EEbeat

Recently developed Holographic Artificial Impedance Surfaces–or Textured Impedance Surfaces, for short–are surface-coating materials from HRL Laboratories (Malibu, CA) that enable any object to become a Tx/Rx antenna. Constructed of thin sheets of dielectric with small metal patterns on them, the materials have a metal backing and can be applied to metal surfaces.

The pattern is generated using two techniques:
(1) An artificial impedance surface, i.e. a structure containing small printed metal patterns. Electromagnetic impedance can be changed by printing different patterns on the surface.
(2) A concept used in optical holography is used to determine how the surface should be patterned. Just as an optical hologram can be created to look like any object, the thin surface material can be printed in such a way as to produce nearly any radiation pattern, regardless of the shape of the object on which it is placed.

During design, HRL needs to know the shape of the object, desired frequency bandwidth, and radiation pattern. The company then generates a file from that information that is used to print the pattern on the surface.

“Fundamentally, there is no (frequency) limit,” said Dan Sievenpiper, HRL’s Director, Applied Electromagnetics Laboratory. “So far, we have demonstrated specific structures from L-band to Ku-band, but not the whole range with a single surface: different surfaces for different bands in that range. It can also be used at higher or lower frequencies, perhaps from UHF to W-band.”

It is useful for any applications where the antenna must be conformal to the shape of a vehicle, aircraft, or other structure. This becomes more important as aircraft get smaller, such as UAVs. Completely passive, the material can handle relatively high electric fields. But Sievenpiper admits the limits have not been studied.