阅读说明：本技术 电磁波吸收体 (Electromagnetic wave absorber ) 是由 宇井丈裕 请井博一 于 2018-06-12 设计创作，主要内容包括：电磁波吸收体(1)具备电磁波吸收层(10)和粘合层(20)。粘合层(20)设置在电磁波吸收层(10)的至少单面。电磁波吸收体(1)能以粘合层(20)与具有高度差的表面接触的状态贴附。粘合层(20)具有从其高度差的高度减去0.1mm而得到的基准高度以上的厚度。对于电磁波吸收体(1),由ΔR＝Rt-Rr定义的反射衰减量ΔR为15dB以上。Rt为对参照试验体的76GHz的电磁波的反射量。Rr为对贴附电磁波吸收体(1)而得到的试验体的76GHz的电磁波的反射量。(The electromagnetic wave absorber (1) is provided with an electromagnetic wave absorbing layer (10) and an adhesive layer (20). The adhesive layer (20) is provided on at least one surface of the electromagnetic wave absorption layer (10). The electromagnetic wave absorber (1) can be attached in a state where the adhesive layer (20) is in contact with a surface having a level difference. The adhesive layer (20) has a thickness of at least a reference height obtained by subtracting 0.1mm from the height of the height difference. The electromagnetic wave absorber (1) has a reflection attenuation amount [ Delta ] R defined by [ Delta ] R [ Rt-Rr ] of 15dB or more. Rt represents the reflection of an electromagnetic wave of 76GHz against the reference specimen. Rr is the reflection amount of an electromagnetic wave of 76GHz against a test piece obtained by attaching the electromagnetic wave absorber (1).)

1, kinds of electromagnetic wave absorbers, comprising:

an electromagnetic wave absorbing layer, and

an adhesive layer provided on at least one surface of the electromagnetic wave absorbing layer,

the electromagnetic wave absorber can be attached in a state where the adhesive layer is in contact with a surface having a height difference,

the adhesive layer has a thickness of 0.1mm or more subtracted from the height of the height difference,

the electromagnetic wave absorber has a reflection attenuation amount DeltaR defined by the following formula of 15dB or more,

ΔR＝Rt-Rr

rt is a reflection amount of an electromagnetic wave of 76GHz measured according to Japanese Industrial Standard (JIS) R1679: 2007 on a reference test specimen obtained by attaching a sample to the surface by bringing the adhesive layer of the sample consisting only of a conductive layer containing a metal foil and an adhesive layer of the same kind as the adhesive layer into contact with the th surface having a height difference of 0.1mm or less in height from a reference thickness obtained by adding 0.1mm to the thickness of the adhesive layer,

rr is a reflection amount of an electromagnetic wave of 76GHz measured in accordance with JIS R1679: 2007 on a test body obtained by bringing the adhesive layer of the electromagnetic wave absorber into contact with a second surface having the same surface shape as the th surface and attaching the electromagnetic wave absorber to the second surface.

2. The electromagnetic wave absorber of claim 1, wherein the adhesive layer has a thickness of 0.5mm to 15 mm.

3. The electromagnetic wave absorber as claimed in claim 1 or 2, wherein the adhesive layer has a young's modulus of 2000MPa or less at 23 ℃.

4. The electromagnetic wave absorber of any of claims 1-3, wherein the adhesive layer has a Young's modulus at-30 ℃ of 2000MPa or less.

5. The electromagnetic wave absorber of any of of claims 1-4, wherein the adhesive layer includes a support layer.

6. The electromagnetic wave absorber of claim 5 wherein the support layer is formed of foam.

7. The electromagnetic wave absorber as claimed in claim 5 or 6, wherein the support layer contains 1 selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, cycloolefin polymer, polyurethane, acrylic urethane resin, polyolefin, polyethylene, polypropylene, synthetic rubber, polyvinyl chloride, and polyvinylidene chloride as a main component.

Technical Field

The present invention relates to an electromagnetic wave absorber.

Background

In recent years, electromagnetic waves in the millimeter wave and quasi-millimeter wave regions having a wavelength of about 1 to 10mm and a frequency of 30 to 300GHz have been used as information communication media. The use of such electromagnetic waves in collision avoidance systems is being investigated. The collision avoidance system is, for example, a system that detects an obstacle in a vehicle and automatically brakes the vehicle, or that measures the speed and the inter-vehicle distance of a neighboring vehicle and adjusts the speed and the inter-vehicle distance of the vehicle.

For example, patent document 1 describes a configuration including a millimeter wave radar, -pair shield fixing members (shrouds) and a mounting plate for mounting the millimeter wave radar, the mounting plate being disposed at a front portion of a vehicle body of an automobile, the left and right end portions of the mounting plate being fixed to -pair shield fixing members by bolts and nuts, the mounting plate having 3 mounting portions, and 3 mounting portions each having a position-adjusting bolt, and the 3 fixing members of a housing of the millimeter wave radar being bolted together by these position-adjusting bolts so as to be adjustable in position in the front-rear direction.

Patent document 2 describes an attachment structure of a radar unit including an upper shield (cowl upper), a lower shield (cowl lower), and a shield fixing member for connecting the upper shield and the lower shield. In the mounting structure, the radar unit is mounted to the shroud fixing member. The upper end portion of the hood fixing member is connected to the upper hood so as to be separated from the upper hood when a predetermined or higher load acts from the front. Therefore, when a load of a predetermined level or more acts from the front in a light collision of the vehicle, the upper end portion of the shroud holder is detached from the upper shroud, and the radar unit attached to the shroud holder moves rearward. This reduces the impact acting on the radar unit, and prevents the radar unit from being damaged.

For proper operation of the collision avoidance system, it is considered important to not receive unwanted electromagnetic waves as much as possible in order to prevent misidentification. Therefore, it is considered to use an electromagnetic wave absorber that absorbs unnecessary electromagnetic waves in a collision avoidance system.

For example, an electromagnetic wave absorber (sometimes referred to as a "λ/4 type electromagnetic wave absorber") provided with an electromagnetic wave reflecting layer, a dielectric layer having a thickness of λ/4(λ is the wavelength of an electromagnetic wave to be absorbed), and a resistance thin film layer is relatively inexpensive and easy to design, and therefore can be produced at low cost, and for example, patent document 3 proposes an electromagnetic wave absorber that exhibits excellent characteristics that functions over a region at an incident angle as a λ/4 type electromagnetic wave absorber, and patent document 4 describes an electromagnetic wave absorbing material having a magnetic material layer.

Disclosure of Invention

Problems to be solved by the invention

Patent documents 1 and 2 do not describe a member having a level difference in the vicinity of the millimeter wave radar to which the electromagnetic wave absorber is attached. Patent document 2 does not describe the separation of the electromagnetic wave absorber when the radar unit receives an impact. In patent documents 3 and 4, the shape of an article to which an electromagnetic wave absorber can be attached is not specifically studied.

Therefore, the present invention provides an electromagnetic wave absorber that can easily exhibit good electromagnetic wave absorption performance when the electromagnetic wave absorber is mounted on a member having a level difference in the vicinity of a millimeter wave radar.

Means for solving the problems

The present invention provides kinds of electromagnetic wave absorbers, which are provided with:

an electromagnetic wave absorbing layer, and

an adhesive layer provided on at least one surface of the electromagnetic wave absorbing layer,

the electromagnetic wave absorber can be attached in a state where the adhesive layer is in contact with a surface having a level difference,

the adhesive layer has a thickness of a reference height or more obtained by subtracting 0.1mm from the height of the height difference,

the electromagnetic wave absorber has a reflection attenuation amount Δ R defined by the following equation of 15dB or more.

ΔR＝Rt-Rr

Rt is a reflection amount of an electromagnetic wave of 76GHz measured according to Japanese Industrial Standard (JIS) R1679: 2007 on a reference test specimen obtained by attaching a sample to the surface by bringing the adhesive layer of the sample consisting only of a conductive layer containing a metal foil and an adhesive layer of the same kind as the adhesive layer into contact with the th surface having a height difference of 0.1mm or less in height from a reference thickness obtained by adding 0.1mm to the thickness of the adhesive layer,

rr is a reflection amount of an electromagnetic wave of 76GHz measured in accordance with JIS R1679: 2007 on a test body obtained by bringing the adhesive layer of the electromagnetic wave absorber into contact with a second surface having the same surface shape as the th surface and attaching the electromagnetic wave absorber to the second surface.

ADVANTAGEOUS EFFECTS OF INVENTION

The electromagnetic wave absorber described above can easily exhibit good electromagnetic wave absorption performance even when it is mounted on a member having a level difference in the vicinity of the millimeter wave radar. Further, the electromagnetic wave absorber is less likely to fall off from the component even when an impact is given to the millimeter wave radar in some cases.

Drawings

Fig. 1 is a cross-sectional view of examples showing an electromagnetic wave absorber of the present invention.

Fig. 2 is a sectional view showing a state in which the electromagnetic wave absorber shown in fig. 1 is mounted in a member having a height difference.

Fig. 3 is a sectional view showing a state in which the electromagnetic wave absorber of the comparative example is mounted in a member having a level difference.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description is illustrative of the present invention, and the present invention is not limited to the following embodiments.

In the millimeter wave radar of the collision avoidance system, if parts of the emitted millimeter waves are reflected and received by a component disposed in the vicinity of the millimeter wave radar, there is a possibility that erroneous recognition occurs in the collision avoidance system.

However, the surface of a member disposed in the vicinity of the millimeter wave radar may have a level difference due to a fastener such as a bolt or a nut, as in the case of the mounting plate described in patent document 1, and the surface of a member disposed in the vicinity of the millimeter wave radar may have a level difference due to the shape of the member itself, and in particular, many automobile members have a complicated shape and thus easily have a large level difference.

As shown in fig. 1, the electromagnetic wave absorber 1 includes an electromagnetic wave absorption layer 10 and an adhesive layer 20. The adhesive layer 20 is provided on at least one surface of the electromagnetic wave absorption layer 10. As shown in fig. 2, the electromagnetic wave absorber 1 can be attached in a state where the adhesive layer 20 is in contact with the surface having a level difference. The adhesive layer 20 has a thickness equal to or greater than a reference height obtained by subtracting 0.1mm from the height of the height difference of the surface. Further, the electromagnetic wave absorber 1 has a reflection attenuation Δ R defined by the following formula (1) of 15dB or more.

Δ R ═ Rt-Rr formula (1)

Rt is a reflection amount of an electromagnetic wave of 76GHz measured according to Japanese Industrial Standard (JIS) R1679: 2007 on a reference test specimen obtained by attaching a sample to the surface by bringing an adhesive layer of the sample consisting of only an electrically conductive layer containing a metal foil and an adhesive layer of the same kind as the adhesive layer 20 into contact with the th surface having a height difference of 0.1mm or less in the thickness of the adhesive layer 20 and having a height difference of a reference thickness or less,

rr is the reflection amount of an electromagnetic wave of 76GHz measured in accordance with JIS R1679: 2007 on a test body obtained by bringing the adhesive layer 20 of the electromagnetic wave absorber 1 into contact with the second surface having the same surface shape as the th surface and attaching the electromagnetic wave absorber 1 to the second surface.

In the present specification, the reflection amount Rt and the reflection amount Rr are reflection amounts when measuring an electromagnetic wave of 76GHz incident perpendicularly to a reference specimen or specimen.

Since the reflection attenuation Δ R of the electromagnetic wave absorber 1 is 15dB or more, the electromagnetic wave absorber 1 easily exhibits good electromagnetic wave absorption performance even when the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with a surface having a level difference.

The adhesive layer 20 of the electromagnetic wave absorber 1 is not particularly limited as long as it has a thickness of not less than a reference height, and has a thickness of, for example, 0.5mm to 15 mm. In this case, for example, as shown in fig. 2, when the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with the surface having the level difference S, the adhesive layer 20 is likely to be deformed in order to eliminate the level difference S appearing on the surface. Therefore, even in the case where the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with the surface having the level difference S, the electromagnetic wave absorption layer 10 is less susceptible to the level difference S appearing on the surface, and the electromagnetic wave absorption layer 10 is less likely to be deformed. As a result, even if the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with the surface having the level difference S, the electromagnetic wave absorber 1 easily exhibits good electromagnetic wave absorption performance. Further, even when a member including a surface having a level difference S is deformed by a collision between a vehicle and a surrounding object, the stress generated by the deformation of the member can be relaxed by the adhesive layer 20, and therefore, the stress applied to the interface between the adhesive layer 20 and the surface having the level difference S is reduced, and the electromagnetic wave absorber 1 is less likely to be peeled off from the member.

As shown in fig. 3, the electromagnetic wave absorber 100 of the comparative example includes an electromagnetic wave absorption layer 10 and an adhesive layer 120. The adhesive layer 120 is provided on one surface of the electromagnetic wave absorption layer 10. With the electromagnetic wave absorber 100, the adhesive layer 120 has a thickness smaller than a reference height obtained by subtracting 0.1mm from the height of the height difference S. As shown in fig. 3, when the electromagnetic wave absorber 100 is attached by bringing the adhesive layer 120 into contact with the surface having the height difference S, the adhesive layer 120 is less likely to eliminate the height difference S appearing on the surface, and the electromagnetic wave absorption layer 10 is likely to be deformed by the influence of the height difference S appearing on the surface. As a result, it is difficult for the electromagnetic wave absorber 100 to exhibit good electromagnetic wave absorption performance when the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with the surface having the level difference S.

The adhesive layer 20 has a young 'S modulus (tensile elastic modulus) of 2000MPa or less at 23 ℃, for example, and thus, in the case where the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with a surface having a height difference S, the adhesive layer 20 is likely to deform along the shape of the height difference, and thus, even if the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with a surface having a height difference S, the electromagnetic wave absorber 1 is likely to exhibit good electromagnetic wave absorption performance, the young' S modulus of the adhesive layer 20 can be measured according to JIS K7161-1, for example, the adhesive layer 20 has an elastic modulus of 2000MPa or less at 23 ℃, and more preferably an elastic modulus of 100MPa or less, further, when the young 'S modulus of the adhesive layer 20 at 23 ℃ is in the above range, the stress generated along with the deformation of the component caused by the impact can be relaxed by the adhesive layer 20, the electromagnetic wave absorber 1 is less likely to peel off from an adherend such as a component, and, for example, when the electromagnetic wave absorber 1 is attached to an automobile component, the automobile can be used in a temperature range of including high temperatures and low temperatures, and therefore, the electromagnetic wave absorber 1 also preferably has a young' S modulus of 2000MPa or.

As shown in fig. 1, the adhesive layer 20 includes, for example, a support layer 22. In this case, the thickness of the adhesive layer 20 can be easily adjusted to a desired range by the support layer 22. Therefore, when the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with the surface having the level difference, the adhesive layer 20 is easily deformed to eliminate the level difference appearing on the surface.

When the adhesive layer 20 includes the support layer 22, for example, as shown in fig. 1, the adhesive layer further includes th adhesive layer 21a and a second adhesive layer 21b, th adhesive layer 21a is disposed between the electromagnetic wave absorption layer 10 and the support layer 22 and is in contact with the electromagnetic wave absorption layer 10 and the support layer 22, the support layer 22 is disposed between the th adhesive layer 21a and the second adhesive layer 21b, and the support layer 22 is in contact with the th adhesive layer 21a and the second adhesive layer 21 b.

The support layer 22 is formed of foam, for example. In this case, when the electromagnetic wave absorber 1 is attached by bringing the adhesive layer 20 into contact with the surface having the level difference, the adhesive layer 20 is likely to be deformed in order to eliminate the level difference appearing on the surface. Support layer 22 is typically a flexible foam.

The support layer 22 contains, for example, 1 selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, an acrylic resin, polycarbonate, a cycloolefin polymer, polyurethane, an acrylic urethane resin, polyolefin, polyethylene, polypropylene, a synthetic rubber, polyvinyl chloride, and polyvinylidene chloride as a main component. In the present specification, the term "main component" refers to a component contained in the largest amount on a mass basis.

The support layer 22 may be formed of an elastomer.

The adhesive layer 20 may not include the support layer 22, and may be, for example, a layer of sheet formed of an adhesive.

The adhesive used in the adhesive layer 20 is not particularly limited, and is, for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, or a silicone adhesive.

As shown in fig. 2, the electromagnetic wave absorber 1 is attached to the member 30 by bringing the adhesive layer 20 into contact with the surface of the member 30 having the height difference S, thereby making it possible to produce the electromagnetic wave absorbing structure 50. the adhesive layer 20 has a thickness of t-0.1mm or more, for example, when the height difference S is t (for example, 0.1mm to 5 mm). the adhesive layer 20 preferably has a thickness of t +0.5mm or more, more preferably t +1.0mm or more, still more preferably a thickness of t +1.5mm or more, and particularly preferably t +2.0mm or more, whereby the electromagnetic wave absorber 1 can be easily attached to the member 30, and the electromagnetic wave absorber 1 can easily exhibit good electromagnetic wave absorbing characteristics despite the height difference S appearing on the surface of the member 30. the adhesive layer 20 preferably has a thickness of 0.5mm to 10mm, more preferably 0.7 to 5mm, still more preferably a thickness of 1.0 to 3.0mm, whereby the electromagnetic wave absorber 1 can be easily attached to the surface of the member 30, and the electromagnetic wave absorber 1 can easily exhibit good electromagnetic wave absorbing characteristics despite the height difference S appearing on the surface of the member 30.

The electromagnetic wave absorber 1 is, for example, a λ/4 type electromagnetic wave absorber, a dielectric loss type electromagnetic wave absorber, or a magnetic loss type electromagnetic wave absorber. The dielectric loss type electromagnetic wave absorber absorbs electromagnetic waves by utilizing dielectric loss caused by polarization of molecules. The magnetic loss type electromagnetic wave absorber absorbs an electromagnetic wave by magnetic loss of a magnetic material.

The electromagnetic wave absorption layer 10 typically has a conductive layer (electromagnetic wave reflection layer). The conductive layer contains, for example, a metal, desirably a metal foil or a metal vapor-deposited film. In this specification, the metal includes an alloy. The metal contained in the conductive layer is, for example, copper, nickel, zinc, or an alloy thereof, aluminum, gold, silver, or stainless steel.

The conductive layer may include a support that is a polymer sheet. In this case, the conductive layer can be easily formed by forming a metal material on the support. Examples of the material of the polymer sheet that can be used as the support of the conductive layer include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), an acrylic resin, Polycarbonate (PC), polyolefin, Polyethylene (PE), polypropylene (PP), cycloolefin polymer (COP), polyurethane, urethane acrylic resin, axially-stretched polypropylene (CPP), and vinylidene chloride resin. The conductive layer may be a laminate in which a resin film such as a polyester resin film is laminated on one surface or both surfaces of a metal foil, for example.

Typically, the conductive layer of the electromagnetic wave absorption layer 10 is in contact with the adhesive layer 20.

When the electromagnetic wave absorber 1 is a λ/4 type electromagnetic wave absorber, the electromagnetic wave absorption layer 10 further includes a dielectric layer having a thickness of λ/4(λ is the wavelength of the electromagnetic wave to be absorbed), for example, and a resistive layer, and the dielectric layer is disposed between the resistive layer and the conductive layer. The λ/4 type electromagnetic wave absorber is represented by the following formula (2) and is defined by the thickness (t) of the dielectric layer and the relative permittivity (. epsilon.) of the dielectric layer_r) To determine the wavelength (lambda) of the electromagnetic wave to be absorbed_O). That is, the electromagnetic wave of the wavelength to be absorbed can be determined by appropriately adjusting the material and thickness of the dielectric layer. In the formula (2), sqrt (epsilon)_r) Refers to the relative dielectric constant (. epsilon.)_r) The square root of (a).

λ_O＝4t×sqrt(ε_r) Formula (2)

When the electromagnetic wave absorber 1 is a lambda/4 type electromagnetic wave absorber, the dielectric layer is formed of, for example, a polymer sheet having a relative dielectric constant of 1 to 20. The dielectric layer is preferably formed of a polymer sheet having a relative dielectric constant of 2 to 20. This makes it easy for the electromagnetic wave absorber 1 to exhibit desired electromagnetic wave absorption characteristics. The relative permittivity of the dielectric layer can be measured by, for example, a free space method.

Examples of the material of the polymer sheet of the dielectric layer include synthetic resins such as ethylene-vinyl acetate copolymer (EVA), polyvinyl chloride, polyurethane, acrylic resin, acrylic urethane resin, polyolefin, polypropylene, polyethylene, silicone resin, polyethylene terephthalate, polyester, polystyrene, polyimide, polycarbonate, polyamide, polysulfone, polyethersulfone, and epoxy resin, and synthetic rubbers such as polyisoprene rubber, polystyrene-butadiene rubber, polybutadiene rubber, chloroprene rubber, acrylonitrile butadiene rubber, butyl rubber, acrylic rubber, ethylene propylene rubber, and silicone rubber. These may be used alone or in combination of 2 or more kinds as the material of the polymer sheet of the dielectric layer.

When the dielectric layer is a multilayer body of a plurality of layers, the relative permittivity of each dielectric layer can be calculated by measuring the relative permittivity of each layer, multiplying the ratio of the thickness of each layer to the thickness of the entire dielectric layer by the relative permittivity of each layer, and adding the relative permittivities.

The resistive layer has a sheet resistance of, for example, 200 to 600 Ω/□, preferably 300 to 500 Ω/□. In this case, the electromagnetic wave absorber 1 becomes easy to selectively absorb electromagnetic waves of wavelengths commonly used in the millimeter wave radar or the quasi-millimeter wave radar. For example, the electromagnetic wave absorber 1a can effectively attenuate an electromagnetic wave of a frequency of 20 to 90GHz, particularly 60 to 90GHz, used in the millimeter wave radar.

The resistance layer includes, for example, a layer (hereinafter referred to as "functional layer") formed of any one of a metal oxide, a conductive polymer, a carbon nanotube, a metal nanowire, and a metal mesh, the metal oxide containing at least selected from the group consisting of indium, tin, and zinc as a main componentThe functional layer of the resist layer is desirably formed of Indium Tin Oxide (ITO). In this case, the material forming the functional layer of the resistive layer preferably contains 20 to 40 wt% of SnO₂More preferably, the ITO of (1) further contains 25 to 35% by weight of SnO₂ITO of (2). For the content of SnO in such a range₂The ITO of (2) is extremely stable in amorphous structure, and can suppress variation in sheet resistance of the resistive layer even in a high-temperature and high-humidity environment. The sheet resistance of the resistive layer is a value obtained by measuring a surface defined by, for example, the functional layer. The functional layer of the resistive layer has a thickness of, for example, 10 to 100nm, preferably 25 to 50 nm. Thus, the electromagnetic wave absorber 1 is easily stabilized in sheet resistance even when subjected to changes over time or environmental changes.

The resistive layer may in turn comprise a support, for example for supporting the functional layer. In this case, the resistive layer 30 can be produced by forming a functional layer on a support by a film formation method such as sputtering or coating (for example, bar coating). In this case, the support also functions as an auxiliary material that can adjust the thickness of the functional layer with high accuracy. The material of the support of the resistive layer is exemplified as the material of the support of the conductive layer. The material of the support of the resistive layer may be the same as or different from the material of the support of the conductive layer. Among them, PET is preferable as the material of the support of the resistive layer from the viewpoint of good heat resistance and dimensional stability, and a balance of cost. The support may be omitted in the resistive layer, as desired.

When the resistive layer includes the support, the functional layer may be disposed at the th layer than the support, or the support may be disposed at the th layer than the functional layer.

When the electromagnetic wave absorber 1a is a λ/4 type electromagnetic wave absorber and the dielectric layer is disposed outside the resistive layer, only a non-porous layer having a relative permittivity of 2 or more is disposed on the dielectric layer. When the electromagnetic wave absorber has a porous body on the surface thereof, the electromagnetic wave absorber may be degraded in electromagnetic wave absorption due to moisture absorption if left in a high-humidity environment for a long period of time.

When the electromagnetic wave absorber 1 is a dielectric loss electromagnetic wave absorber, the electromagnetic wave absorbing layer 10 includes a dielectric layer in addition to the conductive layer, and does not include a resistance layer. The conductive layer is disposed between the dielectric layer and the adhesion layer 20. In the dielectric loss type electromagnetic wave absorber, the polarization of molecules cannot follow the change of an electric field, and energy of an electromagnetic wave is lost as heat. The dielectric layer in the dielectric loss type electromagnetic wave absorber has, for example, the following configuration: the dielectric loss agent such as carbon particles is dispersed in the synthetic resin or the synthetic rubber mentioned above as a material of the polymer sheet that functions as a dielectric layer in the λ/4 type electromagnetic wave absorber.

When the electromagnetic wave absorber 1 is a magnetic loss type electromagnetic wave absorber, the electromagnetic wave absorbing layer 10 includes a magnetic layer in addition to the conductive layer, and does not include a resistance layer. The conductive layer is disposed between the magnetic layer and the adhesive layer 20. In the magnetic loss type electromagnetic wave absorber, the magnetic moment cannot follow the change of the magnetic field, and the energy of the electromagnetic wave is lost as heat. The magnetic layer in the magnetic loss electromagnetic wave absorber has, for example, the following configuration: the synthetic resin or the synthetic rubber is dispersed with particles of a magnetic material such as ferrite, iron, or nickel, as a material of the polymer sheet that functions as a dielectric layer in the λ/4 type electromagnetic wave absorber.