Development of double-positive metamaterial composites for antenna volume reduction
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] An investigation was conducted into the engineering of fully machinable advanced double-positive metamaterials for use in reducing the wavelength of electro magnetic waves within high power antennas while also matching the wave impedance of the antenna to free space. A magneto-dielectric metamaterial composite was utilized to tailor the permittivity, magnetic permeability, and dielectric strength of the material. The engineered composites were made up of powdered Nickel-Zinc ferrite mixed in a high dielectric strength polymer. Nickel-Zinc ferrite was selected due to it having magnetic permeability values in the thousands, permittivity values in the teens, and reasonably low eddy current losses at frequencies as high as 2 GHz. The use of a dielectric polymer as the binder allowed for the composites to be fully machinable. Three different particle distributions were investigated in order to examine how density and composite order effected the dielectric strength and electromagnetic frequency response. The particle distributions utilized were a normal distribution with particle diameters ≤ 45 x 10-6 m; a bimodal distribution of 5 _ 10-6 m and 3010-9 m diameter particles; and a trimodal distribution of 45 x 10-6 m, 5 x 10-6m, and 30_10-9 m diameter particles. The frequency response was tested using the Nicolson-Ross-Weir method between 20 MHz and 2 GHz and the dielectric strength of the composites were tested under pulsed conditions. It was found that the metamaterial composites utilizing a bimodal distribution have the best overall combination of electromagnetic and dielectric properties with an average electric field at break down of 27.5 MV m-1 and a wavelength size reduction factor of 7.1 at 500 MHz. Composites made with a normal distribution have the highest values of initial permeability and size reduction factors on the order of 7 but average electric fields at break down of around 17 MV m-1.
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