TECHNOLOGY AREA(S): Air Platform, Ground/Sea Vehicles

ACQUISITION PROGRAM: PMW 770 Multi-Function Mast (OE-538) ACAT III

OBJECTIVE: Develop a coating or material that can absorb radio frequency (RF) radiation across the Very Low Frequency (VLF) through Ultra High Frequency (UHF) band yet can be tuned to allow a relatively narrow range of frequencies (e.g., 3-30MHz) to pass.� Demonstrate that the coating or material can be applied to a metallic surface such as a submarine mast.

DESCRIPTION: The submarine fleet within the U.S. Navy has been successful in a wide range of missions.� For many of these missions, success or failure depends on the submarine�s ability to be stealthy and remain undetected by opposing forces.� While submerged, maintaining stealth is relatively easy as most electromagnetic (EM) waves (radio, radar, visible light, etc.) experience high attenuation when propagating through water.� However, this high attenuation of EM waves also means communications with submarines is more challenging than with other naval platforms.� The Navy employs a variety of methods to communicate with submerged submarines, but the methods used today are generally low data rate, one-way, and/or compromise stealth.� As a result, the preferred way to conduct high data-rate two-way communications is for the submarine to come to periscope depth and deploy a communications mast.� Unfortunately, once the mast is deployed, it can be detected by radar.� For this reason, reduction of the mast�s Radar Cross Section (RCS) is of high importance.

The goal of this topic is to produce a material or coating that will absorb most RF signals yet can be tailored to allow the desired communications frequencies to pass.� Such a material would reduce the RCS of the mast, which will reduce the likelihood of detection by opposing forces, without degrading communications.� In fact, it would likely improve communications as it would prevent unwanted out-of-band signals from entering the antenna and distorting the incoming communications signal.

The final product of this topic will be a material or coating that absorbs RF radiation and can be applied to the outside surface of a submarine mast such as the OE-538 [11].� The application process needs to be relatively simple and safe for the personnel applying it.� For example:� if the material can be applied to the outside of the mast in a manner similar to paint or wall paper that would be considered acceptable.� Application process that would require the removal of the mast from the submarine would be considered too complicated.� It will need to be rugged enough to withstand the mast�s operating environment without falling off or degrading the mast.� Environmental conditions to be mindful of include salt water corrosion, water pressure at depth, and temperature/humidity at the surface.� In addition, the coating/material will need to have an RF frequency response similar to a bandpass filter that can be adjusted (during manufacturing) for any arbitrary frequency range across the VLF through UHF band.� This will allow the desired communications signals to penetrate the mast and be received by the mast antennas, yet will prevent radar reflections.

PHASE I: Identify a coating or material that exhibits the best RF absorption yet can be tuned during manufacturing to allow any arbitrary range of frequencies to pass.� Demonstrate and quantify RF absorption and transmission performance over a range of frequencies in a laboratory environment.� Verify through simulation and modeling that the coating/material can be manufactured so that the passband can be varied across any frequency range in the VLF through UHF band.� Simulated results should be compared to laboratory results to demonstrate the credibility of the model.� Define the process for applying the coating/material.� Develop prototype plans for Phase II.

PHASE II: Develop and optimize the prototype coating or material identified in Phase I.� The final coating/material should have sufficient transmission across the passband so that communications are not degraded, yet absorption at all other frequencies is maximized.� Produce multiple samples of the optimized material, each one tuned to a different passband.� Demonstrate the tunability of the passband by measuring the frequency response of each sample in a laboratory environment.� Confirm that the measured passband is consistent with the expected passband.� This will demonstrate that the passband of the material can be deliberately set to the desired frequency range (i.e., �tuned�).� Demonstrate the application process on material similar to, if not identical to, the outer material on the OE-538 mast antenna.� Show that the application process is simple, safe, and does not damage the mast.� Confirm the durability of the coating/material by exposing it to salt water, temperature extremes, humidity, etc. Qualitatively confirm durability through visual inspection of the coating after environmental exposure.� Note any visual indications of damage (peeling, flaking, cracking, etc.) Quantitatively confirm durability by repeating RF absorption and transmission measurements.

PHASE III DUAL USE APPLICATIONS: Deliver final coating or material to a Navy facility in sufficient quantity for testing on an OE-538 antenna.� Support initial application of material to OE-538 antenna.� Support Government laboratory testing and Environmental Qualification Testing.

Commercial uses of this material could include: 1) application to wallets and/or clothing to protect radio-frequency identification (RFID) chip in credit cards or passports from hackers, and 2) application to walls of homes (to include houses and apartments) to prevent neighbors from piggybacking on Wi-Fi channels.

REFERENCES:

1. Cheng, E. M., Malek, F. et al. "The Use of Dielectric Mixture Equations To Analyze The Dielectric Properties Of A Mixture Of Rubber Tire Dust And Rice Husks In A Microwave Absorber." Progress In Electromagnetics Research, Vol. 129, 559-578, 2012 2. http://m.jpier.org/PIER/pier129/29.12050312.pdf

2. Liu, Y. H., Tang, J.M. and Mao, Z. H. "Analysis of bread dielectric properties using mixture equations." Journal of Food Engineering, Vol. 93, 72-79, 2009. http://www.sciencedirect.com/science/article/pii/S0260877408006298

3. Micheli, Davide. "Radar Absorbing Materials and Microwave Shielding Structures Design By using Multilayer Composite Materials, Nanomaterials and Evolutionary Computation." Lambert Academic Publishing, ISBN:978-3-8465-5939-0, 2012 4. https://www.researchgate.net/publication/260018692_Radar_Absorbing_Materials_and_Microwave_Shielding_Structure_Design

4. Tong, X.C. "Advanced Materials and Design for Electromagnetic Interference Shielding." CRC Press, ISBN 978-1-4200-7358-4, 2009. https://www.crcpress.com/Advanced-Materials-and-Design-for-Electromagnetic-Interference-Shielding/Tong/p/book/9781420073584

5. Vinoy, K.J. and Jha, R.M. "Radar Absorbing Materials." Kluwer Academic Press, ISBN 13:978-1-4613- 8065-8, 1996. http://www.worldcat.org/title/radar-absorbing-materials-from-theory-to-design-and-characterization/oclc/36029856

6. Feng, Bo-Kai, "Extracting Material Constitutive Parameters from Scattering Parameters." Naval Postgraduate School, Monterey California, September 2006. http://www.dtic.mil/dtic/tr/fulltext/u2/a456941.pdf

7. Baker-Jarvis, J., Geyer, R. G., and Domich, P. D.� "A nonlinear least-squares solution with causality constraints applied to transmission line permittivity and permeability determination." IEEE Transactions on Instrumentation and Measurement, vol. 41, no. 5, pp. 646-652, Oct. 1992. http://ieeexplore.ieee.org/document/177336/

8. Weir, W. B. "Automatic measurement of complex dielectric constant and permeability at microwave frequencies." Proceedings of the IEEE, vol. 62, no. 1, pp. 33-36, Jan. 1974. http://ieeexplore.ieee.org/document/1451312/

9. Chalapat, K., Sarvala, K., Li, Jian and Paraoanu, G. S. "Wideband Reference-Plane Invariant Method for Measuring Electromagnetic Parameters of Materials." IEEE Transactions on Microwave Theory and Techniques, vol. 57, no. 9, pp. 2257-2267, Sep. 2009.� http://ieeexplore.ieee.org/document/5204113/

10. �TangiTek CleanSignal� Technology Evaluation.� U.S. Federal Research Lab Test Report, September 2012. http://www.tangitek.com/downloads/testdata/10-TangiTek-CleanSignal%20Technology%20Evaluation%20Report-FederalLab.pdf

11. Lockheed Martin. �OE-538/BRC Multifunction Communication Mast Antenna System.� 2006.� http://cdn.thomasnet.com/ccp/01150582/110349.pdf

KEYWORDS: RF Absorption; Radar Cross Section; RCS; Cosite; Coating; VLF; UHF; Communications; Stealth