Search

JP-7854778-B2 - Laminated sheet for radar unit

JP7854778B2JP 7854778 B2JP7854778 B2JP 7854778B2JP-7854778-B2

Inventors

  • 松居 久登
  • 遠山 秀旦
  • 合田 亘

Assignees

  • 東レ株式会社

Dates

Publication Date
20260507
Application Date
20200929

Claims (8)

  1. A laminated sheet for use in a radar unit having an antenna substrate that emits millimeter waves, characterized in that it has all of the following features (1) to (5). (1) Includes a laminated unit in which 13 or more layers of A and B layers with different compositions are stacked alternately. (2) At least one of layer A and layer B contains an electromagnetic wave suppression material, and at least one of the electromagnetic wave suppression materials is a carbon material. (3) Within the frequency band of 20 to 100 GHz, there exists a return loss peak with a peak top where the return loss RL is 15 dB or more. (4) At least one of the outermost layers is layer A, and when the amounts of electromagnetic wave suppression material contained in layer A and layer B are wA and wB, respectively, the condition wA < wB is met. (5) When the major axis of the higher-order structure formed by the carbon material, which is the most abundant component in the laminated sheet of the electromagnetic wave suppression material, is X nm, and the average layer thickness of the layer containing the carbon material among the A layer and the B layer is Y nm, then X/Y is 0.01 or more and 10.0 or less.
  2. The laminated sheet for a radar unit according to claim 1, characterized in that, within a frequency band of 20 to 100 GHz, when the attenuation of the return attenuation peak with the greatest attenuation at the top of the return attenuation is RL dB, the frequency is f GHz, and the total thickness of the laminated sheet is t mm, RL/(t × f) is 0.4 or more and 15 or less.
  3. The laminated sheet for a radar unit according to claim 1 or 2, wherein at least one of the carbon materials is carbon black.
  4. A laminated sheet for a radar unit according to any one of claims 1 to 3, wherein the total content of the electromagnetic wave suppression material, when the total components constituting the laminated sheet are considered as 100% by mass, is 1% by mass or more and 15% by mass or less.
  5. A laminated sheet for a radar unit according to any one of claims 1 to 4, provided to the side or rear of the radar unit when viewed from the millimeter-wave transmission direction.
  6. A laminated sheet for a radar unit according to any one of claims 1 to 5, used as a housing for enclosing the antenna substrate.
  7. A radar unit comprising a laminated sheet for a radar unit as described in any one of claims 1 to 6.
  8. A transportation system equipped with a laminated sheet for a radar unit as described in any one of claims 1 to 6.

Description

This invention relates to a laminated sheet that is suitable for use in radar units that emit millimeter waves, possessing high electromagnetic wave shielding, millimeter wave selective cutting properties, and thin-film moldability. In recent years, information and communication technologies using electromagnetic waves have expanded, and electromagnetic waves of various frequency bands, such as meter waves in the hundreds of MHz to several GHz range, quasi-millimeter waves in the several GHz to tens of GHz range, and millimeter waves in the tens of GHz to hundreds of GHz range, are flying around in the atmosphere. Meter waves are mainly used in mobile phones and wireless communication, while quasi-millimeter waves are mainly used in mobile communications such as 4G and 5G, and wireless LAN (Wi-Fi) communications. In the field of automotive technology, electromagnetic wave-based information and communication technology is used in collision avoidance systems that automatically apply the brakes upon detecting obstacles, and control the vehicle's speed and distance by measuring the position and speed of surrounding vehicles. To achieve higher detection performance, these collision avoidance systems are increasingly utilizing millimeter waves (76-79 GHz), which have stronger directivity, higher energy, and are more easily reflected from material surfaces than conventional frequencies (24 GHz). In collision avoidance systems using millimeter-wave radar, it is crucial that the system responds only to electromagnetic waves emitted from and reflected by the radar unit. Therefore, electromagnetic wave absorption technology is sometimes used to cut out unwanted noise and prevent malfunctions caused by unwanted electromagnetic waves (noise) incident from the surroundings. (Patent Documents 1 and 2) Specifically, this is used in the housing portion to protect the antenna base of the radar unit, and as a side lobe cut sheet for millimeter waves that spread in a direction different from the radar's transmission direction. As a technology for absorbing high-frequency electromagnetic waves, commonly used methods include magnetic electromagnetic wave absorbers containing magnetic materials capable of absorbing high-frequency electromagnetic waves, such as ε-iron oxide (Patent Document 3), and λ/4 type electromagnetic wave laminated absorbers (Patent Document 4), which utilize resistive loss by laminating a resistive layer, a dielectric layer, and a conductive reflective layer. In the case of magnetic electromagnetic wave absorbers, a high concentration of ε-iron oxide is required, leading to problems such as increased total weight and high cost. Furthermore, in the case of λ/4 type electromagnetic wave absorbers utilizing resistive loss, losses occur due to interference cancellation with electromagnetic waves reflected by the conductive reflective layer. This results in a thick electromagnetic wave absorber (in the millimeter to centimeter range), making it difficult to mold and conform to the complex shape of radar unit housings. Japanese Patent Publication No. 2004-312696Japanese Patent Publication No. 2018-63159Japanese Patent Publication No. 2019-075571International Publication No. 2020-067145 This is an example of a cross-sectional view of a radar unit that can suitably utilize the laminated sheet of the present invention.This is a schematic diagram showing the electromagnetic wave components emitted from an antenna.This is a schematic diagram showing the full width at half maximum and electromagnetic wave attenuation of the reflection loss peak with the largest reflection loss at the peak top among the peaks obtained by measuring the reflection loss peak of a laminated sheet according to one embodiment of the present invention.This is a schematic diagram showing the full width at half maximum and electromagnetic wave attenuation of the reflection loss peak with the largest reflection loss at the peak top among the peaks obtained by measuring the reflection loss peak of a laminated sheet according to one embodiment of the present invention.This is a schematic diagram showing the full width at half maximum and electromagnetic wave attenuation of the reflection loss peak with the largest reflection loss at the peak top among the peaks obtained by measuring the reflection loss peak of a laminated sheet according to one embodiment of the present invention.This is a schematic diagram showing the full width at half maximum and electromagnetic wave attenuation of the reflection loss peak with the largest reflection loss at the peak top among the peaks obtained by measuring the reflection loss peak of a laminated sheet according to one embodiment of the present invention. The laminated sheet of the present invention is a laminated sheet for use in a radar unit having an antenna substrate that emits millimeter waves, and is characterized by having all of the following features (1) to (3). (1) Includes a laminated unit in which f