Joseph D. Neff

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.

Maintenance of chaos in a computational model of a thermal pulse combustor

The dynamics of a thermal pulse combustor model are examined. It is found that, as a parameter related to the fuel flow rate is varied, the combustor will undergo a transition from periodic pulsing to chaotic pulsing to a chaotic transient leading to flameout. Results from the numerical model are compared to those obtained from a laboratory-scale thermal pulse combustor. Finally the technique of maintenance (or anticontrol) of chaos is successfully applied to the model, with the result that the operation of the combustor can be continued well into the flameout regime. (c) 1997 American Institute of Physics.

Pulse-enhanced stochastic resonance

Abstract By adding constant-amplitude pulses to a noisy bistable system, we enhance its response to monochromatic signals, significantly magnifying its unpulsed stochastic resonance. We observe the enhancement in both numerical simulations and in analog electronic experiments. This simple noninvasive control technique should be especially useful in noisy bistable systems that are difficult or impossible to modify internally.

A novel floating gate circuit family with subthreshold voltage swing for ultra-low power operation

The behavior of emerging wireless sensor networks is often characterized by short bursts of computation and communication followed by long periods of inactivity. As the unit devices are typically powered by batteries, conservation of energy - particularly during idle time - is paramount. Subthreshold logic has been proposed for providing lower energy per operation than traditional CMOS, but does so with a significant degradation of performance. This paper describes a novel approach of dynamically switching between sub- and super-threshold operation through the use of floating gate techniques in order to provide high performance during active periods and low leakage during idle periods.

A drive-free vibratory gyroscope

Computational and analytical works have shown that certain coupling schemes can lead to significant enhancements in sensitivity, accuracy, and lower costs for a wide range of sensor devices whose output and performance depends directly on the ability of individual units to generate stable limit cycle oscillations. Vibratory gyroscopes are very good candidates for this new paradigm as their accuracy and sensitivity are directly dependent on the ability of a driving signal to produce and maintain oscillations with stable amplitude, phase, and frequency. To achieve higher accuracy, we show proof of concept of a novel scheme: a drive-free coupled gyroscope system in which the coupling alone can lead to self-regulated limit cycle oscillations in the drive- and sense-axes with stable constant amplitude and phase-locking.

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.

An Overview of A Perturbation Analysis for Uni‐directionally Coupled Vibratory Gyroscopes

The complex behaviours of gyroscope systems have been scientifically researched and thoroughly studied for decades. Most of scientific research involving gyroscopes specifically concentrates on studying the designs and fabrications at the circuitry level. Although gaining a recent popularity with the low cost of MEMS device that offers an attractive approach for gyroscope fabrications, its performance is far from meeting the requirements for an inertial grade guidance system. To improve the performance, our current research is theoretically focusing upon investigating the dynamics of vibratory gyroscopes coupled in a ring configuration. Particularly, a certain topology of arrangements among coupled gyroscopes can be designed and studied to enhance robustness. The main operation depends mostly on an external source for a stable oscillation in the drive axis, while an oscillatory motion in the sense axis, which is used to detect an angular rate of rotation, is enabled through the transfers of energy from th...

Dynamics in Non-Uniform Coupled SQUIDs

Recently there is growing interest in Superconducting Quantum Interference Filters (SQIFs) in the science community. Much in the way that antenna array technology has moved from uniform arrays to non-uniform, sparsely populated arrays, SQIF devices open the trade space from traditional uniform SQUID arrays to unconventional SQIF structures making these mesoscopic quantum devices (for RF reception) a feasible concept. Computational modeling of SQIFs exhibits a non-periodic voltage response vs. external flux where an anti-peak is present only around the zero applied magnetic field. Improved dynamics range is investigated in this work by considering inductive coupling, number of loops in an array, and unconventional grating structures. We show that changes in these parameters can lead to a significant performance enhancement.