Patent Application
20240380106
The present invention relates to an electromagnetic shield and a radar cover.
Sensing systems using radio waves have been known. For example, collision avoidance systems including a radar using a radio wave with a given wavelength are under discussion in the automotive technical field. Such collision avoidance systems, for example, detect obstacles, measure the speed of nearby vehicles, measure a distance to a nearby vehicle, and adjust the speed of a vehicle equipped with the system and a vehicle-to-vehicle distance. For normal operation, it is important for a collision avoidance system not to receive unnecessary radio waves that can be noise.
Patent Literature 1 describes the use of an electromagnetic wave absorber for absorption of unnecessary electromagnetic waves that can cause a driver-assistance system to malfunction. In the electromagnetic wave absorber described in Patent Literature 1, scattering bodies made of a second dielectric material and each having a particular shape are cyclically arranged in a matrix made of a first dielectric material.
Patent Literature 2 describes a radar device attached to and supported by a rear bumper using an attaching member (refer to
Patent Literature 3 describes an automotive radar module (refer to
Patent Literature 4 describes a side shield for radar transceivers. A non-uniform delay structure is arranged over the side shield. The non-uniform delay structure delays a radar signal propagating through the side shield by a variable amount depending on the wavelength of the radar signal and where in the side shield the radar signal propagates. The radar signal is thereby steered and diffused after propagation through the side shield.
Patent Literature 1: JP 2004-153135 A
Patent Literature 2: JP 5696781 B2
Patent Literature 3: U.S. Pat. No. 10,074,907 B2
Patent Literature 4: WO 2021/058450 A1
Electromagnetic shielding is conceivable for prevention of reception of unnecessary radio waves. Projecting strips may be formed on a surface of an electromagnetic shield to impart an electromagnetic shielding function to the electromagnetic shield, the surface being configured to allow electromagnetic waves to be incident thereon. A situation where projecting strips are formed on a surface of an electromagnetic shield and water is on the surface is not expected in the above patent literatures, the surface being configured to allow electromagnetic waves to be incident thereon.
In view of these circumstances, the present invention provides an electromagnetic shield that is advantageous in facilitating drainage of water on a surface of the electromagnetic shield, the surface having projecting strips.
The present invention provides an electromagnetic shield including:
The present invention provides a radar cover including the above electromagnetic shield.
The above electromagnetic shield is advantageous in facilitating drainage of water on the surface configured to allow an electromagnetic wave to be incident thereon.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following embodiments.
As shown in
base 5 having a first surface 10 and a second surface 20. The first surface 10 is a surface configured to allow an electromagnetic wave to be incident on the first surface 10. The second surface 20 is distant from the first surface 10 and extends along the first surface 10. The first surface 10 and the second surface 20, for example, face opposite directions. The electromagnetic shield 1a includes projecting strip portions 11. The electromagnetic shield 1a includes a dielectric. The electromagnetic shield 1a has a space 15 forming either a gap or a hole, and the gap or the hole is in contact with the projecting strip portion 11 along a direction intersecting with a longitudinal direction of the projecting strip portion 11. The term “electromagnetic shield” herein refers to an article that can exhibit a function of attenuating the energy of an electromagnetic wave. The principle on which an electromagnetic shield attenuates the energy of an electromagnetic wave is not limited to a particular principle. The principle can be, for example, one using a phenomenon, such as reflection, transmission, absorption, diffraction, or interference, accompanying an interaction between an electromagnetic wave and an electromagnetic shield and a phenomenon, such as scattering or diffusion of the electromagnetic wave, caused by the former phenomenon. When a given electromagnetic wave is incident on the first surface 10 of the electromagnetic shield 1a, the energy of the electromagnetic wave is attenuated.
The electromagnetic shield 1a may be used in an environment where water can be placed on the first surface 10 due to rainfall, washing, condensation, etc. Assuming that an electromagnetic shield having a surface with a projecting strip is disposed such that the projecting strip projects in a horizontal direction and extends along the horizontal direction, when water is placed above the projecting strip on the surface, it is likely that the projecting strip prevents drainage of the water and the water stays near the projecting strip. A permittivity exhibited near the projecting strip in the case where water stays near the projecting strip on the surface with the projecting strip is different from a permittivity exhibited near the projecting strip in the case where no water stays near the projecting strip. The permittivity near the projecting strip can be crucial for the performance of the electromagnetic shield. Therefore, water staying near the projecting strip on the surface with the projecting strip is likely to decrease the performance of the electromagnetic shield, making it difficult to attenuate a radio wave incident on the surface with the projecting strip to a desired state.
On the other hand, since the electromagnetic shield 1a has the space 15 in contact with the projecting strip portion 11, it is easy to drain water placed near the projecting strip portion 11 away through the space 15. In other words, the space 15 can function as a drainage path. Therefore, water is less likely to stay near the projecting strip portion 11, and thus the performance of the electromagnetic shield 1a is less likely to decrease.
As shown in
In the case where the space 15 is formed as a gap, the space 15 is placed, for example, between a pair of the projecting strip portions 11 arranged in the longitudinal direction of the projecting strip portion 11.
The shape and the dimensions of the space 15 are not limited to a particular embodiment. In the case where the space 15 is formed as a gap, a maximum dimension H of the space 15 in the longitudinal direction of the projecting strip portion 11 is not limited to a particular value. The maximum dimension H is, for example, more than 1 mm. In such a configuration, it is easier to drain water placed near the projecting strip portion 11 away through the space 15.
The maximum dimension H of the space 15 is desirably 1.2 mm or more, more desirably 1.5 mm or more, even more desirably 2 mm or more. The maximum dimension H is, for example 15 mm or less, desirably 12 mm or less, even more desirably 10 mm or less. In these cases, the electromagnetic shield 1a is likely to exhibit high electromagnetic shielding performance. The maximum dimension H may be 8 mm or less, 6 mm or less, 5 mm or less, or 4 mm or less.
In the case where the space 15 is formed as a gap, a cross-section of a flow path defined by the space 15 may have the shape of a rectangle, a triangle, or a figure including a curve such as an arc. A depth of the space 15 may be the same as a projection length P of the projecting strip portion 11, smaller than the projection length P, or greater than the projection length P. The depth of the space 15 is, for example, 1 mm or more, and may be 2 mm or more, 3 mm or more, or 4 mm or more.
In
As shown in
As shown in
The projecting strip portions 11 are, for example, in a row in a direction perpendicular to the longitudinal direction of the projecting strip portion 11. In this case, a distance D between the projecting strip portions 11 adjacent to each other in the direction perpendicular to the longitudinal direction of the projecting strip portion 11 is not limited to a particular value. The distance D is, for example, greater than the maximum dimension H of the space 15 in the longitudinal direction of the projecting strip portion 11. In such a configuration, water placed between the projecting strip portions 11 adjacent to each other is less likely to stay between the projecting strip portions 11.
A length L of the projecting strip portion 11 in the longitudinal direction of the projecting strip portion 11 is not limited to a particular value. The length L is, for example, 100 mm or less. In such a configuration, a distance that water placed near the projecting strip portion 11 travels to be led to the space 15 tends to be shorter, and water placed near the projecting strip portion 11 is likely to drain away in a short period of time.
The length L may be 95 mm or less, 90 mm or less, 75 mm or less, 60 mm or less, or 50 mm or less. The length L is, for example 5 mm or more, and may be 10 mm or more, or 15 mm or more. The length L may be 100 mm or more.
In the electromagnetic shield 1a, arrangement of the spaces 15 is not limited to particular arrangement. As shown in
The shapes of the electromagnetic shield 1a and the base 5 are not limited to particular shapes. As shown in
As shown in
The projecting strip portions 11 project, for example, in a direction perpendicular to the lower base of a truncated pyramid, a truncated cone, or a truncated elliptic cone being the outer shape of the electromagnetic shield 1a or the base 5. In such a configuration, the electromagnetic shield 1a is likely to have even higher electromagnetic shielding performance. Moreover, such a configuration is advantageous in manufacturing, for example, in that the electromagnetic shield 1a made by injection molding can be released from a simple mold without a structure such as a slide core.
The projecting strip portion 11 may have a draft angle toward a direction away from the base 5. A corner portion of the projecting strip portion 11 may be formed of a curved surface having a given curvature radius. Such a configuration is desirable, for example, in manufacturing the electromagnetic shield 1a by injection molding from the viewpoint of release of a molded article from a mold.
The electromagnetic shield 1a may be modified to an electromagnetic shield 1b as shown in
The electromagnetic shield 1a can be used, for example, as an electromagnetic shield for millimeter-wave radars, millimeter-wave radio communication, millimeter-wave sensing, or the like. A device including the electromagnetic shield 1a can be used, for example, in automobiles and wireless base stations. When the electromagnetic shield 1a is for millimeter-wave radars, the electromagnetic shield 1a can be included in a millimeter-wave radar using one frequency band selected from the group consisting of the 24 GHz band, the 60 GHz band, the 76 GHz band, and the 79 GHz band. The electromagnetic shield 1a is not just for blocking only an electromagnetic wave with a particular wavelength, and may block electromagnetic waves in a wide wavelength region. It is also possible to regard an electromagnetic wave with a particular wavelength λ as a “shielding target” of the electromagnetic shield 1a. For example, in the case of the electromagnetic shield installed with a vehicle-mounted millimeter-wave radar configured to irradiate an object with an electromagnetic wave practically having frequencies of 76 to 77 GHZ, i.e., having practical irradiation wavelengths of 3.89 to 3.94 mm, 3.92 mm which is the wavelength of the center frequency, 76.5 GHZ, can be understood as the wavelength λ, namely, the shielding target of this electromagnetic shield. In the case where the electromagnetic shield is for vehicle-mounted millimeter-wave radars using an electromagnetic wave having frequencies of 77 to 81 GHZ, i.e., using an electromagnetic wave having wavelengths of 3.70 to 3.89 mm, 3.79 mm, which is the wavelength of the center frequency, 79 GHZ, can be understood as the wavelength λ, namely, the shielding target of this electromagnetic shield. In the case where the electromagnetic shield is for vehicle-mounted millimeter-wave radars using an electromagnetic wave having frequencies of 24.05 to 24.25 GHZ, i.e., using an electromagnetic wave having wavelengths of 12.36 to 12.47 mm, 12.41 mm, which is the wavelength of the center frequency, 24.15 GHZ, can be understood as the wavelength λ, namely, the shielding target of this electromagnetic shield. In the case where the electromagnetic shield is for millimeter-wave radars using an electromagnetic wave having frequencies of 60.0 to 60.1 GHZ, i.e., using an electromagnetic wave having wavelengths of 4.99 to 5.00 mm, 4.99 mm, which is the wavelength of the center frequency, 60.05 GHZ, can be understood as the wavelength λ, namely, the shielding target of this electromagnetic shield. In the case where the electromagnetic shield is for millimeter-wave radio communication using an electromagnetic wave having frequencies of 27 to 29.5 GHZ, i.e., using an electromagnetic wave having wavelengths of 10.16 to 11.10 mm, 10.61 mm, which is the wavelength of the center frequency, 28.25 GHZ, can be understood as the wavelength λ, namely, the shielding target of this electromagnetic shield. In the case where the electromagnetic shield is, for example, sold with a label saying that its supporting frequencies are 70 to 90 GHZ, i.e., its supporting wavelengths are 3.33 to 4.28 mm, 3.75 mm, which is the wavelength of the center frequency, 80 GHZ, can be understood as the wavelength λ, namely, the shielding target of this electromagnetic shield.
In the electromagnetic shield 1a, the projection length P of the projecting strip portion 11 is not limited to a particular value. When the particular wavelength λ, namely, the shielding target of the electromagnetic shield 1a and the projection length P are compared, the projection length P is, for example, 0.25λ or more. This allows the electromagnetic shield 1a to block an electromagnetic wave in a more desired state. The projection length P is desirably 0.51λ or more, and more desirably 0.77λ or more. The projection length P is, for example, 5.1λ or less, and may be 3.5λ or less, or 3.0λ or less.
In the electromagnetic shield 1a, the projection length P of at least one of the projecting strip portions 11 desirably satisfies a requirement 0.25λ≤P≤1.3λ. In this case, the electromagnetic shield 1a is likely to have even higher electromagnetic shielding performance.
When the requirement 0.25λ≤P≤1.3λ is satisfied, the projection length P may be 0.30λ or more, 0.35λ or more, 0.40λ or more, 0.45λ or more, or 0.5λ or more. The projection length P may be 1.2λ or less, 1.1λ or less, 1.0λ or less, or 0.9λ or less.
Fifty percent or more of the projecting strip portions 11 on a number basis satisfy, for example, the requirement 0.25λ≤P≤1.3λ. Sixty percent or more of the projecting strip portions 11 on a number basis may satisfy the requirement 0.25λ≤P≤1.3λ. Seventy percent or more of the projecting strip portions 11 on a number basis may satisfy the requirement 0.25λ≤P≤1.3λ. Eighty percent or more of the projecting strip portions 11 on a number basis may satisfy the requirement 0.25λ≤P≤1.3λ. Ninety percent or more of the projecting strip portions 11 on a number basis may satisfy the requirement 0.25λ≤P≤1.3λ. All projecting strip portions 11 may satisfy the requirement 0.25λ≤P≤1.3λ.
A width W of the projecting strip portion 11 is not limited to a particular value. When the particular wavelength λ, namely, the shielding target of the electromagnetic shield 1a and the width W are compared, the width W is, for example, 0.12λ or more. This allows the electromagnetic shield 1a to block an electromagnetic wave in a more desired state. The width W is desirably 0.25λ or more, more desirably 0.51λ or more. The width W is, for example, 5.1λ or less, and may be 3.5λ or less, or 3.0λ or less. The width W is a dimension of the projecting strip portion 11 in a direction perpendicular to the longitudinal and projecting directions of the projecting strip portion 11.
In the electromagnetic shield 1a, the width W of at least one of the projecting strip portions 11 desirably satisfies a requirement 0.51λ≤W≤1.6λ. In this case, the electromagnetic shield 1a is likely to have even higher electromagnetic shielding performance.
When the requirement 0.51λ≤W≤1.6λ is satisfied, the width W may be 0.55λ or more, 0.60λ or more, 0.65λ or more, 0.70λ or more, or 0.75λ or more. The width W may be 1.5λ or less, 1.4λ or less, 1.3λ or less, 1.2λ or less, 1.1λ or less, or 1.0λ or less.
Fifty percent or more of the projecting strip portions 11 on a number basis satisfy, for example, the requirement 0.51λ≤W≤1.6λ. Sixty percent or more of the projecting strip portions 11 on a number basis may satisfy the requirement 0.51λ≤W≤1.6λ. Seventy percent or more of the projecting strip portions 11 on a number basis may satisfy the requirement 0.51λ≤W≤1.6λ. Eighty percent or more of the projecting strip portions 11 on a number basis may satisfy the requirement 0.51λ≤W≤1.6λ. Ninety percent or more of the projecting strip portions 11 on a number basis may satisfy the requirement 0.51λ≤W≤1.6λ. All projecting strip portions 11 may satisfy the requirement 0.51λ≤W≤1.6λ.
The distance D between the projecting strip portions 11 adjacent to each other in the direction perpendicular to the longitudinal and projecting directions of the projecting strip portion 11 is not limited to a particular value. When the particular wavelength λ, namely, the shielding target of the electromagnetic shield 1a and the distance D are compared, the distance D is, for example, 5.1λ or less. This allows the electromagnetic shield 1a to block an electromagnetic wave in a more desired state. The distance D is desirably 3.10λ or less, more desirably 2.04λ or less. The distance D is, for example, 1.0λ or more, and may be 1.2λ or more, or 1.5λ or more.
In the electromagnetic shield 1a, the distance D desirably satisfies a requirement 0.51λ≤D≤1.6λ. In this case, the electromagnetic shield 1a is likely to have even higher electromagnetic shielding performance. When the requirement 0.51λ≤D≤1.6λ is satisfied, the distance D may be 0.55λ or more, 0.60λ or more, 0.65λ or more, 0.70λ or more, or 0.75λ or more. The distance D may be 1.5λ or less, 1.4λ or less, or 1.3λ or less.
As shown in
A thickness of the base 5 is not limited to a particular value. The thickness of the base 5 is, for example, 0.5 mm to 3 mm. The thickness of the base 5 may be 0.7 mm or more, or 0.8 mm or more. The thickness of the base 5 may be 2.5 mm or less, or 2 mm or less.
The shape of the projecting strip portion 11 is not limited to a particular shape. As shown in
As described above, the electromagnetic shield 1a includes a dielectric. A relative permittivity of the dielectric is not limited to a particular value. An imaginary part ε″ of the relative permittivity of the dielectric at at least one frequency fg in a range of 10 GHz to 300 GHz is, for example, 0.1 or less. It appears that the imaginary part ε″ of the dielectric is desirably large in the case of attenuating an electromagnetic wave using a dielectric loss. However, even if the imaginary part ε″ of the relative permittivity of the dielectric is as small as 0.1 or less, the electromagnetic shield 1a is likely to exhibit desired performance by adjusting a phenomenon caused by an interaction between the electromagnetic shield 1a and an electromagnetic wave. The imaginary part ε″ may be 0.07 or less, 0.05 or less, or 0.01 or less.
A real part ε′ of the relative permittivity of the dielectric included in the electromagnetic shield 1a is not limited to a particular value. For example, the real part ε′ of the relative permittivity of the dielectric at the frequency fg is 2.0 to 4.0. Even in this case, the electromagnetic shield 1a is likely to exhibit desired performance by adjusting a phenomenon caused by an interaction between the electromagnetic shield 1a and an electromagnetic wave. The real part ε′ may be 3.8 or less, 3.6 or less, 3.4 or less, 3.2 or less, 3.0 or less, 2.8 or less, 2.6 or less, or 2.4 or less. The real part ε′ is desirably 2.1 or more and 3.5 or less, more desirably 2.2 or more and 3.0 or less.
The electromagnetic shield 1a is, for example, free of an electrically conductive portion. For electromagnetic shielding, it is conceivable that, for example, an electrically conductive portion such as a metal film is used to reflect an electromagnetic wave. However, the electromagnetic shield 1a can block an electromagnetic wave without an electrically conductive portion. The electromagnetic shield 1a may consist of the dielectric. The electromagnetic shield 1a may include an electrically conductive portion.
The electromagnetic shield 1a is, for example, a resin molded article. In this case, the cost of manufacturing the electromagnetic shield 1a is likely to be low. The resin included in the resin molded article is not limited to a particular resin.
The resin is, for example, a thermoplastic resin. Examples of the resin include polyethylene, polypropylene, polyvinyl alcohol, polyethylene terephthalate, polybutylene terephthalate, ethylene-vinyl acetate copolymer, polystyrene, acrylonitrile styrene, acrylonitrile-butadiene-styrene copolymer, ASA resin, AES resin, acrylic resins such as PMMA, MS resin, MBS resin, cycloolefin resin, polyacetal resin, polyamide resin, polyester resin, polycarbonate resin, polyurethane resin, liquid crystal polymer, EPDM, PPS, PEEK, PPE, polysulfone-based resin, polyimide-based resin, fluorine resin, thermoplastic elastomers such as an olefin-based thermoplastic elastomer (TPO), and acrylic elastomers. The resin may be a thermosetting resin. The thermosetting resin is, for example, an epoxy resin, an acrylic resin, or a silicone resin. The resin molded article may include only one resin or two or more resins.
The electromagnetic shield 1a may include, for example, a filler. The filler may be a colorant such as carbon black, an inorganic reinforcement such as talc, glass fibers, or a mineral, or a softener. The electromagnetic shield 1a may include an additive such as a flame retardant or a plasticizer. The electromagnetic shield 1a may be free of a filler. In this case, the cost of manufacturing the electromagnetic shield 1a is likely to be low.
In the case where the electromagnetic shield 1a is a resin molded article, the method for molding the electromagnetic shield 1a is not limited to a particular method. The electromagnetic shield 1a can be manufactured by injection molding, press molding, blow molding, or vacuum molding.
An application of the electromagnetic shield 1a is not limited to a particular application. As shown in
As shown in
Unnecessary radio waves incident on the internal surface of the radar cover 30 are attenuated by the electromagnetic shield 1a and transmitted in an attenuated state. This can consequently prevent a radar from receiving unnecessary radio waves.
In
The electromagnetic shield 1a can be modified in various respects. For example, the electromagnetic shield 1a may be modified to an electromagnetic shield 1c as shown in
As shown in
In the electromagnetic shield 1c, a maximum dimension S1 of the through hole formed by the space 15 in the longitudinal direction of the projecting strip portion 11 and a maximum dimension S2 of the through hole formed by the space 15 in the projection direction of the projecting strip portion 11 are not limited to particular values. The maximum dimension S1 is, for example, 3 mm or more. In such a configuration, it is easier to drain water placed near the projecting strip portion 11 away through the space 15. The maximum dimension S1 is desirably 3.2 mm or more, more desirably 3.5 mm or more, even more desirably 4 mm or more. The maximum dimension S1 is, for example, 10 mm or less, and may be 9 mm or less, or 8 mm or less.
The maximum dimension S2 is, for example, 3 mm or more. In such a configuration, it is easier to drain water placed near the projecting strip portion 11 away through the space 15. The maximum dimension S2 is desirably 3.2 mm or more, more desirably 3.5 mm or more, even more desirably 4 mm or more. The maximum dimension S2 is, for example, 10 mm or less, and may be 9 mm or less, or 8 mm or less.
A distance M between a longitudinal end of the projecting strip portion 11 and the space 15 is not limited to a particular value. The distance M is, for example, 100 mm or less. In such a configuration, a distance that water placed near the projecting strip portion 11 travels to be led to the space 15 tends to be shorter, and water placed near the projecting strip portion 11 is likely to drain away in a short period of time.
The distance M may be 90 mm or less, or 80 mm or less. The distance M is, for example 5 mm or more, and may be 10 mm or more, or 15 mm or more. The distance M may be 100 mm or more.
In the electromagnetic shields 1a, 1b, and 1c, an interaction occurring between the electromagnetic shield and an electromagnetic wave for blocking of the electromagnetic wave is not limited to a particular interaction. Each of the electromagnetic shields 1a, 1b, and 1c, for example, transmits at least a portion of an electromagnetic wave incident on the first surface 11 and allows a scattered electromagnetic wave to emerge from the second surface 12. In other words, each of the electromagnetic shields 1a, 1b, and 1c can function as a radio-wave transmitting-scattering body. Electromagnetic shielding can therefore be achieved with a simple configuration.
Each of the electromagnetic shields 1a, 1b, and 1c has a scattering ratio of, for example, 0.1% or more. The term “scattering ratio” refers to a ratio of an intensity of a particular transmitted-scattered wave to an intensity of a straight transmitted wave emerging from the second surface 20, the intensities being measured when a radio wave is perpendicularly incident on the first surface 10. The scattering ratio is determined, for example, by the following equation (1). In the equation (1), “Intensity of transmitted-scattered wave” is, for example, a sum of intensities measured for a transmitted-scattered wave at scattering angles of 15°, 30°, 45°, 60°, and 75°. The term “scattering angle” refers to an angle between an emergent direction of a straight transmitted wave and an emergent direction of a transmitted-scattered wave.
Scattering ratio=Intensity of transmitted-scattered wave/Intensity of straight transmitted wave Equation (1)
The intensity of the transmitted-scattered wave and the intensity of the straight transmitted wave can be determined with reference to Japanese Industrial Standards (JIS) R 1679: 2007, for example, by allowing a radio wave to be perpendicularly incident on the first surface 10 and measuring a transmission attenuation in a straight direction and a transmission attenuation at a given scattering angle. Each transmission attenuation is expressed by the following equation (2). In the equation (2), Pi is a received electric power, and P0 is a transmitted electric power. |Pi/Po| corresponds to the intensity of a transmitted wave. “Log” represents a common logarithm.
The scattering ratio of each of the electromagnetic shields 1a, 1b, and 1c may be 1% or more, 5% or more, 10% or more, 20% or more, 50% or more, 100% or more, 150% or more, or 200% or more.
A structure of each of the electromagnetic shields 1a, 1b, and 1c on the first surface 10 side with the projecting strip portion 11 is thought to function, for example, as a diffraction grating. Regarding light diffraction, a zero-order light transmittance lo through a diffraction grating having a rectangular cross-section is expressed by the following equation (3) in accordance with a scalar diffraction theory. In the equation (3), εr is the real part of the relative permittivity of the material of the diffraction grating, and sqrt (εr) is a square root of εr. The symbol h is a height of a protruding portion of the diffraction grating. The symbol λ is the wavelength of light.
According to Bragg's law, a direction (scattering angle) of a scattered-transmitted wave generated by diffraction is determined by a pitch of protruding portions of a diffraction grating. Constructive interference and destructive interference between diffraction waves having passed between the protruding portions generate an interference fringe. It is thought that in this case, a transmitted-scattered wave is observed as a result of constructive interference between diffraction waves. Constructive interference between diffraction waves can be expressed by an equation (4), while destructive interference between diffraction waves can be expressed by an equation (5). In the equations (4) and (5), d is a pitch of protruding portions of a diffraction grating, θ is an angle at which constructive interference or destructive interference between diffraction waves occurs, m is an integer of 0 or greater, and λ is the wavelength of an incident wave. It is understood that when λ is constant, the scattering angle of a transmitted-scattered wave can vary depending on the pitch of the protruding portions of the diffraction grating. Table 1 shows an example of a relation between the scattering angle θ at which constructive interference between diffraction waves occurs and the pitch d.
The present invention will be described hereinafter in more details by examples. The present invention is not limited to the examples given below. First, evaluation methods for the examples will be described.
A radio wave having a frequency of 76.5 GHz or 24 GHz was allowed to be incident on a first surface of each sample to measure a transmission attenuation in a straight direction of the radio wave using a radio transceiver EAS02 manufactured by KEYCOM Corporation with reference to JIS R 1679: 2007. A radar device manufactured by SHARP TAKAYA ELECTRONICS INDUSTRY CO., LTD. was used to generate the radio wave having a frequency of 24 GHZ. In the measurement using the radio wave having a frequency of 76.5 GHZ, a measurement region had a diameter of 30 mm. The transmission attenuation was determined by the above equation (2). Tables 2 and 3 show the results.
In a state where a projection direction and a longitudinal direction of projecting strips were horizontal and a plate-shaped base of the sample was disposed to be perpendicular to a horizontal plane, 2 cm3 of water was dropped to a side of a topmost projecting strip of the sample, and the time required for 30% or more of the water on a volume basis to drain away through a through hole or a gap was measured. In the case of a sample having a through hole or a gap, the 2 cm3 of water was dropped to a through hole or a gap in contact with the topmost projecting strip. If the water stayed on the side of the projecting strip, in the through hole, or in the gap and did not drain away, the drainage performance of the sample was evaluated as “Not Good”. Tables 2 and 3 show the results.
A plate-shaped resin molded article having two principal surfaces was obtained by molding an olefin-based thermoplastic elastomer (TPO). One of the principal surfaces had six linearly-extending projecting strips projecting from a flat-plate-shaped base, and the other principal surface was flat. A sample 1A was obtained in this manner. The real part ε′ of the complex relative permittivity of the olefin-based thermoplastic elastomer at a frequency of 76.5 GHz was 2.43. In the sample 1A, the one principal surface having the six projecting strips was formed as the first surface, while the other principal surface was formed as the second surface. The projecting strips were disposed parallel to each other and were in a row in a direction perpendicular to a longitudinal direction of the projecting strip. A distance between the projecting strips in the direction perpendicular to the longitudinal direction of the projecting strip was 6 mm. Each projecting strip had a projection length of 4 mm, a length of 50 mm in the longitudinal direction, and a width of 2 mm. A cross-section of the projecting strip was rectangular, the cross-section being perpendicular to the longitudinal direction of the projecting strip.
A through hole having a diameter of 4 mm was provided in each projecting strip of the sample 1A. A cross-section of the through hole was circular. A distance between one longitudinal end of the projecting strip and the through hole was 23 mm, and a distance between the other longitudinal end of the projecting strip and the through hole was 23 mm. The six through holes in the six projecting strips were arranged on a straight line in the direction perpendicular to the longitudinal direction of the projecting strip.
A sample 1B was produced in the same manner as the sample 1A, except that no through holes were formed in each projecting strip.
A sample 2A was produced in the same manner as the sample 1A, except that the distance between the projecting strips in the direction perpendicular to the longitudinal direction of the projecting strip was changed to 8 mm and the number of projecting strips was changed to five.
A sample 2B was produced in the same manner as the sample 2A, except that no through holes were formed in each projecting strip.
A sample 3A-1 was produced in the same manner as the sample 1A, except for the following points. In the sample 3A-1, the distance between the projecting strips in the direction perpendicular to the longitudinal direction of the projecting strip was 4 mm. A pair of the projecting strips were arranged in the longitudinal direction of the projecting strip, and a gap, instead of a through hole, was provided between the paired projecting strips. Eight such pairs of the projecting strips were arranged such that the projecting strips were in two rows in the direction perpendicular to the longitudinal direction of the projecting strip, and gaps were provided between the rows of the projecting strips. A width of the gap in the longitudinal direction of the projecting strip was 2 mm. The shape of a cross-section of the projecting strip along the longitudinal direction of the projecting strip was rectangular. A length of each pair of the projecting strip in the longitudinal direction of the projecting strip was 50 mm. The gaps were arranged on a straight line in the direction perpendicular to the longitudinal direction of the projecting strip.
A sample 3A-2 was produced in the same manner as the sample 3A-1, except that the width of the gap in the longitudinal direction of the projecting strip was changed to 3 mm.
A sample 3A-3 was produced in the same manner as the sample 3A-1, except that the width of the gap in the longitudinal direction of the projecting strip was changed to 4 mm.
A sample 3A-4 was produced in the same manner as the sample 1A, except that the distance between the projecting strips in the direction perpendicular to the longitudinal direction of the projecting strip was changed to 4 mm and the diameter of the through hole was changed to 5 mm.
A sample 3B-1 was produced in the same manner as the sample 3A-4, except that no through holes were formed.
A sample 3B-2 was produced in the same manner as the sample 3A-4, except that the diameter of the through hole was changed to 4 mm.
A sample 3B-3 was produced in the same manner as the sample 3A-1, except that the width of the gap in the longitudinal direction of the projecting strip was changed to 1 mm.
A sample 4A-1 was produced in the same manner as the sample 1A, except for the following points. In the sample 4A-1, three projecting strips were arranged parallel to each other and were in a row in the direction perpendicular to the longitudinal direction of the projecting strip. A distance between the projecting strips in the direction perpendicular to the longitudinal direction of the projecting strip was 12 mm. Each projecting strip had a projection length of 12 mm, a length of 150 mm in the longitudinal direction, and a width of 12 mm. A cross-section of the projecting strip was square, the cross-section being perpendicular to the longitudinal direction of the projecting strip.
A through hole having a diameter of 4 mm was provided in each projecting strip of the sample 4A-1. A cross-section of the through hole was circular. A distance between one longitudinal end of the projecting strip and the through hole was 73 mm, and a distance between the other longitudinal end of the projecting strip and the through hole was 73 mm. The three through holes in the three projecting strips were arranged on a straight line in the direction perpendicular to the longitudinal direction of the projecting strip.
A sample 4A-2 was produced in the same manner as the sample 4A-1, except for the following points. In the sample 4A-2, the distance between the projecting strips in the direction perpendicular to the longitudinal direction of the projecting strip was 12 mm. A pair of the projecting strips were arranged in the longitudinal direction of the projecting strip, and a gap, instead of a through hole, was provided between the paired projecting strips. Three such pairs of the projecting strips were arranged such that the projecting strips were in two rows in the direction perpendicular to the longitudinal direction of the projecting strip, and three gaps were provided between the rows of the projecting strips. The width of the gap in the longitudinal direction of the projecting strip was 2 mm. The shape of a cross-section of the projecting strip along the longitudinal direction of the projecting strip was rectangular. The length of each pair of the projecting strip in the longitudinal direction of the projecting strip was 150 mm. The gaps were arranged on a straight line in the direction perpendicular to the longitudinal direction of the projecting strip.
A sample 4A-3 was produced in the same manner as the sample 4A-1, except that the diameter of the through hole was changed to 6 mm.
A sample 4A-4 was produced in the same manner as the sample 4A-2, except that the width of the gap in the longitudinal direction of the projecting strip was changed to 10 mm.
A sample 4A-5 was produced in the same manner as the sample 4A-1, except that the diameter of the through hole was changed to 8 mm.
A sample 4A-6 was produced in the same manner as the sample 4A-2, except that the width of the gap in the longitudinal direction of the projecting strip was changed to 12 mm.
A sample 4B-1 was produced in the same manner as the sample 4A-1, except that no through holes were formed.
A sample 4B-2 was produced in the same manner as the sample 4A-1, except that the diameter of the through hole was changed to 2 mm.
A sample 4B-3 was produced in the same manner as the sample 4A-2, except that the width of the gap in the longitudinal direction of the projecting strip was changed to 1 mm.
As shown in Tables 2 and 3, the drainage time was eight seconds or shorter for the samples 1A, 2A, 3A-1 to 3A-4, and 4A-1 to 4A-6, which means that these samples exhibited good drainage performance. On the other hand, the samples 1B, 2B, 3B-1, 3B-3, and 4B-1 failed in drainage. For the samples 3B-2, 4B-2, and 4B-3, drainage was able to be accomplished although the drainage time was longer than eight seconds.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-121074 | Jul 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/028280 | 7/20/2022 | WO |
