JP6674436B2 - Noise suppression sheet - Google Patents

Description

  The present invention relates to a noise suppression sheet capable of suppressing high frequency noise.

  Patent Literature 1 discloses a soft magnetic molded body that can be used as a noise suppression sheet.

  The soft magnetic molded body disclosed in Patent Literature 1 is obtained by bonding flat soft magnetic powder with a binder, and can be formed into a sheet having a thickness of about 0.4 mm, for example. The sheet-shaped soft magnetic molded body can be used as a noise suppression sheet.

JP-A-2015-175047

  In the soft magnetic molded body of Patent Literature 1, the flat soft magnetic powder is oriented parallel to the sheet surface. The soft magnetic molded body thus formed has a high magnetic loss component in a plane parallel to the sheet surface. In particular, the noise suppression sheet of Patent Document 1 can sufficiently suppress noise in a frequency band of 1 to 2 GHz. On the other hand, when the noise suppression sheet of Patent Document 1 is used, there has been a problem that noise in a frequency band of 3 to 6 GHz cannot be appropriately suppressed.

  Therefore, an object of the present invention is to provide a noise suppression sheet capable of suppressing noise in a frequency band of 3 to 6 GHz.

In general, a material having a high magnetic loss component μ ″ (an imaginary component of the complex relative magnetic permeability μ) such as the soft magnetic molded body of Patent Document 1 has a high dielectric loss component ε ″ (an imaginary component of the complex relative permittivity ε). Having. Further, there is a relationship of σ = 2π · ε ″ · f between the dielectric loss component ε ″ and the frequency f and the conductivity σ. Further, the penetration depth of the noise (electromagnetic wave) into the object (that is, the skin depth) δ is represented by an expression of δ = {1 / (π · μ · σ · f)}. When the frequency f is low, the product of the conductivity and the frequency (σ · f = 2π · ε ″ · f ² ) does not become so high even if the dielectric loss ε ″ is high, so that the skin depth is somewhat large. However, when the frequency f is high, as the dielectric loss ε ″ increases, the product of the conductivity and the frequency (σ · f = 2π · ε ″ · f ² ) becomes too large to be ignored, and the skin depth becomes shallow. For this reason, it is considered that noise in the frequency band of 3 to 6 GHz hardly enters the noise suppression sheet of Patent Document 1, and is easily reflected on the surface of the noise suppression sheet. Then, this invention provides the noise suppression sheet | seat provided with the structure for making the noise of the frequency band of 3-6 GHz penetrate deeply. More specifically, the present invention provides the following noise suppression sheet.

The present invention provides, as a first noise suppression sheet,
A noise suppression sheet including a composite magnetic sheet having a first layer and a second layer,
The first layer has a main surface that is an incident surface on which the electromagnetic wave enters the noise suppression sheet from outside the noise suppression sheet,
The first layer has a first dielectric loss component and a first magnetic loss component in a plane parallel to the main surface,
The second layer is located on a side opposite to the main surface of the first layer,
The second layer has a second dielectric loss component and a second magnetic loss component in a plane parallel to the main surface,
The first dielectric loss component is lower than the second dielectric loss component;
The second magnetic loss component provides a higher noise suppression sheet than the first magnetic loss component.

Further, the present invention is a first noise suppression sheet as a second noise suppression sheet,
The first layer includes a metal soft magnetic powder having an average aspect ratio of less than 2, and an organic binder.
The second layer provides a noise suppression sheet including a flat metal soft magnetic powder having an average sectional aspect ratio of 20 or more and less than 100 and an organic binder.

Further, the present invention is a second noise suppression sheet as a third noise suppression sheet,
The first layer contains 50% by volume or more of the metal soft magnetic powder,
The second layer provides a noise suppression sheet including the flat metal soft magnetic powder in an amount of 40% by volume or more.

Further, the present invention is any one of the first to third noise suppression sheets as a fourth noise suppression sheet,
Provided is a noise suppression sheet in which the thickness of the composite magnetic sheet is 25 μm or more and 100 μm or less.

Further, the present invention provides any one of the first to fourth noise suppression sheets as a fifth noise suppression sheet,
In a frequency band of 3 to 6 GHz, the first dielectric loss component is lower than 1, and the second magnetic loss component provides a noise suppression sheet higher than 6.

Further, the present invention provides any one of the first to fifth noise suppression sheets as a sixth noise suppression sheet,
A noise suppression sheet comprising a metal layer located on the second layer is provided.

  In the noise suppression sheet according to the present invention, electromagnetic waves (noise) first enter the first layer. At this time, since the dielectric loss component of the first layer is low, the reflection of the electromagnetic wave on the incident surface can be suppressed, and the electromagnetic wave can be attenuated in the first layer. The electromagnetic wave passing through the first layer is incident on the second layer having a high magnetic loss component, and can be further attenuated in the second layer. According to the present invention, noise in a frequency band of 3 to 6 GHz can be effectively suppressed by the above two-layer structure.

It is a perspective view showing typically a noise suppression sheet by an embodiment of the invention. Noise incident on the main surface of the noise suppression sheet is schematically depicted by a broken line. It is sectional drawing which shows the noise suppression sheet of FIG. 1 typically along the II-II line. Noise incident on the main surface of the noise suppression sheet is schematically depicted by a broken line. 2 is a graph showing dielectric loss components of a first layer and a second layer of the noise suppression sheet of FIG. 2 is a graph showing magnetic loss components of a first layer and a second layer of the noise suppression sheet of FIG. FIG. 3 is a diagram schematically illustrating a measurement system for measuring noise coupling of the noise suppression sheet according to the first embodiment. FIG. 9 is a diagram schematically illustrating a measurement system for measuring noise coupling of the noise suppression sheets of Comparative Examples 1 and 2. 7 is a graph illustrating a noise coupling ratio of the noise suppression sheet of Comparative Example 1 measured by the measurement system of FIG. 6. 7 is a graph illustrating a noise coupling ratio of the noise suppression sheet of Comparative Example 2 measured by the measurement system of FIG. 6. 6 is a graph showing the noise coupling ratio of the noise suppression sheet of Example 1 measured by the measurement system of FIG.

  Referring to FIGS. 1 and 2, a noise suppression sheet 10 according to an embodiment of the present invention has a thin sheet shape with a thickness of about 0.1 mm, for example, and is a small electronic device (hereinafter, referred to as a mobile phone). ) Can be mounted inside a limited space such as the inside of a “small electronic device”. The noise suppression sheet 10 according to the present embodiment includes a composite magnetic sheet 20 having a first layer 30 and a second layer 40, and a metal layer 50. Each of the first layer 30 and the second layer 40 is a thin sheet containing a magnetic material. The metal layer 50 is a metal plate made of a metal material such as copper. However, the present invention is not limited to this. For example, the metal layer 50 may be provided as needed, as described later. The noise suppression sheet 10 may further include a magnetic layer in addition to the first layer 30 and the second layer 40.

Each of the first layer 30, the second layer 40, and the metal layer 50 extends on a plane parallel to a horizontal plane (XY plane). The first layer 30 has a main surface 30P parallel to the XY plane. The main surface 30 </ b> P is an incident surface where the electromagnetic wave 80 enters the noise suppression sheet 10 from outside the noise suppression sheet 10. In the present embodiment, main surface 30P is exposed to the outside. However, the present invention is not limited to this. For example, main surface 30P may be covered with an insulating film. That is, the noise suppression sheet 10 may include a layer such as an insulating film.

  The first layer 30, the second layer 40, and the metal layer 50 are stacked in the stacking direction (Z direction). More specifically, the second layer 40 has a surface 40S that is parallel to the XY plane, and is arranged such that the surface 40S contacts the surface of the first layer 30 opposite to the main surface 30P. In other words, the second layer 40 is located on the side opposite to the main surface 30P of the first layer 30. The metal layer 50 is located on the second layer 40. That is, the second layer 40 is sandwiched between the first layer 30 and the metal layer 50 in the Z direction.

  Referring to FIG. 2, the first layer 30 of the composite magnetic sheet 20 includes a spherical metal soft magnetic powder 32 and an organic binder 38, and the second layer 40 of the composite magnetic sheet 20 has a flat shape. , And a flat metal soft magnetic powder 42 and an organic binder 48. The composite magnetic sheet 20 is produced, for example, as follows.

  First, the metal soft magnetic powder 32 having a spherical shape is mixed with the organic binder 38 in a sol form, and the mixture is stirred so that the metal soft magnetic powder 32 is uniformly dispersed in the organic binder 38 to prepare a slurry. Next, a sheet-like first thin film is formed from the slurry by, for example, a doctor blade method. Next, the spherical metal soft magnetic powder is flattened using an apparatus such as a ball mill to produce a flat metal soft magnetic powder 42. The flat metal soft magnetic powder 42 is mixed with a sol-like organic binder 48, and the slurry is prepared by stirring so that the flat metal soft magnetic powder 42 is uniformly dispersed in the organic binder 48. Next, a sheet-like second thin film is formed from the slurry by, for example, a doctor blade method. In the second thin film, the flat metal soft magnetic powder 42 is oriented on a plane (in-plane) parallel to the sheet surface. Next, the first thin film and the second thin film are laminated, and the first thin film (first layer 30) compressed by pressing in a direction perpendicular to the sheet surface and the second thin film (second layer 40) are compressed. ) Is formed.

  The first layer 30 contains a magnetic material (metallic soft magnetic powder 32), and has a first dielectric loss component and a first magnetic loss component in a plane parallel to the main surface 30P (in the XY plane). doing. The first dielectric loss component is an imaginary component (ε ″) of the complex relative permittivity (ε = ε′−jε ″) in the XY plane of the first layer 30, and the first magnetic loss component is Is the imaginary component (μ ″) of the complex relative magnetic permeability (μ = μ′−jμ ″) in the XY plane. Similarly, the second layer 40 includes a magnetic material (flat metal soft magnetic powder 42), and has a second dielectric loss component and a second magnetic loss component in a plane parallel to the main surface 30P (in the XY plane). And components. The second dielectric loss component is an imaginary component (ε ″) of the complex relative permittivity (ε) of the second layer 40 in the XY plane, and the second magnetic loss component is a complex component of the second layer 40 in the XY plane. This is the imaginary component (μ ″) of the relative magnetic permeability (μ).

  In the first layer 30, the spherical metal soft magnetic powder 32 is relatively densely and uniformly distributed in the organic binder 38 having a relatively high electric resistivity. In the second layer 40, the flat-shaped flat metal soft magnetic powder 42 extending along a plane parallel to the XY plane is relatively densely and uniformly distributed in the organic binder 48 having a relatively high electric resistivity. This reduces the electrical resistivity in the plane of the second layer 40 in a plane parallel to the XY plane. As shown in FIGS. 3 and 4, comparing the first layer 30 and the second layer 40 thus formed, the dielectric loss component (first dielectric loss component) of the first layer 30 is the second layer 30. The magnetic loss component (second magnetic loss component) of the second layer 40 is lower than the dielectric loss component (second dielectric loss component) of the first layer 30 and the magnetic loss component of the first layer 30 (first magnetic loss component). Higher than.

  Referring to FIGS. 1 and 2, in the noise suppression sheet 10, the electromagnetic wave 80 first enters the first layer 30. At this time, since the dielectric loss component of the first layer 30 is low, the reflection of the electromagnetic wave 80 on the incident surface (the main surface 30P) can be suppressed. Further, there is a relationship of σ = 2π · ε ″ · f between the dielectric loss component and the frequency f of the electromagnetic wave 80 and the conductivity σ. In addition, the penetration depth of the electromagnetic wave 80 into the first layer 30 ( That is, the skin depth) δ is expressed by the following equation: δ = {1 / (π · μ · σ · f)} Since the dielectric loss component of the first layer 30 is extremely low (see FIG. 3). Therefore, the electromagnetic wave 80 incident on the first layer 30 reaches the surface 40S of the second layer 40 while being attenuated in the first layer 30.

  The second layer 40 has a high dielectric loss component (see FIG. 3). Therefore, when the electromagnetic wave 80 having a high frequency is directly incident on the second layer 40 from the space, the second layer 40 easily reflects the electromagnetic wave 80. On the other hand, the wavelength of the electromagnetic wave 80 incident on the first layer 30 is shortened, whereby the reflection of the electromagnetic wave 80 on the surface 40S of the second layer 40 is suppressed. That is, the electromagnetic wave 80 passing through the first layer 30 enters the second layer 40 having a high magnetic loss component, and is further attenuated in the second layer 40. According to the present embodiment, the electromagnetic wave 80 in the frequency band of 3 to 6 GHz can be effectively suppressed by the above two-layer structure.

  The noise suppression sheet 10 according to the present embodiment is mainly used by being arranged in the internal space of a small electronic device. In an internal space of a small electronic device (hereinafter, referred to as “small space”), electromagnetic waves 80 in a frequency band of 3 to 6 GHz are easily generated. For example, the wavelength λ of the electromagnetic wave 80 having a frequency of 3 GHz is 10 cm, and λ / 2π that defines the near field is less than 16 mm. That is, the small space is in the near field where the wave impedance is separated into a high impedance field where the minute dipole antenna (electric field component) is the wave source and a low impedance field where the minute loop antenna (magnetic field component) is the wave source. For this reason, it is difficult to match the impedance of the small space with the impedance of the main surface of the noise suppression sheet. However, since the noise source (wave source) in a small space is a small loop antenna (magnetic field component) in most cases, the noise suppression sheet according to the present embodiment suppresses the noise of the magnetic field component by the magnetic loss μ ″. A larger noise suppression effect can be obtained by increasing the penetration depth δ of the magnetic field component .. The noise suppression sheet 10 according to the present embodiment does not match the interface impedance of the main surface 30P with the impedance of the small space. , The electromagnetic wave 80 propagating in the near field can be suppressed.

  The noise suppression sheet 10 of the present embodiment includes a metal layer 50. For this reason, the electromagnetic wave 80 that has passed through the second layer 40 is reflected by the metal layer 50 and goes out of the noise suppression sheet 10 while being further attenuated via the second layer 40 and the first layer 30. That is, by providing the metal layer 50, noise in the frequency band of 3 to 6 GHz can be more effectively suppressed. In addition, the metal layer 50 prevents the electromagnetic wave 80 from going outside from the side opposite to the main surface 30P of the noise suppression sheet 10, and is thereby located on the side opposite to the main surface 30P of the noise suppression sheet 10. Electronic parts are electromagnetically shielded. However, the present invention is not limited to this, and the metal layer 50 may be provided as needed. For example, when the noise suppression sheet 10 is attached to a metal housing of a small electronic device, the metal layer 50 is unnecessary. Further, the metal layer 50 is not limited to a copper plate and can be formed from various metal materials. For example, the metal layer 50 may be an aluminum tape.

  In the present embodiment, characteristics such as the shape, composition, and volume filling factor of the magnetic powder (the metal soft magnetic powder 32 and the flat metal soft magnetic powder 42) are not particularly limited. However, as described below, by setting these features in a preferable range, the effect of the present embodiment can be enhanced.

  In terms of effectively suppressing noise in the frequency band of 3 to 6 GHz, the dielectric loss component (first dielectric loss component) of the first layer 30 is preferably lower than 1 in the frequency band of 3 to 6 GHz. The magnetic loss component of the second layer 40 (second magnetic loss component) is preferably higher than 6.

  From the viewpoint of sufficiently reducing the dielectric loss component of the first layer 30, it is preferable that the first layer 30 contains 50% by volume or more of the metal soft magnetic powder 32. Further, from the viewpoint of sufficiently increasing the magnetic loss component of the second layer 40, it is preferable that the second layer 40 contains the flat metal soft magnetic powder 42 of 40% by volume or more.

  From the viewpoint of sufficiently reducing the dielectric loss component of the first layer 30, the metal soft magnetic powders 32 are preferably sufficiently separated from each other and have a small surface area. For this reason, the shape of the metal soft magnetic powder 32 is ideally a true spherical shape. However, it is difficult to form the metal soft magnetic powder 32 into a true spherical shape. Considering this point as well, the metal soft magnetic powder 32 preferably has an average aspect ratio of less than 2, and more preferably has an average aspect ratio of less than 1.2.

  From the viewpoint of sufficiently increasing the magnetic loss component of the second layer 40, the flat metal soft magnetic powder 42 preferably has an average sectional aspect ratio of 20 or more. On the other hand, from the viewpoint of easily manufacturing the second layer 40 industrially and increasing the volume occupancy of the flat metal soft magnetic powder 42 in the second layer 40 to sufficiently increase the second magnetic loss component, The flat metal soft magnetic powder 42 preferably has an average sectional aspect ratio of 100 or less, more preferably 50 or less.

Generally, the higher the dielectric loss component or the magnetic loss component, the lower the surface resistivity, and the lower the dielectric loss component or the magnetic loss component, the higher the surface resistivity. In order to reduce the dielectric loss component (first dielectric loss component) of the first layer 30, the surface resistivity of the main surface 30P of the first layer 30 must be 1 × 10 ⁸ (Ω / sq.) Or more. Is preferably 1 × 10 ¹⁰ (Ω / sq.) Or more. On the other hand, in order to increase the magnetic loss component of the second layer 40, the surface resistivity of the surface 40S of the second layer 40 is preferably 1 × 10 ¹¹ (Ω / sq.) Or less, preferably 1 × 10 ¹¹ (Ω / sq.). ⁶ (Ω / sq.) Or less. However, when forming the second layer 40 using a general material, it is difficult to make the surface resistivity of the surface 40S smaller than 1 × 10 ² (Ω / sq.). Therefore, the surface resistivity of the surface 40S may be 1 × 10 ² (Ω / sq.) Or more.

  The noise suppression sheet 10 needs to be thin in order to be installed inside a limited space. Therefore, the thickness (size in the Z direction) of the composite magnetic sheet 20 is preferably 0.3 mm or less. In particular, when the noise suppression sheet 10 is mounted inside a small electronic device (inside a small space), the thickness of the composite magnetic sheet 20 is more preferably 0.1 mm (100 μm) or less. However, if the thickness of the composite magnetic sheet 20 is too small, it becomes difficult to provide the first layer 30 and the second layer 40. Therefore, the thickness of the composite magnetic sheet 20 is preferably 0.025 mm (25 μm) or more.

  From the viewpoint of reducing the thickness of the composite magnetic sheet 20, the average particle diameter D50 of the metal soft magnetic powder 32 of the first layer 30 is preferably 30 μm or less, and more preferably 10 μm or less. On the other hand, from the viewpoint of easily producing the first layer 30 industrially, the average particle diameter D50 of the metal soft magnetic powder 32 is preferably 1 μm or more.

  The magnetic powder (metal soft magnetic powder 32 and flat metal soft magnetic powder 42) can be made from various magnetic materials. For example, the magnetic powder can be made from an Fe-Si-Al alloy, an Fe-Si-Cr alloy, an Fe-Al alloy, an Fe-Ni alloy, or an Fe-Co-V alloy. On the surface of the flat metal soft magnetic powder 42, a high resistance film made of an oxide film of a base element or a silica film may be formed. However, from the viewpoint of not reducing the volume occupancy of the magnetic material in the second layer 40, the thickness of the high resistance film is preferably as thin as possible. Similarly, from the viewpoint of not lowering the volume occupancy of the magnetic material in the first layer 30 and the second layer 40, each of the metal soft magnetic powder 32 and the flat metal soft magnetic powder 42 is combined with a nonmagnetic material such as ceramics. Preferably, it is not.

  According to the present embodiment, while each of the first layer 30 and the second layer 40 does not contain an inorganic filler or a carbon-based filler, an organic binder (the organic binder 38 or the organic binder 48) is used. )It is included. For this reason, the composite magnetic sheet 20 of the present embodiment is easily bent and can be attached to various places. For example, organic binders include (meth) acrylic polymers such as acrylic rubber and alkyl acrylate copolymer, acrylonitrile-butadiene rubber (NBR), silicone rubber, polyurethane, polyethylene, ethylene propylene rubber (EPM), ethylene Various materials such as olefin rubber such as propylene / diene rubber (EPDM), polyphenylene oxide (PPO), and bismuth triazine resin may be used alone or in combination of two or more.

  The first layer 30 (second layer 40) is composed of one or two kinds of melamine cyanurate, red phosphorus, aluminum hydroxide, magnesium hydroxide, phosphazene and the like dispersed in the organic binder 38 (organic binder 48). The above may be included.

  Hereinafter, the effects of the present invention will be described in more detail using specific examples and comparative examples.

(Preparation of the first thin film)
Spherical carbonyl iron powder was prepared as the metal soft magnetic powder, and acrylic rubber was prepared as the organic binder. The average particle size D50 of the carbonyl iron powder was 4 μm, and the average aspect ratio was 1.1. A slurry having viscosity was prepared by mixing carbonyl iron powder and acrylic rubber. The slurry contained 60% by volume carbonyl iron powder and 40% by volume acrylic rubber. A thin film (first thin film) having a thickness of 0.1 mm was formed from the slurry by a doctor blade method.

(Preparation of the second thin film)
Flat carbonyl iron powder was prepared as the flat metal soft magnetic powder, and acrylic rubber was prepared as the organic binder. The average particle diameter D50 of the carbonyl iron powder was 14 μm, and the average sectional aspect ratio was 28. A slurry having viscosity was prepared by mixing carbonyl iron powder and acrylic rubber. The slurry contained 50% by volume carbonyl iron powder and 50% by volume acrylic rubber. A thin film (second thin film) having a thickness of 0.1 mm was prepared from the slurry by a doctor blade method.

(Preparation of the noise suppression sheet of Example 1)
Referring to FIG. 5, one first thin film and one second thin film were laminated and heated and pressed to produce a composite magnetic sheet 20X (noise suppression sheet 10X) of Example 1. In the composite magnetic sheet 20X, the thickness of the first layer 30 made of the first thin film was 0.05 mm, and the thickness of the second layer 40 made of the second thin film was 0.05 mm. That is, the thickness of the composite magnetic sheet 20X (the noise suppression sheet 10X) was 0.1 mm (100 μm).

(Production of Noise Suppression Sheets of Comparative Examples 1 and 2)
Referring to FIG. 6, a thin film having a thickness of 0.2 mm was formed from the same material as the first thin film of Example 1. The thin film was heated and pressed to produce a magnetic sheet 20Y of Comparative Example 1 (noise suppressing sheet 10Y). The thickness of the magnetic sheet 20Y was 0.1 mm (100 μm). Similarly, a thin film having a thickness of 0.2 mm was formed from the same material as the second thin film of Example 1. The thin film was heated and pressed to produce a magnetic sheet 20Z of Comparative Example 2 (a noise suppression sheet 10Z). The thickness of the magnetic sheet 20Z was 0.1 mm (100 μm).

(Preparation of measurement system)
Referring to FIG. 5, a first measurement system for measuring noise coupling of the noise suppression sheet 10X was prepared. Referring to FIG. 6, in addition, a second measurement system for measuring noise coupling of the noise suppression sheets 10Y and 10Z was prepared. The measurement target of the first measurement system was the noise suppression sheet 10X, and the measurement target of the second measurement system was the noise suppression sheets 10Y and 10Z. Except for this point, the first measurement system and the second measurement system had the same configuration as each other. In the following description, each of the first measurement system and the second measurement system is simply referred to as a “measurement system”.

  Referring to FIGS. 5 and 6, the measurement system simulates the inside of a smartphone, and includes a noise suppression sheet (noise suppression sheets 10X, 10Y, 10Z), a metal plate 60X, and a transmission antenna 72 including a coil antenna. And a receiving antenna 74 composed of a coil antenna. The transmitting antenna 72 imitates a noise source inside the smartphone, and the receiving antenna 74 imitates a receiving antenna inside the smartphone. In each of the measurement systems, the metal plate 60X imitated a smartphone housing.

(Measurement of the noise coupling ratio of the noise suppression sheet)
An electromagnetic wave simulating noise was generated from the transmitting antenna 72. The generated electromagnetic wave passes through the inside of the noise suppression sheet and is reflected on the surface of the metal plate 60X. The reflected electromagnetic wave again passed through the inside of the noise suppression sheet and was received by the receiving antenna 74. The noise suppression sheet attenuated an electromagnetic wave passing through the inside by a magnetic loss component μ ″. The noise coupling rate of each of the noise suppression sheets was measured using a network analyzer. The evaluation results are shown in FIGS. 7 to 9. 7 to 9, the noise coupling ratio (Coupling ratio) is represented by Coupling ratio = S21-S21 ', where S21 is a noise suppression sheet as shown in FIGS. , And S21 'is a transmission coefficient when the noise suppression sheet is not arranged (in FIG. 5 and FIG. 6, the place where the noise suppression sheet is arranged is a space).

(Evaluation of electromagnetic coupling)
Referring to FIG. 7, the electromagnetic waves in the 3 to 6 GHz band slightly decrease by passing through the inside of the noise suppression sheet 10Y, and the noise coupling ratio decreases by about 0.1 dB to 0.5 dB. Referring to FIG. 8, the electromagnetic wave in the 3.5 to 6 GHz band hardly enters the inside of the noise suppression sheet 10 </ b> Z and is reflected on the surface of the noise suppression sheet Z, so that the noise coupling rate increases rather. I have. On the other hand, referring to FIG. 9, the electromagnetic wave in the 3 to 6 GHz band is greatly reduced by passing through the inside of the noise suppression sheet 10 </ b> X, and the noise coupling ratio is reduced by about 0.3 dB to 1.1 dB. As described above, the first embodiment of the present invention has a large decoupling characteristic.

  The noise suppression sheet according to the present invention can be used by being mounted inside a small electronic device. For example, by attaching the composite magnetic sheet to the inside of the device such that the main surface is exposed, electromagnetic waves generated in the internal space of the device due to the operation of various electronic components can be absorbed and attenuated. Also, by attaching or winding the main surface of the composite magnetic sheet on the transmission line, electromagnetic waves generated from the transmission line can be absorbed and attenuated.

10, 10X, 10Y, 10Z Noise suppression sheet 20, 20X Composite magnetic sheet 20Y, 20Z magnetic sheet 30 First layer 30P Main surface 32 Metal soft magnetic powder 38 Organic binder 40 Second layer 40S Surface 42 Flat metal soft magnetic powder 48 Organic binder 50 Metal layer 60X Metal plate 72 Transmitting antenna 74 Receiving antenna 80 Electromagnetic wave (electromagnetic noise)

Claims (3)

A noise suppression sheet including a composite magnetic sheet having a first layer and a second layer,
The first layer includes a metal soft magnetic powder having an average aspect ratio of less than 2, and an organic binder.
The second layer includes a flat metal soft magnetic powder having an average cross-sectional aspect ratio of 20 or more and less than 100, and an organic binder,
The thickness of the composite magnetic sheet is 25 μm or more, and 100 μm or less,
The first layer has a main surface that is an incident surface on which the electromagnetic wave enters the noise suppression sheet from outside the noise suppression sheet,
The first layer has a first dielectric loss component and a first magnetic loss component in a plane parallel to the main surface,
The second layer is located on a side opposite to the main surface of the first layer,
The second layer has a second dielectric loss component and a second magnetic loss component in a plane parallel to the main surface,
The first dielectric loss component is lower than the second dielectric loss component;
Said second magnetic loss component, rather higher than the first magnetic loss component,
The noise suppression sheet wherein the first dielectric loss component is lower than 1 and the second magnetic loss component is higher than 6 in a frequency band of 3 to 6 GHz . The noise suppression sheet according to claim 1,
The first layer contains 50% by volume or more of the metal soft magnetic powder,
The noise suppression sheet, wherein the second layer contains 40% by volume or more of the flat metal soft magnetic powder. The noise suppression sheet according to claim 1 or 2 ,
A noise suppression sheet comprising a metal layer located on the second layer.

Images