JP2008243906A - Frequency selective electromagnetic wave shielding material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily improve shielding performance when shielding an electromagnetic wave of a specified frequency. <P>SOLUTION: On one flat surface of a basic material 11, a plurality of conductive loop forms 1 are formed. The conductive loop forms 1 are regularly arranged with intervals d, wherein four arcs of the same lengths are connected to one another to form a loop. Each arc forms a concave inside the loop form. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a frequency selective electromagnetic shielding material that reflects, scatters or absorbs electromagnetic waves.

  In recent years, as the use of wireless communication systems such as mobile phone networks and wireless LANs has expanded, it has become necessary to suppress the propagation of radio waves carrying information. For example, in order to protect the confidentiality of business information, radio waves radiated from wireless LAN terminals in the office are blocked from propagating to the outside, or radio waves that can cause interference to improve frequency utilization efficiency are blocked. It is requested to do. For this reason, a frequency-selective electromagnetic shielding material that shields an electromagnetic wave having a specific frequency has been studied.

Examples of conventional frequency-selective electromagnetic shielding materials are disclosed in Patent Documents 1 and 2, for example. In the frequency-selective electromagnetic wave shielding material of Patent Document 1, an antenna pattern is formed by an aggregate of conductors having a width of 50 micrometers or less on at least one surface of a transparent substrate. The frequency-selective electromagnetic wave shielding material of Patent Document 2 has a conductive loop pattern in which a plurality of loop shapes regularly having conductivity are arranged on one plane, and has at least four loop shapes having conductivity. A plurality of conductive loop blocks are formed. As the conductive loop pattern, a conductive pattern, in particular, a square loop shape arranged in a lattice shape is preferable.
JP 2003-258487 A JP 2001-177293 A

  However, the conventional frequency-selective electromagnetic wave shielding material described above has a problem that it is difficult to improve the shielding performance when shielding an electromagnetic wave having a specific frequency.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a frequency selective electromagnetic wave shielding material capable of easily improving the shielding performance when shielding electromagnetic waves of a specific frequency. There is.

  In order to solve the above problems, the frequency-selective electromagnetic wave shielding material according to the present invention has a plurality of conductive loop shapes formed on one plane of the base material and regularly arranged at intervals. The loop shape is formed by connecting four arcs having the same length in a loop shape, and each arc has a concave recess inside the loop shape.

  In the frequency-selective electromagnetic wave shielding material according to the present invention, a loop shape having a second conductivity is further arranged in a gap between the loop shapes having the first conductivity arranged in a lattice shape. And

  In the frequency selective electromagnetic wave shielding material according to the present invention, the loop shape having the first conductivity and the loop shape having the second conductivity have different arc lengths.

  In the frequency selective electromagnetic shielding material according to the present invention, the radius of curvature of the arc is not constant.

  The frequency-selective electromagnetic wave shielding material according to the present invention is characterized in that a plurality of types of loop shapes having the conductivity are formed with different arc lengths.

  The frequency-selective electromagnetic wave shielding material according to the present invention is characterized in that, in one loop shape having conductivity, a distance between connecting portions facing each other with respect to the connecting portion of the arc is different.

  ADVANTAGE OF THE INVENTION According to this invention, the shielding performance when shielding the electromagnetic wave of a specific frequency can be improved easily.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a plan view showing a loop shape 1 having conductivity according to the first embodiment of the present invention. In FIG. 1, a loop shape 1 having conductivity is formed by connecting four arcs 2 having the same length in a loop shape. Each arc 2 has a concave recess inside the loop shape 1 in the loop shape 1 having conductivity. The radius of curvature R of the arc 2 is constant. The curvature center 3 corresponding to the curvature radius R is outside the loop shape 1 having conductivity. The loop shape 1 having conductivity has a line width W. Although not shown in FIG. 1, the conductive loop shape 1 has a thickness D. The conductive loop shape 1 is made of a conductive material (for example, a metal such as copper or aluminum).

  FIG. 2 is a schematic diagram showing a configuration example of the frequency selective electromagnetic wave shielding material 10 according to the first embodiment of the present invention. In FIG. 2, the frequency-selective electromagnetic wave shielding material 10 is formed by forming a plurality of conductive loop shapes 1 on one plane of a base material 11. The loop shape 1 having conductivity is arranged in a lattice pattern on one plane of the base material 11 with an interval d. The space | interval d is the distance between the connection parts of the arc 2 in the loop shape 1 which has adjacent electroconductivity. The distance d may be determined with reference to a length twice as long as the line width W of the loop shape 1 having conductivity. The base material 11 is comprised with an insulating material (for example, a plastic film, glass, etc.). The respective loop shapes 1 having conductivity are electrically insulated from each other.

  In addition, as a method of forming a plurality of conductive loop shapes on one plane of the substrate, a conventional known technique may be used. For example, any method of printing, etching, electroless plating, or vapor deposition may be used, or a method combining a plurality of them may be used.

  Next, the detailed structural requirements (arc length, line width and thickness) of the loop shape 1 having conductivity will be described.

The frequency of the electromagnetic wave to be cut off is f (unit: hertz (Hz)) and the wavelength is λ (unit: meter (m)). If the effective dielectric constant based on the dielectric constant of the substrate 11 and the dielectric constant of air is ε, the wavelength shortening rate N can be calculated by the equation “N = 1 ÷ √ε”. At this time, the length L (unit: meter) of the arc 2 constituting the loop shape 1 having conductivity can be calculated by the following equation.
L = λ × N / 4

Further, the line width W (unit is meter) and thickness D (unit is meter) of the loop shape 1 having conductivity may be equal to or greater than the skin depth δ (unit is meter) represented by the following formula.
δ = √ (2 ÷ (ω × μ × σ))
However, ω = 2 × π × f, μ is magnetic permeability, and σ is conductivity.

According to the present embodiment, the area required for arranging the conductive loop shape can be reduced when shielding electromagnetic waves of the same frequency as compared to the conventional square loop shape having conductivity. it can. This point will be described.
From the length L of one side, the area required to arrange one square loop shape having conductivity is “L × L”. On the other hand, the minimum area required for arranging one loop shape 1 having conductivity according to the present embodiment is as follows from the condition “R = 2 × L ÷ π” where the radius of curvature R is minimum. √2 × R × √2 × R = 8 × L × L ÷ (π × π) ”. Here, π is the circumference ratio.

  Therefore, the loop shape 1 having conductivity according to the present embodiment occupies an area “8 ÷ (π × π)” (approximately 0.81) times as large as the square loop shape having conductivity. In other words, the conductive loop shape 1 according to the present embodiment is “(π × π) ÷ 8” (about 1.23) times per unit area as compared to the square loop shape having conductivity. Can be arranged in density.

  As described above, according to the present embodiment, when conductive loop shapes are arranged in a grid pattern on one plane of the substrate, the number of conductive loop shapes per unit area is increased as compared to the conventional case. be able to. As the number of loop shapes having conductivity per unit area increases, the shielding performance of electromagnetic waves is improved accordingly. That is, by using the loop shape 1 having conductivity according to the present embodiment, the number of loop shapes having conductivity per unit area can be increased, and the shielding performance when shielding electromagnetic waves of a specific frequency can be achieved. The special effect that it can be improved easily is obtained.

  In addition, although it is considered that the polarization direction of the electromagnetic wave varies due to propagation, according to the loop shape 1 having conductivity according to the present embodiment, even if the polarization direction varies, a plurality of polarizations are caused by the arc 2. A shielding effect can be given to the direction component. This contributes to improvement of electromagnetic wave shielding performance.

[Second Embodiment]
FIG. 3 is a schematic diagram illustrating a configuration example of the frequency selective electromagnetic wave shielding material 20 according to the second embodiment of the present invention. The frequency selective electromagnetic shielding material 20 shown in FIG. 3 is obtained by further increasing the density of the loop shape 1 having conductivity per unit area with respect to the frequency selective electromagnetic shielding material 10 of FIG. In FIG. 3, the loop shape 1 having further conductivity is arranged in the gap between the loop shapes 1 having conductivity arranged in a grid pattern in the frequency selective electromagnetic wave shielding material 10 of FIG. This arrangement can be realized by providing a gap when the conductive loop shape 1 has a loop recess by the arc 2. Note that a gap d is provided between the loop shapes 1 having conductivity, and the loop shapes 1 having conductivity are electrically insulated from each other.

  According to the second embodiment described above, the density of the loop shape 1 having conductivity per unit area can be further increased. Thereby, the electromagnetic wave shielding performance is further improved.

[Third Embodiment]
FIG. 4 is a plan view showing a loop shape 1a having conductivity according to the third embodiment of the present invention. The conductive loop shape 1a shown in FIG. 4 has the same configuration as the conductive loop shape 1 shown in FIG. 1, but the radius of curvature of the arc 2a is not constant. For this reason, in the conductive loop shape 1 of FIG. 1, the distances between the connecting portions facing each other with respect to the connecting portion of the arc 2 are all equal, but in the conductive loop shape 1a of FIG. The distance between connecting parts is different.

  FIG. 5 is a schematic diagram illustrating a configuration example of the frequency selective electromagnetic wave shielding material 30 according to the third embodiment of the present invention. The frequency-selective electromagnetic wave shielding material 30 shown in FIG. 5 has a plurality of conductive loop shapes 1a formed on one plane of the substrate 11 in the same manner as the frequency-selective electromagnetic wave shielding material 10 of FIG. At the same time, they are arranged in a lattice pattern with an interval d. The conductive loop shapes 1a are electrically insulated from each other.

[Fourth Embodiment]
FIG. 6 is a plan view showing a loop shape 1b having conductivity according to the fourth embodiment of the present invention. The conductive loop shape 1b shown in FIG. 6 is a modification of the conductive loop shape 1a of FIG. 1 in the same manner as the conductive loop shape 1a of FIG. 4, and the radius of curvature of the arc 2b is not constant. Absent.

  FIG. 7 is a schematic diagram illustrating a configuration example of the frequency selective electromagnetic wave shielding material 40 according to the fourth embodiment of the present invention. In the frequency selective electromagnetic wave shielding material 40 shown in FIG. 7, a plurality of conductive loop shapes 1 a and conductive loop shapes 1 b are formed on one plane of the substrate 11. The conductive loop shape 1a and the conductive loop shape 1b are arranged in a grid pattern on the one plane of the base material 11 with an interval d alternately. The conductive loop shapes 1a and 1b are electrically insulated.

  The conductive loop shapes 1a and 1b according to the third and fourth embodiments described above also have the following configuration requirements (the length of the arc, the line width W and the thickness D of the conductive loop shape). This is the same as the loop shape 1 having conductivity described above.

[Fifth Embodiment]
FIG. 8 is a plan view showing loop shapes 1c and 1d having conductivity according to the fifth embodiment of the present invention. The conductive loop shapes 1c and 1d shown in FIG. 8 have the same configuration as the conductive loop shape 1 shown in FIG. 1, but the arcs 2c and 2d have different lengths. As shown in the constituent requirements of the loop shape 1 having conductivity described above, the lengths of the arcs 2c and 2d are determined from the frequency of the electromagnetic wave to be cut off. Therefore, the loop shapes 1c and 1d having conductivity with different arc lengths shield different frequencies f1 and f2, respectively.

  In the example of FIG. 8, the loop shape 1c having conductivity has a shorter arc length than the loop shape 1d having conductivity. Accordingly, the frequency f1 of the electromagnetic wave shielded by the conductive loop shape 1c is higher than the frequency f2 of the electromagnetic wave shielded by the conductive loop shape 1d.

  FIG. 9 is a schematic diagram showing a configuration example of the frequency selective electromagnetic wave shielding material 50 according to the fifth embodiment of the present invention. The frequency-selective electromagnetic wave shielding material 50 shown in FIG. 9 has further conductivity in the gaps between the loop shapes 1d having conductivity arranged in a lattice shape, like the frequency-selective electromagnetic wave shielding material 20 of FIG. A loop shape 1c is provided. A gap d1 is provided between the loop shapes 1d having conductivity. A gap d2 is provided between the loop shapes 1c having conductivity. The electrically conductive loop shapes 1c and 1d are electrically insulated.

  According to the fifth embodiment described above, it is possible to block electromagnetic waves having different frequencies.

  FIG. 10 is a graph of the simulation result according to the present invention. In FIG. 10, the horizontal axis represents frequency (Hz) and the vertical axis represents electric field strength (decibel (dB)). A waveform 101 is a frequency characteristic when the frequency selective electromagnetic shielding material is not used. A waveform 102 is a frequency characteristic when the frequency selective electromagnetic wave shielding material 10 shown in FIG. 2 is used. The simulation conditions are: the cutoff target frequency is 2.4 GHz, the length L of the arc 2 of the conductive loop shape 1 is 24.31 millimeters, the line width W of the conductive loop shape 1 is 0.25 millimeters, The thickness D of the conductive loop shape 1 is 6 millimeters, the radius of curvature R of the arc 2 of the conductive loop shape 1 is 16.75 millimeters, the relative dielectric constant of the base material 11 is 7.4, and the base material 11 The spacing d between the upper conductive loop shapes 1 is 2 millimeters.

  As shown in FIG. 10, according to the frequency selective electromagnetic wave shielding material 10 according to the first embodiment, an attenuation effect of about 25 dB can be obtained.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

It is a top view which shows loop shape 1 with conductivity concerning a 1st embodiment of the present invention. It is a schematic diagram which shows the structural example of the frequency selective electromagnetic wave shielding material 10 which concerns on 1st Embodiment of this invention. It is a schematic diagram which shows the structural example of the frequency selective electromagnetic wave shielding material 20 which concerns on 2nd Embodiment of this invention. It is a top view which shows the loop shape 1a with conductivity which concerns on 3rd Embodiment of this invention. It is a schematic diagram which shows the structural example of the frequency selective electromagnetic wave shielding material 30 which concerns on 3rd Embodiment of this invention. It is a top view which shows the loop shape 1b with conductivity which concerns on 4th Embodiment of this invention. It is a schematic diagram which shows the structural example of the frequency-selective electromagnetic wave shielding material 40 which concerns on 4th Embodiment of this invention. It is a top view which shows loop shape 1c, 1d with conductivity which concerns on 5th Embodiment of this invention. It is a schematic diagram which shows the structural example of the frequency selective electromagnetic wave shielding material 50 which concerns on 5th Embodiment of this invention. It is a graph figure of the simulation result concerning the present invention.

Explanation of symbols

1, 1a, 1b, 1c, 1d ... conductive loop shape, 2, 2a, 2b, 2c, 2d ... arc, 10, 20, 30, 40, 50 ... frequency selective electromagnetic shielding material, 11 ... substrate

Claims (6)

A plurality of conductive loop shapes are formed on one plane of the substrate and regularly arranged at intervals,
The loop shape is formed by connecting four arcs of equal length in a loop shape, and each arc forms a concave recess inside the loop shape.
A frequency-selective electromagnetic shielding material characterized by that.   2. The frequency-selective electromagnetic wave shield according to claim 1, wherein a loop shape having a second conductivity is further arranged in a gap between the loop shapes having the first conductivity arranged in a lattice shape. Wood.   The frequency-selective electromagnetic wave shielding material according to claim 2, wherein the loop shape having the first conductivity and the loop shape having the second conductivity have different arc lengths.   The frequency selective electromagnetic shielding material according to claim 1, wherein the radius of curvature of the arc is not constant.   The frequency-selective electromagnetic wave shielding material according to claim 1, wherein a plurality of types of conductive loop shapes having different arc lengths are formed.   2. The frequency-selective electromagnetic wave shielding material according to claim 1, wherein, in the one loop shape having conductivity, a distance between connecting portions facing each other with respect to the connecting portion of the arc is different.

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