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PrefaceIn the 1970's and 1980's, we saw phenomenal advancement in nonlinear science, which had led to many important discoveries that greatly improve our understanding of the physical world. Among them, the discovery of chaos in deterministic systems is unarguably one of the most revolutionary scientific findings. We are now able to explain the apparent complexity and subtle order exhibited by many physical systems under the unified framework of chaos theory.The past decade has seen heightened interest in the exploitation of chaos for useful applications in engineering systems. One application area that has attracted a great deal of attention is communications. Chaotic signals, by virtue of their wide band characteristic, are natural candidates for carrying information in a spread-spectrum communication environment. The use of chaotic signals in communications thus naturally inherits the advantages that are currently being offered by conventional spread-spectrum communication systems, such as robustness in multi path environments, resistance to jamming, low probability of interception, etc. In addition, chaotic signals are easy to generate and hence offer a potentially low-cost solution to spreadspectrum communications.Although many practical problems need to be solved before chaos-based communications can be realized in practice, the field has advanced rapidly during the past few years and it now reaches a point where abstract concepts from physics and mathematics have been fruitfully ported to techniques that allow information to be carried by chaotic signals.This book is intended to address the basic system design, operation, analysis, and performance evaluation of a few selected chaos-based digital communication systems. We put emphasis on the analytical approach taken to study chaos-based communication systems, and focus our attention on a few performance aspects that are of practical importance. In particular, we discuss in this book the modulation techniques, error rate calculations, anti-jamming capabilities, and coexistence with conventional communication systems. We believe that the materials covered in this book will be useful to graduate students, researchers, communication engineers and technology developers who wish to exploit chaos for communication applications.viii We begin in Chapter 1 with an overview of spread-spectrum communication systems and the potential benefits of carrying information with chaotic signals. In Chapter 2 we introduce chaos-based digital modulations and discuss the salient concepts in encoding information with chaotic signals. A review of the various modulation schemes is given. Chapter 2 also contains a discussion on the use of equivalent discrete-time baseband models for studying chaos-based digital communication systems. This kind of models will be used throughout the book. Chapters 3 and 4 provide an indepth treatment of analytical techniques for calculating bit error probabilities of chaos-based digital communication systems. Both single-user and multi-user systems are...

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Secondary series and parallel compensations are widely used in inductive power transfer (IPT) systems for various applications. These compensations are often studied under some isolated constraints of maximum power transfer, optimal efficiency at a particular loading condition, etc. These constraints constitute an insufficient set of requirements for engineers to select appropriate compensation techniques to be used as a voltage converter with optimal efficiency and loading conditions. This paper studies the characteristics of the IPT system at various frequencies of operation utilizing the two compensation techniques to work as a voltage converter. The frequencies that can provide maximum efficiency of operation and load-independent voltage-transfer ratio are analyzed. The optimal frequencies corresponding to the two compensation techniques are found and compared to facilitate the design of voltage converters with efficient power conversion and loadindependent frequency of operation. The analysis is supported by experimental measurements.

Based on a generic transcutaneous transformer model, a remote power supply using a resonant topology for use in artificial hearts is analyzed and designed for easy controllability and high efficiency. The primary and secondary windings of the transcutaneous transformer are positioned outside and inside the human body, respectively. In such a transformer, the alignment and gap may change with external positioning. As a result, the coupling coefficient of the transcutaneous transformer is also varying, and so are the two large leakage inductances and the mutual inductance. Resonant-tank circuits with varying resonant-frequency are formed from the transformer inductors and external capacitors. For a given range of coupling coefficients, an operating frequency corresponding to a particular coupling coefficient can be found, for which the voltage transfer function is insensitive to load. Prior works have used frequency modulation to regulate the output voltage under varying load and transformer coupling. The use of frequency modulation may require a wide control frequency range which may extend well above the load insensitive frequency. In this paper, study of the input-to-output voltage transfer function is carried out, and a control method is proposed to lock the switching frequency at just above the load insensitive frequency for optimized efficiency at heavy loads. Specifically, operation at above resonant of the resonant circuits is maintained under varying coupling-coefficient. Using a digital-phase-lock-loop (PLL), zero-voltage switching is achieved in a full-bridge converter which is also programmed to provide output voltage regulation via pulsewidth modulation (PWM). A prototype transcutaneous power regulator is built and found to to perform excellently with high efficiency and tight regulation under variations of the alignment or gap of the transcutaneous transformer, load and input voltage.

Based on a survey on over 1400 commercial LED drivers and a literature review, a range of LED driver topologies are classified according to their applications, power ratings, performance and their energy storage and regulatory requirements. Both passive and active LED drivers are included in the review and their advantages and disadvantages are discussed. This paper also presents an overall view on the technical and cost aspects of the LED technology, which is useful to both researchers and engineers in the lighting industry. Some general guidelines for selecting driver topologies are included to aid design engineers to make appropriate choices.

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