Circuits, both linear and nonlinear, remain the core components of most electronic and mechatronic equipment and devices to date. As industrial electronics and mechatronics become mature, better functionality and reliability of these technologies require more intriguing use of nonlinear circuits. This calls for thorough investigation of dynamical characteristics and largest possible operating regimes of nonlinear circuits and systems. Of particular interest is the fundamental nonlinear circuit theory that is still in the evolving phase of its development today. In view of the exciting emergence of nano-technology and the attractive quantum-computing future, nonlinear circuits have become even more important and fundamental.

The fact that chaos is ubiquitous in nonlinear circuits has been one of the major motivations for studying nonlinear circuit theory in recent years. A number of workshop and conference proceedings, research monographs and textbooks, special journal issues, and experimental results published previously were focused on analysis and characterization of chaotic phenomena in various nonlinear circuits. There were also many reports on chaos generation via circuit design, mostly performed on platforms of some hypothetical systems such as Chua's circuit. These studies were essential in laying a foundation for further development of both basic theory and engineering design of nonlinear circuits.

Yet, the traditional trend of understanding and analyzing chaos has evolved into the new tasks of ordering and utilizing chaos over the past decade. A new research direction in the field of applied chaos technology not only includes controlling chaos, which means to weaken or completely suppress chaos when it is harmful, but also includes anti-control of chaos, known also as chaotification, which refers to enhancing existing chaos or purposely generating chaos when it is useful and beneficial. One has witnessed increasing interest not only in the traditional chaos analysis and chaos generation via circuitry but also in the new consideration of utilizing chaos in real physical systems. This shows that electronic engineers are really giving chaos more and more serious thought, and it is believed that there is a significant change in attitude of engineers of our generation toward this kind of engineering research. This book aims to bridge the gap between these two phases of development and also to open up some discussion of real applications where chaos can be put to technological use, including communication, power electronics design, and so on.

Chaos, when under control, promises to have a major impact on many novel, time- and energy-critical applications, such as high-performance circuits and devices (e.g., delta-sigma modulators and power converters), liquid mixing, chemical reactions, biological systems (e.g., in the human brain, heart, and in perceptual processes), crisis management (e.g., in jet-engines and power networks), secure information processing (e.g., chaos-based encryption), and decision-making in critical events. This new and challenging research area has embraced both analog and digital technologies and has become a scientific inter-discipline, involving engineers in the fields of controls, systems, electronics, mechanics, and biomedicine, as well as applied mathematicians, theoretical and experimental physicists and, above all, circuit engineers and instrumentation specialists. This book is a collection of some state-of-the-art surveys, tutorials, and overview articles written by some experts in this area.

It is our hope that this book can serve as an updated and handy reference for university professors, graduate students, laboratory researchers and industrial practitioners, as well as applied mathematicians and physicists who are interested in chaos in circuits and systems.
 

Guanrong Chen, City University of Hong Kong
Tetsushi Ueta, Tokushima University, Japan