60 seconds on... stealth materials

Materials World magazine
1 Dec 2015

What is it?

As radar technology improves, formerly stealthy fighter jets have more chance of being identified in the sky. This tunable ultra-thin broadband active frequency selective surface (AFSS) absorber with a stretching transformation (ST) pattern is for use in the ultrahigh-frequency (UHF) band (reflectivity of 0.7–1.9 GHz below −10 dB) that some modern radars are now able to scan. 

What is it made of?

It is a layered material incorporating a top layer of an FR-4 glass-reinforced epoxy laminate sheet with a thickness of 0.8mm for mechanical strength. The next layer is the AFSS, fabricated on a printed circuit board loaded with resistors and capacitors soldered between two units. The thickness of the copper in this layer is 0.04mm. The third layer, used as a separation layer, is a 7.0mm honeycomb. The fabricated example had measurements of 500x500x7.8mm, with a total specific mass of 0.189g/cm2. The total thickness is ~λ/54 of the lower limit frequency, ~λ/29 of the centre frequency, and ~λ/20 of the higher limit frequency.

Who is involved?

A team from the School of Optical and Electronic Information and the Key Lab of Functional Materials for Electronic Information, at Huazhong University of Science and Technology, China.

What could it replace?

Microwave absorbers reduce the radar cross sections of aircraft. Radars have improved to be able to approach near-metre microwave wavelengths, so improved stealth coatings are needed. Current examples, at frequencies below 2GHz, are limited in application due to their thickness and narrow absorption bandwidth. The authors of the paper note, 'As radar detection equipment continues to improve, our thin absorbers with broad bandwidth and working in the UHF band will be widely useful.'

To view the full Journal of Applied Physics paper, An ultra-thin broadband active frequency selective surface absorber for ultrahigh-frequency applications, visit bit.ly/1MjQlf