Optical Stack With RF Anti-Reflection for Radar-Transparent Covers
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Solution Overview
Problem
Radar devices in automobiles face difficulties in detecting weak reflected waves from human bodies and compact vehicles due to interference from cover members, which are typically made of metal and reflective to radio waves and infrared light, making it challenging to achieve high accuracy in detection.
Innovation Solution
An optical stack is designed that includes a substrate, a radio-wave anti-reflection sheet, and a multilayer optical film, which reduces radio wave reflection and allows transmission of both radio waves and infrared radiation, providing a reflective appearance without interfering with radar and other devices. The optical stack features a multilayer optical film that is reflective in the visible wavelength range and transmissive in near-infrared and radio-frequency ranges, and is free of significant metal interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metal cover member is used for the radar device, then the structural strength and protection are improved, but the radio wave reflection increases causing detection interference
Solution Approach 1:
The patent applies composite materials by combining a metal substrate with a dielectric layer to create a cover member that maintains structural strength while reducing radio wave reflection. The metal substrate provides mechanical support, while the dielectric layer with specific thickness (λ/4 at operating frequency) and permittivity creates impedance matching to minimize reflection of radar signals.
Solution Approach 2:
The patent changes the physical parameters of the cover member by introducing a dielectric layer with specific thickness and permittivity values. The layer thickness is set to one-quarter of the radar wavelength at the operating frequency, and the permittivity is selected to achieve impedance matching, thereby transforming the reflective metal surface into a low-reflection composite structure.
2Object-affected harmful factors
If a metal cover member is used, then the protective function is improved, but the infrared transmission is blocked interfering with infrared devices
Solution Approach 1:
The patent uses composite materials by combining metal substrate with infrared-transmissive dielectric materials. The dielectric layer is specifically selected to be transparent in the infrared wavelength range (3-14 μm) while providing the necessary radio wave reflection reduction, thus maintaining protection while enabling infrared transmission for thermal imaging and other infrared-based safety systems.
3Object-generated harmful factors
If a non-metallic material is used for the cover member, then the radio wave transmission is improved, but the structural strength and protection are reduced
Solution Approach 1:
The patent resolves this contradiction by creating a composite structure where the metal substrate provides structural strength and the dielectric layer provides radio wave transmission. This combination allows the cover member to maintain mechanical integrity while achieving the desired electromagnetic wave transmission characteristics for radar operation.
4Ease of manufacture
If a simple single-layer cover is used, then the manufacturing complexity is reduced, but the radar detection accuracy deteriorates due to reflection interference
Solution Approach 1:
The patent applies local quality by adding a dielectric layer specifically at the interface between the metal substrate and the external environment. This localized modification at the critical reflection interface achieves the desired radar signal transmission while maintaining simple manufacturing processes for the overall cover member structure.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The optical stack effectively reduces radar signal reflection by at least 10 dB across a wide frequency range, allowing for accurate detection of human bodies and compact vehicles while maintaining a metallic appearance and enabling the integration of infrared transmitters and receivers without interference.
Implementation Method 1
a radio-wave anti-reflection sheet configured to reduce reflection from the optical stack of radio waves emitted from a transmitter at a predetermined operating frequency
Implementation Method 2
a multilayer optical film disposed between the radio-wave anti-reflection sheet and the substrate, such that for light substantially normally incident on the multilayer optical film and for at least one polarization state: an average optical reflectance of the multilayer optical film may be greater than about 70% in a first wavelength range of about 420 nm to about 680 nm
Data Source
AI summary
An optical stack (100) includes a substrate (110), a radio-wave anti-reflection sheet (130) configured to reduce reflection from the optical stack (100) of radio waves at a predetermined operating frequency (f), and a visible light reflective, infrared light transmissive multilayer optical film (120) disposed between the radio-wave anti-reflection sheet (130) and the substrate (110). For radiation substantially normally incident on the radio-wave anti-reflection sheet (130) and for a first frequency range at least 20 GHZ wide, centered on the predetermined operating frequency (f), and disposed between about 1 GHZ and about 120 GHZ, a return loss of the optical stack (100) is asymmetric about the predetermined operating frequency (f) in the first frequency range. The optical stack (100) has a largest return loss S11L in the first frequency range of less than −10 dB and a difference between the largest return loss S11L and a smallest return loss S11S in the first frequency range is less than about 2 dB.