Chaotic sequences for noisy environments.

There have been many attempts to apply chaotic signals to communications or radar, but one obstacle has been that there is no effective way to recover chaotic signals from noise larger than the signal. In this work, we create "pseudo-chaotic" signals by concatenating dictionary sequences generated from a chaotic attractor. Because the number of dictionary sequences is finite, these pseudo-chaotic signals are not actually chaotic, but they can still contain some of the desirable properties of chaos.

Using filtering effects to identify objects.

Reflecting signals off of targets is a method widely used to locate objects, but the reflected signal also contains information that can be used to identify the object. In radar or sonar, the signal amplitudes used are small enough that only linear effects are present, so we can consider the effect of the target on the signal as a linear filter. Using the known effects of linear filters on chaotic signals, we can create a reference that allows us to match a particular target to a particular reflected signal.

Phase space correlation to improve detection accuracy.

The standard method used for detecting signals in radar or sonar is cross correlation. The accuracy of the detection with cross correlation is limited by the bandwidth of the signals. We show that by calculating the cross correlation based on points that are nearby in phase space rather than points that are simultaneous in time, the detection accuracy is improved.

Simulations of ferrite-dielectric-wire composite negative index materials.

We perform extensive finite difference time domain simulations of ferrite based negative index of refraction composites. A wire grid is employed to provide negative permittivity. The ferrite and wire grid interact to provide both negative and positive index of refraction transmission peaks in the vicinity of the ferrite resonance.

Optical properties of an ideal homogeneous causal left-handed material slab.

The optical properties of a homogeneous slab of material characterized by causal permittivity epsilon (f) , and permeability mu (f) are investigated through finite difference time domain simulations. Lorentzian epsilon (f) and mu (f) are used to produce values of interest in the resulting index n (f) , namely, n<0 , 0 View Article and Find Full Text PDF

Dynamics of transients in yttrium-iron-garnet.

Yttrium-iron-garnet (YIG) is an important technological material used in microwave devices. In this paper we use dual microwave (1-4 GHz) drives to study the dynamical bifurcation behavior of magnetostatic and spin-wave modes in YIG spheres and rectangular films. The samples are placed in a dc magnetic field and driven by cw and pulse-modulated microwave excitations at magnetostatic mode frequencies.

Electromagnetic waves focused by a negative-index planar lens.

We demonstrate that negative refraction occurs for both cw and pulsed electromagnetic waves when traversing from a "right-handed" (index > 0) to a "left-handed" (index < 0) material (LHM) which has causal dispersive intrinsic properties. We also demonstrate that a divergent line source spaced a distance H in front of a planar LHM slab and excited by either an impulse cw or a Gaussian frequency pulse is imaged at a distance H away, inside the LHM, and at H to the other side of the slab. The image size is approximately lambda consistent with limitations dictated by wave optics.

Calculations and measurements of wire and/or split-ring negative index media.

Broadband calculations (70 MHz-20 GHz) and measurements (2-15 GHz) were performed on planar stacks of two-dimensional double-split rings arrays interspersed with arrays of thin wires. Recent work on similar composite structures infers a negative index of refraction (n<0) over a narrow frequency range. We have performed finite-difference time-domain (FDTD) calculations on various combinations of ring geometries, wire arrays, and stack spacings.

Detecting functional relationships between simultaneous time series.

We describe a method to characterize the predictability and functionality between two simultaneously generated time series. This nonlinear method requires minimal assumptions and can be applied to data measured either from coupled systems or from different positions on a spatially extended system. This analysis generates a function statistic, Theta(c(0)), that quantifies the level of predictability between two time series.

Functional dependence and quasiperiodicity in the spatiotemporal dynamics of yttrium iron garnet films.

When thin films of yttrium iron garnet (YIG) are placed in a magnetic field and driven at microwave (rf) frequencies, nonlinear interactions within the material cause the normal microwave spin precession to be modulated at lower frequencies. We measure these lower frequency (kHz) signals at two spatially separated locations on the YIG film and use linear and nonlinear analysis to study the functional dependence of the spin dynamics at one location on the spin dynamics at the other location. We see dynamical states where nonlinear analysis can detect a functional dependence that the linear analysis fails to reveal.

Spatiotemporal nonlinear dynamics of a magnetoelastic ribbon.

Magnetoelastic materials have a strong coupling between strain and magnetization, so applying a magnetic field to a magnetoelastic material can change its shape. This coupling leads to interesting dynamics. We have studied the dynamics of a wide ribbon of Metglass 2605sc which was driven by a magnetic field.