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05/19/2016 : 157564
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DNA Powers Color-Changing Metamaterial
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Posted by Okachinepa on 05/20/2025 @
Courtesy of SynEVOL
Credit: Weinberg College of Arts and Science at Northwestern University
Utilizing DNA as a crucial instrument, the team manipulated gold nanoparticles of various sizes and shapes, organizing them in two and three dimensions to create optically active superlattices. The researchers state that structures with particular configurations can be designed by selecting particle types and specific DNA patterns and sequences to display nearly any color within the visible spectrum.
“Architecture plays a crucial role in the design of new materials, and we now possess a novel method to accurately regulate particle architectures across extensive regions,” states Chad A. Mirkin, a chemistry professor in the Weinberg College of Arts and Sciences at Northwestern University. "Chemists and physicists will have the capability to create nearly countless new structures featuring a variety of intriguing properties." “No existing method can create these structures.”
The approach merges a traditional manufacturing technique—top-down lithography, which is the same process employed in creating computer chips—with a novel method—programmable self-assembly powered by DNA. The research group is the first to integrate the two for achieving control over individual particles in three dimensions.
Researchers will utilize this powerful and versatile technique to create metamaterials—substances not existing in nature—for various applications, including sensors for both medical and environmental purposes.
The scientists employed a mix of numerical simulations and optical spectroscopy methods to pinpoint specific nanoparticle superlattices that capture certain wavelengths of visible light. The nanoparticles modified with DNA—gold in this instance—are arranged on a pre-designed template composed of complementary DNA. Piles of formations can be created by adding a second, followed by a third DNA-modified particle containing DNA that pairs with the next layers.
Aside from their unique structures, these materials react to stimuli: the DNA strands connecting them alter their length when introduced to different environments, including solutions of varying ethanol concentrations. The researchers discovered that the alteration in DNA length led to a color shift from black to red to green, allowing for significant adjustment of optical traits.
"Adjusting the optical characteristics of metamaterials presents a major challenge, and our research accomplishes one of the largest ranges of tunability reached so far in optical metamaterials," states Koray Aydin, assistant professor of electrical engineering and computer science.
"Our innovative metamaterial platform—facilitated by exact and extensive control over the shape, size, and spacing of gold nanoparticles—offers great potential for future optical metamaterials and metasurfaces," Aydin states.
The research outlines a novel method for arranging nanoparticles in both two and three dimensions. The scientists employed lithography techniques to create tiny apertures—just one nanoparticle in width—in a polymer resist, forming “landing pads” for nanoparticle elements altered with DNA strands. According to Mirkin, the landing pads are crucial because they maintain the vertical growth of the structures.
The tiny landing pads are altered with a specific DNA sequence, while the gold nanoparticles are adjusted with corresponding complementary DNA. By interspersing nanoparticles with matching DNA, the scientists created nanoparticle structures with exceptional positional precision and across an extensive area. The particles may vary in size and shape, such as spheres, cubes, and disks.
"This method can be utilized to create periodic lattices from optically active particles like gold, silver, and other materials that can be altered with DNA, achieving remarkable nanoscale accuracy," states Mirkin, director of Northwestern's International Institute for Nanotechnology. Mirkin additionally serves as a medicine professor at Feinberg School of Medicine and teaches chemical and biological engineering, biomedical engineering, and materials science and engineering at the McCormick School.
The success of the described DNA programmable assembly depended on proficiency with hybrid (soft-hard) materials and exceptional nanopatterning and lithographic skills to attain the necessary spatial resolution, precision, and accuracy over extensive substrate regions. The project team sought the expertise of Vinayak P. Dravid, a seasoned associate of Mirkin’s known for his skills in nanopatterning, advanced microscopy, and the characterization of soft, hard, and hybrid nanostructures.
Dravid, a professor in materials science and engineering as well as the founding director of the NUANCE center, which contains the advanced patterning, lithography, and characterization methods employed in DNA-programmed structures, provided his expertise and aided in developing the nanopatterning and lithography approach along with the characterization of the novel exotic structures.
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6G Signals Vulnerable to New Eavesdropping Tool
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Posted by Okachinepa on 05/20/2025 @
Courtesy of SynEVOL
Credit: Rice University
In the research, Knightly, along with Brown University engineering professor Daniel Mittleman and his team, demonstrated that an attacker could effortlessly create a piece of office paper adorned with 2D foil patterns—a metasurface—and employ it to redirect a portion of a 150 gigahertz "pencil beam" transmission between two individuals.
They named the assault “Metasurface-in-the-Middle” to reference both the hacker's instrument and how it is utilized. Metasurfaces are slender layers of material featuring patterned designs that control light or electromagnetic waves. “Man-in-the-middle” is a term used in the computer security field to describe attacks where an attacker discreetly positions themselves between two parties.
The 150 gigahertz frequency surpasses the frequencies utilized in current 5G cellular or Wi-Fi networks. However, Knightly notes that wireless providers aim to deploy 150 gigahertz and comparable frequencies referred to as terahertz waves or millimeter waves in the coming decade.
“Wireless technology of the next generation will utilize elevated frequencies and focused beams to facilitate wide-band applications such as virtual reality and self-driving cars,” states Knightly, who will share the research alongside coauthor Zhambyl Shaikhanov, a graduate student in his laboratory.
In the research, the scientists utilize the names Alice and Bob to denote the two individuals whose messages are compromised. The person who listens in is named Eve.
To initiate the attack, Eve first creates a metasurface that will redirect some of the focused signal to her position. To illustrate their findings, the researchers created a design featuring hundreds of rows of divided rings. Each resembles the letter C, yet they are not the same. The exposed section of every ring differs in dimensions and direction.
"Shaikhanov states that those openings and orientations are precisely designed to direct the signal to diffract in the exact way Eve desires." "Once she creates the metasurface, she prints it using a standard laser printer, and afterward, she applies a hot stamping method typically employed in crafting." She puts a sheet of metal foil over the printed paper, runs it through a laminator, and the heat along with pressure forms a bond between the foil and the toner.
Mittleman and his research partner Hichem Guerboukha, a postdoctoral fellow at Brown, demonstrate in a study from 2021 that the hot-stamping technique could create split-ring metasurfaces with resonances reaching 550 GHz.
“We created this method to reduce the obstacles associated with the production of metasurfaces, enabling researchers to rapidly and affordably test a variety of designs,” Mittleman states. "Naturally, this also reduces the obstacles for eavesdroppers."
The researchers express their desire that the study will eliminate a prevalent misunderstanding in the wireless industry that higher frequencies are naturally secure.
“Individuals have stated that millimeter-wave frequencies are ‘secretive’ and ‘extremely classified’ and that they ‘ensure safety,’” Shaikhanov mentions. The idea is, ‘With a very narrow beam, no one can intercept the signal since they would need to be physically positioned between the transmitter and the receiver.’ We have demonstrated that Eve does not need to be intrusive to execute this attack.
The study indicates that it would be hard for Alice or Bob to notice the attack at present. Although the metasurface needs to be positioned between Alice and Bob, "it might be concealed within the surroundings," Knightly states. “You might hide it using other sheets of paper, for example.”
Knightly states that since wireless researchers and equipment makers are aware of the attack, they can investigate it further, create detection systems, and integrate those into terahertz networks from the outset.
“If we had been aware from the very beginning, when the internet was first introduced, that there would be denial-of-service attacks and efforts to disrupt web servers, we would have created it in a different way,” Knightly states. “If you construct initially, await assaults, and then attempt to fix things, that is a far pricier and more expensive route than ensuring secure design from the start.”
"Millimeter-wave frequencies and metasurfaces represent emerging technologies that can both enhance communication; however, whenever we acquire a new communication capability, we must consider the question, 'What if the opponent possesses this technology?" What new abilities will it provide them that were unavailable before? And what measures can we take to establish a secure network against a formidable opponent?
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Can Curved Light Boost Wireless Communication?
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Posted by Okachinepa on 05/20/2025 @
Courtesy of SynEVOL
Credit: Brown University and Rice University
Although cellular networks and WiFi systems have become more sophisticated than before, they are rapidly approaching their bandwidth capacities. Researchers understand that soon they must shift to significantly greater communication frequencies than those used by current systems, but several—quite literal—barriers must be overcome first.
Researchers at Brown University and Rice University report that they’ve moved one step nearer to overcoming solid barriers, such as walls, furniture, and even individuals—achieving this by bending light.
In the recent study published in Communications Engineering, the researchers explain how they are contributing to resolving one of the major bottlenecks appearing in wireless communication. Present systems utilize microwave radiation for data transmission; however, it has become evident that the future norm for data transfer will employ terahertz waves, which can carry up to 100 times more data than microwaves. A persistent problem is that, contrary to microwaves, terahertz signals are obstructed by many solid materials, necessitating a clear line of sight between the transmitter and the receiver.
"Many individuals likely utilize a WiFi base station that saturates the area with wireless signals," states Daniel Mittleman, a professor at Brown’s School of Engineering and the senior author of the research. "Regardless of where they go, they keep the connection." At the elevated frequencies we're discussing here, you won't be able to accomplish that anymore. Rather, it will be a directional beam. If you shift positions, that beam must track your movement to keep the connection intact; otherwise, if you step out of the beam's reach or something interferes with it, you won't receive any signal.
The researchers bypassed this issue by generating a terahertz signal that navigates a curved path around an obstacle, rather than being obstructed by it. The innovative approach presented in the research has the potential to transform wireless communication and underscores the future viability of wireless data networks operating at terahertz frequencies, as stated by the researchers.
“We aim for increased data per second,” Mittleman states. “To achieve that, you require additional bandwidth, which is not available with standard frequency bands.”
In the research, Mittleman and his team present the idea of self-accelerating beams. The beams are unique arrangements of electromagnetic waves that inherently bend or arc to one side while traveling through space. The beams have been examined at optical frequencies but are currently being investigated for terahertz communication.
The scientists employed this concept as a starting point. They created transmitters with precisely crafted designs, enabling the system to control the strength, intensity, and timing of the generated electromagnetic waves. By controlling the light in this way, the researchers enable the waves to function together more efficiently, preserving the signal when a solid object obstructs part of the beam.
Basically, the light beam adapts to the obstruction by reallocating data through the configurations that the researchers designed into the transmitter. If one pattern is obstructed, the data moves to the subsequent one, and then to the next if that is also obstructed. This maintains the signal connection entirely intact. Without this degree of control, when the beam is obstructed, the system cannot adjust, resulting in no signal passing through.
This allows the signal to curve around obstacles as long as the transmitter is not fully obstructed. If it is entirely obstructed, an alternative method for delivering the data to the recipient will be required.
"Curving a beam does not address every potential blockage issue, yet it effectively resolves certain ones and does so more efficiently than previous attempts," states Hichem Guerboukha, who conducted the research as a postdoctoral fellow at Brown and is presently an assistant professor at the University of Missouri–Kansas City.
The researchers confirmed their results by conducting extensive simulations and experiments that involved maneuvering around obstacles to ensure that communication links remained highly reliable and intact. The research expands on an earlier investigation by the team which demonstrated that terahertz data connections can reflect off walls in a room without losing significant amounts of information.
Through the utilization of these curved beams, the researchers aim to eventually enhance the reliability of wireless networks, even in dense or obstructed settings. This may result in quicker and more reliable internet connections in locations such as workplaces or urban areas where barriers are frequent. Before reaching that stage, though, there is a significant amount of fundamental research that needs to be conducted and many obstacles to tackle, as terahertz communication technology remains in its early stages.
"One of the main inquiries we receive is about how much you can curve and how far it extends," says Mittleman. "We've made some rough assessments of these matters, but we haven't properly measured them yet, so we aim to outline it."
The project received support from the National Science Foundation and the Air Force Office of Scientific Research.
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Next-Gen Antenna Delivers Mobile 5G
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Posted by Okachinepa on 05/20/2025 @
Courtesy of SynEVOL
Credit: University of Notre Dame
Worldwide, two billion individuals utilize fifth-generation (5G) wireless networks. These users have achieved faster upload and download speeds, reduced latency, and improved reliability on their mobile devices.
However, the introduction of 5G technology has also brought a significant energy expense. 5G networks consume more energy than earlier generations, with each base station using power equivalent to that of 73 US households.
Currently, with financial support from the US Army, scientists at the University of Notre Dame are initiating a project that might assist in reversing this trend.
The team will utilize previous research performed at the university regarding the physics of low-power antennas. Collaborating with a group of industry partners, they intend to create an antenna that provides 5G-level performance while consuming under 10% of the energy.
The group is directed by Jonathan Chisum, an associate professor in the electrical engineering department and a member of Notre Dame’s Wireless Institute. Chisum states that the essential element of the new antenna is a type of synthetic dielectric substance created and constructed in his laboratory.
“Currently, a significant part of the expenses to run a cellular network is for electricity.” According to Chisum, the reason is clear when observing a cell tower: it employs a distinct antenna for each band, which depends on active, powered chips.
"Our original concept was straightforward: What if we could integrate comparable features into a single very wideband antenna by allowing the properties of materials to perform the functions typically handled by numerous energy-consuming chips?"
The latest low-power antenna is a variant of the millimeter-wave gradient index (GRIN) lens antenna. Even though GRIN lenses have been around for more than a hundred years, the concept of creating a GRIN lens antenna for 5G networks once appeared unrealistic to many researchers in wireless technology. In the last eight years, Chisum and his laboratory have achieved revolutionary findings in the basic science of wideband beam steering. These results enabled Chisum and his team to develop a single antenna that functions across all frequency bands for 5G, a task previously considered unachievable.
The antenna's broadband, low-energy features render it particularly beneficial for the U.S. Army. The Army participated in advancing 5G technology and depends on it not only for secure communications but also for equipment tracking and monitoring soldiers' health. Nonetheless, implementing current 5G technologies is challenging and expensive to establish, move, and manage in the field.
"The Army must manage 5G networks internationally," Chisum clarifies, "and these networks function at various frequencies around the world." Therefore, a solution with wideband capabilities like ours is a crucial feature. Moreover, as it requires minimal power and is compact and light, it can be incorporated into a mobile platform.
Upon implementation, the technology will offer a "5G-on-the-go" solution that enhances efficiency, safety, and adaptability.
Chisum also highlights that creating this new technology is the initial step in incorporating it into mobile networks for public use.
The installation of 5G millimeter-wave base stations in existing 5G networks has come to a halt as operators find the expenses of the present multi-antenna solutions prohibitive. “Yet, wideband 5G antennas that utilize GRIN lenses present new opportunities for reducing expenses and enhancing efficiency in commercial wireless networks,” Chisum states.
Up to this point, Chisum and his team have created a functional prototype of their design manufactured in the lab one thin layer at a time via an intricate 100-hour procedure. The team is creating a streamlined and economical method to produce the device utilizing advanced 3D printing technology. It will enable Chisum’s team to showcase the technology in real-world settings, facilitating its incorporation into a 5G network.
To move this technology from the laboratory to practical use, Chisum's lab has assembled a group of industry collaborators. The group will consist of several top vendors with specialized knowledge in wireless networking, antennas, and additive manufacturing, specifically tailored for GRIN media.
Nicolas Garcia, the CEO of Cheshir Industries, states, “The team at Cheshir Industries is thrilled and honored to spearhead the lens and array design initiatives for Notre Dame’s 5G-on-the-go antenna development project." This initiative signifies not just a crucial advancement in enhancing our nation's wireless technologies but also a significant achievement in the commercialization and evolution of wideband GRIN antenna systems.
Cheshir Industries was started with assistance from Notre Dame’s IDEA Center. Chisum co-founded it along with two alumni from Notre Dame’s Electrical Engineering doctoral program: Nicolas Garcia and Nicholas Estes.
Karlo Delos Reyes, chief customer officer and cofounder of Fortify, states, “As the frontrunner in RF design and manufacturing, we at 3D Fortify are excited to team up with the University of Notre Dame and our industry collaborators to provide advanced technology.” This collaboration enables us to utilize our enhanced skills to expand the limits of what can be achieved in GRIN lens antenna design. Collectively, we are collaborating throughout the value chain to create a groundbreaking solution that will set the foundation for upcoming civilian uses.
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First Room-Temperature 2D Altermagnet Discovered by Physicists
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Posted by Okachinepa on 05/20/2025 @
Courtesy of SynEVOL
Credit: Hong Kong University of Science and Technology
Altermagnets are a recently identified category of materials that exhibit momentum-dependent spin splitting without the need for spin-orbit coupling (SOC) or overall magnetization. These materials have recently attracted global interest.
A research group headed by Prof. Junwei Liu from the Department of Physics at the Hong Kong University of Science and Technology (HKUST), along with experimental partners, released pioneering results in Nature Physics. Their research presents the first experimental detection of a two-dimensional layered altermagnet that remains stable at room temperature, validating theoretical predictions proposed by Prof. Liu in Nature Communications in 2021.
The capacity to create and manage spin-polarized electronic states is crucial for progressing spintronics, a field that utilizes spin to store and manipulate information. Traditionally, spin polarization occurs due to the interaction between an electron's spin and other characteristics, like orbital motion or magnetic fields. This coupling may happen via SOC, resulting in momentum-dependent spin splitting in crystals without inversion symmetry (as observed in the Rashba-Dresselhaus effect), or due to the breaking of time-reversal symmetry in ferromagnets, which results in momentum-independent Zeeman-type splitting.
Courtesy of SynEVOL
Credit: Hong Kong University of Science and Technology
Prof. Liu and his team suggested an alternative mechanism in antiferromagnets. In this model, specific crystal symmetries enable sublattices to interact via exchange coupling, resulting in significant spin splitting. This interaction leads to an unusual phenomenon known as C-paired spin-valley locking.
Notably, this process does not depend on SOC or magnetization. It provides the reliability of antiferromagnetic systems combined with prolonged spin lifetimes. These nontraditional materials are referred to as “altermagnets.” Their finding was acknowledged as one of the top 10 breakthroughs of 2024 by Science magazine.
Courtesy of SynEVOL
Credit: Hong Kong University of Science and Technology
Despite considerable theoretical and experimental work to investigate unconventional antiferromagnets utilizing new materials such as α-MnTe, CrSb, MnTe2, and RuO2, none satisfy the symmetry and conductivity criteria for nonrelativistic spin-conserved spin currents stemming from altermagnetism. The magnetic sublattices in α-MnTe and CrSb exhibit C₃ symmetry, resulting in isotropic conductivity and unpolarized currents.
In MnTe2, spin conservation is not observed because of its noncoplanar magnetic configuration, and its low critical temperature (87 K) restricts practical uses. For RuO2, there is still debate over whether its ground state is antiferromagnetic or nonmagnetic, even with evidence of the anomalous Hall effect and spin splitting.
Courtesy of SynEVOL
Credit: Hong Kong University of Science and Technology
Furthermore, these materials lack layering, limiting their ability for exfoliation and combination with other substances to manipulate properties at the microscopic scale. This constraint restricts the investigation of phenomena in 2D materials, including topological superconductors through the superconducting proximity effect, adjustable electronic characteristics via gating, and moiré superlattices.
Consequently, investigating layered materials in altermagnets is crucial for creating high-density, high-speed, and low-energy-use spintronic devices. Prof. Liu’s examination of a two-dimensional layered altermagnet at room temperature provides new insights into this field.
Drawing on theoretical forecasts from Prof. Liu’s group regarding V₂Te₂O and V₂Se₂O in 2021, this study illustrates the achievement of C-paired spin-valley locking (SVL) in a layered, room-temperature antiferromagnetic (AFM) material Rb1-δV2Te2O by employing spin and angle-resolved photoemission spectroscopy (Spin-ARPES), scanning tunneling microscopy/spectroscopy (STM/STS), and first-principles computations.
Courtesy of SynEVOL
Credit: Hong Kong University of Science and Technology
Significant discoveries encompass the direct observation of C-paired SVL via Spin-ARPES measurements, which uncover contrasting spin polarization signs between neighboring X and Y valleys linked by crystal symmetry C. Temperature-dependent ARPES assessments indicate SVL stability remains intact up to room temperature, aligning with the AFM phase transition temperature.
Moreover, ARPES data verify a pronounced two-dimensional nature with minimal dispersion in the kz direction, while quasi-particle interference patterns obtained from STM images show reduced inter-valley scattering resulting from spin selection rules.
Prof. Liu's research showcases the initial layered room-temperature AFM metal featuring alternating magnetic sublattices and a novel spin-splitting effect, presenting an excellent foundation for additional investigations and applications in spintronics and valleytronics. Notably, all experimental findings correlate strongly with first-principles calculations, bolstering trust in the theoretical efforts and indicating possible access to spin-conserved currents and unique piezomagnetism. Comparable spin-valley locking has been noted in K-intercalated V₂Se₂O, which further supports Prof. Liu’s theoretical predictions made in 2021.
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