Brian Meadows

Nonlinear antenna technology

Nonlinear antennas combine advances in nonlinear dynamics, active antenna design, and analog microelectronics to generate beam steering and beam forming across an array of nonlinear oscillators. Nonlinear antennas exploit two phenomena typically shunned in traditional designs: nonlinear unit cells and interelement coupling. The design stems from nonlinear coupled differential equation analysis that by virtue of the dynamic control is far less complex than the linear counterparts by eliminating the need for phase shifters and beam forming computers. These advantages arise from incorporating nonlinear dynamics rather than limiting the system to linear quasisteady state operation. A theoretical framework describing beam shaping and beam forming by exploiting the phase, amplitude, and coupling dynamics of nonlinear oscillator arrays is presented. Experimental demonstration of nonlinear beam steering is realized using analog microelectronics.

CONTROL OF HUMAN ATRIAL FIBRILLATION

Chaos control has been applied to control atrial fibrillation in humans. Results are presented on the application and evaluation of chaos control for slowing and regularizing local electrical activation of the right atrium of humans during induced atrial fibrillation.

Can Neurons Distinguish Chaos from Noise

Recent studies suggesting evidence for determinism in the stochastic activity of the heart and brain have sparked an important scientific debate: Do biological systems exploit chaos or are they merely noisy? Here, we analyze the spike interval statistics of a simple integrate-and-fire model neuron to investigate how a real neuron might process noise and chaos, and possibly differentiate between the two. In some cases, our model neuron readily distinguishes noise from chaos, even discriminating among chaos characterized by different Lyapunov exponents. However, in other cases, the model neuron does not decisively differentiate noise from chaos. In these cases, the spectral content of the input signal may be more significant than its phase space structure, and higher-order spectral characterizations may be necessary to distinguish its response to chaotic or noisy inputs.

A CMOS coupled nonlinear oscillator array

This paper details an experimental nonlinear beamforming array fabricated in a CMOS process. The unit cell oscillator is a nonlinear second order circuit, which demonstrates self-sustaining oscillation. In this paper experimental results from a test oscillator and a linearly coupled array of oscillators are reported. The circuit equations of motion are shown to be equivalent to the van der Pol oscillator, from which a weakly nonlinear phase-amplitude model is derived. This model forms a basis of understanding for the experimental nonlinear beamforming array.

Self-induced oscillations in coupled fluxgate magnetometer: a novel approach to operating the magnetic sensors

A fluxgate magnetometer is one of the numerous devices that belong to a class of nonlinear systems known as the overdamped bistable system. Its dynamics can be described by the generic form x=-/spl nabla/U(x), where U(x) is the potential energy function with two minima that form the bases for the bistability. It is well known that an overdamped system does not oscillate on its own. To switch states, the system is forced by an external periodic signal with large enough amplitude to overcome the potential energy barrier that separates the two minima. However, well-designed coupling schemes, together with the appropriate choice of initial conditions can induce oscillations when a control parameter exceeds a threshold value. The self-induced oscillation, therefore, eliminates the necessity of the forcing function. We demonstrate these concepts numerically and experimentally using three single-domain fluxgate magnetometers that are coupled unidirectionally in a ring.

Simultaneous, multi-frequency synchronous oscillator antenna

As signal bandwidth increases, the inherent limitations of analog-to-digital converter technology become significant. Compounding the difficulty of direct-to-digital operation, at such high frequencies the sheer volume of data generated (on a per-element basis) could result in unattainably high throughput rates and processing power requirements. This paper reviews the design, construction and testing of coupled nonlinear oscillator arrays capable of phase-shifterless beam-steering and null generation at multiple simultaneous frequencies. This ongoing effort by Georgia Tech Research Institute (GTRI) and SPAWAR-SSC is intended to yield significant insight into this novel approach which exploits coupling and nonlinearities in antenna design in order to provide improved performance (increased null depth, simplified parameter controls, BER reduction) on SIGINT platforms. If successful, this design could represent a possible enabling technology for the realization of low-cost, phased arrays at micro- and millimeter wave frequencies, impacting a diverse range of potential commercial, military and aerospace applications.

Applied Nonlinear Dynamics: Advances in Antenna Technology

As bandwidth requirements and operating frequencies increase, the fundamental limitations of solid‐state devices become significant. These limitations include a considerable decrease in power‐combining efficiency due to increased ohmic losses at these higher frequencies and maximum output powers proportional to 2f‐ owing to size reductions necessary to diminish capacitive and time‐delay effects. To address these issues, the coherent addition of the output from arrays of individual solid‐state elements has been proposed. Realization of this solution has relied on exploiting the dynamics of coupled, nonlinear oscillators. Viewing these devices as dynamical systems, antenna technology stands to benefit from the leveraging of decades of research in nonlinear dynamics, allowing for novel approaches towards beam forming and signal processing. The focus of this presentation will be a review of the development of the underlying theory of coupled oscillator synchronization and its relevance to antenna design. In addition, current efforts, both theoretical and experimental, in this field by the authors will be presented as well as directions for future research.As bandwidth requirements and operating frequencies increase, the fundamental limitations of solid‐state devices become significant. These limitations include a considerable decrease in power‐combining efficiency due to increased ohmic losses at these higher frequencies and maximum output powers proportional to 2f‐ owing to size reductions necessary to diminish capacitive and time‐delay effects. To address these issues, the coherent addition of the output from arrays of individual solid‐state elements has been proposed. Realization of this solution has relied on exploiting the dynamics of coupled, nonlinear oscillators. Viewing these devices as dynamical systems, antenna technology stands to benefit from the leveraging of decades of research in nonlinear dynamics, allowing for novel approaches towards beam forming and signal processing. The focus of this presentation will be a review of the development of the underlying theory of coupled oscillator synchronization and its relevance to antenna design. In a...

Noise-induced synchronized switching in coupled bistable systems

We consider a network of bistable dynamic elements with local, linear coupling, subject to noise and a time periodic signal. The response (quantified by an output signal to noise ratio, SNR) of a single element can be substantially enhanced when it is coupled into an array of like elements. In fact we show that noise and coupling cooperate to organize spatio temporal order across the array, corresponding to an increase in the output SNR of the reference element. The results shed new light on the potentially beneficial role of background noise in nonlinear dynamic devices and networks of neuron like elements.