Theoretical and Numerical Analysis can be used by research students to design different systems to generate electric fields with required characteristics. Says author K.A.G. Rao, "When I was doing my Ph.D. thesis, I used some mathematical models. In 2005, I got the idea that I could use the same models for designing different kinds of electric fields. So I started working on nonconventional systems like curved surfaces and flat elliptic surfaces, both conducting and nonconducting. The work, which was mostly mathematical, took me nearly three years."

The analysis of nonlinear hybrid electromagnetic systems poses significant challenges that essentially demand reliable numerical methods. In recent years, research has shown that finite-difference time-domain (FDTD) cosimulation techniques hold great potential for future designs and analyses of electrical systems. Time-Domain Computer Analysis of Nonlinear Hybrid Systems summarizes and reviews more than 10 years of research in FDTD cosimulation. It first provides a basic overview of the electromagnetic theory, the link between field theory and circuit theory, transmission line theory, finite-difference approximation, and analog circuit simulation. The author then extends the basic theory of FDTD cosimulation to focus on techniques for time-domain field solving, analog circuit analysis, and integration of other lumped systems, such as n-port nonlinear circuits, into the field-solving scheme. The numerical cosimulation methods described in this book and proven in various applications can effectively simulate hybrid circuits that other techniques cannot. By incorporating recent, new, and previously unpublished results, this book effectively represents the state of the art in FDTD techniques. More detailed studies are needed before the methods described are fully developed, but the discussions in this book build a good foundation for their future perfection.

The first nonlinear optical effect was observed in the 19th century by John Kerr. Nonlinear optics, however, started to grow up only after the invention of the laser, when intense light sources became easily available. The seminal studies by Peter Franken and Nicolaas Bloembergen, in the 1960s, paved the way for the development of today’s nonlinear photonics, the field of research that encompasses all the studies, designs, and implementations of nonlinear optical devices that can be used for the generation, communication, and processing of information. This field has attracted significant attention, partly due to the great potential of exploiting the optical nonlinearities of new or advanced materials to induce new phenomena and achieve new functions. According to Clarivate Web of Science, almost 200,000 papers were published that refer to the topic “nonlinear optic*”. Over 36,000 papers were published in the last four years (2015–2018) with the same keyword, and over 17,000 used the keyword “nonlinear photonic*”. The present Special Issue of Micromachines aims at reviewing the current state of the art and presenting perspectives of further development. Fundamental and applicative aspects are considered, with special attention paid to hot topics that may lead to technological and scientific breakthroughs.

Advances in Electronics and Electron Physics