Electrically controlled reflective films, as presented by Younjung Park and Heeyeon Kim of NANOSILIKHAN Advanced Materials, have taken a class of technologies long known in smart glazing and displays and adapted it specifically for high-security identification documents.
In their paper ‘Digitizing Optical Security Features for the Future: Electrically Controlled Reflective Film with High Security 1’ in the Optical & Digital Document Security 2025 Proceedings, they describe a passive film whose colour and gloss can be modulated electrically to display dynamic, serialised information with high counterfeit resistance.
Technically, this work sits in the broader family of electrically switchable optical films.
Electrochromic devices, for example, use redox reactions in a thin active layer to reversibly change optical properties such as colour, transmittance, reflectance and emissivity under low applied voltages 2. These systems – typically built as multilayer thin-film stacks with transparent electrodes and an electrolyte – already underpin smart windows, switchable mirrors and reflective displays.
Parallel developments in polymer-dispersed liquid crystal and related ‘smart films’ show how electrically driven changes in scattering can switch a film between transparent and opaque, or between clear and frosted states, at practical voltages over large areas. More recent work couples electrochemical modulation with engineered thin-film interference and structural colour, enabling reflective surfaces whose hue and brightness can be tuned dynamically while maintaining high durability 3.
Park and Kim essentially take this electro-optical toolbox and redesign it for the constraints of secure documents. Their electrically controlled reflective film is conceived as a thin, laminated layer on a reflective substrate, incorporating an electro-responsive medium, transparent electrodes and suitable encapsulation.
Under zero bias, the film behaves like a conventional optically variable device, with a characteristic colour and gloss that can be inspected visually. When an external reader applies an electric field, the internal microstructure of the active layer changes – for instance via ion insertion – altering the film’s reflectance and gloss in a controlled, reversible way.
In the implementation discussed in the proceedings, this modulation is engineered to reveal time-dependent, spatially resolved patterns that encode serialised information, turning the film into a low-resolution reflective display optimised for security rather than for human-readable text.
For ID-1 format cards, this enables a link between the physical credential and electronic data. Any attempt to counterfeit the card has to reproduce both the chip content and the correct electro-optical dynamics of the film, rather than imitating a static graphic or colour-shift effect.
This approach allows for inspection at several layers. In routine checks, inspectors can rely on familiar first-line behaviour, tilting the card and observing its characteristic colour and gloss as with existing diffractive or interference-based OVDs. For higher assurance, a desktop or handheld reader applies a short, low voltage pulse sequence and records the resulting optical response.
From a card-engineering perspective, Park and Kim recognise the need to integrate this electro-optic stack into standard polycarbonate constructions without compromising lamination, durability or chip operation. The film must withstand long-term UV exposure, thermal cycling, humidity and flexing over a five- to 10-year service life. Furthermore, any electrical interface – whether via contact pads or inductive coupling – must remain compatible with ISO/IEC constraints on card dimensions and smartcard modules.
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Overview of the full development process for the security tag, from functional microflake particle design to driving module integration (© NANOSILIKHAN).
The technical background of electrochromic and electrically switchable films shows that such durability and low-voltage operation are achievable in principle; smart windows and automotive mirrors already demonstrate millions of switching cycles in harsh environments 4.
What is new in Park and Kim’s work is not simply the ability to change appearance, but the use of that capability to encode and reveal structured, serialised security information in a form tailored to identity cards. By applying the mature physics of electro-optic thin films with specific threats to document security, their electrically controlled reflective film offers a credible path towards ID cards in which the card surface itself becomes a digitally active security element.
1 - Tuffy, F. (ed.) 2025, Proceedings of the Optical & Digital Document Security (ODDS) Conference, Reconnaissance International, ISSN 2978-5510 (online), https://estore.reconnaissance.net/product/proceedings-of-the-optical-digital-document-security-conference-2025-odds/
2 - www.jim.org.cn/EN/10.15541/jim20200465
3 - www.nature.com/articles/s41377-020-00366-9
4 - www.sciencedirect.com/science/article/pii/S2451929423002474
