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RF Polymer Composites for Electromagnetic Systems

These materials can be used in electromagnetic systems such as GPS, radomes, and WiFi.

Design of polymer composites with specific engineered electromagnetic properties are of use in a variety of physical electromagnetic systems above 100 MHz. In physical electromagnetic systems such as GPS, radomes, WiFi, etc., proper choice of the material can be transformative in that it can yield considerably better performance. Of interest in this work is the possible development of low-loss magneto-dielectric composites. This project investigates various aspects of material systems, starting with possible composite designs, to design of measurement techniques, to development of finite element models for complex waveguide and conformal antenna configurations that use these materials.

RF polymeric composites offer a new design space to radio frequency (RF) engineers. Specifically, the current interest in magneto-dielectric polymer nanocomposites is due to the fact that these materials can have non-trivial permeability and permittivity. Such material properties offer designers the ability to miniaturize certain common passive RF components, such as antennas, radomes, and transmission lines. The rationale for using these materials is that at a given frequency, the wavelength in the material is smaller than that in air or in a non-magnetic material with identical permittivity.

In this work, progress has been made in understanding the design principles for magneto-dielectric composite materials. The methods investigated are suitable for layered media and for medial comprised of rods of inclusions within a polymer matrix. These methods permit the simulation of composite materials to predict viable compositions and volume fractions to achieve desired results.

Generally, it was found that layered designs resulted in a higher effective permeability relative to rods. In both cases, the material is anisotropic due to the structure of the inhomogeneity. This will impact design of RF components since such anisotropy must be considered in the design due to the fact that anisotropic materials “look” different to different orientations of the dynamic electric and magnetic fields. The finite element method is well suited for analyzing anisotropic materials; however, it is noted that the wave matrix-based simulation also accounts for anisotropy.

Secondly, measurement techniques were developed for assessment of magneto- dielectric materials. This includes noninvasive, contact measurement techniques, as well as more traditional waveguide (e.g. geometrically prescriptive) methods. These methods are important since measurement fixtures and inversion techniques are generally not well developed for magneto-dielectric materials.

Thirdly, the radiation performance of candidate magneto-dielectric materials was evaluated using full-wave, rigorous computational electromagnetics computer programs. A significant conclusion is that the enhanced bandwidth realized by the most promising of these materials is attributed to loss mechanisms rather than inherent design features. This indicates that significant work on synthesis methods is still needed.

This work was done by Leo Kempel and Shanker Balasubramaniam of Michigan State University for the Air Force Research Laboratory. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp  under the Materials category. AFRL-0135

Topics:
Antennas Composite materials Electric power grid Electronic equipment Hazardous materials Hazards and emergency operations Insulation Magnetic materials Materials Polymers Radiation Radio equipment Radio frequency Simulation and modeling
This Brief includes a Technical Support Package (TSP).
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RF Polymer Composites for Electromagnetic Systems

(reference AFRL-0135) is currently available for download from the TSP library.

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    Defense Tech Briefs Magazine

    This article first appeared in the December, 2009 issue of Defense Tech Briefs Magazine (Vol. 3 No. 6).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document titled "RF Polymer Research — II" is a final report detailing a research project conducted at Michigan State University under the sponsorship of the Air Force Office of Scientific Research (AFOSR). The project, which ran from February 15, 2006, to November 30, 2008, was led by Dr. Leo C. Kempel and focused on the design and development of polymer composites with engineered electromagnetic properties, particularly magneto-dielectric composites.

    The primary objective of the research was to create materials that could significantly enhance the performance of various electromagnetic systems operating above 100 MHz, such as GPS, radomes, and WiFi. The report emphasizes the challenges associated with achieving a significant relative permeability (between 2 and 10) without incurring substantial losses across a wide bandwidth, which is crucial for rapid communication rates. It highlights that traditional methods, such as simply dispersing crushed magnetic materials in a polymer matrix, often lead to demagnetization and high loss factors, thus failing to meet the desired performance criteria.

    The report outlines the project's approach to overcoming these challenges through interface engineering and advanced synthesis methods. It discusses the inadequacies of classical mixing models in predicting the properties of these composites and the necessity for accurate simulation methods to assess their performance in practical applications. The research also aimed to provide guidance on the design and use of magneto-dielectric materials based on first-principles electromagnetics.

    Throughout the project, significant progress was made in understanding the design principles for these composite materials, with methods suitable for layered media and composites containing rod-like inclusions within a polymer matrix being investigated. The report also notes the project's contribution to developing talent, as it supported several graduate students, many of whom were U.S. citizens or permanent residents.

    In summary, the document encapsulates a comprehensive study on the design, characterization, and application of magneto-dielectric polymer composites, addressing both theoretical and practical aspects while contributing to advancements in electromagnetic materials science. The findings and methodologies presented in this report are expected to have a lasting impact on the field and support future research and development efforts in related areas.

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