Bistable Watermark Using Cholesteric Liquid Crystals for Secure Authentication
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Solution Overview
Problem
Current security markings, such as diffraction gratings and liquid crystalline materials, require special equipment for detection or are difficult to produce, necessitating a watermark that is easy to form and difficult to reproduce.
Innovation Solution
A watermark comprising a substrate with a layer of bistable material, such as cholesteric liquid crystals, that can be addressed with an electric field to form an image, retaining the image after the field is removed, allowing for easy formation and high security against reproduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional security markings (diffraction gratings, holograms, liquid crystalline materials) are used, then security against copying is improved, but ease of manufacture and detection deteriorates
Solution Approach 1:
The patent applies parameter changes by utilizing the bistable properties of liquid crystalline materials that can switch between two stable states (e.g., twisted and untwisted) in response to changes in physical parameters such as temperature, electric field, or magnetic field. This allows the security marking to be formed through simple parameter changes during manufacturing while maintaining high security through the bistable characteristic that prevents easy duplication.
Solution Approach 2:
The patent employs the copying principle by creating a security marking that can be replicated through the bistable material's ability to be rewritten multiple times. The material can be written in one state, then switched to another state, allowing for easy formation during manufacturing while the bistable nature ensures security against unauthorized copying or tampering.
2Reliability
If traditional security markings require special equipment for detection, then security is improved, but ease of operation deteriorates
Solution Approach 1:
The patent applies color changes by utilizing the optical property changes that occur when bistable liquid crystalline materials switch between their two stable states. The material can change its optical characteristics (such as reflectivity, transparency, or color) in response to applied fields or temperature changes, allowing for easy detection with common equipment while maintaining security through the controlled bistable behavior.
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 bistable watermark provides an easily formed and difficult-to-reproduce mark for verifying authenticity, suitable for security purposes, decorative art, or information carrying, with the ability to remain visible or hidden based on energy levels applied.
Implementation Method 1
the bistable material has an imagewise pattern... the bistable material can be addressed with an electric field to form an image
Implementation Method 2
A material having a watermark is described, wherein the watermark comprises a substrate and a layer of bistable material... the ability to remain visible or hidden based on energy levels applied
Implementation Method 3
The ability of the liquid crystal to reflect light at a certain wavelength, wherein the wavelength is dependent on the incident angle of the light
Implementation Method 4
U.S. Pat. No. 6,061,122 to Hoshino et al. discloses an optical identification system using high-polymer cholesteric liquid crystals
Data Source
AI summary
A watermark formed of a bistable material, and a method of forming the watermark, are described.