Making waves with high-power materials
n addition to the CAREER award, Assistant Professor Nader Behdad has received two more prestigious young investigator awards. He has received funding from the U.S. Air Force Office of Scientific Research and the U.S. Office of Naval Research. The programs are designed to foster creative basic research in science and engineering and enhance early-career development of outstanding young researchers.
For the U.S. Air Force program, Behdad is studying a class of synthetic structures known as metamaterials. The structures are composed of layers of metals, dielectrics and other materials that, when layered together, function as a distinct material as far as an electromagnetic wave is concerned. When a wave hits a material, what happens to it is determined by the material’s index of refraction. By creating particular patterns in a synthetic structure, Behdad is able to engineer functional indexes of refraction out of materials robust enough to survive very high power levels.
These structures are a promising alternative to current materials that cannot withstand mega and gigawatt levels of electromagnetic power. At high power levels, most materials get too hot and burn. Materials also can break down when the electric field density gets too high, which is similar to when the electric density between clouds is so great that the air between the clouds breaks down, causing lightning.
Behdad is designing structures that could be used in high-power phased-arrays, radar systems and satellites. He also plans to study antenna apertures that can shape electromagnetic pulses, which are short duration, high-energy pulses that break down most electronic devices in a given area generated. Conversely, Behdad will also look at structures that could act as shields against enemy electromagnetic pulses.
In addition, Behdad is looking at techniques to allow metamaterial-based devices to generate a broader array of waveforms. Currently, high-power sources can only produce a few, simple waveforms. Behdad is exploring ways to make high-power devices more flexible in terms of producing a variety of complex waves with different frequency components. “Think of it as a huge dish antenna. Currently, antenna generally focus or receive radiated energy in a given direction,” Behdad says. “With new techniques, we could use antenna to focus and change the shape of signals or pulses radiated by high-power systems.”
The U.S. Navy program is supporting a project by Behdad titled “Closely coupled multi-mode radiators: A new concept for improving the performance of electrically small antennas.”ll, directional antennas is one of those things we tell students can’t happen,” Behdad says. “But the question is, what if it can be done?”