The Submillimeter Technology Laboratory(STL) at the University of Massachusetts Lowell has developed a methodology of tailoring the complex refractive index for artificial dielectrics at terahertz frequencies. A wide range of precisely controlled optical properties have been achieved for materials such as vinyl acetate, silicone, polyethylene and epoxy resin when combined with powdered loading agents such as boron nitride, silicon, graphite, iron oxide and stainless steel flake. Using this technology, STL has successfully fabricated both narrow-band and wide-band anechoic structures. The method of characterizing materials for the purpose of tailoring their dielectric properties at terahertz frequencies is presented along with several demonstrated applications. 2. Introduction Because of the increase in the number of optical and quasi-optical measurement systems operating at terahertz frequencies, new materials providing alternative solutions to the design of system components are required. In response to this, STL’s recent activities include an aggressive program to evaluate a wide range of materials for terahertz frequency applications(1-3). Using inhouse expertise in the technique of tailoring artificial dielectrics and the polarimetric characterization of materials, a variety of composite structures have been created as far-infrared radiation absorbing material (FIRAM)(4,5). metal substrate dielectric layer { { incident radiation

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Tailoring Artificial Dielectric Materials at Terahertz Frequencies

: In the realm of materials science, terahertz frequency measurement systems provide significant utility in the characterization of material properties. With support primarily from the U.S. Army National Ground Intelligence Center (NGIC), Submillimeter Technology Laboratory (STL) researchers have been advancing the field of terahertz technology to the application of modeling millimeter-wave and microwave radar for more than a decade. Research in modeling radar requires design of a wide range of measurements systems using current submillimeter-wave source/detector technology, establishment of precise calibration standards, production of high fidelity scale replicas of complex metallic structures, and scaling of millimeter-wave dielectric properties of composites at submillimeter-wave frequencies. This paper explores four measurement techniques typically employed by STL to perform the characterization of materials: (1) laser-based submillimeter-wave ellipsometry; (2) high-precision reflectometry; (3) laser-based Brewster' s angle measurements; and, (4) FIR Fourier transform spectroscopy (FTS).

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Characterization of Material Properties at Terahertz Frequencies

The technique of tailoring the complex refractive index of an artificial dielectric material has been developed at the University of Lowell Research Foundation (ULRF). Low reflection coatings, generally referred to as Dallenbach layers, have been designed for metal substrates using the artificial dielectric. The method of characterizing materials for the purpose of tailoring their dielectric properties at terahertz frequencies will be discussed. Results will be shown for a typical dielectric coated aluminum plate specifically designed for low reflection behavior at ? 0.6 terahertz.

Design and fabrication of narrow band radar absorbing materials at terahertz frequencies

: Development of two measurement techniques has made polarimetric study of dielectric materials at submillimeter wavelengths possible. The first technique, a linearly polarized(LP) transmit/receive measurement system probes polarimetric behavior of a dielectric material through observation of the material's Brewster angle. The second technique, utilizes the recently developed submillimeter quarter wave plate(QWP) to perform ellipsometric determination of the dielectric material's complex refractive index. In this paper submillimeter wavelength measurement techniques are used to polarimetrically characterize a variety of dielectric materials and demonstrate the feasibility of modeling clutter at microwave and millimeter wavelengths.

W. Reinhold

Papers

Submillimeter Wavelength Modeling of Dielectric Materials in Polarimetric Radar Approaches