The present invention relates to ground planes for use on an interior or exterior of metallic or composite cured aircraft skins and methods of forming the same, and more particularly, to a conductive thermoplastic ground plane that facilitates electrical continuity and flexibility.
A ground plane is an electrically conductive surface that serves as part of an antenna to reflect radio waves from other antenna elements. The ground plane may function as lightening protection, and/or shield to protect electronic equipment, particularly sensitive electronic equipment such as computers, and communications equipment against electromagnetic interference. In the aircraft industry, electromagnetic interference may cause aircraft instruments to malfunction and can result in navigational errors and even the loss of the aircraft. In the past, the metal skin of the aircraft served as the ground plane. However, at least some known aircraft use composite laminates as the skin material to reduce weight. In such cases, the laminate skin itself is no longer electrically conductive and a conductive ground plane may need to be integrated therein.
At least some known ground planes for use in an aircraft composite skin include embedded structural materials within the composite, such as non-woven fiber mats, which may be heavy and brittle. Additionally, the fiber mats may cause electrical discontinuity at the manufacturing joint between adjacent composite panels. Another known method of introducing a conductive ground plane to nonconductive composite skin is to apply a sprayed-on conductive material, such as a paint, to the surface of the skin. However, such paints are prone to damage and chipping and lose their continuous electrical conductivity where such damage occurs.
Furthermore, when openings are drilled through the composite skin to accommodate fasteners, both embedded structural materials and sprayed-on materials lose their continuous electrical conductivity where the openings are drilled. Also, in cases where the ground plane also serves as lightning protection for the aircraft, the aircraft is no longer lightning protected at the locations of the fasteners. Moreover, neither embedded structural materials nor sprayed-on materials are able to flex and elongate along with the composite skin and return to its static structural position without incurring fatigue damage.
Thus there exists a need for a material that can easily and significantly stretch in all directions, is highly conductive in all states of flexure, can withstand repeated elongations with no degradation in shielding effectiveness or material properties, is thin and light weight, and which is tough enough to withstand severe aerospace environments, such as are encountered when the aircraft is operating within cold environments, at high altitudes, and/or other flight conditions.