# 1: Preliminary Concepts

- Page ID
- 3901

A field is the continuum of values of a quantity as a function of position and time. The quantity that the field describes may be a scalar or a vector, and the scalar part may be either real- or complex-valued. In electromagnetics, the electric field intensity \({\bf E}\) is a real-valued vector field that may vary as a function of position and time, and so might be indicated as “\({\bf E}(x,y,z,t)\),” “\({\bf E}({\bf r},t)\),” or simply “\({\bf E}\).” When expressed as a phasor, this quantity is complex-valued but exhibits no time dependence, so we might say instead “\(\widetilde{\bf E}({\bf r})\)” or simply “\(\widetilde{\bf E}\).” An example of a scalar field in electromagnetics is the electric potential, \(V\); i.e., \(V({\bf r},t)\). A *wave* is a time-varying field that continues to exist in the absence of the source that created it and is therefore able to transport energy.

- 1.1: What is Electromagnetics?
- The topic of this book is applied engineering electromagnetics. This topic is often described as “the theory of electromagnetic fields and waves,” which is both true and misleading. The truth is that electric fields, magnetic fields, their sources, waves, and the behavior these waves are all topics covered by this book. The misleading part is that our principal aim shall be to close the gap between basic electrical circuit theory and the more general theory.

- 1.2: Electromagnetic Spectrum
- ectromagnetic fields exist at frequencies from DC (0 Hz) to at least 1020 Hz – that’s at least 20 orders of magnitude! At DC, electromagnetics consists of two distinct disciplines: electrostatics, concerned with electric fields; and magnetostatics, concerned with magnetic fields. At higher frequencies, electric and magnetic fields interact to form propagating waves. Waves having frequencies within certain ranges are given names based on how they manifest as physical phenomena.

- 1.3: Fundamentals of Waves
- In this section, we formally introduce the concept of a wave and explain some basic characteristics.

- 1.4: Guided and Unguided Waves
- Broadly speaking, waves may be either guided or unguided. Unguided waves include those that are radiated by antennas, as well as those that are unintentionally radiated. Once initiated, these waves propagate in an uncontrolled manner until they are redirected by scattering or dissipated by losses associated with materials. Examples of guided waves are those that exist within structures such as transmission lines, waveguides, and optical fibers.

- 1.5: Phasors
- In many areas of engineering, signals are well-modeled as sinusoids. Also, devices that process these signals are often well-modeled as linear time-invariant (LTI) systems. The response of an LTI system to any linear combination of sinusoids is another linear combination of sinusoids having the same frequencies.

- 1.6: Units
- The term “unit” refers to the measure used to express a physical quantity

- 1.7: Notation
- The list below describes notation used in this book

Thumbnail: Examples of phasors, displayed here as points in the real-imaginary plane.

#### Contributors

Ellingson, Steven W. (2018) Electromagnetics, Vol. 1. Blacksburg, VA: VT Publishing. https://doi.org/10.21061/electromagnetics-vol-1 Licensed with CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0. Report adoption of this book here. If you are a professor reviewing, adopting, or adapting this textbook please help us understand a little more about your use by filling out this form.