This book basically comprises the results of many original research papers of the authors' research group, in which many authors of these original papers have done a great deal of detailed and creative research work. Therefore, we are much obliged to our contributing authors for their high‐quality work.

We acknowledge the continuous support of our research by the National Natural Science Foundation of China (No. 61401385), the Fundamental Research Funds for the Central Universities (No. lzujbky‐2017‐37), the Hunan Natural Science Foundation of China (No. 2017JJ3257), the Hong Kong Research Grants Council Early Career Scheme (No. 25214015), the Hong Kong Polytechnic University (Nos G‐YBMU, G‐UA7L, 4‐ZZHD, F‐PP2C, and 4‐BCCS), and also by the Research Foundation of Education Bureau of Hunan Province, China (No. 17C1299). In addition we would like to thank the editors sincerely for their time and efforts spent in handling this book, as well as for their constructive comments and suggestions. We are very grateful to the staff at Wiley and IEEE for their invaluable support during the preparation and publication of this book.

To all these wonderful people we owe a deep sense of gratitude especially now that the research projects and the book have been completed.