Tomasz M. Grzegorczyk

A Study of Using Metamaterials as Antenna Substrate to Enhance Gain

Using a commercial software, simulations are done on the radiation of a dipole antenna embedded in metamaterial substrates. Metamaterials under consideration are composed of a periodic collection of rods, or of both rods and rings. The S-parameters of these metamaterials in a waveguide are analyzed and compared with their equivalent plasma or resonant structure. Farfield radiation is optimized by analytic method and is simulated numerically. The metamaterial is shown to improve the directivity.

Guided modes with imaginary transverse wave number in a slab waveguide with negative permittivity and permeability

The guidance conditions of modes with both real and imaginary transverse wave numbers inside a dielectric slab with negative permittivity and permeability are solved. We show that for real transverse wave numbers, cutoffs exist for all modes, unlike in conventional media where the first even mode is always propagating. In addition, we also show that guided modes exist for imaginary transverse wave numbers, with the power concentrated at the interfaces instead of having maxima inside the slab. A graphical method of determining the imaginary transverse wave numbers of the guided modes is introduced which clearly identifies the different conditions of propagation depending on the properties of the slab. In particular, propagation of guided waves inside less dense negative media is shown to be possible.

Experimental Study on Several Left-Handed Matamaterials

Left-handed materials (LHM) are engineered structures that exhibit electromagnetic properties not found in nature. Real applications of LHM need substrates with low loss, wide bandwidth as well as stable mechanical characteristics. In this paper, we summarize some experimental as well as numerical results of lefthanded materials with different configurations of rods and splitring resonators (SRRs). Hot-press technics utilized in PC board manufacture are used to produce solid-state multi-layer left-handed materials. Either mechanical or electromagnetic characteristics of LH samples are notably improved.

Metamaterial exhibiting left-handed properties over multiple frequency bands

We present experimental measurements at microwave frequencies of a double band left-handed metamaterial. The sample of metamaterial is composed of an extended version of the S-shaped resonators that exhibit simultaneously a negative permittivity and a negative permeability response at comparable frequencies. The experimental results clearly show that there exist two frequency bands where the refraction index is negative. The double left-handed passbands are due to the multiple capacitances and inductances induced in the structure, which can be further tuned to realize a metamaterial with multiple (more than two) left-handed frequency bands.

Čerenkov radiation in materials with negative permittivity and permeability

The mathematical solution for Cerenkov radiation in a novel medium, left-handed medium (LH medium), which has both negative permittivity and permeability, is introduced in this paper. It is shown that the particle motion in the LH medium generates power that propagates backward. In this paper, both dispersion and dissipation are considered for the LH medium. The results show that in such a material, both forward power and backward power exist. In addition, we show that the losses will affect the Cerenkov angle. The idea of building a Cerenkov detector using LH medium is introduced, which could be useful in particle physics to identify charged particles of various velocities.

Negative refraction of a combined double S-shaped metamaterial

We present a combined double S-shaped metamaterial structure that exhibits a left-handed property over a wide frequency band of 6GHz. The transmission experiment, phase measurement, and prism refraction experiment from the structure confirm the presence of the negative index of refraction.

Controllable left-handed metamaterial and its application to a steerable antenna

A controllable left-handed metamaterial based on a varactor-loaded S-shaped resonator structure is presented to realize an active radome. By controlling the phase properties of the radome, the antenna exhibits continuous scanning capability in a range of ±40°, which is confirmed by theoretical analysis.

Magnetic Properties of S - Shaped Split - Ring Resonators

We present a theoretical analysis of the radiation of an S-shaped split ring resonator (S-SRR) for the realization of a metamaterial exhibiting left-handed properties. It is shown that the structure is resonant due to its internal capacitances and inductances, which can be adjusted such that the electric plasma frequency and magnetic plasma frequency, both due to the S-SRR only, appear within the same frequency band. Using the same idea, we also present some extended S-shaped split-ring resonator structures with improved performance.

Refraction laws for anisotropic media and their application to left-handed metamaterials

The refraction of phase and power at the interface between free space and anisotropic media is studied. Under a TE incidence (electric field along y/spl circ/) and k/sub y/=0 incidence (where k/sub y/ is the y/spl circ/ component of the wave vector), a closed-form generalization of Snells laws is proposed. The two relations (one for the phase and one for the power) are expressed in terms of the incident angle, the constitutive parameters of the anisotropic medium (which can take negative values), and the tilting angle of the dispersion relation. In addition, both positive and negative dispersions are discussed, making the formulas directly usable for the design of left-handed metamaterials. The validation is done by two methods. First, the electromagnetic fields in layered anisotropic media are computed analytically. The angle of refraction of the wave vector is thus directly obtained, while that of the power is obtained by computing the time-average Poynting power. Second, numerical simulations are performed using HFSS to record the deflection of the power by a prism characterized by positive or negative constitutive parameters. For the specific prism experiment, in which the incident angle is equal to the tilting angle of the dispersion relation, we show that the refraction laws reduce to a simple Snells law form.

Reflection Coefficients and Goos-Hanchen Shifts in Anisotropic and Bianisotropic Left-Handed Metamaterials

We show in this paper that metamaterials in which some components of the permittivity and permeability tensors can have negative real values (thus associated with left-handed metamaterials) call for a reconsideration of the common concepts of critical angle and Brewster angle. By studying the reflection coefficient for isotropic and biaxial half-spaces and slabs, we show that a metamaterial for which the Brewster angle appears beyond the critical angle is realizable. In addition, we also show that the Goos-Hanchen shift induced by left- handed isotropic slabs is not necessarily negative but could be positive when the second interface of the slab supports a surface plasmon. Finally, upon studying a bianisotropic metamaterial, we show that propagation at a negative angle can occur, although it would not if only the permittivity and permeability tensors were considered. All the results have been obtained using an eigenvalue method which we extend to bianisotropic media in this paper.