John McVay

High impedance metamaterial surfaces using Hilbert-curve inclusions

A metamaterial surface, composed of a periodic arrangement of Hilbert Curve inclusions above a conducting ground plane, is analyzed numerically and is shown to possess the properties of a high impedance surface by investigating the phase and magnitude of the reflection coefficient, /spl Gamma/, for a plane wave of normal incidence. A parametric study is presented with respect to the iteration order of the Hilbert curve, the surface height above the ground plane, and the separation distance between the neighboring Hilbert elements within the surface array.

Space-filling curve RFID tags

A completely passive radio frequency tag is proposed, utilizing the scattering from electrically small but resonant inclusions. When placing these space-filling curve inclusions in an array and scaling each element within the array such that each element has its own separate resonant frequency, a radio frequency barcode can be developed from the radar cross section of the array. The narrow bandwidth inherent to such inclusions can be helpful in packing the overall signature into a relatively small frequency spectrum. Such radio frequency tags may have potential use in some applications of radio frequency identification systems.

Thin absorbers using space-filling-curve high-impedance surfaces

In this work, high-impedance ground planes (HIGP), created using a periodic arrangement of space-filling curves, are studied with respect to their use as an electromagnetic energy absorber. Two different surfaces are studied, corresponding to surfaces comprised of Peano curve inclusions of order 2 and Hilbert curve inclusions of order 3. The substrate effects of these surfaces are numerically studied using a periodic method of moment code with an emphasis on substrate losses in the region where the surfaces behave as an HIGP.

Theory and Experiments on Peano and Hilbert Curve RFID Tags

Recently, there has been considerable interest in the area of Radio Frequency Identification (RFID) and Radio Frequency Tagging (RFTAG). This emerging area of interest can be applied for inventory control (commercial) as well as friend/foe identification (military) to name but a few. The current technology can be broken down into two main groups, namely passive and active RFID tags. Utilization of Space-Filling Curve (SFC) geometries, such as the Peano and Hilbert curves, has been recently investigated for use in completely passive RFID applications [1, 2]. In this work, we give an overview of our work on the space-filling curves and the potential for utilizing the electrically small, resonant characteristics of these curves for use in RFID technologies with an emphasis on the challenging issues involved when attempting to tag conductive objects. In particular, we investigate the possible use of these tags in conjunction with high impedance ground-planes made of Hilbert or Peano curve inclusions [3, 4] to develop electrically small RFID tags that may also radiate efficiently, within close proximity of large conductive objects [5].

Miniaturization of top-loaded monopole antennas using Peano-curves

Many wireless applications require planar antennas but with monopole-like, vertically polarized radiation, a design challenge that cannot be easily achieved by using conventional microstrip patch or other types of printed antennas. In addition, while there have been significant advances in design of low-profile printed patch-type antennas in the frequency ranges of L-band and above, the patch antennas are not suitable for lower frequency applications, such as those in VHF and UHF bands, because of their relatively large dimensions. These requirements provide challenging problems in optimization and design of the future generation of low-profile reconfigurable antenna systems. In the present work, we discuss the use of printed metallic paths in the form of Peano and Hilbert space-filling curves (H. Sagan, 1994) to provide top-loading properties that miniaturizes monopole antenna elements. The full-wave simulation together with measured results shows that the proposed electrically small antenna results in a perfect mono-polar radiation pattern with relatively wideband characteristics. Some initial numerical results of this work were recently presented in J. McVay and A. Hoorfar, (2006)

Small dipole-antenna near Peano high-impedance surfaces

We numerically analyze the radiation performance of an electrically small dipole antenna placed above and within close proximity to a Peano high-impedance surface, which is a metamaterial surface consisting of a 2D periodic array of electrically small, metallic, planar inclusions in parallel with, and a small distance above, a metallic ground plane. The inclusions are created utilizing Peano space-filling curves, a mathematical concept dating back to the late 1800s, The effects of various parameters of the Peano surface on radiation resistance, directivity and efficiency of the dipole antenna are studied, and it is shown that in certain circumstances the radiation performance can be enhanced.

Radiation characteristics of microstrip dipole antennas over a high-impedance metamaterial surface made of Hilbert inclusions

We analyze numerically the radiation characteristics of center-fed microstrip short dipoles and half-wave dipoles near a high-impedance surface made of Hilbert shape flat inclusions. We study the input impedance, pattern and gain of such radiating structures. We show that the radiation resistance of a microstrip dipole increases noticeably at certain frequencies near the resonant frequency of the Hilbert surface. Moreover, antenna gain enhancement at certain frequencies is observed for all dipole sizes we have analyzed.

Adaptive polarization-difference imaging algorithms for through-the-wall microwave imaging scenarios

The preliminary results of application of the adaptive polarization-imaging algorithm for through-the-wall microwave imaging problems are presented. Use of complete polarization information in the scattered field from the object together with the adaptation technique provides enhancement in detection of target movement.

Numerical study and parameter estimation for double-negative metamaterials with Hilbert-curve inclusions

The electromagnetic wave interaction with metallic Hilbert-curve inclusions of the 3/sup rd/ order embedded in a homogenous isotropic host medium is numerically studied. The electric and magnetic polarizability tensors for this inclusion are analyzed and the Maxwell-Garnett and periodic mixing formulations are applied to this class of inclusions in order to obtain approximate values for the effective permittivity and permeability of the bulk media. In addition, the effective parameters of the bulk medium are also extracted from the S-parameters of a finite element method (FEM) waveguide simulation and the agreement between these various approaches is examined.

Bandwidth Enhancement and Polarization Dependence Elimination of Space-filling Curve Artificial Magnetic Conductors

This work examines the use of multiple spacefilling curve inclusions as sub-cells to form the basis of a larger inclusion to provide relatively electrically small and self-resonant inclusions for artificial magnetic conductors with enhanced bandwidth performance as well as polarization independence.