N132-123 TITLE: Infrared-Transparent Electromagnetic Shield

TECHNOLOGY AREAS: Air Platform, Materials/Processes, Weapons

ACQUISITION PROGRAM: Unmanned Carrier-Launched Airborne Surveillance and Strike (UCLASS)

RESTRICTION ON PERFORMANCE BY FOREIGN CITIZENS (i.e., those holding non-U.S. Passports): This topic is "ITAR Restricted". The information and materials provided pursuant to or resulting from this topic are restricted under the International Traffic in Arms Regulations (ITAR), 22 CFR Parts 120 - 130, which control the export of defense-related material and services, including the export of sensitive technical data. Foreign Citizens may perform work under an award resulting from this topic only if they hold the "Permanent Resident Card", or are designated as "Protected Individuals" as defined by 8 U.S.C. 1324b(a)(3). If a proposal for this topic contains participation by a foreign citizen who is not in one of the above two categories, the proposal will be rejected.

OBJECTIVE: Demonstrate an infrared-transparent, electromagnetic shielding coating that can be applied to electro-optic sensor windows and domes. Transmission should be at least 90% in the 3-5 micron wavelength region. Sheet resistance should be less than 10 ohms per square. The coating must be chemically stable in the atmosphere and in sunlight and be resistant to erosion by rain and solid particles. It is desirable that the coating be able to operate at temperatures up to 600C.

DESCRIPTION: Electromagnetic shielding of electro-optic sensor electronics in military systems is currently provided by electrically conductive metal grids applied to the sensor window or dome. Grids provide excellent electrical shielding, but compromise the optical system through geometric blockage, diffraction, and undesired reflection of light. In addition, grids are difficult to deposit on curved shapes. Grids are poorly resistant to erosion damage by rain and particle impact on the external surface of a window or dome. A continuous thin-film coating that has both electrical conductivity and optical transparency could provide adequate electromagnetic shielding and superior optical performance. The conductive layer must be part of a stack of layers to minimize reflection losses and provide erosion resistance. It is desirable that most of the optical loss comes from reflection, not absorption.

Experimental evidence for the plausibility of any material that is chosen for the conductive layer must be provided. In general, previous attempts to use graphene or carbon nanotubes to make a transparent, conductive layer did not provide adequate transparency when they had enough electrical conductivity. Proposals to use graphene, carbon nanotubes, or metal nanowires will need strong experimental justification to be considered.

PHASE I: Demonstrate an infrared-transparent, electrically conductive coating with strong potential to achieve at least 90% transmission in the 3-5 micron wavelength region and a sheet resistance less than 10 ohms per square. The coating should be deposited on an infrared-transparent substrate such as sapphire or silicon to allow infrared optical properties to be measured. Silicon can be used only if it is chemically inert under the film deposition conditions. Measure the optical constants n and k so a case can be made for the potential of the coating to meet the optical requirements of the solicitation when incorporated into an anti-reflection stack.

PHASE II: Optimize the coating for simultaneous maximum optical transmission and maximum electrical conductivity. Design and demonstrate an anti-reflection structure to provide >90% transmittance in the 3-5 micron wavelength region. Incorporate hard layers in the anti-reflection stack to provide erosion resistance. Conduct sand and rain erosion testing of the coating. Demonstrate stability of the coating in the atmosphere and in sunlight. Criteria for erosion and environmental testing will be established by mutual agreement with the Government.

PHASE III: Demonstrate commercial production capability for coating windows and domes.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Optically transparent, electrically conductive coatings could become components of photovoltaic cells.

REFERENCES:
1. L. F. Johnson, M. B. Moran "Infrared Transparent Conductive Oxides," Proc. SPIE 2001, Volume 4375, p 289.

2. H. Kawazoe, M. Yasukawa, H. Hyodo, M. Kurita, H. Yanagi, and H. Honsono, "p-Type Electrical Conduction in Transparent Thin Films of CuAlO2," Nature, 1997, Volume 389, p. 939.

3. F. A. Benko and F.P. Koffyberg, "Opto-electronic Properties of p- and n- Type Delafossite CuFeO2," J. Phys. Chem. Solids 1987, Volume 48, p. 431.

4. M. Joseph, H. Tabata, and J. Kawai, J., "p-Type Electrical Conduction in ZnO Thin Films by Ga and N Codoping," Jpn. J. Appl. Phys. Part 2: Lett.1999, Volume 38, p. L1205.

KEYWORDS: conductive coating; optical coating; electrically conductive coating; electromagnetic shielding; transparent conductive coating

** TOPIC AUTHOR (TPOC) **

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