TW202344183A - Electromagnetic wave absorber and sensing system - Google Patents

Abstract

This electromagnetic wave absorber is an interference-type electromagnetic wave absorber that comprises a resistance layer, a dielectric layer, and a reflective layer in this order, and that absorbs a specific frequency band of electromagnetic waves. The electromagnetic wave absorber exhibits a maximum absorption amount A0 of less than or equal to 15 dB in the frequency band, and satisfies at least one of expressions (1) and (2). (1): A0-A1 ≤ 8(dB) (2): A0-A2 ≤ 8(dB) (In expression (1) or (2), if the peak frequency when the amount of absorption is at a maximum is f0(GHz), A1 represents the amount of absorption (dB) at f0-7(GHz), and A2 represents the amount of absorption (dB) at f0+7(GHz).).

Description

Electromagnetic wave absorber and sensing system

This disclosure relates to electromagnetic wave absorbers and sensing systems.

In recent years, information transmission technology through wireless communication such as wireless LAN (Local Area Network) has been used in offices, factories, warehouses, etc. Radio wave obstruction, interference and other radio waves that occur in an office such as the one described above due to radio waves from the outside, interaction between a plurality of communication devices, or interaction between communication devices and parts of the building such as walls and floors. obstacles. In order to prevent the above-mentioned radio wave interference, electromagnetic wave absorbers are installed on walls, ceilings, or floors in offices and the like.

Electromagnetic wave absorbers are roughly divided into interference type and penetration type. Interference-type electromagnetic wave absorption systems reduce electromagnetic waves by causing interference between incident electromagnetic waves and reflected electromagnetic waves to cancel them. Penetrating electromagnetic wave absorption systems utilize magnetic bodies and dielectrics with electromagnetic wave absorption capabilities to reduce electromagnetic waves by allowing electromagnetic waves to pass through layers containing these. Among them, interference-type electromagnetic wave absorbers are often used because there is no need to design a material for a dielectric that absorbs electromagnetic waves of a specific frequency. The reflection of electromagnetic waves of any frequency can be attenuated by adjusting the thickness corresponding to the dielectric coefficient. For example, the following Patent Document 1 discloses an interference type electromagnetic wave absorber including a resistive layer, a dielectric layer, and a reflective layer in this order. This interference type electromagnetic wave absorption system ensures high absorption at specific frequencies by optimizing the surface resistance value of the material used in the resistive layer. [Prior technical literature] [Patent Document]

Patent Document 1: Japanese Patent Application Publication No. 10-13082

[Problem to be solved by the invention]

In addition, in recent years, due to the worsening of the aging population and low birthrate, which are social issues, and the spread of the new coronavirus (coronavirus) pneumonia epidemic, safe care systems for elderly singles using radar technology and non-contact care systems have been developed. The demand for non-face-to-face sensing technology is rapidly increasing. Among them, sensing technologies such as fall detection, presence/absence monitoring, and human breathing and heartbeat detection using radar in the millimeter wave band are currently attracting particular attention. It is assumed that the sensing system used for the above-mentioned purposes divides a specific frequency band (for example, 60 GHz to 66 GHz) transmitted from the radar into a plurality of frequency bands, and uses the plurality of frequency bands separately to sense position information and the like.

However, the electromagnetic wave absorption system described in the above-mentioned Patent Document 1 has the following problems. That is, the electromagnetic wave absorption system described in the above-mentioned Patent Document 1 ensures a high absorption amount at a specific frequency by optimizing the surface resistance value of the material used for the resistance layer. However, on the other hand, the absorption decreases as the specific frequency deviates. The quantity also decreased rapidly. Therefore, when electromagnetic waves of a plurality of frequency bands constituted by the radar transmission band are incident on an electromagnetic wave absorber, electromagnetic waves of a specific frequency are largely absorbed by the electromagnetic wave absorber installed on walls or the like, while electromagnetic waves of other frequencies are not fully absorbed. As a result, for example, when the intensity of electromagnetic waves transmitted from a radar in a plurality of frequency bands is constant, among the electromagnetic waves received by the radar, even if the intensity of electromagnetic waves other than a specific frequency is high, the intensity of electromagnetic waves of a specific frequency is quite small. Therefore, in the sensing system, for electromagnetic waves of a specific frequency, the signal-to-noise (S/N) ratio is quite small, and since it is not easy to identify the signal as a signal, it is difficult to perform appropriate sensing. Here, you can consider introducing a program into the sensing system to correct the intensity of the electromagnetic wave at a specific frequency. However, this type of program requires complex programming, so the development of the program will take a huge amount of time and cost. .

The present disclosure is made in view of the above-mentioned issues, and aims to provide an electromagnetic wave absorber and a sensing system that can appropriately perform sensing without introducing a program that requires complex programming into the sensing system. [Means used to solve problems]

The inventors of the present case conducted research on the causes of the above-mentioned problems. As a result, the inventors of the present application speculated that the cause of the above-mentioned problem is that electromagnetic waves of a specific frequency are absorbed in a large amount in a specific frequency band of a radar transmitted from a sensing system, and electromagnetic waves of frequencies deviating from the specific frequency are absorbed in a small amount. The difference between the maximum absorption amount and the minimum absorption amount of electromagnetic waves in this specific frequency band becomes large. In view of this, the inventors of the present invention have been conducting research to reduce the difference between the maximum absorption amount and the minimum absorption amount of electromagnetic waves in a specific frequency band. As a result, they have found that the above problems can be solved through the following disclosure.

That is to say, the present disclosure is an electromagnetic wave absorber, which is an interference type electromagnetic wave absorber that has a resistive layer, a dielectric layer and a reflective layer in sequence, and absorbs electromagnetic waves in a specific frequency band; it exhibits a maximum absorption amount A ₀ of less than 15dB in the aforementioned frequency band. And satisfy at least one of the following formula (1) and the following formula (2). A ₀ -A ₁ ≦8(dB) … (1) A ₀ -A ₂ ≦8(dB) … (2) (In the above equation (1) or the above equation (2), when the absorption amount is assumed to be the maximum When the peak frequency is f ₀ (GHz), A ₁ represents the absorption amount (dB) at f ₀ -7 (GHz), and A ₂ represents the absorption amount (dB) at f ₀ +7 (GHz). )

According to this electromagnetic wave absorber, in a sensing system including an electromagnetic wave transmitting/receiving device that transmits and receives electromagnetic waves in a frequency band absorbed by the electromagnetic wave absorber and can process the received electromagnetic waves, when the electromagnetic wave transmitting/receiving device transmits When an electromagnetic wave of a specific frequency band is injected from the resistive layer side, the electromagnetic wave passes through the resistive layer and the dielectric layer and is reflected on the reflective layer. At this time, in the dielectric layer, the incident electromagnetic wave and the reflected reflected wave cancel each other, thereby absorbing the electromagnetic wave. Therefore, the absorption amount of the electromagnetic wave of a specific frequency becomes maximum. However, at this time, the difference between the maximum absorption amount and the minimum absorption amount can be reduced in the above frequency band by the electromagnetic wave absorber exhibiting a maximum absorption amount of 15 dB or less and satisfying at least one of the above equations (1) and (2). Therefore, when the intensity of the electromagnetic wave in the frequency band transmitted from the electromagnetic wave transmitting/receiving device is constant, among the electromagnetic waves received by the electromagnetic wave transmitting/receiving device, the intensity of the electromagnetic wave other than the specific frequency can be maintained at a high intensity, so that the intensity of the electromagnetic wave of the specific frequency can be maintained The decline is fully suppressed. Therefore, in the sensing system, the decrease in the signal-to-noise (S/N) ratio for electromagnetic waves of a specific frequency is suppressed, and since the signal becomes easily identifiable, there is no need to introduce a program that requires complex programming into the sensing system. Sensing appropriately.

Preferably, in the electromagnetic wave absorber of the present disclosure, the absolute value of the reflection coefficient Γ calculated by the following equation (3) to the following equation (5) is 3.12 to 5.62 at the peak frequency f ₀ (GHz). [Formula 1] (In the above equations (3) to (5), Γ represents the reflection coefficient, and Z _L represents the input impedance (impedance) (Ω/□) viewed from the surface of the resistance layer opposite to the reflection layer. Z ₀ represents the vacuum impedance (Ω/□), Z´ _L represents the input impedance (Ω/□) viewed from the reflective layer side of the resistive layer toward the reflective layer, and R represents the surface resistance value of the resistive layer (Ω /□), ε _r represents the complex relative dielectric coefficient of the aforementioned dielectric layer, d represents the thickness of the aforementioned dielectric layer (μm), and λ represents the wavelength of the incident electromagnetic wave (μm).) In addition, and The system indicates that Γ, Z _L , Z´ _L and ε _r are complex numbers.

At this time, since the absolute value of the reflection coefficient Γ is 5.62 or less at the peak frequency f ₀ (GHz), the electromagnetic wave of the specific frequency in the specific frequency band can be more fully absorbed, so that the radio wave interference can be further suppressed. In addition, when the absolute value of the reflection coefficient Γ is 3.12 or more at the peak frequency f ₀ (GHz), the difference between the maximum absorption amount and the minimum absorption amount in the above-mentioned frequency band can be further reduced. Therefore, when the intensity of the electromagnetic wave in the frequency band transmitted from the electromagnetic wave transmitting/receiving device is constant, the intensity of electromagnetic waves other than the specific frequency among the electromagnetic waves received by the electromagnetic wave transmitting/receiving device is maintained at a high intensity, and the specific frequency can be further suppressed. The intensity of electromagnetic waves decreases. Therefore, in the sensing system, for electromagnetic waves of a specific frequency, the decrease in the signal-to-noise (S/N) ratio is further suppressed. Since the signal becomes easier to identify, there is no need to introduce programs that require complex programming into the sensing system. That is, sensing can be performed more appropriately.

Preferably, the electromagnetic wave absorption system satisfies at least one of the following formula (6) and the following formula (7). A ₀ -B ₁ ≦0.5(dB)…(6) A ₀ -B ₂ ≦0.5(dB)…(7) (In the above equation (6) or the above equation (7), B ₁ represents f ₀ - The absorption amount (dB) at 2 (GHz), B ₂ represents the absorption amount (dB) at f ₀ +2 (GHz).)

At this time, in the sensing system, for electromagnetic waves of specific frequencies, the decrease in the signal-to-noise (S/N) ratio is further suppressed, and since the signal becomes easier to identify, there is no need to introduce complex programming in the sensing system. The program can then go one step further and perform sensing appropriately. Preferably, the electromagnetic wave absorber satisfies both the above-mentioned equation (6) and the above-mentioned equation (7). At this time, the electromagnetic wave absorber can reduce the difference between the maximum absorption amount and the minimum absorption amount of electromagnetic waves in a specific frequency band (hereinafter, also referred to as the "absorption amount difference") at the frequency used by the sensing system.

Preferably, in the electromagnetic wave absorber, the real part of the complex relative permittivity of the dielectric layer is 10 or more.

In this case, the dielectric coefficient of the dielectric layer can be increased, and the thickness of the dielectric layer can be reduced, so that the electromagnetic wave absorber can be made even thinner. The above-mentioned electromagnetic wave absorber may also exhibit a maximum absorption amount A ₀ of 3dB or more in the aforementioned frequency band. Preferably, the electromagnetic wave absorber satisfies both the above-mentioned formula (1) and the above-mentioned formula (2). At this time, the electromagnetic wave absorber can easily perform sensing with good accuracy.

In addition, the present disclosure is a sensing system, which is provided with: the above-mentioned electromagnetic wave absorber; and an electromagnetic wave transmitting/receiving device, which transmits/receives the electromagnetic wave in the aforementioned frequency band absorbed by the aforementioned electromagnetic wave absorber, and can detect the received electromagnetic wave. for processing.

According to this sensing system, when an electromagnetic wave of a specific frequency band transmitted from the electromagnetic wave transmitting/receiving device is incident from the resistive layer side, the electromagnetic wave passes through the resistive layer and the dielectric layer and is reflected on the reflective layer. At this time, in the dielectric layer, the incident electromagnetic wave and the reflected reflected wave are destructive and the electromagnetic wave is absorbed. Therefore, the absorption amount of the electromagnetic wave of a specific frequency becomes maximum. However, in this case, by having the maximum absorption amount be 15 dB or less and satisfying at least one of the above equations (1) and (2), the difference between the maximum absorption amount and the minimum absorption amount can be reduced in the above frequency band. Therefore, when the intensity of the electromagnetic wave in the frequency band transmitted from the electromagnetic wave transmitting/receiving apparatus is constant, among the electromagnetic waves received by the electromagnetic wave transmitting/receiving apparatus, the intensity of the electromagnetic wave other than the specific frequency is maintained at a high intensity, and the electromagnetic wave of the specific frequency is maintained at a high intensity. The intensity drop can be fully suppressed. Therefore, in the sensing system, the decrease in the signal-to-noise (S/N) ratio for electromagnetic waves of a specific frequency is suppressed, and since the signal becomes easily identifiable, appropriate sensing can be performed without introducing a program that requires complex programming. Test. In the above sensing system, the electromagnetic wave transmitting/receiving device may also be a radar device. Preferably, in the above sensing system, the aforementioned radar device is called a frequency modulated continuous wave radar device. At this time, a high signal-to-noise (S/N) ratio can be achieved even without high transmission power from the radar device. [Effects of the invention]

According to the present disclosure, it is possible to provide an electromagnetic wave absorber and a sensing system that can properly perform sensing without introducing a program that requires complex programming into the sensing system.

[Form used to implement the invention]

Hereinafter, embodiments of the present disclosure will be described in detail.

＜Electromagnetic wave absorber＞ First, an embodiment of the electromagnetic wave absorber of the present disclosure will be described with reference to FIG. 1 . FIG. 1 is a cross-sectional view showing an embodiment of the electromagnetic wave absorber of the present disclosure.

As shown in FIG. 1 , the electromagnetic wave absorber 100 is an interference type electromagnetic wave absorber that absorbs electromagnetic waves in a specific frequency band, and includes a resistive layer 10 , a dielectric layer 20 and a reflective layer 30 in this order. In addition, the resistive layer 10 and the dielectric layer 20 may be directly connected or connected through an adhesive layer. Similarly, the dielectric layer 20 and the reflective layer 30 can be directly connected or connected through an adhesive layer.

The electromagnetic wave absorber 100 exhibits a maximum absorption amount A ₀ of 15 dB or less in the above-mentioned frequency band and satisfies at least one of the following equations (1) and (2). A ₀ -A ₁ ≦8(dB) … (1) A ₀ -A ₂ ≦8(dB) … (2) (In the above equation (1) or the above equation (2), when the absorption amount is assumed to be the maximum When the peak frequency is f ₀ (GHz), A ₁ represents the absorption amount (dB) at f ₀ -7 (GHz), and A ₂ represents the absorption amount (dB) at f ₀ +7 (GHz).)

According to the electromagnetic wave absorber 100, which is capable of transmitting/receiving electromagnetic waves in the frequency band absorbed by the electromagnetic wave absorber 100, in the sensing system of the electromagnetic wave transmitting/receiving device capable of processing the received electromagnetic waves, when the electromagnetic wave transmitting/receiving device is sent from When electromagnetic waves in a specific frequency band of the device are incident from the resistive layer 10 side, the electromagnetic waves pass through the resistive layer 10 and the dielectric layer 20 and are reflected on the reflective layer 30 . At this time, in the dielectric layer 20 , the incident electromagnetic wave and the reflected reflected wave cancel each other, thereby absorbing the electromagnetic wave. Therefore, the absorption amount of the electromagnetic wave of a specific frequency becomes maximum. However, at this time, by exhibiting a maximum absorption amount of 15 dB or less and satisfying at least one of the above equations (1) and (2), the difference between the maximum absorption amount and the minimum absorption amount can be reduced in the above frequency band. Therefore, when the intensity of the electromagnetic wave in the frequency band transmitted from the electromagnetic wave transmitting/receiving apparatus is constant, the intensity of electromagnetic waves other than the specific frequency among the electromagnetic waves received by the electromagnetic wave transmitting/receiving apparatus is maintained at a high intensity, and the electromagnetic wave of the specific frequency is maintained at a high intensity. The intensity drop can be fully suppressed. Therefore, in the sensing system, for electromagnetic waves of a specific frequency, the decrease in the signal-to-noise (S/N) ratio can be suppressed. Since the signal becomes easy to identify, there is no need to introduce a program that requires complex programming into the sensing system. Sensing can be performed appropriately.

Hereinafter, the resistive layer 10 , the dielectric layer 20 and the reflective layer 30 will be described in detail.

(resistance layer) The resistive layer 10 is a layer that allows electromagnetic waves incident from the outside to reach the dielectric layer 20 . The resistance layer 10 is generally a layer for realizing impedance matching, but in the present disclosure, it functions as a layer for not realizing impedance matching.

The resistance layer 10 includes a layer made of at least one of a conductive inorganic material and a conductive organic material. Examples of conductive inorganic materials include indium tin oxide (ITO; Indium Tin Oxide), indium zinc oxide (IZO; Indium Zinc Oxide), aluminum zinc oxide (AZO; Aluminum Zinc Oxide), carbon ( Select one or more from the group consisting of carbon, graphene, Ag, Al, Au, Pt, Pd, Cu, Co, Cr, In, Ag-Cu, Cu-Au and Ni. The shape of the conductive inorganic material is not particularly limited, and may be in the form of particles or wires, for example. Examples of conductive organic materials include polythiophene derivatives, polyacetylene derivatives, polyaniline derivatives, and polypyrrole derivatives. Especially for conductive organic materials, from the viewpoint of flexibility, film-forming properties, stability, and surface resistance, conductive polymers (polymers) containing polyethylenedioxythiophene (PEDOT) are preferred. . The resistance layer 10 may also be a mixture (PEDOT/PSS) containing polyethylenedioxythiophene (PEDOT) and polystyrene sulfonate (PPS). The resistance layer 10 may be composed of only a layer composed of at least one of a conductive inorganic material and a conductive organic material, or a layer composed of at least one of a conductive inorganic material and a conductive organic material may be provided on the base material Made from above. Examples of the base material include polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and the like. Particularly from the viewpoints of flexibility, film-forming properties, stability, and surface resistance, the resistance layer 10 is preferably composed of a PET film formed of a conductive polymer containing PEDOT.

The surface resistance value of the resistive layer 10 can be appropriately set according to the selection of the conductive inorganic material or the conductive organic material and the adjustment of the thickness of the resistive layer 10 , for example. For example, the surface resistance value of the resistive layer 10 can be measured using Loresta-GP MCP-T610 (trade name, manufactured by Mitsubishi Chemical Analytech Co., Ltd.). The resistive layer 10 may be a single layer or a laminate composed of a plurality of layers.

The thickness (film thickness) of the resistance layer 10 is appropriately determined according to the surface resistance value _R1 . As long as the resistance layer 10 is made of an inorganic material, it is preferably set in the range of 0.1 nm to 100 nm, and more preferably set in the range of 0.1 nm to 100 nm. Within the range of 1nm to 50nm. When the film thickness is 0.1 nm or more, the resistive layer 10 is easily formed as a uniform film, and the function of the resistive layer 10 tends to be more fully achieved. On the other hand, when the film thickness is 100 nm or less, the electromagnetic wave absorber 100 can maintain sufficient flexibility, and can more reliably prevent the resistive layer 10 from being damaged due to external reasons such as bending and stretching after film formation. The resistive layer 10, which is a thin film, tends to crack and suppress damage and shrinkage due to heat applied to the base material. If the resistance layer 10 is made of an organic material, the thickness (film thickness) of the resistance layer 10 is preferably set in the range of 0.1 μm to 2.0 μm, and more preferably is set in the range of 0.1 μm to 0.4 μm. When the film thickness is 0.1 μm or more, the resistive layer 10 can be formed as a uniform film, and the function of the resistive layer 10 tends to be more fully achieved. On the other hand, when the film thickness is 2.0 μm or less, the electromagnetic wave absorber 100 can maintain sufficient flexibility, and it is possible to more reliably prevent the film from being damaged due to external reasons such as bending and stretching after the resistive layer 10 is formed. That is, the resistance layer 10 tends to have cracks.

(dielectric layer) The dielectric layer 20 is a layer for attenuating the incident electromagnetic wave by destructing the incident wave and the reflected wave of the electromagnetic wave of a specific frequency through interference. Dielectric layer 20 contains resin. Examples of the resin include (meth)acrylic resin, polyurethane resin, polyester resin, polyethylene resin, and polycarbonate. ) resin, polypropylene resin, polystyrene resin, polyamide resin, polyvinyl formal resin, polyvinyl chloride resin, polyacrylonitrile resin, polymethacrylic acid Methylmethacrylate resin, polyacetal resin, polyvinylidene fluoride resin, epoxy resin, phenol resin, urea resin, polychloroprene (polychloroprene) resin. Among them, in terms of resins, (meth)acrylate resin, polyurethane, polyester, polyethylene, polycarbonate, polypropylene, polystyrene, Polyamide or a mixture of two or more of them. In particular, when the dielectric coefficient of the resin is high, the amount of dielectric particles added can be reduced, and (1) thin film, (2) formability, and (3) low cost can be achieved. Therefore, in terms of resin, Preferred are (meth)acrylate resin, polyurethane resin or a mixed resin thereof.

The dielectric layer 20 may further contain dielectric particles having a relative dielectric coefficient greater than that of the resin. Regarding the dielectric particles, inorganic compounds are preferred from the viewpoint of dispersion stability and high dielectric constant of the dielectric layer 20 . As an inorganic compound, an inorganic oxide is preferable. Examples of inorganic oxides include barium titanate, titanium oxide, zinc oxide, aluminum oxide and zirconium oxide. Among them, among the inorganic oxides, barium titanate, titanium oxide or aluminum oxide.

Although the relative dielectric coefficient of the dielectric layer 20 is not particularly limited, from the viewpoint of thinning the dielectric layer 20 , the larger the better. Specifically, the relative permittivity of the dielectric layer 20 is preferably 10.0 or more, more preferably 15.0 or more.

The real part of the complex relative permittivity of the dielectric layer 20 is not particularly limited, but is preferably 10 or more, and more preferably 15.0 or more. When the real part of the complex relative dielectric coefficient of the dielectric layer 20 is 10 or more, the dielectric coefficient of the dielectric layer 20 can be increased, and the thickness of the dielectric layer 20 can be reduced. Therefore, the electromagnetic wave absorber 100 can be made thinner. . However, the real part of the complex relative permittivity of the dielectric layer 20 is preferably 30.0 or less, more preferably 20.0 or less. When the real part of the complex relative permittivity of the dielectric layer 20 is 20.0 or less, the dielectric layer can have more sufficient strength.

The thickness of the dielectric layer 20 is appropriately adjusted according to the value of the maximum absorption amount that should be set in the electromagnetic wave absorber 100, and is preferably 20 μm or more, and more preferably 50 μm or more. Setting the thickness of the dielectric layer 20 to 50 μm or more can make the dielectric layer 20 less likely to be damaged.

However, the thickness of the dielectric layer 20 is preferably 1000 μm or less, more preferably 400 μm or less. At this time, when the dielectric layer 20, the resistive layer 10, and the reflective layer 30 are laminated, phenomena such as wrinkles, tunneling, and delamination are less likely to occur.

(reflective layer) The reflective layer 30 is a layer that reflects electromagnetic waves incident from the dielectric layer 20 and reaches the dielectric layer 20 . For example, the reflective layer 30 includes a layer made of at least one of a conductive inorganic material and a conductive organic material. Examples of conductive inorganic materials include indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), carbon, graphene, Ag, Al, Au, Pt, and Pd. Select one or more from the group consisting of , Cu, Co, Cr, In, Ag-Cu, Cu-Au and Ni. The shape of the conductive inorganic material is not particularly limited, and may be in the form of particles or lines, for example. Examples of conductive organic materials include polythiophene derivatives, polyacetylene derivatives, polyaniline derivatives, and polypyrrole derivatives. The reflective layer 30 may be composed of only a layer composed of at least one of a conductive inorganic material and a conductive organic material, or may be provided on a base material with a layer composed of at least one of a conductive inorganic material and a conductive organic material. . Examples of the base material include polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and the like. Especially from the viewpoint of flexibility, film-forming property, stability, and surface resistance, the reflective layer 30 is preferably composed of a PET film formed of an aluminum vapor-deposited film. The surface resistance value of the reflective layer 30 is not particularly limited, but is preferably 100Ω/□ or less. The reflective layer 30 may be a single layer or a laminate composed of a plurality of layers.

The thickness of the reflective layer 30 is not particularly limited, but is preferably 0.05 μm to 100 μm, more preferably 12 μm to 80 μm. When the film thickness is 0.05 μm or more, it is easier to form a uniform film, and the function as the reflective layer 30 tends to be more fully achieved. On the other hand, when the film thickness is 100 μm or less, sufficient flexibility can be provided to the reflective layer 30, and the tendency of the reflective layer 30 to crack due to external factors such as bending and stretching of the electromagnetic wave absorber 100 can be further suppressed. .

(adhesive layer) The adhesive layer is a layer that bonds the dielectric layer 20 and the resistive layer 10 together or bonds the dielectric layer 20 and the reflective layer 30 together. For the adhesive layer, for example, adhesives such as urethane adhesives, rubber adhesives, acrylic adhesives, and silicone adhesives can be used. Among them, the use of urethane adhesive is particularly preferred because it can effectively bond the dielectric layer 20 and the resistive layer 10 together and the dielectric layer 20 and the reflective layer 30 together at low cost.

(Maximum absorption amount) The maximum absorption amount A ₀ in a specific frequency band is 15 dB or less, but preferably 13 dB or less. However, the maximum absorption amount A ₀ is preferably 3dB or more, more preferably 5dB or more. For example, the maximum absorption amount A ₀ can be adjusted by appropriately adjusting the thickness and relative dielectric coefficient of the dielectric layer 20 . In addition, the maximum absorption amount A ₀ can also be adjusted by adjusting the surface resistance value of the resistive layer 10 .

(A ₀ -A ₁ and A ₀ -A ₂ ) The electromagnetic wave absorber 100 satisfies at least one of the above formula (1) and the above formula (2). Based on this, the electromagnetic wave absorber 100 can satisfy both of the above equations (1) and (2), and can also satisfy either one of the above equations (1) and (2). However, from the viewpoint of enabling simple and highly accurate sensing, the electromagnetic wave absorber 100 is preferably one that satisfies both the above equation (1) and the above equation (2).

A ₀ -A ₁ only needs to be 8 dB or less. However, from the viewpoint of reducing the difference in absorption amounts at the frequency used in the sensing system, it is preferably 5 dB or less, and more preferably 3 dB or less.

A ₀ -A ₂ only needs to be 8 dB or less. However, from the viewpoint of reducing the difference in absorption amounts at the frequency used in the sensing system, it is preferably 5 dB or less, and more preferably 3 dB or less.

A ₀ -A ₁ and A ₀ -A ₂ may be the same as each other or different.

(Absolute value of reflection coefficient Γ) In the electromagnetic wave absorber 100, the absolute value of the reflection coefficient Γ calculated from the following equation (3) to the following equation (5) is not particularly limited, but at the peak frequency f ₀ (GHz) Preferably it is 3.12 to 5.62. [Formula 2]

In the above equations (3) to (5), Γ represents the reflection coefficient, Z _L represents the input impedance (Ω/□) viewed from the surface of the resistive layer 10 opposite to the reflective layer 30 , and Z ₀ represents Vacuum impedance (Ω/□), Z´ _L represents the input impedance (Ω/□) viewed from the reflective layer 30 side of the resistive layer 10 toward the reflective layer 30, and R represents the surface resistance value of the resistive layer 10 (Ω/□) , ε _r represents the complex relative dielectric coefficient of the dielectric layer 20 , d represents the thickness of the dielectric layer 20 (μm), and λ represents the wavelength of the incident electromagnetic wave (μm). The reflection coefficient Γ can be obtained using the above equation (3) to the above equation (5) as long as Z ₀ , R, d, λ and ε _r are determined.

The absolute value of the reflection coefficient Γ is preferably 3.2 to 5.62, and particularly preferably 4.0 to 5.62.

The absolute value of the reflection coefficient Γ can be adjusted by adjusting the surface resistance value of the resistive layer 10 . In addition, the absolute value of the reflection coefficient Γ can be adjusted by appropriately adjusting the thickness of the dielectric layer 20 and the complex relative dielectric coefficient.

(A ₀ -B ₁ and A ₀ -B ₂ ) The electromagnetic wave absorber 100 preferably satisfies at least one of the above equations (6) and (7). Based on this, the electromagnetic wave absorber 100 may satisfy both of the above equations (6) and (7), or may satisfy any one of the above equations (6) and (7). However, from the viewpoint of reducing the difference in absorption amounts at the frequency used in the sensing system, the electromagnetic wave absorber 100 preferably satisfies both the above equation (6) and the above equation (7).

A ₀ -B ₁ only needs to be 0.5dB or less, but from the viewpoint of enabling simple and highly accurate sensing, it is preferably 0.4dB or less, and more preferably 0.3dB or less.

A ₀ -B ₂ only needs to be 0.5dB or less, but from the viewpoint of enabling simple and highly accurate sensing, it is preferably 0.4dB or less, and more preferably 0.3dB or less.

The electromagnetic wave absorber 100 can be obtained by attaching the resistive layer 10 and the reflective layer 30 to the dielectric layer 20 using a dry lamination method or a thermal lamination method respectively.

The specific frequency band of electromagnetic waves that the electromagnetic wave absorber 100 can absorb is not particularly limited, but is usually 1 GHz to 350 GHz. The specific frequency band can be appropriately determined according to the use of the electromagnetic wave absorber 100 . At this time, the specific frequency band is set to include the frequency at which the absorption amount of electromagnetic waves reaches the maximum. The frequency at which the absorption amount of electromagnetic waves reaches the maximum can be adjusted by appropriately adjusting the thickness of the dielectric layer 20 and the value of the complex relative dielectric coefficient of the dielectric layer 20 .

(verify) Next, it was verified through simulation whether the electromagnetic wave absorber of the present disclosure can reduce the difference between the maximum absorption amount and the minimum absorption amount in a specific frequency band. At this time, it is assumed that the following layers are used as the resistive layer, dielectric layer, and reflective layer constituting the electromagnetic wave absorber. In addition, the complex relative dielectric coefficient is measured in accordance with JIS-C2138:2007. Specifically, the complex relative permittivity is measured using a cavity resonator method permittivity measuring device (manufactured by Agilent Technologies, product name "Agilent E4991A RF impedance/material analyzer"). ), measured at a frequency of 1GHz, a temperature of 25°C, and a relative humidity of 50%. (resistance layer) ． Resistive layer A: PET (S-10 made by Toray, thickness 50 μm) is coated with PEDOT (Clevios PH1000) made by Heraeus. ． Resistance layer B: An ITO film was formed by sputtering on PET (S-10, thickness 50 μm) manufactured by Toray using an ITO target. ． Resistance layer C: A molybdenum-containing film is formed by sputtering a molybdenum-containing target on PET (S-10, thickness 50 μm) manufactured by Toray. (dielectric layer) ． Dielectric layer A: Coated film using silicone adhesive KR-3700 manufactured by Shin-Etsu Chemical Industry (real part of complex relative dielectric coefficient: 3.2, imaginary part: 0.0) ． Dielectric layer B: Coating film (plural) prepared by blending SAIVINOL OC3405 manufactured by Sakai Chemical Industries, Ltd. with perovskite BT-01 (barium titanate) manufactured by Sakai Chemical Industries, Ltd. at a volume percentage of 35%. Real part of relative permittivity: 10.6, imaginary part: 1.0) (reflective layer) ． TETOLIGHT SC (aluminum evaporated PET) made by Oike Industrial Co., Ltd.

(Simulation A1 to Simulation A20) For the reflective layer, the above-mentioned reflective layer is used, and for the resistive layer and dielectric layer, the resistive layer and dielectric layer shown in Table 1 below are used. Constitute an electromagnetic wave absorber. And for this electromagnetic wave absorber, through simulation, the relationship between the frequency and the absorption amount was obtained when the frequency band was set to 50 GHz to 70 GHz as shown in Table 1 below. The results are shown in Figures 2 to 4. In addition, in Figures 2 to 4, the reflection attenuation amount is the value obtained by multiplying the absorption amount by -1. In addition, Table 1 below shows the surface resistance value R ₁ (Ω/□) of the resistive layer, the absorption amount (maximum absorption amount) A ₀ (dB) at the peak frequency f ₀ , and the absorption amount at f ₀ -7 (GHz). The amount A ₁ (dB), A ₀ -A ₁ , the absorption amount A ₂ (dB) at f ₀ +7 (GHz), the absolute value of the reflection coefficient Γ at the peak frequency f ₀ , the absolute value of the reflection coefficient Γ at f ₀ -2 (GHz) ), the absorption amount B ₁ (dB), A ₀ -B ₁ , the absorption amount B ₂ (dB) at f ₀ +2 (GHz), A ₀ -B ₂ , the difference between the maximum absorption amount and the minimum absorption amount ΔA ( dB) absolute value. From the results shown in Figures 2 to 4 and Table 1 below, it can be seen that an electromagnetic wave absorber exhibits a maximum absorption amount A ₀ of 15 dB or less in the frequency band and satisfies at least one of the above equations (1) and (2), Compared with an electromagnetic wave absorber that exhibits a maximum absorption amount A ₀ greater than 15 dB or does not satisfy either of the above equations (1) and (2), ΔA becomes significantly smaller.

(Simulation B1 to Simulation B4) For the reflective layer, the above-mentioned reflective layer is used, and for the resistive layer and dielectric layer, the resistive layer and dielectric layer shown in Table 2 below are used. Constitute an electromagnetic wave absorber. And for this electromagnetic wave absorber, through simulation, the relationship between the frequency and the absorption amount was obtained when the frequency band was set to 20 GHz to 40 GHz as shown in Table 2 below. The results are shown in Figure 5. In addition, in Fig. 5, the reflection attenuation amount is the value obtained by multiplying the absorption amount by -1. In addition, Table 2 below shows the surface resistance value R ₁ (Ω/□) of the resistive layer, the absorption amount (maximum absorption amount) A ₀ (dB) at the peak frequency f ₀ , and the absorption amount at f ₀ -7 (GHz). The amount A ₁ (dB), A ₀ -A ₁ , the absorption amount A ₂ (dB) at f ₀ +7 (GHz), the absolute value of the reflection coefficient Γ at the peak frequency f ₀ , the absolute value of the reflection coefficient Γ at f ₀ -2 (GHz) ), the absorption amount B ₁ (dB), A ₀ -B ₁ , the absorption amount B ₂ (dB) at f ₀ +2 (GHz), A ₀ -B ₂ , the difference between the maximum absorption amount and the minimum absorption amount ΔA( dB) absolute value. It can be seen from the results shown in Figure 5 and Table 2 below that an electromagnetic wave absorber that exhibits a maximum absorption amount A ₀ of 15 dB or less in the frequency band and satisfies at least one of the above equations (1) and (2) has a better performance than For an electromagnetic wave absorber that exhibits a maximum absorption amount A ₀ greater than 15 dB or does not satisfy either of the above equations (1) and (2), ΔA becomes extremely small.

(Simulation C1 to Simulation C4) For the reflective layer, the above-mentioned reflective layer is used, and for the resistive layer and dielectric layer, the resistive layer and dielectric layer shown in Table 3 below are used. Constitute an electromagnetic wave absorber. And for this electromagnetic wave absorber, through simulation, the relationship between the frequency and the absorption amount was obtained when the frequency band was set to 70 GHz to 90 GHz as shown in Table 3 below. The results are shown in Figure 6. In addition, in Fig. 6, the reflection attenuation amount is the value obtained by multiplying the absorption amount by -1. In addition, Table 3 below shows the surface resistance value R ₁ (Ω/□) of the resistive layer, the absorption amount (maximum absorption amount) A ₀ (dB) at the peak frequency f ₀ , and the absorption amount at f ₀ -7 (GHz). The amount A ₁ (dB), A ₀ -A ₁ , the absorption amount A ₂ (dB) at f ₀ +7 (GHz), the absolute value of the reflection coefficient Γ at the peak frequency f ₀ , the absolute value of the reflection coefficient Γ at f ₀ -2 (GHz) ), the absorption amount B ₁ (dB), A ₀ -B ₁ , the absorption amount B ₂ (dB) at f ₀ +2 (GHz), A ₀ -B ₂ , the difference between the maximum absorption amount and the minimum absorption amount ΔA ( dB) absolute value. It can be seen from the results shown in Figure 6 and Table 3 below that an electromagnetic wave absorber that exhibits a maximum absorption amount A ₀ of 15 dB or less in the frequency band and satisfies at least one of the above equations (1) and (2) has a better performance than For an electromagnetic wave absorber that exhibits a maximum absorption amount A ₀ greater than 15 dB or does not satisfy either of the above equations (1) and (2), ΔA becomes extremely small.

[Table 1] Frequency band(GHz) resistive layer dielectric layer R ₁ (Ω/□) Absorption amount A ₀ (dB) at peak frequency f ₀ (GHz) Absorption amount A ₁ (dB) at f ₀ -7(GHz) A ₀ -A ₁ Absorption amount A ₂ (dB) at f ₀ +7(GHz) A ₀ -A ₂ The absolute value of the reflection coefficient Γ at the peak frequency f ₀ (GHz) Absorption amount B ₁ (dB) at f ₀ -2(GHz) A ₀ -B ₁ Absorption amount B ₂ (dB) at f ₀ +2(GHz) A ₀ -B ₂ ΔA (dB) Analog A1 50-70 A A 540 14.8 11.8 3.0 11.8 3.0 5.5 14.5 0.3 14.4 0.4 6.2 Analog A2 50-70 A A 261 14.9 13.2 1.7 13.2 1.7 5.6 14.8 0.1 14.8 0.1 4.3 Analog A3 50-70 A B 801 14.9 8.6 6.3 9.1 5.8 5.6 13.9 1 13.9 1 10.2 Analog A4 50-70 A B 300 14.4 10.5 3.9 10.8 3.6 5.2 13.9 0.5 13.9 0.5 7.1 Analog A5 50-70 A B 1002 12.1 7.6 4.5 8.0 4.1 4.0 11.5 0.6 11.5 0.6 8.0 Analog A6 50-70 B A 580 13.3 10.9 2.4 10.9 2.4 4.6 13.0 0.3 13.0 0.3 5.2 Analog A7 50-70 B A 233 12.7 11.7 1.0 11.7 1.0 4.3 12.6 0.1 12.6 0.1 2.7 Analog A8 50-70 B B 797 14.9 8.6 6.3 9.1 5.8 5.6 13.9 1 14.0 0.9 10.2 Analog A9 50-70 B B 280 13.2 10.2 3.0 10.3 2.9 4.6 12.9 0.3 12.8 0.4 5.9 Analog A10 50-70 C A 543 14.7 11.7 3.0 11.8 2.9 5.4 14.3 0.4 14.3 0.4 6.1 Analog A11 50-70 C A 245 13.6 12.3 1.3 12.4 1.2 4.8 13.5 0.1 13.5 0.1 3.3 Analog A12 50-70 C B 810 14.7 8.6 6.1 9.1 5.6 5.5 13.7 1 13.8 0.9 10 Analog A13 50-70 C B 310 14.9 10.6 4.3 11.0 3.9 5.6 14.4 0.5 14.5 0.4 7.7 Analog A14 50-70 A A 379 46.9 16.0 30.9 16.2 30.7 220.2 26.9 20 26.9 20 35.9 Analog A15 50-70 A A 430 23.1 14.8 8.3 14.9 8.2 14.2 21.4 1.7 21.4 1.7 12.8 Analog A16 50-70 A B 600 21.9 10.1 11.8 10.6 11.3 12.4 18.5 3.4 18.5 3.4 16.2 Analog A17 50-70 B A 360 34.6 16.1 18.5 16.3 18.3 54.0 26.4 8.2 26.5 8.1 23.5 Analog A18 50-70 B B 468 37.8 11.0 26.8 11.5 26.3 77.4 21.8 16 21.8 16 31.3 Analog A19 50-70 C A 400 29.3 15.6 13.7 15.7 13.6 29.3 24.8 4.5 24.8 4.5 18.7 Analog A20 50-70 C B 499 38.5 10.8 27.7 11.4 27.1 84.2 21.4 17.1 21.9 16.6 32.2

[Table 2] Frequency band(GHz) resistive layer dielectric layer R ₁ (Ω/□) Absorption amount A ₀ (dB) at peak frequency f ₀ (GHz) Absorption amount A ₁ (dB) at f ₀ -7(GHz) A ₀ -A ₁ Absorption amount A ₂ (dB) at f ₀ +7(GHz) A ₀ -A ₂ The absolute value of the reflection coefficient Γ at the peak frequency f ₀ (GHz) Absorption amount B ₁ (dB) at f ₀ -2(GHz) A ₀ -B ₁ Absorption amount B ₂ (dB) at f ₀ +2(GHz) A ₀ -B ₂ ΔA (dB) Analog B1 20-40 A A 540 14.9 7.2 7.7 7.3 7.6 5.6 13.4 1.5 13.4 1.5 11.4 Analog B2 20-40 B B 960 10.5 3.1 7.4 4.0 6.5 3.3 8.7 1.8 8.8 1.7 8.7 Analog B3 20-40 A A 398 31.0 8.8 22.2 9.0 twenty two 35.3 19.4 11.6 19.3 11.7 26.5 Analog B4 20-40 B B 544 28.4 4.8 23.6 5.7 22.7 26.3 14.5 13.9 15.1 13.3 25.3

[table 3] Frequency band(GHz) resistive layer dielectric layer R ₁ (Ω/□) Absorption amount A ₀ (dB) at peak frequency f ₀ (GHz) Absorption amount A ₁ (dB) at f ₀ -7(GHz) A ₀ -A ₁ Absorption amount A ₂ (dB) at f ₀ +7(GHz) A ₀ -A ₂ The absolute value of the reflection coefficient Γ at the peak frequency f ₀ (GHz) Absorption amount B ₁ (dB) at f ₀ -2(GHz) A ₀ -B ₁ Absorption amount B ₂ (dB) at f ₀ +2(GHz) A ₀ -B ₂ ΔA (dB) Analog C1 70-90 A A 540 14.7 12.6 2.1 12.7 2.0 5.4 14.5 0.2 14.5 0.2 3.9 Analog C2 70-90 B B 856 13.8 9.6 4.2 10.0 3.8 4.9 13.2 0.6 13.3 0.5 6.3 Analog C3 70-90 A A 450 20.4 16.4 4 15.8 4.6 10.5 19.7 0.7 19.8 0.6 7.6 Analog C4 70-90 B B 602 21.3 11.9 9.4 12.3 9.0 11.6 19.2 2.1 19.2 2.1 12.1

＜Sensing system＞ Next, implementation forms of the sensing system of the present disclosure will be described. FIG. 7 is a cross-sectional view (schematic diagram) showing an embodiment of the sensing system of the present disclosure.

As shown in Figure 7, the sensing system 200 is provided in the space S: an electromagnetic wave absorber 100; an electromagnetic wave transmitting/receiving device 201, which transmits/receives electromagnetic waves in the frequency band absorbed by the electromagnetic wave absorber 100, and can detect the received electromagnetic wave. Electromagnetic waves are processed.

According to the sensing system 200 , when the electromagnetic wave of a specific frequency band transmitted from the electromagnetic wave transmitting/receiving device 201 is incident from the resistive layer 10 side, the electromagnetic wave passes through the resistive layer 10 and the dielectric layer 20 and is reflected on the reflective layer 30 . At this time, in the dielectric layer 20 , the incident electromagnetic wave and the reflected reflected wave cancel each other, thereby absorbing the electromagnetic wave. Therefore, the absorption amount of the electromagnetic wave of a specific frequency becomes maximum. However, at this time, if the maximum absorption amount is 15 dB or less and satisfies at least one of the above equations (1) and (2), the difference between the maximum absorption amount and the minimum absorption amount can be reduced in the above frequency band. Therefore, when the intensity of the electromagnetic wave in the frequency band transmitted from the electromagnetic wave transmitting/receiving apparatus 201 is constant, among the electromagnetic waves received by the electromagnetic wave transmitting/receiving apparatus 201, the intensity of electromagnetic waves other than the specific frequency is maintained at a high intensity, and the intensity of the electromagnetic wave of the specific frequency is maintained at a high intensity. The decrease in the intensity of electromagnetic waves can be fully suppressed. Therefore, in the sensing system 200 , the decrease in the signal-to-noise (S/N) ratio for electromagnetic waves of a specific frequency is suppressed, and since the signal becomes easily identifiable, it can be appropriately performed without introducing a program that requires complex programming. sensing.

Examples of the electromagnetic wave transmitting/receiving device 201 include a radar device. Examples of radar devices include pulse radar devices and frequency modulation continuous wave (FM-CW; Frequency Modulation-Continuous Wave) radar devices. Among them, the FM-CW radar device is particularly preferred because it can achieve a high signal-to-noise (S/N) ratio even without high transmission power from the radar device.

The radar device includes a transmitting antenna, a receiving antenna, a transmitting unit, a receiving unit, and a signal processing unit. Only when the radar device has a duplexer that switches transmission and reception, the transmitting antenna can also serve as a receiving antenna.

An example of the sensing system 200 is a system that detects activities of an elderly person or the like.

10:Resistance layer 20: Dielectric layer 30: Reflective layer 100:Electromagnetic wave absorber 200: Sensing system 201: Electromagnetic wave transmitting/receiving device

FIG. 1 is a cross-sectional view showing an embodiment of the electromagnetic wave absorber of the present disclosure. FIG. 2 is a graph showing the relationship between frequency and reflection attenuation (absorption amount) in the 50 GHz to 70 GHz frequency band obtained through simulation using the electromagnetic wave absorber of the present disclosure. FIG. 3 is a graph showing the relationship between frequency and reflection attenuation (absorption amount) in the 50 GHz to 70 GHz frequency band obtained through simulation using the electromagnetic wave absorber of the present disclosure. FIG. 4 is a graph showing the relationship between frequency and reflection attenuation (absorption amount) in the 50 GHz to 70 GHz frequency band obtained through simulation using the electromagnetic wave absorber of the present disclosure. FIG. 5 is a graph showing the relationship between frequency and reflection attenuation (absorption amount) in the 20 GHz to 40 GHz frequency band obtained through simulation using the electromagnetic wave absorber of the present disclosure. FIG. 6 is a graph showing the relationship between frequency and reflection attenuation (absorption amount) in the 70 GHz to 90 GHz frequency band obtained through simulation using the electromagnetic wave absorber of the present disclosure. FIG. 7 is a schematic diagram showing an implementation form of the sensing system of the present disclosure.

without.

Claims (10)

An electromagnetic wave absorber, which is an interference type electromagnetic wave absorber that has a resistive layer, a dielectric layer and a reflective layer in order, and absorbs electromagnetic waves in a specific frequency band; exhibits a maximum absorption amount A ₀ of less than 15dB in the aforementioned frequency band and satisfies the following formula (1 ) and at least one of the following formula (2); A ₀ -A ₁ ≦8(dB) … (1) A ₀ -A ₂ ≦8(dB) … (2) (In the aforementioned formula (1) or the aforementioned ( In 2), when the peak frequency when the absorption amount is maximum is f ₀ (GHz), A ₁ represents the absorption amount (dB) at f ₀ -7 (GHz), and A ₂ represents the absorption amount (dB) at f ₀ +7 (GHz). ) absorption amount (dB)). For the electromagnetic wave absorber of claim 1, the absolute value of the reflection coefficient Γ calculated by the following equation (3) to the following equation (5) is 3.12 to 5.62 at the peak frequency f ₀ (GHz); [Formula 1] (In the above-mentioned formulas (3) to (5), Γ represents the reflection coefficient, Z _L represents the input impedance (Ω/□) seen from the side of the resistance layer opposite to the reflection layer, Z ₀ represents the vacuum impedance (Ω/□), Z´ _L represents the input impedance (Ω/□) viewed from the reflective layer side of the resistive layer toward the reflective layer, and R represents the surface resistance value of the resistive layer (Ω/□ ), ε _r represents the complex relative dielectric coefficient of the aforementioned dielectric layer, d represents the thickness of the aforementioned dielectric layer (μm), and λ represents the wavelength of the incident electromagnetic wave (μm)). For example, the electromagnetic wave absorber of claim 1 or 2 satisfies at least one of the following equations (6) and (7): A ₀ -B ₁ ≦0.5 (dB) ... (6) A ₀ -B ₂ ≦0.5 (dB) … (7) (In the aforementioned formula (6) or the aforementioned (7), B ₁ represents the absorption amount (dB) at f ₀ -2 (GHz), and B ₂ represents the absorption at f ₀ +2 (GHz) The amount of absorption (dB)). An electromagnetic wave absorber according to claim 3, which satisfies both the above-mentioned formula (6) and the above-mentioned formula (7). The electromagnetic wave absorber according to any one of claims 1 to 4, wherein the real part of the complex relative permittivity of the dielectric layer is 10 or more. The electromagnetic wave absorber according to any one of claims 1 to 5, which exhibits a maximum absorption amount A ₀ of more than 3 dB in the aforementioned frequency band. The electromagnetic wave absorber according to any one of claims 1 to 6, which satisfies both the aforementioned formula (1) and the aforementioned formula (2). A sensing system having: Such as the electromagnetic wave absorber in any one of claims 1 to 7; and The electromagnetic wave transmitting/receiving device transmits and receives electromagnetic waves in the frequency band absorbed by the electromagnetic wave absorber, and is capable of processing the received electromagnetic waves. The sensing system of claim 8, wherein the electromagnetic wave transmitting/receiving device is a radar device. The sensing system of claim 9, wherein the aforementioned radar device is a frequency modulated continuous wave radar device.