Beverly Turchinetz

Negative index metamaterial for selective angular separation of microwaves by polarization

Materials with simultaneously negative electric permittivity and magnetic permeability are referred to as left handed, and are also called backward wave and double negative media. The first experimental demonstration of such a metamaterial combined metallic split ring resonators with posts etched on opposite sides of dielectric boards. The boards are usually stacked in parallel planes with insulating spacers to form highly anisotropic prisms. We have demonstrated that this anisotropic. prism exhibits both positive and negative refractive indices and can split an incident beam into two components. The positive and negative indices are accessible by the choice of polarization of the electric field. Using an electric field parallel to the posts, negative refraction is observed. Rotating the electric fields 90/spl deg/ yields a positively refracted signal. Intermediate angles of polarization can achieve refraction in both negative and positive directions simultaneously, or the receiver polarization can be chosen to select either signal separately, The values of the positive and negative index and the wedge angle of the prism determine the separation angle of the output beams. This effect has potential application for a unique type of angular beam splitter.

Validation of Negative Refraction in a Metamaterial Wedge using QPSK Modulated Signals

The phenomenon of negative refraction in a Metamaterial wedge is known to be relatively narrowband. Here, we first experimentally estimate the negative refraction bandwidth of a Metamaterial wedge using a slab and a series of CW measurements. We subsequently measure the RF bandwidth of the Metamaterial wedge using a series of simple QPSK modulated signals. The measured RF bandwidth correlates well with the bandwidth estimate made using the slab and CW measurements.

Measured Polarization Response of Negative Index Metamaterial

Free space microwave measurements are reported of a split ring and post type metamaterial that exhibits negative index of refraction in a frequency band near 13.5 GHz. Varying azimuthal angles and magnitudes are achieved by changing the polarization of the transmitter and receiver relative to each other and to the anisotropic material. The amplitude of the cross-polarized transmission has been measured at 50% of the co-polarization level. This polarization conversion is a significant loss mechanism

Experimental verification that a metamaterial wedge supports the propagation of a bandlimted modulated signal

We have performed CW measurements on the metamaterial wedge providing detailed insight into its behavior and operating bandwidth limitations. Measurements with a narrowband modulated signal have demonstrated that negative refraction exists with a practical QPSK signal modulation scheme. The CW measurements indicated that the metamaterial wedge would not allow the successful transmission of a QPSK modulated signal having bandwidths in excess of 4% to 5%. This bandwidth limitation was demonstrated experimentally where successful transmission of a modulated signal having 406.4 MHz was performed. A modulated signal having a bandwidth of 838 MHz could not be successfully transmitted through the wedge.

Free space measured loss comparison of single and double Ring resonators for negative index media

Our work here investigates the combination of similar broadside coupled rings (BCRs) with negative permittivity posts in a metamaterial prism, rather than the previous guided-wave medium. Free space measurement of negative refraction through a prism has become our standard for proof of negative index.

The microwave behavior of an anisotropic negative index medium

Free space microwave measurements are reported for a split ring and post type metamaterial which exhibits negative refraction in a frequency band between 13.5 and 14.5 GHz. Varying azimuthal angles and magnitudes are achieved by changing the polarization of the transmitter and receiver relative to each other and to the anisotropic axes of the material. The amplitude of the cross- polarized transmission has been measured at 50% of the co- polarization level. The maximum amplitude was achieved at a polarization angle of 20 degrees relative to the initial polarization. This polarization conversion indicates there are other losses besides ohmic losses.