduction to EMC", Mimatsu Data System, 1996/02 publication pp700-705

  When a helical type or uniform helical type coil is housed in a casing using a metal shielding plate for preventing electromagnetic field leakage, and a current is passed through the coil, the coil is placed in the shielding plate in a direction parallel to the coil conductor. Eddy current is generated in the opposite direction of the current.

  This eddy current reduces the Q (quality) of the coil. The eddy current increases as the coil current increases or the distance between the coil and the shielding plate decreases. Therefore, in order to avoid the influence on Q, it is necessary to increase the distance between the shielding plate and the coil or to reduce the current.

  However, when the distance between the shielding plate and the coil is increased, there is a problem that the volume of the housing is increased.

  The present invention solves the above-described problems, and an object of the present invention is to provide an electromagnetic shielding housing capable of reducing the volume of the housing without reducing the Q of the coil.

  The electromagnetic shielding case according to claim 1 for solving the above problem is a shielding plate for a conductor surrounding the coil in a case in which a wound coil is accommodated, and a direction of a current flowing in the coil It is characterized in that a shielding plate is provided in which cut portions that are orthogonal to each other are provided at predetermined intervals along the current direction.

  According to the said structure, the flow of the eddy current induced by a shielding board can be inhibited by the notch | incision part, it can prevent that Q of a coil falls, and the distance between a coil and a shielding board can be comprised small.

  Further, in the electromagnetic shielding case according to claim 2, the shielding plate is configured by first and second shielding plates arranged to face each other, and is orthogonal to the direction of the current flowing through the coil. It is characterized in that a portion other than the cut portion of the second shielding plate is disposed so as to face the cut portion of the provided first shielding plate.

  According to the said structure, it can prevent that an electromagnetic field and a magnetic flux leak from a notch part.

  Further, in the electromagnetic shielding case according to claim 3, a gap d is provided between the first shielding plate and the second shielding plate, and the width of the cut portion in the direction along the current direction is Wa, When the installation interval of the notches is Wc, d is small, and the direction of the current is along the overlapping portion where the portions other than the notches of the first shielding plate and the second shielding plate face each other. The above-described Wa and Wc are set so that the length of the direction l = (Wc−Wa) / 2 becomes large.

  According to the said structure, while being able to take ventilation with the gap | interval d, the leakage of an electromagnetic field and magnetic flux can further be prevented.

  The electromagnetic shielding case according to claim 4 has an auxiliary coil that generates magnetic flux in a direction that cancels out the electromagnetic flux generated from the coil and leaking from the shielding plate, at an outer peripheral portion in the coil radial direction in the vicinity of the shielding plate. It is characterized by being arranged.

  According to the said structure, since the electromagnetic flux which leaks from a coil to the coil radial direction outer peripheral side can be negated, magnetic flux can be concentrated in the length direction (axial direction) of a coil.

  Further, the maximum length of the cut portion is formed to be 1/8 or less of the wavelength λ of the current flowing through the coil.

  According to the said structure, the leakage prevention effect of an electromagnetic field and magnetic flux can further be improved.

(1) According to the inventions of the first to fifth aspects, the flow of eddy currents induced in the shielding plate can be inhibited by the cut portions. For this reason, the distance between the coil and the shielding plate can be reduced without reducing the Q of the coil, and the volume of the housing can be reduced.
(2) According to invention of Claim 2, it can prevent that an electromagnetic field and a magnetic flux leak from a notch part.
(3) According to the invention described in claim 3, ventilation can be taken by the gap d, and leakage of electromagnetic field and magnetic flux can be further prevented.
(4) According to the invention described in claim 4, since the electromagnetic flux leaking from the coil to the outer circumference side in the radial direction of the coil can be canceled out, the magnetic flux can be concentrated in the length direction (axial direction) of the coil. .
(5) By forming the maximum length of the cut portion to be 1/8 or less of the wavelength λ of the current flowing through the coil, the effect of preventing leakage of electromagnetic fields and magnetic flux can be further enhanced.

1 shows an embodiment of the present invention, (a) is a front view, and (b) is a plan view with a cover removed. FIG. The other embodiment example of this invention is shown, (a) is a front view, (b) is the top view which removed the cover. The other embodiment example of this invention is shown, (a) is principal part sectional drawing of two shielding boards, (b) is a front view of a notch part. The other embodiment example of this invention is shown, (a) is a front view, (b) is a top view, (c) is the perspective view which saw through the principal part. The equivalent circuit schematic of the coil and auxiliary coil in the other embodiment of this invention. Explanatory drawing in the principal part in the other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments.

  1A and 1B show an electromagnetic shielding casing 100 according to an embodiment of the present invention, in which FIG. 1A shows a front view and FIG. 1B shows a plane. The electromagnetic shielding casing 100 is configured as a rectangular casing with a ceiling portion opened using a shielding plate 10 made of a conductor (for example, metal), and a coil 50 wound in a regular square shape is accommodated therein. Has been.

  The shielding plate 10 includes a bottom shielding plate 10V, a right shielding plate 10R, a left shielding plate 10L, a front shielding plate 10F, and a rear shielding plate 10B. Each shielding plate 10 has a current flowing in the coil 50 in the direction of current. On the other hand, a plurality of cut portions 11 that are orthogonal to each other are provided at predetermined intervals along the current direction.

  A resinous cover 12 is provided at the ceiling opening portion of the electromagnetic shielding casing 100, and is not shown in FIG.

  The notch 11 provided in the shielding plate 10 inhibits the flow of eddy current induced in the shielding plate 10 when a current is passed through the coil 50.

  The cut portion 11 is formed by cutting the shielding plate 10 into, for example, a rectangular shape as shown in FIG. 3B, and the length of the linearly longest portion (generally a diagonal line) of the space generated by the cut. It is desirable that it is at least 1/8 or less of the wavelength λ of the current flowing through the coil 50 (the wavelength derived from the resonance frequency when resonating with the adjacent coil).

  For the shielding plate 10, a soft magnetic material may be used instead of the metal shielding plate, or a soft magnetic layer may be laminated on the metal layer. Examples of the soft magnetic material include amorphous alloy, permalloy, electromagnetic soft iron, silicon steel plate, and soft magnetic ferrite.

  Next, FIG. 2 shows an embodiment in which the electromagnetic shielding casing 110 is configured by overlapping the shielding plate 20 so as to cover the cut portion 11 on the outer peripheral portion of the shielding plate 10.

  2, the same parts as those in FIG. 1 are denoted by the same reference numerals. The shielding plate 20 is disposed to face the shielding plate 10 with a distance (d). As with the shielding plate 10, the shielding plate 20 includes a bottom shielding plate 20V, a right shielding plate 20R, a left shielding plate 20L, a front shielding plate 20F, and a rear shielding plate 20B. Each shielding plate 20 includes a coil. A plurality of cut portions 21 that are orthogonal to the direction of the current flowing through 50 are provided at predetermined intervals along the direction of the current.

  The shielding plate 20 is disposed so that a portion other than the notch 21 in the shielding plate 20 faces the notch 11 of the shielding plate 10.

  The distance d between the shielding plates 10 and 20 is desirably λ / 8 or less. The gap between the shielding plates 10 and 20 has the effect of ventilating while preventing leakage of the electromagnetic field. Furthermore, covering the notches on the sides facing each other also has an effect of preventing leakage of magnetic flux.

  Here, the shielding effect of the electromagnetic wave surrounded by the metal wall will be described by the rectangular waveguide management theory. Consider a rectangular waveguide with an inner diameter of d filled with a dielectric (corresponding to the distance d between the shielding plates 10 and 20 in this example). Assuming that the phase velocity of the electromagnetic wave propagating in the waveguide is vr, the speed of light is c, and the relative dielectric constant is εr, the cutoff frequency is given by the following equation (1).

  The attenuation factor α of the rectangular waveguide is given by the following equation (2) from Non-Patent Document 1.

  Accordingly, the attenuation (shielding effect SE) of the waveguide of length l is given by the following equation (3).

  Therefore, a narrow and long path for radio wave leakage is effective in preventing radio wave leakage.

  Therefore, in this embodiment, as shown in FIG. 3A showing a cross section of the shielding plate, the width in the direction along the current direction of the coil in the notch 11 on the shielding plate 10 side is Wa, and the installation interval (shielding) of the notch 11 When the length of the plate 10 along the current direction of the coil is Wc (the same applies to the shielding plate 20 side), the distance d between the shielding plates 10 and 20 is reduced, and the shielding plate 10 Wa and Wc are set such that the length l = (Wc−Wa) / 2 in the direction along the current direction of the coil at the portion where the two and 20 are opposed to each other is large.

  As another embodiment, as shown in FIG. 4, an auxiliary coil (ring coil) 60 is provided in the vicinity of the shielding plate to generate a magnetic flux in a direction that crosses the leakage magnetic flux and cancels the leakage electromagnetic wave.

  4, the same parts as those in FIG. 2 are denoted by the same reference numerals. 4 differs from FIG. 2 in that an auxiliary coil 60 that generates a magnetic flux in a direction that cancels out the electromagnetic flux generated from the coil 50 and leaks from the shielding plates 10 and 20 is disposed near the shielding plates 10 and 20 (electromagnetic shielding casing). 110 (on the ceiling side of 110) is arranged and held in the radially outer peripheral portion of the coil 50, and the others are configured in the same manner as in FIG.

  A means for holding the position where the auxiliary coil 60 is disposed is not shown.

  Further, in FIG. 4A, the notch in the front shielding plate shows only the notch 11 in the inner front shielding plate 10F, and the notch 21 in the outer front shielding plate 20F is not shown. .

  FIG. 4C is a perspective view of the inside of the electromagnetic shielding housing 110 seen through. The coil 50 is not shown, and the notches of the front shielding plates 10F and 20F and the right shielding plates 10R and 20R are shown. 11 and 21 are not shown.

Here, assuming that the current flowing through the coil 50 is i ₁ , the current flowing through the auxiliary coil 60 is i ₂ , the inductance of the coil 50 is L ₁ , the inductance of the auxiliary coil 60 is L ₂ , and the mutual inductance is M, the equivalent circuit is shown in FIG. It becomes like 5.
This can be written in the following equation:

If the resistance R ₂ of the auxiliary coil 60 is small, the phase of the current flowing through the auxiliary coil 60 is reversed from that of the current flowing through the coil 50. Accordingly, the magnetic flux is also reversed, and the magnetic flux distribution suppresses the leakage magnetic flux around the electromagnetic shielding plates (10, 20). As a result, the magnetic flux can be concentrated on the front surface of the coil (the length (axis) direction of the coil 50).

  The auxiliary coil 60 may be electrically connected to the metal shielding plates 10 and 20. Further, a magnetic layer may be laminated on the conductor of the auxiliary coil 60.

  When ventilation is not performed, the space between the two shielding plates 10 and 20 can be filled with resin or the like. Furthermore, the shielding plate can be multi-layered into three or more layers. In addition, as shown in FIG. 6, by providing a conductive connecting wall 30 between the shielding plates 10 and 20, it is possible to reduce the opening and lower the cutoff frequency.

  The shape of the coil 50 may be any of a polygonal shape, a circular shape, an elliptical helical shape, and a uniform spiral shape, and the cross section of the coil 50 may be any of a rectangular shape, a circular shape, and an elliptical shape.

DESCRIPTION OF SYMBOLS 10,20 ... Shielding plate 11,21 ... Cut part 12 ... Cover 30 ... Connection wall 50 ... Coil 60 ... Auxiliary coil 100, 110 ... Electromagnetic shielding housing

Claims (4)

In a housing that houses a wound coil,
A shield plate for a conductor surrounding the coil, comprising a shield plate provided with notches that are orthogonal to the direction of current flowing in the coil at predetermined intervals along the current direction. An electromagnetic shielding housing. The shielding plate is composed of first and second shielding plates arranged to face each other, and with respect to a cut portion of the first shielding plate provided in a direction orthogonal to the direction of the current flowing through the coil. The electromagnetic shielding casing according to claim 1, wherein the second shielding plate is disposed so that portions other than the cut portion are opposed to each other. A gap d is provided between the first shielding plate and the second shielding plate,
When the width in the direction along the current direction of the cut portion is Wa and the installation interval of the cut portions is Wc,
The length l in the direction along the direction of the current l = (Wc−Wa) / in an overlapping portion where the portion d is small and the portions other than the cut portions of the first shielding plate and the second shielding plate face each other. The electromagnetic shielding casing according to claim 2, wherein the Wa and Wc are set so that 2 is large. 4. An auxiliary coil that generates magnetic flux in a direction that cancels out electromagnetic flux generated from the coil and leaking from the shielding plate is disposed at an outer peripheral portion in the coil radial direction in the vicinity of the shielding plate. The electromagnetic shielding housing according to any one of claims.

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