A programmable surface, called a metasurface, allows engineers to control and focus transmissions in the terahertz band of the electromagnetic spectrum. Terahertz, a frequency range located between microwaves and infrared light, can transit much more data than current radio-based wireless systems.
Unlike radio waves that easily pass through obstructions such as walls, terahertz works best with a relatively clear line of sight for transmission. The metasurface device, with the ability to control and focus incoming terahertz waves, can beam the transmissions in any desired direction. This not only enables dynamically reconfigurable wireless networks but also opens up new high-resolution sensing and imaging technologies for the next generation of robotics, cyberphysical systems, and industrial automation. Because the metasurface is built using standard silicon chip elements, it is low-cost and can be mass-produced for placement on buildings, street signs, and other surfaces.
The metasurface features hundreds of programmable terahertz elements, each less than 100 micrometers (millionths of a meter) in diameter and 3.4 micrometers tall, made of layers of copper and coupled with active electronics that collectively resonate with the structure. This allows adjustments to their geometry at a speed of several billions of times per second. These changes — which are programmable, based on the desired application — split a single incoming terahertz beam up into several dynamic, directable terahertz beams that can maintain line of sight with receivers.
The metasurface was fabricated as tiles onto standard silicon chips, showing that the metasurface can be configured into low-cost, scalable arrays of tiles. The researchers tested tile arrays measuring 2 × 2 with 576 such programmable elements and demonstrated beam control by projecting (invisible) terahertz holograms. These elements are scalable across larger arrays.
One possible way to incorporate these flat tiles into the built environment as next-generation communications network components would be to plaster them as a sort of “smart surface” wallpaper. Other applications include gesture recognition and imaging as well as industrial automation and security. Another potential application is autonomous or self-driving cars that require precise sensing and imaging to make sense of the external world in real time. Semi-autonomous cars today use 77-GHz radars to detect pedestrians and other vehicles. For full, driverless autonomy, cars would benefit by “seeing” the road and obstacles better with terahertz-band sensors and cameras, along with being able to communicate with other vehicles more rapidly.