Nav: Home

Researchers use metamaterials to create two-part optical security features

September 12, 2019

WASHINGTON --Researchers have developed advanced optical security features that use a two-piece metamaterial system to create a difficult-to-replicate optical phenomenon. Metamaterials are engineered to have a property that is not found in naturally occurring materials. The new security features could offer improved forgery protection for high-value products or banknotes and enhance encryption of information such as pin numbers that are physically sent to recipients.

Optical security features are often used today to verify the authenticity of currency, identification cards and valuable products such as electronics. These features include holograms that change color at different viewing angles or patterns that appear only under ultraviolet light. Security features with many hard-to-replicate features are the most secure because they are difficult to reproduce.

"An ideal optical security feature must be hard to copy by unlicensed people, easy to produce in mass, and be interrogated conveniently," said research team leader Gokhan Bakan from the University of Manchester in the UK. "Our approach satisfies all these requirements and could offer more secure goods and information transactions for everyone."

In The Optical Society (OSA) journal Optics Letters, the researchers describe a system in which two thin optical pieces must be placed together to form a metamaterial that reveals a hidden message or QR code that is readable to the naked eye. Re-encryption is performed by peeling off the top part, which contains no information, from the bottom portion that encodes a message.

To protect sensitive information such as a credit card pin, a customer could get the top part of the security feature (the key) from the bank at the time of application. When the encrypted pin arrives by mail the customer would use the key to reveal the pin. If the printout with the encrypted pin number on it is stolen, it would be impossible to decrypt it without the key.

Revealing the secret message

The new two-part security features have a bottom portion that is formed by coating a thin insulating material, or dielectric, on a silver film that is about 120 nanometers thick. This bottom portion is essentially a mirror in that it reflects most of the incoming light. Because its optical properties are defined by the silver film and not affected by the dielectric layer's thickness a message can be hidden on the dielectric by simply adding more dielectric in the shape of the message.

The top part of the security feature is a transparent elastic substrate coated with a metal layer that is about 10 nanometers thick. This part, which acts as a key, doesn't hold any information and appears semi-transparent. When the two parts are put together, with the thin metal on the top part facing the bottom part, it forms an optical cavity whose properties, such as surface color, strongly depend on the dielectric thickness. Thus, as the two pieces are placed together, a stark color contrast appears and reveals the hidden message, which is readable to the naked eye. The approach can be used to create keys that are specific to each message or to make a master key that would work for any message.

"When the two parts of the security feature are stuck together, it creates an optical phenomenon known as the plasmonics-enhanced optical cavity effect," said Bakan. "Although this effect is commonly employed for a variety of applications such as optical filters, we uniquely separated the optical cavity into two, allowing information to be hidden in one part in a way that can only be revealed with the right key."

Flexible security

The researchers demonstrated their new approach by encoding QR codes on rigid substrates as well as flexible substrates that could be used on almost any surface, including banknotes. The QR codes were invisible to the naked eye until an adhesive patch made of the transparent elastic substrate was applied. They also used the approach to encode various patterns and words.

Although the researchers demonstrated an application specific to optical security, the approach could also be used for optical sensing for chemical or biological applications. For example, if certain proteins attached to a thin-film, the modular metamaterial could produce a read-out that was visible to the naked-eye or readable to a camera.

The researchers plan to further develop the new optical security feature by using it with other optical phenomena. They also want to communicate the technology with developers of security tags and banks so that the technology could be tested and developed for real-world applications.

"Our research shows that converting static optical features to modular ones can open up completely new applications," said Bakan. "This offers a new perspective that scientists could use to expand other established optical methods."
-end-
Paper: G. Bakan, S. Ayas, M. Serhatlioglu, A. Dana, C. Elbuken, "Reversible decryption of covert nanometer-thick patterns in modular metamaterials," Opt. Lett., 44, 18, 4507-4510 (2019).

DOI: https://doi.org/10.1364/OL.44.004507.

About Optics Letters

Optics Letters offers rapid dissemination of new results in all areas of optical science with short, original, peer-reviewed communications. Optics Letters accepts papers that are noteworthy to a substantial part of the optics community. Published by The Optical Society and led by Editor-in-Chief Xi Cheng Zhang, University of Rochester, USA. Optics Letters is now available online at OSA Publishing.

About The Optical Society

Founded in 1916, The Optical Society (OSA) is the leading professional organization for scientists, engineers, students and business leaders who fuel discoveries, shape real-life applications and accelerate achievements in the science of light. Through world-renowned publications, meetings and membership initiatives, OSA provides quality research, inspired interactions and dedicated resources for its extensive global network of optics and photonics experts. For more information, visit osa.org.

Media Contact:

mediarelations@osa.org

The Optical Society

Related Metamaterial Articles:

BU researchers design 'intelligent' metamaterial to make MRIs affordable and accessible
Boston University researchers have developed a new, 'intelligent' metamateria l-- which costs less than ten bucks to build -- that could revolutionize magnetic resonance imaging (MRI), making the entire MRI process faster, safer, and more accessible to patients around the world.
Machine learning finds new metamaterial designs for energy harvesting
Electrical engineers at Duke University have harnessed the power of machine learning to design dielectric (non-metal) metamaterials that absorb and emit specific frequencies of terahertz radiation.
New metamaterial morphs into new shapes, taking on new properties
Electrochemical reactions drive shape change in new nanoarchitected metamaterial.
Researchers demonstrate first all-metamaterial optical gas sensor
At FiO + LS conference, researchers will discuss the first fully integrated, non-dispersive infrared (NDIR) gas sensor enabled by specially engineered synthetic materials known as metamaterials.
NUS 'smart' textiles boost connectivity between wearable sensors by 1,000 times
Researchers from the National University of Singapore have incorporated metamaterials into conventional clothing to dramatically improve signal strength between wearable electronic devices.
BU researchers develop new metamaterial that can improve MRI quality and reduce scan time
New magnetic metamaterial could be used as an additive technology to increase the imaging power of lower-strength MRI machines, increasing the number of patients seen by clinics and decreasing associated costs, without any of the risks that come with using higher-strength magnetic fields.
Scientists take a 'metamaterials' approach to earthquake damage
At the SSA 2019 Annual Meeting, seismologists from around the world will discuss how metamaterial theory might be applied to everything from developing deflective barriers to manipulating the layout of buildings within a city as a way to minimize the impact of damaging surface seismic waves.
BU researchers develop 'acoustic metamaterial' that cancels sound
Boston University researchers, Xin Zhang, a professor at the College of Engineering, and Ghaffarivardavagh, a Ph.D. student in the Department of Mechanical Engineering, released a paper in Physical Review demonstrating it's possible to silence noise using an open, ringlike structure, created to mathematically perfect specifications, for cutting out sounds while maintaining airflow.
'Meta-mirror' reflects sound waves in any direction
Researchers at Duke University have constructed a 'meta-mirror' device capable of perfectly reflecting sound waves in any direction.
Researchers discover a metamaterial with inherently robust sound transport
Researchers at the Advanced Science Research Center (ASRC) at The Graduate Center of The City University of New York and at the City College of New York (CCNY) have developed a metamaterial that can transport sound in unusually robust ways along its edges and localize it at its corners.
More Metamaterial News and Metamaterial Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#543 Give a Nerd a Gift
Yup, you guessed it... it's Science for the People's annual holiday episode that helps you figure out what sciency books and gifts to get that special nerd on your list. Or maybe you're looking to build up your reading list for the holiday break and a geeky Christmas sweater to wear to an upcoming party. Returning are pop-science power-readers John Dupuis and Joanne Manaster to dish on the best science books they read this past year. And Rachelle Saunders and Bethany Brookshire squee in delight over some truly delightful science-themed non-book objects for those whose bookshelves are already full. Since...
Now Playing: Radiolab

An Announcement from Radiolab