Unlocking the terahertz band to aid military communications
StoryFebruary 05, 2021
The clamor for more bandwidth for military use grows louder all the time, especially as 5G [fifth-generation wireless] networks promise to boost access to mission-critical communications, improve virtual reality/augmented reality tools for troops, and better support autonomous vehicles. In fact, the U.S. Department of Defense (DoD), in its May 2020 report outlining the government’s 5G strategy, called 5G broadband a “critical strategic technology” that the U.S. telecommunications industry must master so as to gain “long-term economic and military advantage.”
One of the numerous projects aimed at dramatically boosting military data throughput is underway at Princeton University’s electrical engineering (EE) department, where researchers – supported in part by the Office of Naval Research (ONR), the Air Force Office of Scientific Research, and the Army Research Office – are working with the terahertz band of the electromagnetic spectrum to control, focus, and increase transmissions.
The research team assembled large-scale programmable metasurfaces using arrays of complementary metal oxide semiconductor (CMOS)-based chip tiles. In a study published in the December 2020 Nature Electronics journal, the researchers reported creation of a key component toward unlocking a communications band that promises to dramatically increase the amount of data wireless systems can transmit.
The programmable surface, termed a metasurface, enables engineers to control and focus transmissions in the terahertz band of the electromagnetic spectrum. The terahertz band is a frequency range located between microwaves and infrared light; if used in communications devices, use of the terahertz band would mean the ability to transmit far greater amounts of data than currently used radio-based wireless systems, according to information on the Princeton EE department website.
The Princeton researchers – including Suresh Venkatesh, a postdoctoral research associate; Kaushik Sengupta, associate professor of electrical engineering; and Hooman Saeidi, a graduate student – have developed a device that focuses and directs terahertz waves that could enhance high-speed communications.
The programmable metasurface device is the key: Unlike radio waves, which easily pass through obstructions including walls, waves in the terahertz band work best with a relatively clear line of sight for transmission. The metasurface device, as it directs and focuses the incoming terahertz waves, is able to beam the transmissions in any desired direction.
This ability, say the researchers, not only could enable dynamically reconfigurable wireless networks, but it could also open up whole new high-rate, high-resolution data applications. The military could employ these capabilities for drone swarms, real-time sensor readings, and precision robotics, they add.
Additionally, because the metasurface is assembled using the same materials used to make standard silicon chips, the cost is fairly low and can be mass-produced and placed in line-of-sight formation where needed. (Figure 1.)
The Nature Electronics article described the design of the metasurface as featuring hundreds of programmable terahertz elements, each less than 100 micrometers in diameter and just 3.4 micrometers tall, consisting of layers of copper and paired with active electronics that collectively resonate with the structure. The electronics enable adjustments to their geometry at a speed of several billions of times per second – programmable, based on desired application and can split a single incoming terahertz beam up into several dynamic, directable terahertz beams that can maintain line of sight with receivers.
As a proof of concept, the Princeton researchers commissioned a silicon-chip foundry to fabricate the metasurface as tiles onto standard silicon chips. “The tiles are like Lego blocks and are all programmable,” Sengupta says.
ONR program officer Kim Pavlovic said of the research: “The work being done by Dr. Sengupta and his colleagues is truly groundbreaking. The ability to work fluidly within the terahertz band of the electromagnetic spectrum will be a pivotal step forward for increased transmission capabilities across all segments of society, including our naval forces.”
Looking ahead, Sengupta says that the programmable metasurfaces will need to be further developed before they can be used as components in innovative, next-generation networks.
“There are so many things that people would like to do that are not possible with current wireless technology,” he continues. “With these new metasurfaces for terahertz frequencies, we’re getting a lot closer to making those things happen.”
