Engineers at Iowa State University have developed cloaking technology that could help make stealth aircraft even more invisible to radar. Typically, stealth aircraft is coated in a material that reduces backscattering (the signals reflected back to a probing radar), but now the Iowa engineers have developed a new cloaking material that suppresses radar waves in all incident directions and observation angles. They call their invention “meta-skin” because it is made from metamaterials— synthetic composites that are engineered to manipulate electromagnetic waves.
By stretching and flexing the new meta-skin, engineers can tune it ot reflect a wide range of radar frequencies. The researchers described their invention in the journal Scientific Reports.
The meta-skin is composed of an array of liquid metallic split ring resonators embedded in a stretchable elastomer. When stretched, the meta-skin performs as a tunable frequency selective surface with a wide resonance frequency tuning range. When wrapped around a curved dielectric material, the meta-skin functions as a flexible “cloaking” surface to significantly suppress scattering from the surface of the dielectric material along different directions.
To make the meta-skin, the researchers used a metal alloy called galistan, which is liquid at room temperature, to create a small liquid wire ring with a 1 millimeter gap. The rings form electric inductors, the gaps create electric capacitors, and together they become resonator that can trap and suppress radar waves. The researchers embedded rows of these tiny liquid-metal rings between sheets of silicone. Stretching the meta-skin changes the size of the rings in the material, which therefore changes the frequency the devices suppress.
The long-term goal is to shrink the size of these devices. Then hopefully we can do this with higher-frequency electromagnetic waves such as visible or infrared light. While that would require advanced nanomanufacturing technologies and appropriate structural modifications, we think this study proves the concept of frequency tuning and broadening, and multidirectional wave suppression with skin-type metamaterials.
