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A method for determining the complex permittivity for material specimens with isotropic or biaxially anisotropic dielectric properties is described and representative measured results are presented. The method extracts the material permittivity through the utilization of computational electromagnetic simulations of specimen transmission measurements made with a broadband (50 MHz to over 500 MHz) coaxial airline with a material specimen which partially fills the waveguide cross-section. A number of independent transmission measurements equal to the number of unknown permittivity terms is required for unique material permittivity determination. For isotropic specimens, a single specimen orientation is required, whereas for anisotropic specimens, different specimen orientations in the airline are required to probe the unknown permittivity axes and thus ensure unique material permittivity determination. Measurements using a 3.5-inch outer diameter coaxial airline were made for known isotropic specimens as well as an anisotropic lossy material specimen. This technique provides the material measurement community with a mechanism to characterize a single specimen of complex shape and biaxial dielectric anisotropy at low frequencies covering multiple rectangular waveguide bands simultaneously and represents a significant advance in the current measurement state-of-the-art particularly at frequencies below 100 MHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1864–1868, 2015

Metasurfaces enable a new avenue to engineered responses of the electromagnetic scattering characteristics through the control and manipulation of the wavefronts. The wavefronts are tuned by altering deeply sub-wavelength structural features on the metasurface. In this work, a heuristic technique is used where the conductive topology of the metasurfaces for a fixed form factor is optimized by a multi-objective genetic algorithm mimicking evolutionary processes. Analysis is performed for the engineered metasurface responses for frequency-selectivity, absorption, rasorber characteristics, and photonic nanojet generation. Computational electromagnetic simulations for these engineered metasurfaces are presented and discussed. The concepts presented in this work can be applied to design metasurfaces and metamaterials from the microwave to the optical regimes.

In this work, we present a new X-band waveguide (WR90) measurement method that permits the broadband characterization of the complex permittivity for low dielectric loss tangent material specimens with improved accuracy. An electrically-long polypropylene specimen that partially fills the cross-section is inserted into the waveguide and the transmitted scattering parameter (S21) is measured. The extraction method relies on computational electromagnetic simulations, coupled with a genetic algorithm, to match the experimental S21 measurement. The sensitivity of the technique to sample length was explored by simulating specimen lengths from 2.54 to 15.24 cm, in 2.54 cm increments. Analysis of our simulated data predicts the technique will have the sensitivity to measure loss tangent values on the order of 10e-3 for materials such as polymers with relatively low real permittivity values. The ability to accurately characterize low-loss dielectric material specimens of polypropylene is demonstrated experimentally. The method was validated by excellent agreement with a free-space focused-beam system measurement of a polypropylene sheet. This technique provides the material measurement community with the ability to accurately extract material properties of low-loss material specimen over the entire X-band range. This technique could easily be extended to other frequency bands., 6 pages, 7 figures, Review of Scientific Instruments