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Making Waves

Smart radar, stealth technology and quantum communication are just some of the fields that rely on the manipulation of electromagnetic waves.

Now, researchers at Nanyang Technological University’s School of Electrical and Electronic Engineering (EEE), Centre for Bio Devices and Signal Analysis (VALENS), led by Professor Liu Ai Qun have developed the first-ever broadband wide-angle multifunctional polarization converter.

It can be tuned to convert electromagnetic waves to different polarisation states. This could be used for a wide range of applications, including “cloak” items and make them invisible to radar.

While metasurfaces – which are flat, ultra-thin optical components – have been used as polarisation converters, they can only convert electromagnetic waves from one specified state to another specified state.

Some researchers have proposed using micro-electromechanical systems (MEMS) to control a metasurface’s elements. This would allow users to change the metasurface continuously so that it can convert electromagnetic waves to different polarisation states.

As a metasurface’s size grows, however, it would require more and more complex MEMS, eventually affecting its performance.

The EEE researchers sidestepped this limitation by developing a liquid metal- based metasurface.

Their invention consists of L-shaped resonators and microfluidic channels with one inlet and two outlets. Each resonator has two arms that are filled with galinstan, a highly conductive and non-toxic liquid metal, and hydrochloric acid vapour.

By increasing or decreasing the amount of vapour in each resonator, the length of galinstan in its arms can be tuned from 0.6 mm to 5 mm. This enables the metasurface to act as a multifunctional polarisation converter.

In experiments, the EEE researchers showed that their invention has a broad working bandwidth larger than 60 percent of central frequency and a large angular tolerance of 45 degrees. It also has broadband reflection and optical attenuation functionalities.

“Our converter provides prospects for various applications, such as smart radar, stealth technology and quantum technology,” Professor Liu said.

 

By Professor Liu Ai Qun

Click here to find out more.

 

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Published on: 14-Nov-2017 ​​​​​