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