Page 67 - Maxwell House

NEOCLASSICAL THEORY OF INTERACTION 47

Introduction

Readers who already know this material are encouraged to skim through the chapter for
notation. The topics in this chapter do not cover all ultra-wide spectrum of possible and
apparently quantum interactions of electromagnetic fields with matters. It should be subject to
a particular book or many books. Eventually, the following can be considered as some digest
as we tried to draw pictures by broad-brush strokes omitting sometimes concrete and less
important details.
The good understanding of the field - material interactions becomes more and more critical in
the practice of engineering. Not rarely enough, the performance of materials starts severely
limiting the ultimate performance of modern radio devices. Therefore, scientists and engineers
realized that the materials existing in nature are not sufficient to satisfy to rigorous requirements
and on the go to synthesize new materials with combinations of properties never seen before.
The central idea is to manipulate the microscopic structure of matter to produce tangible effects
that can be recorded macroscopically by certain effective parameters like , μ, or . The worthy
example is the class of material with negative permittivity and permeability, modern
ferromagnetics and ferrimagnetics, etc. The important aspect of the following discussion is an
understanding and modeling of the relationship between the atomic structure of materials and
their physical properties thereby putting our reader into this field.
Loosely speaking, we know that all matter is made up of atoms and each atom is composed of
electrons, protons, and neutrons. Electrons and protons are the charged particles and carriers of
magnetic moments. As well, they have small but finite masses and resist any attempts to change
their existing state. In other words, the external electrical or magnetic fields exerting a force on
their charges and magnetic moments cannot change at once their orientation or direction of
movements. In particular, it must be an extremely short but finite delay and energy loss. As
soon as the applied fields are static or vary relatively slow, we can disregard both effects (see
Chapter 1). But, in fact, many modern systems such as spread spectrum communication systems
1
or radars with ultrashort pulses are extremely broadband covering multi-octave frequency
bands up to optical that requires much more accurate estimation of the material conductivity,
permeability, and permittivity. The typical engineering description of them turns out to be not
quite right and might cause biased or completely incorrect results in the numerical analysis
where our instantaneous control under the calculation is restricted. Before undertaking a general
review, let consider the simplest case of permeability and permittivity using information in the
context of Chapter 1. First, we concentrate on the torque or rotating effect due to the fact that
the alternative EM fields are capable not only move charges and their assemblies along a
straight line but force them to rotate.

2.1 TORQUE EXERTED BY ELECTRIC AND MAGNETIC FIELD
2.1.1 Mechanical Torque Examples

We assume that our reader is familiar with the mechanical phenomenon known as torque, rotary
force or moment of force from the physics course. It is nothing more than a twisting force that
tends to cause rotation of the object around its axis. The torque is directed normal to both the
force and force variation direction by the right-hand rules. Numerically the torque is the

1 −12 s pulse covers 10 Hz = 1 THz bandpass.
12
For example, the spectrum of 1 picosecond = 10