Exploitation of Omnidirectional Reflectivity

Period of Performance: 08/20/2002 - 08/20/2003

$100K

Phase 1 STTR

Recipient Firm

Mission Research Corp.
735 State Street
Santa Barbara, CA 93101
Principal Investigator
Firm POC

Research Institution

Michigan State University
Office of Sponsored Programs
East Lansing, MI 48824
Institution POC

Abstract

Omnidirectional reflectors, with nearly perfect reflectivity, have been demonstrated both in academic laboratories and in industrial applications. These designs are similar to multilayer radome designs in that either wide bandwidth or wide angle coverage is obtained by utilizing many layers of dielectric with differing dielectric constants. In radome design, the objective is to achieve nearly perfect transmission over a specified bandwidth and coverage field-of-view. The omnidirectional reflector turns that problem around to achieve nearly perfect reflection without the use of lossy materials such as metals. Another difference between demonstrated omnidirectional reflectors and radomes is the current band of operation (visible and infrared) and number of layers. Commercial applications to date include films for windows that reduce radiant heat through windows as an energy conservation technology. These films, consisting of something like one thousand layers of alternating materials, have been tuned for maximum IR reflection and acceptable visible light transmission. Mission Research Corporation (MRC) has over 20 years of experience designing, fabricating, and testing unique radome configurations for the US Air Force and other customers. One of the aspects of MRC's research and design program over the years is the development of specialized design tools for radome development. One of these, MRC_TLM, uses a transmission line model coupled with a Monte Carlo optimizer to design multilayer radomes. MRC will utilize MRC_TLM to determine the feasibility and anticipated performance associated with a planar multilayer stack designed to be an omnidirectional reflector. However, planar configurations are not the only useful geometry. Concentric layers of cylindrical shells is also of tremendous interest as a dielectric waveguide. Improvements are needed in design to reduce the loss associated with leaky waves. Hence, MRC in collaboration with Michigan State University (MSU), will develop the necessary formulation for implementing a version of MRC_TLM for concentric dielectric shells. Provided the use of multilayer structures is demonstrated in Phase I, a user-friendly computer program (similar to the available MRC_TLM program for the planar case) will be written in Phase II to implement the cylindrical case. In addition, test cases will be designed, fabricated, and tested as part of Phase II for tool validation and demonstration of proof-of-concept. The commercial benefits of the proposed research will have an impact on all applications in national defense technology and telecommunications. A partial list of these applications include: 1) MMW/MW circuitry for better mode control in broadband/high gain/high power amplifiers for high resolution radar systems, 2) remote sensors, 3) low-probability of intercept communications, 4) fly-by-wire control systems, 5) ultra-low loss waveguides (optical fibers), 6) laser cavities, and 7) chemical detection using surface waves. The benefits of this research will impact each of these applications by simply making the applications possible or enhancing them. Solid mathematical formulation and numerical analysis will help to develop accurate and efficient computational algorithms for the study of multilayered structures. These tools will be extremely valuable in designing omnidirectional reflectors and low loss optical fibers for lower frequencies (millimeter-wave/microwave). As an example, a mathematical investigation shows that optimal structures for coating design problems frequently consist of multilayers of two alternating materials with high refractive index ratio. The mathematical formulation and numerical algorithm resulting from our proposed research can be used in optimal design codes (Phase II) which will lead to the development and production of low-loss omnidirectional reflectors and low-loss optical fibers for lower frequencies. The fabrication of these products can be carried out by MRC and its potential partners.