Multilayer Optical Film with Overlapping Harmonics

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Solution Overview

Problem

Conventional window films reflect infrared and visible light, leading to excessive heat buildup and non-uniform thermal expansion, and may block cell phone signals due to metalization, while lacking efficient reflection and transmission properties across a wide spectral range.

Innovation Solution

A multilayer optical film with a packet of microlayers arranged into optical repeat units, providing overlapping harmonic reflection bands that cover visible and infrared wavelengths, including a 1st, 2nd, and optionally a 3rd order reflection band, with a fixed-index f-ratio varying monotonically across the thickness, to achieve a single wide reflection band and reduce heat buildup.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Temperature

If conventional window films use metalized layers to reflect infrared and visible light, then heat reflection capability is improved, but cell phone signal transmission is blocked

Engineering Contradiction:

Improveheat reflection capabilityVSAvoidcell phone signal transmission

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent removes metalized layers from the window film structure entirely, extracting the harmful component that blocked cell phone signals while retaining the heat reflection function through alternative non-metallic multilayer optical designs

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent employs composite multilayer optical structures consisting of multiple dielectric layers with different refractive indices to achieve infrared and visible light reflection without using metals, thereby maintaining signal transmission while providing thermal control

Inventive Principle:

Principle #40Composite materials

2Temperature

If conventional window films absorb heat through dyes or metalization, then infrared reflection is improved, but excessive heat buildup occurs causing non-uniform thermal expansion

Engineering Contradiction:

Improveinfrared reflectionVSAvoidthermal uniformity

Core Design Contradiction:

TemperatureVSStability of the object's composition

Solution Approach 1:

The patent converts the harmful heat absorption mechanism into a beneficial reflection mechanism by using constructive interference in multilayer optical structures to reflect infrared radiation before it can be absorbed, preventing heat buildup while maintaining thermal stability

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent replaces the thermal absorption mechanism (dyes and metalization) with an optical interference mechanism (multilayer dielectric structures) that reflects heat through wave interference rather than thermal conversion, eliminating the source of non-uniform thermal expansion

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Temperature

If multilayer optical films use many thin microlayers to achieve wide spectral reflection, then reflection bandwidth is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvereflection bandwidthVSAvoidmanufacturing complexity

Core Design Contradiction:

TemperatureVSDevice complexity

Solution Approach 1:

The patent divides the optical film into multiple thin microlayers with specific thicknesses and refractive indices, where each layer contributes to the overall spectral reflection characteristics, enabling wide bandwidth control through segmented functional layers

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent systematically varies key parameters including layer thickness, refractive index, and layer sequence to optimize the reflection spectrum across wide bandwidths while maintaining manufacturability through standardized layer design rules and scalable fabrication processes

Inventive Principle:

Principle #35Parameter changes

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 film effectively reduces heat entry and glare, maintains visible light transmission, and avoids heat buildup issues while providing a shiny appearance without degrading cell phone signal transmission.

Implementation Method 1

the reflection and transmission characteristics of the optical film are determined in large part by constructive and destructive interference of light reflected from the layer interfaces

Methodology Applied

Scientific EffectInterference: Interference

Implementation Method 2

The optical layer is an anti-glare layer and/or an absorbing layer

Methodology Applied

Scientific EffectAbsorption (EM radiation): Absorption (EM radiation)

Data Source

PatentUS9823395B2Multilayer optical film having overlapping harmonics

Publication Date: 2017.11.21 3M INNOVATIVE PROPERTIES CO

AI summary

A multilayer optical film including a stack of microlayers arranged into optical repeat units. At a design angle of incidence, such as normal incidence, the stack provides a 1st order reflection band, a 2nd order reflection band, and optionally a 3rd order reflection band. The 2nd order reflection band substantially overlaps the 1st and/or 3rd order reflection bands to form a single wide reflection band. The wide reflection band may cover at least a portion of visible and infrared wavelengths. The multilayer optical film may include an additional optical layer which maybe be an anti-glare layer and/or may be an absorbing layer. The multilayer optical film is suitable for use as a window film.