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A Bistable Microelectronic Circuit for Sensing an Extremely Low Electric Field

This circuit can be used in developing an extremely sensitive electric-field sensor.

Bistable systems are prevalently found in many sensor systems. It is well established that a well-designed coupling scheme, together with an appropriate choice of initial conditions, can induce oscillations (i.e. periodic switching between stable fixed points) in over-damped bistable dynamical systems when a control parameter exceeds a threshold value. This behavior was demonstrated in a specific prototype system comprised of three unidirectionally coupled ferromagnetic cores, the basis of a coupled core fluxgate magnetometer. Another prototypical (quartic potential based) system of coupled over-damped Duffing elements has been applied to describe the dynamics of the polarization inside a ferroelectric material, the basis of an electric-field sensor currently under development.

The analysis showed that N (odd) unidirectionally coupled elements with cyclic boundary conditions would oscillate when a control parameter (i.e. coupling strength) exceeded a critical value. Note that the oscillatory behavior can also be seen for large, even N. Typically, the oscillations emerge with an infinite period through a hetero-clinic-cycle bifurcation (i.e. a global bifurcation) to a collection of solution trajectories that connects sequences of equilibria and/or periodic solutions. In the particular case of overdamped bistable systems, the cycle includes mainly saddle-node equilibria. As a control parameter (usually the coupling strength) approaches from above a critical value, the frequency of the oscillations decreases, approaching zero at the critical point. Past the critical value, the oscillations disappear, and the system dynamics settles into an equilibrium.

The basin of attraction of the oscillations spans almost the entire phase space with the exception of a small region near the symmetrical initial conditions, in which case, the coupled system settles asymptotically to its stable fixed points. The emergent oscillations, in either the ferromagnetic or ferroelectric systems mentioned above, have been used to detect very weak “target” (dc and ac) signals via the (signal-induced) changes in the oscillation characteristics, e.g., duty cycle and frequency. It is important to emphasize that this emergent oscillatory behavior is quite general; in a non-sensor application, it has led to interesting frequency-selective properties of interacting neural networks.

The above phenomena open up new possibilities for the exploitation of a large class of (normally) non-oscillatory systems for a variety of practical applications that involve the use of the emergent self-sustained oscillations as a reference. The latest realization of a system in this class is an overdamped bistable system as one of the active elements in a microcircuit, which is intended to be used for measuring minute voltage or current changes that may be injected into the system.

Overall, the analysis and results of the microcircuit dynamics are in very good agreement with previous theoretical results. There are, however, important differences in the characteristic function and coupling function of the microcircuit device that can lead to far richer and more complex behavior in the detection of ac signals than in the theoretical models. For instance, additional branches of steady states and the

possibility of chaotic behavior in the microcircuit are possible.

This work was done by Visarath In, Patrick Longhini, Norman Liu, Andy Kho, Joseph D. Neff, and Adi R. Bulsara of the Space and Naval Warfare Systems Center; and Antonio Palacios of San Diego State University. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp  under the Electronics/Computers category. NRL-0041

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A Bistable Microelectronic Circuit for Sensing an Extremely Low Electric Field

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    Defense Tech Briefs Magazine

    This article first appeared in the June, 2010 issue of Defense Tech Briefs Magazine (Vol. 4 No. 3).

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    Overview

    The document discusses the development and analysis of a bistable microelectronic circuit designed for sensing extremely low electric fields. The research focuses on a coupled bistable system implemented through a microelectronic circuit, which is characterized by its ability to exhibit complex dynamical behavior in response to external signals.

    The study begins with a description of the circuit's design, which utilizes operational transconductance amplifiers (OTAs) based on differential pair configurations. These components are crucial for introducing nonlinearity into the system, allowing for the exploration of its dynamical properties. The governing equations of the system are derived, providing a foundation for understanding its behavior under various conditions.

    The document highlights the response of the experimental system to direct current (dc) signals, validating the experimental results against theoretical predictions. It notes that while the system can also detect alternating current (ac) signals, the behavior in response to ac inputs is more intricate and will be addressed in future publications.

    Key findings include the identification of a critical coupling coefficient, which is essential for determining the system's stability and response characteristics. The experimental data confirm the theoretical models, demonstrating that the circuit can effectively respond to input signals within a specified range. However, it is noted that the injected current should not exceed 530 nA to prevent overloading the microcircuit.

    The document emphasizes the potential applications of this bistable microelectronic circuit in ultra-sensitive sensing technologies. The ability to detect low electric fields could have significant implications for various fields, including environmental monitoring, biomedical applications, and advanced communication systems.

    In conclusion, the research presents a comprehensive analysis of a bistable microelectronic circuit, showcasing its potential for high-sensitivity electric field detection. The findings contribute to the understanding of coupled bistable systems and pave the way for future advancements in sensor technology. The document sets the stage for further exploration of the circuit's capabilities, particularly in the context of ac signal detection and the development of more sophisticated sensing applications.

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