Optical Stack With Multilayer Film for Low-Reflection Radar Covers
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Solution Overview
Problem
Radar devices in automobiles face challenges in detecting weak reflected waves from human bodies or compact vehicles due to interference from waves reflected by the cover member, which is typically metallic and reflective to both radio waves and infrared light.
Innovation Solution
An optical stack comprising a substrate, a radio-wave anti-reflection sheet, and a multilayer optical film is designed to reduce reflection of radio waves and allow transmission of both radio waves and infrared radiation, while providing a reflective appearance similar to metal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a metallic cover member is used, then structural strength and durability are improved, but radio wave reflection increases causing detection interference
Solution Approach 1:
The patent applies composite materials by combining a metallic substrate with multiple functional coating layers (optical interference layers with specific refractive indices and thicknesses). This composite structure maintains the structural strength of metal while the coated layers modify the surface properties to reduce radio wave reflection and control optical appearance, resolving the contradiction between strength and radio wave interference.
Solution Approach 2:
The patent changes physical parameters of the cover member surface by applying layers with specific refractive indices (n1, n2, n3) and controlled thicknesses (d1, d2, d3). By adjusting these optical parameters, the surface reflectsivity at radio wave frequencies is reduced while maintaining visible metallic appearance, thus resolving the contradiction between structural integrity and radio wave reflection.
2Ease of manufacture
If a metallic cover member is used, then ease of manufacture is improved, but detection precision deteriorates due to reflected waves
Solution Approach 1:
The patent uses composite materials (metal substrate + functional coatings) that can be manufactured using existing industrial coating technologies. The multi-layer structure with controlled thicknesses and refractive indices reduces radar reflection while maintaining ease of manufacture through established deposition processes, thus resolving the contradiction between manufacturing simplicity and detection precision.
Solution Approach 2:
The patent applies local quality by creating a multi-layer coating structure with different refractive indices and thicknesses at the surface level, while the bulk metal substrate remains unchanged. This localized modification of surface properties reduces radio wave reflection without complicating the overall manufacturing process, resolving the contradiction between ease of manufacture and detection precision.
3Object-generated harmful factors
If an anti-reflection sheet is added, then radio wave reflection is reduced, but device complexity increases
Solution Approach 1:
The patent merges the anti-reflection function directly into the cover member by integrating multiple functional layers as part of the cover structure itself. Rather than adding separate anti-reflection sheets or components, the solution combines structural cover and radio wave management functions into a single integrated multi-layer component, reducing overall device complexity while maintaining effectiveness.
Solution Approach 2:
The patent uses composite materials where the cover member itself becomes a multi-functional element. The metallic substrate provides structural support while the deposited layers provide radio wave reflection control and optical appearance. This composite approach eliminates the need for separate anti-reflection components, resolving the contradiction between reducing harmful reflections and maintaining simple device 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 suppresses reflections from the cover member, enabling accurate detection of weak reflected waves from pedestrians and compact vehicles, and allows for the placement of radar and other devices behind a metallic-luster appearance without interference.
Implementation Method 1
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
Implementation Method 2
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
Data Source
AI summary
An optical stack includes a substrate, a radio-wave anti-reflection sheet configured to reduce reflection from the optical stack of radio waves at a predetermined operating frequency, and a visible light reflective, infrared light transmissive multilayer optical film disposed between the radio-wave anti-reflection sheet and the substrate. For radiation substantially normally incident on the radio-wave anti-reflection sheet and for a first frequency range at least 20 GHz wide, centered on the predetermined operating frequency, and disposed between about 1 GHz and about 120 GHz, a return loss of the optical stack is asymmetric about the predetermined operating frequency in the first frequency range. The optical stack 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.