Chinese scientists have developed an ultra-thin, tunable microwave absorber that can operate over a broad range of frequencies, demonstrating its potential in improving aircraft cloaking, warship stealth and broadband antenna
Microwave absorbers are a kind of material that can effectively absorb incident microwave energy to make objects invisible to radar; therefore they are commonly used in aircraft cloaking and warship stealth.
Recently, as radar detection devices have been improved to detect the near-meter microwave length regime, scientists are working on high-performance absorbers that can cloak objects in the equivalent ultra-high frequency regime (from 300 megahertz to two gigahertz). However, conventional absorbers for the ultra-high regime are usually thick, heavy or have narrow absorption bandwidth, making them unsuitable for stealth missions.
To solve this problem, a team of researchers from Huazhong University of Science and Technology in China has developed an ultra-thin, tunable broadband microwave absorber for ultra-high frequency applications. This ultra-thin absorbing surface, called an active frequency-selective surface absorber, consists of arrays of patterned conductors loaded with two common types of circuit elements known as resistors and varactors.
The unit patterned cell absorbs microwaves and can also be actively controlled by stretching to expand the tunable bandwidth. In a paper published this week in the Journal of Applied Physics, from AIP Publishing, the researchers presented this work.
“Our proposed absorber was fabricated with a stretching transformation pattern, which is both thin and can absorb a wide range of frequencies for near-meter microwave application,” said Wenhua Xu, the primary researcher in the team led by Jianjun Jiang, a professor of School of Optical and Electronic Information at the Huazhong University of Science and Technology, China.
“Its absorption range covers a broad band from 0.7 to 1.9 gigahertz below -10 decibel, and the total thickness of the absorber is only 7.8 millimeters, which is one of the thinnest microwave absorbers reported.”
“Usually the thickness of conventional radar absorbers is a quarter the wavelength of the incident microwave. In the high frequency regime, take one gigahertz as an example, the thickness of the absorber would be around 7.5 centimeters, which is too thick and heavy to be used in aircrafts or warships. Our proposed absorber is almost ten times thinner than conventional ones,” Xu said.
Other alternative absorbers, such as metamaterial absorbers made from a resonant metallic structure printed on a dielectric substrate, though significantly thinner than the wavelengths absorbed, have a narrow working bandwidth.
To develop a novel absorber that is both thin and with broadband performance, Jiang’s team employed a type of thin, light periodic structure called a frequency-selective surface, which consists of an assembly of patterned conductors arranged in a two-dimensional array, usually backed by a thin dielectric, to reflect incident microwaves according to their frequency.
In the experiment, Jiang’s team fabricated a broadband active frequency-selective surface with a stretching transformation pattern on a printed circuit board, and soldered the resistors and varactors between each of the two unit patterned cells. The fact that the surface could be stretched meant that the parameters of the unit patterned cell can be actively controlled by stretching.
By modeling the absorber using a transmission line, the researchers found that the varactor provides a variable capacitance at varying bias voltage, which produces the device’s tunability, while the lumped resistor with constant resistance reliably produces strong absorption at the resonance frequency. Besides the lumped impedances of the loaded elements, the researchers discovered that the parameters of the unit patterned cells contribute to the device’s absorption performance as well.
“We applied various stretching transformation coefficients to the unit cell pattern to obtain the available parameters to expand the tunable bandwidth,” Xu said. “Our results suggest that a cell pattern with a smaller stretching transformation coefficients ratio (i.e. width to length ratio of the unit cell) leads to higher resonance frequency absorption and produces a wider tunable bandwidth as well.”
Xu noted that it is the first time that stretching transformation pattern is used in the active frequency-selective surface absorber to expand the bandwidth, which turns out to be an effective technique for producing broadband tunability.
“At frequencies below two gigahertz, conventional microwaves absorbers are limited in application by their thickness and narrow absorption bandwidth. Our proposed absorber has achieved broadband tunability and ultra-thin film simultaneously,” Xu said. “The total thickness of 7.8 millimeters is around one twenty-ninth wavelength of the central frequency of incident microwaves, and the ultra-thin absorber with broad bandwidth may be widely used in warship stealth, airplane cloaking and tunable, broadband antennae.”
The researchers’ next step is to study the polarization and the oblique incidence performance for the proposed active frequency-selective surface absorber.
The article "An ultra-thin broadband active frequency-selective surface absorber for ultrahigh-frequency applications" is authored by Wenhua Xu, Yun He, Peng Kong, Jialin Li, Haibing Xu, Ling Miao, Shaowei Bie and Jianjun Jiang. It will be published in the Journal of Applied Physics on November 10, 2015 (DOI: 10.1063/1.4934683). After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/jap/118/18/10.1063/1.4934683
The authors of this study are affiliated with Huazhong University of Science and Technology, China.
ABOUT THE JOURNAL
Journal of Applied Physics is an influential international journal publishing significant new experimental and theoretical results of applied physics research. See: http://jap.aip.org
Jason Socrates Bardi
Jason Socrates Bardi | newswise
APEX takes a glimpse into the heart of darkness
25.05.2018 | Max-Planck-Institut für Radioastronomie
First chip-scale broadband optical system that can sense molecules in the mid-IR
24.05.2018 | Columbia University School of Engineering and Applied Science
The more electronics steer, accelerate and brake cars, the more important it is to protect them against cyber-attacks. That is why 15 partners from industry and academia will work together over the next three years on new approaches to IT security in self-driving cars. The joint project goes by the name Security For Connected, Autonomous Cars (SecForCARs) and has funding of €7.2 million from the German Federal Ministry of Education and Research. Infineon is leading the project.
Vehicles already offer diverse communication interfaces and more and more automated functions, such as distance and lane-keeping assist systems. At the same...
A research team led by physicists at the Technical University of Munich (TUM) has developed molecular nanoswitches that can be toggled between two structurally different states using an applied voltage. They can serve as the basis for a pioneering class of devices that could replace silicon-based components with organic molecules.
The development of new electronic technologies drives the incessant reduction of functional component sizes. In the context of an international collaborative...
At the LASYS 2018, from June 5th to 7th, the Laser Zentrum Hannover e.V. (LZH) will be showcasing processes for the laser material processing of tomorrow in hall 4 at stand 4E75. With blown bomb shells the LZH will present first results of a research project on civil security.
At this year's LASYS, the LZH will exhibit light-based processes such as cutting, welding, ablation and structuring as well as additive manufacturing for...
There are videos on the internet that can make one marvel at technology. For example, a smartphone is casually bent around the arm or a thin-film display is rolled in all directions and with almost every diameter. From the user's point of view, this looks fantastic. From a professional point of view, however, the question arises: Is that already possible?
At Display Week 2018, scientists from the Fraunhofer Institute for Applied Polymer Research IAP will be demonstrating today’s technological possibilities and...
So-called quantum many-body scars allow quantum systems to stay out of equilibrium much longer, explaining experiment | Study published in Nature Physics
Recently, researchers from Harvard and MIT succeeded in trapping a record 53 atoms and individually controlling their quantum state, realizing what is called a...
25.05.2018 | Event News
02.05.2018 | Event News
13.04.2018 | Event News
25.05.2018 | Event News
25.05.2018 | Machine Engineering
25.05.2018 | Life Sciences