Researchers Develop Two-Layer Conformal Coating for Shrinking Waveguides

The characteristics of materials can  behave in funny ways. For instance, if one characteristic is adjusted to render a device less leaky or small in size, some other characteristic may get altered in an unwanted manner, hence engineers have to constantly balance one characteristic against the other.

At present, a group of electrical engineers from Penn State have discovered a technique for controlling disparate optical characteristics of dielectric waveguides at the same instance by means of a two-layer coating. Each layer in the coating has a near-zero weight and thickness.

Rod shaped waveguide with two quasi-two dimensional conformal coatings that shield the waveguide from crosstalk and blocking and allow the waveguide to be smaller. CREDIT: Werner Lab/Penn State.

Imagine the water faucet in your home, which is an essential every-day device. Without pipes to carry the water from its source to the faucet, the device is worthless. It is the same with ‘waveguides.’ They carry electromagnetic or optical signals from the source to the device—an antenna or other microwave, millimeter-wave or terahertz device. Waveguides are an essential component in any electromagnetic or optical system, but they are often overlooked because much of the focus has been on the devices themselves and not the waveguides.

Douglas H. Werner, John L. and Genevieve H. McCain Chair Professor of Electrical Engineering.

Zhi Hao Jiang—former postdoctoral fellow at Penn State and a professor at Southeast University, Nanjing, China, at present—stated that metasurface coatings enable scientists to reduce the diameter of waveguides and regulate the waveguiding properties with unparalleled flexibility.

The team created a very thin material that is nearly two-dimensional and having properties that control and improve the characteristics of the waveguide.

They created and investigated two conformal coatings—one for the purpose of signal guiding and the other to cloak the waveguide. They developed the coatings by sensibly engineering the patterns on the surfaces to ensure innovative and transformative waveguide performance. The coatings are spread on a Teflon waveguide that is rod-shaped, where the guiding layer is in contact with the Teflon and the cloaking layer is applied on the outer side.

Such a quasi two-dimensional conformal coating designed to be a cloaking material can be a solution to prevent crosstalk and blockage. In general, dielectric waveguides are not used as a single waveguide but in bundles. However, it is a lamentable fact that traditional waveguides are prone to leak; hence the signal from one waveguide hinders the neighboring ones.

The study has been published in the latest issue of the journal Nature Communications on 25 August 2017 where the team has explained that “the effectiveness of the artificial coating can be well maintained for waveguide bends by properly matching the dispersion properties of the metasurface unit cells.” Despite the fact that the coating can be spread on a bend in the waveguide, after applying the coating, the waveguide cannot be bent.

The size of the waveguides can be made small by enhancing the characteristics of the waveguide to cautiously regulate polarization and other features. Eliminating the crosstalk enables the smaller waveguides to be packed more closely, which can result in increased miniaturization.

In terms of applications these would include millimeter-wave/terahertz/infrared systems for sensing, communications, and imaging that need to manipulate polarization, squeeze signals through waveguides with a smaller cross-section, and/or require dense deployment of interconnected components.


Lei Kang, research associate in electrical engineering from Penn State, was also a part of this research.

This study was funded by the National Science Foundation through the Penn State Materials Research Science and Engineering Center.

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