CHUA CIRCUIT 10 YEARS LATER

More than 200 papers, two special issues (Journal of Circuits, Systems, and Computers, Vol.3, Nos. 1 and 2, 1993; IEEE Transactions on Circuits and Systems, Vol. 40 No 10, 1993), an international workshop on 'Chua's Circuit: Chaotic Phenomena and Applications' at NOLTA '93, and a book (R. N. Madan (ed.), Chua's Circuit: A Paradigm for Chaos, World Scientific, Singapore, 1993) on Chua's circuit have been published since its inception a decade ago. This review paper attempts to present an overview of these timely publications, almost all within the last six months, and to identify four milestones of this very active research area. An important milestone is the recent fabrication of a monolithic Chua circuit. The robustness of this IC chip demonstrates that an array of Chua circuits can also be fabricated into a monolithic chip, thereby opening the floodgate to many unconventional applications in information technology, synergetics and even music. The second milestone is the recent global unfolding of Chua's circuit obtained by adding a linear resistor in series with the inductor to obtain a canonical Chua circuit-now generally referred to as Chua's oscillator. This circuit is most significant because it is structurally the simplest (it contains only six circuit elements) but dynamically the most complex among all non-linear circuits and systems described by a 21-parameter family of continuous odd-symmetric piecewise-linear vector fields. The third milestone is the recent discovery of several important new phenomena in Chua's circuits, e.g. stochastic resonance, chaos-chaos-type intermittency, 1/f noise spectrum, etc. These new phenomena could have far-reaching theoretical and practical significance. The fourth milestone is the theoretical and experimental demonstration that Chua's circuit can be easily controlled from a chaotic regime to a prescribed periodic or constant orbit, or it can be synchronized with two or more identical Chua circuits operating in an oscillatory or chaotic regime. These recent breakthroughs have ushered in a new era where chaos is deliberately created and exploited for unconventional applications e.g. secure communication.