Khalid Z. Rajab

All-dielectric invisibility cloaks made of BaTiO3-loaded polyurethane foam

Transformation optics has led the way in the development of electromagnetic invisibility cloaks from science fiction to engineering practice. Invisibility cloaks have been demonstrated over a wide range of the electromagnetic spectrum, and with a variety of different fabrication techniques. However, all previous schemes have relied on the use of metamaterials consisting of arrays of sub-wavelength inclusions. We report on the first cloaking structure made of a high-κ dielectric-loaded foam mixture. A polyurethane foam mixed with different ratios of barium titanate is used to produce the required range of permittivities, and the invisibility cloak is demonstrated to work for all incident angles over a wide range of microwave frequencies. This method will greatly facilitate the development and large-scale manufacture of a wide range of transformation optics-based structures.

Stability of active magnetoinductive metamaterials

Passive metamaterials suffer from narrow bandwidths and high losses due to limits imposed by causality. Actively loaded metamaterials on the other hand may be designed to overcome these limitations, with the caveat that stability may be difficult to ensure. In this letter, loops with active non-Foster loads, in which resistance, capacitance, and inductance are negative, are arranged in a periodic lattice to form an effective medium with either negative-Re μ or μ-near-zero magnetic properties over a broad range of frequencies. The stability and effective magnetic properties are examined analytically, as well as with numerical simulations. Furthermore, the tradeoffs between stability, bandwidth, and the lower bounds of the permeability are detailed.

Microwave characterization of vertically aligned multiwalled carbon nanotube arrays

Vertically aligned multiwalled carbon nanotube (VACNT) films have been characterized by rectangular waveguide measurements. The complex scattering parameters (S-parameters) are measured by a vector network analyzer at X-band frequencies. The effective complex permittivity and permeability of the VACNT films have been extracted. The extracted parameters are verified by full wave simulations and very good agreement has been obtained. The results of the systematic error analysis are presented and the errors are within the acceptable range. The performance of VACNT films as an absorber is examined, and comparison with the conventional carbon loaded materials shows that a 90% size reduction is possible while maintaining the same absorption level.

Size reduction of microstrip antennas using metamaterials

In this paper we present the design of a novel compact microstrip patch antenna (MPA) whose size is reduced via the use of metamaterials. The MPA is loaded with a miniaturized multilayered left-handed (LH) transmission line that increases the effective wavelength of the antenna, and thus lowers the resonant frequency of the radiating mode. This, in turn, leads to a substantial reduction in its size as compared to the conventional half-wavelength (/spl lambda//2) MPA. With an impedance bandwidth of around 3%, the performance of the loaded MPA is similar to that of /spl lambda//2 MPA.

Characterization of active metamaterials based on negative impedance converters

Negative impedance converters (NICs) are used to create impedance loads that can effectively cancel the inductive properties of magnetic dipoles, resulting in active metamaterials with increased bandwidth and reduced loss for μ-near-zero (MNZ) and negative-Re(μ) (MNG) media. We demonstrate techniques for analyzing the stability and characterizing the magnetic properties of effective media loaded with NICs. Specifically, we apply the Nyquist criterion to validate the stability of sample active metamaterials. It is shown that the practical NIC-loaded metamaterial may maintain stability and reduce dispersion, albeit with reduced performance as compared to the ideal NIC load.

Experimental demonstration of broadband transmission through subwavelength aperture

Based on coordinate transformation techniques, a simplified all-dielectric extraordinary-transmission device for broadband transmission through a subwavelength aperture is verified experimentally in this paper. The device is made from isotropic dielectric blocks with permittivity values ranging from 2.1 to 6. It is shown both numerically and experimentally that the device can provide transmission with a −3 dB bandwidth of more than 1 GHz, in a region which would otherwise be a stop band caused by the subwavelength aperture in an X-band waveguide.

Broadband Dielectric Characterization of Aluminum Oxide (Al2O3)

Applications for low-temperature cofired ceramics (LTCC) and high-temperature cofired ceramics (HTCC) are advancing to higher frequencies. In order to design ceramic microsystems and electronic packages, the electrical properties of materials must be well characterized over a broad frequency range. In this study, the dielectric properties of commercial aluminum oxide (Al2O3) with different glass loadings are characterized using three different measurement techniques: the split-post cavity, terahertz (THz) time-domain spectroscopy, and Fourier transform IR spectroscopy (FTIR). Specifically, the dielectric properties will be characterized from 10 GHz to IR frequencies. A split-post cavity was employed for determination of dielectric properties in the 10 GHz range. A broadband THz spectroscopy technique was used to characterize the specimens using measured time-domain transmission data. The dielectric constant and loss were extracted from the samples frequency-domain transmission characteristics, providing ...

Noise analysis of broadband active metamaterials with non-Foster loads

Active metamaterials loaded with non-Foster inclusions may exhibit broadband and low-loss material properties, as compared to their passive counterparts. However, the study of their noise performance still remains to be explored. In addition to the Johnson-Nyquist noise from lossy conductors, nonlinear materials used for the design of negative impedance converters (NICs) will give rise to noise as well. In this paper, a general analytical model is developed for the prediction of the noise performance of broadband, stable active metamaterials based on NICs. The noise performance is analyzed in relation to stability, and the effective material properties. The techniques developed in this paper can be applied generally to metamaterials for which equivalent circuit models exist, and results are shown demonstrating the power spectral density and the noise figure of the specific case of an active metamaterial consisting of loaded loop arrays. Results are compared to and verified with circuit simulations.

Quantitative Study of Two Experimental Demonstrations of a Carpet Cloak

An all-dielectric carpet cloak, formulated using the optical transformation technique, is presented here. The carpet cloak was fabricated by implementing a dielectric disk matrix (DDM) with varying periods. To demonstrate that it is functional for multiple angles of incidence, the cloak is measured in a near-field scanner. The performance of this cloak is then quantitatively compared to that of a carpet cloak composed of a nanoparticle-loaded polyurethane foam using a novel technique that can be applied to evaluate the performance of other devices.

Dielectric property measurement using a resonant nonradiative dielectric waveguide structure

This letter describes a new dielectric characterization technique, based on the resonant nonradiative waveguide structure described by Yoneyama and Nishida , for permittivity measurements at microwave and mm-wave frequencies. The measurement system is modeled as a resonator comprised of two parallel conducting plates with a rectangular dielectric slab sandwiched in-between. Resonant frequencies of the longitudinal section electric (LSE) modes and the unloaded Q of the cavity are used to determine the permittivity of the dielectric and its loss tangent, respectively. The technique is shown to be accurate for measuring the dielectric properties of a wide array of polymer and oxide materials. For materials with small dielectric loss tangents, an accuracy of better than /spl plusmn/0.4% is attained in the measurement of the relative dielectric constant of the material.