Unclonable Anti‐Counterfeiting Labels Based on Microlens Arrays and Luminescent Microparticles

Abstract

Micron‐scale randomness during manufacturing can create unique and unclonable anti‐counterfeiting labels. The security of such labels typically comes at the expense of complex hardware being required for authentication. This work demonstrates unclonable labels that can be authenticated using simple hardware such as a standard light‐emitting diode and smartphone camera. These labels consist of a microlens array laminated to a luminescent‐microparticle‐doped polymer film, and thereby present a new method of making microscopic particle distributions visible on the macroscopic scale. The current novel design offers two significant practical advantages: 1) use of an incoherent source; and 2) authentication independent of the detector position. A comparison of 100 test images against 100 different reference images (total of 10,000 comparisons out of which 100 should authenticate and 9900 should not), demonstrates that authentication is robust with an estimated probability of a false positive on the order of 10−15. Finally, a proof‐of‐concept is demonstrated through successful authentication of a label by a single smartphone, simultaneously providing both excitation and detection on the front side of the label.

Expanding the Angle of Incidence Tolerance of Unclonable Anticounterfeiting Labels Based on Microlens Arrays and Luminescent Microparticles

“…The mathematical expression of the lateral shift of foci, owing to a change of AOI () is , where F is the focal length of ML. [ 9 ] For AOIs close to normal thus, simplifying to . In our previous work, we used an MLA with F = 1900 μm, leading to μm/°.…”

“…This is a slightly modified version of the previously reported method, which allows the lenses with a shorter focal length to be used. [ 9 ] First, a thin PDMS layer doped with the DS phosphor is deposited on a glass slide. The S, M, or L, phosphor particles are first mixed in the PDMS base (SYLGARD 184, Dowsil, RTV‐615, Component A) using a high‐speed dispersion device (CAT M. zipper GmbH) such that the end concentration of the phosphors in the PDMS layer is 0.5 wt%.…”

“…In our previous work, we established an algorithm to binarize the bright point patterns, then compare a test image to a reference image. [ 9 ] The algorithm outputs a number of “votes” which represents the number of points it considers for matching between the two images. A threshold number of votes, above which the test and reference images are considered to be the same, can be determined by the analysis of a sufficiently large set of images with known reference and test pairs.…”

“…Previously, we performed such analysis on 10 000 image comparisons for four equivalent labels, with equivalent being understood as having the same processing conditions, but naturally different bright point‐patterns owing to the uniqueness of each label attributed to stochastic variation in microparticle positions. [ 9 ] This led to a threshold number of 15 votes above which one could consider the test and reference as matching and therefore the label as authentic. As described in Section 4 of the Supporting Information, we perform a similar analysis for these new labels.…”

“…In our previous work, we implemented a microlens array (MLA) and an UC phosphor‐doped PDMS matrix to develop an unclonable label. [ 9 ] Upon illumination of the label with 980 nm laser light, a bright point‐pattern of visible luminescence was generated. This point‐pattern was caused due to much brighter emission from a microparticle phosphor when it lies in the focus of a microlens.…”