An Analysis of Cholesteric Spherical Reflector Identifiers for Object Authenticity Verification

Abstract

Arrays of Cholesteric Spherical Reflectors (CSRs), microscopic cholesteric liquid crystals in a spherical shape, have been argued to become a game-changing technology in anti-counterfeiting. Used to build identifiable tags or coating, called CSR IDs, they can supply objects with unclonable fingerprint-like characteristics, making it possible to authenticate objects. In a previous study, we have shown how to extract minutiæ from CSR IDs. In this journal version, we build on that previous research, consolidate the methodology, and test it over CSR IDs obtained by different production processes. We measure the robustness and reliability of our procedure on large and variegate sets of CSR IDs’ images taken with a professional microscope (Laboratory Data set) and with a microscope that could be used in a realistic scenario (Realistic Data set). We measure intra-distance and interdistance, proving that we can distinguish images coming from the same CSR ID from images of different CSR IDs. However, without surprise, images in Laboratory Data set have an intra-distance that on average is less, and with less variance, than the intra-distance between responses from Realistic Data set. With this evidence, we discuss a few requirements for an anti-counterfeiting technology based on CSRs.

Cholesteric spherical reflectors as innovative optical elements with vast application potential

“…Using standard digital microscopes connected to a laptop or mobile phone, our algorithms can probe the pattern of a CSR 'tag' incorporated into any physical item of interest, telling if the item is original or not by comparing with pre-recorded characteristics stored in a database. 27 An example where a minuscule CSR tag (less than a millimeter in diameter) is incorporated onto a ring is shown in Fig. 6.…”

Unclonable human-invisible machine vision markers leveraging the omnidirectional chiral Bragg diffraction of cholesteric spherical reflectors

“…Robots can also manipulate physical objects identified through their CSR markers to carry out changes that were planned in the digital twin. Moreover, the rich optical characteristics of CSRs 30 – 40 gives each marker a unique fingerprint that allows the reading unit to distinguish an original from a fake 28 , 35 , 38 , 41 , 42 , or to track a certain object throughout its lifetime. This is of great use for increased supply chain transparency and circular economy solutions involving recycled materials and components.…”

“…What this means is that every individual sample created by a sufficiently disperse mixture of CSRs carries a unique fingerprint that can be accessed by microscopic investigation, even if all samples generate the same macroscopic pattern. Arenas et al showed that the identity space is large and that each CSR sample is sufficiently distinct that a certain sample can reliably be re-identified as original, while a different sample will be detected as non-original 41 . This is extremely powerful, because it means that patterns created using CSRs can be deterministic at macroscopic scale, in order to encode easily readable patterns like QR-codes onto an object surface, yet each individual copy of the pattern is unique and identifiable, allowing reliable authentication of the objects carrying the encoding.…”

Birefringence-modulated total internal reflection in liquid crystal shells

“…After demonstrating that the lifetime of shells can be extended by polymer stabilization (Noh et al (2016a); Geng et al (2016a)) or complete polymerization (Fleischmann et al (2012); Jampani et al (2018,2019); Geng et al (2021); Sharma et al (2021)), applications of nematic liquid crystal shells became viable, for instance as exotic sphere-shaped soft liquid crystal elastomer actuators (Fleischmann et al (2012); Jampani et al (2018Jampani et al ( , 2019), where the actuation pattern can be templated by topological defects (Sharma et al (2021)), or for sensing of biologically active molecules such as lipids (Sharma et al (2022)). Most efforts to apply liquid crystal shells have, however, utilized cholesteric liquid crystals with short enough pitch to exhibit selective Bragg reflection, since the resulting unique optical properties (Geng et al (2016a); Lee et al (2017); Geng et al (2018); Park et al ( 2020)) open for innovative applications across diverse areas, from sensing (Kim and Park (2017); Myung and Park (2019)), lasing (Uchida et al (2013); Iwai et al (2020)), realization of microactuators (Zhang et al (2021)) and amplifying photonic upconversion (Kang et al (2017)) to anti-counterfeiting (Geng et al (2016a); Schwartz et al (2018); Arenas et al (2022)) and assisting robots and Augmented Reality devices in interpreting their surroundings (Schwartz et al (2018); Geng et al (2021); Schwartz et al (2021)).…”