The underused part of the electromagnetic spectrum receives an optical impulse from the metamaterial

Terahertz, or T-ray, radiation has barely been exploited compared to most of the rest of the electromagnetic spectrum. However, T-rays potentially have applications in next-generation (6G / 7G) wireless communications, security systems, biomedicine, and even art history. A new device to control T-rays using a specially designed ‘meta-surface’ with properties not found in nature could begin to realize this potential.

The findings are published in the peer-reviewed journal. Express Optic on July 13, 2020.

Terahertz gap is a term used by engineers to describe the little technology that uses the frequency band in the electromagnetic spectrum between microwaves and infrared radiation: terahertz radiation (also called T-rays).

While it is easy to generate and handle microwaves and infrared radiation, practical technologies that work at room temperature and can do the same thing with T-rays are inefficient and impractical. It is a great shame, as the properties of T-rays would make them extremely useful if we could take advantage of them.

T-rays can penetrate opaque objects like X-rays, but they are not ionizing, making them much safer. They can also pass through clothing, wood, plastics and ceramics, making them of interest to the security and surveillance sector to obtain real-time images to identify hidden weapons or explosives. For this same reason, terahertz radiation applications are also promising for cultural heritage science, offering art historians and museums a radiation-free option for investigating artifacts ranging from paintings to mummies.

Terahertz technology that enables the generation, detection and application of terahertz waves has taken off in the last decade or so, bridging the terahertz gap somewhat. But the performance and dimensions of conventional optical components capable of manipulating terahertz waves have not kept up with this rapid development. One reason is the lack of suitable natural materials for the terahertz waveband.

However, researchers at the Tokyo University of Agriculture and Technology (TUAT) led by Associate Professor and Terahertz wave engineer Takehito Suzuki have recently developed an optical component that can more easily manipulate T-rays and in a practical way, using a material that does not not occur in nature.

Conventionally, a collimator, a device that narrows rays or waves, usually consisting of a curved lens or mirror, that can manipulate T-rays is a bulky three-dimensional structure made of natural materials.

But TUAT researchers Takehito Suzuki, Kota Endo and Satoshi Kondoh have devised a collimator as an ultrathin plane (2.22 microns) made of a ‘meta-surface’, a material designed to have properties impossible or difficult to find in nature. . These properties come not from the metal or plastic base substance of which they are composed, but from the geometry and arrangement of the material in small repetitive patterns that can bend electromagnetic waves in a way that natural substances cannot.

In this case, the material has an extremely high refractive index (how slow light travels through it) and low reflectance (proportion of light reflected after hitting a surface). The collimator consists of 339 pairs of metaatoms arranged so that the refractive index increases concentrically from the outside to the center of the device.

“The meta-surface design is unprecedented,” said Suzuki, “offering much higher performance that should accelerate the development of a wide range of applications, including next-generation wireless communications (6G / 7G) and even radiation control devices. thermal “.

Provided by Tokyo University of Agriculture and Technology