Preface by Dr. C.Y.Meng
Preliminary and qualitative knowledge of static magnetism and electricity
were acquired by mankind since very ancient times. However, an in-depth
and quantitative analysis was not available until the beginning of the 19th
Century, while magnetism and electricity are still recognized as two indepen-
dent and irrelevant topics. Then, in the sixties of the 19th century, incon-
sequence and non-self-consistency was discovered by J. C. Maxwell when he
tried to sum up the known laws of electricity and magnetism. However, this
was eliminated after his creative introduction of the idea of displacement cur-
rent, and the well known Maxwell equations were formed consequently as the
foundation of electromagnetism. From these equations, it is understood that
electricity and magnetism are by no means non-related, but two aspects of
just one thing. Maxwell not only unified electricity and magnetism, but also
proved that light is actually a part of the electromagnetic spectrum, which
extends from super long, long, medium, short, ultra short, meter, decimeter,
centimeter and millimeter waves all the way down to far infra-red, infra-
red, visible and ultra-violet lights, and even X- and γ-ray radiations. Their
frequency range covers from 10
1
Hz to 10
20
Hz, the widest for a physical
quantity.
Using damping wave in the ultra-short wave band, H. Hertz experimen-
tally confirmed the existence of electromagnetic wave, and measured some of
its properties. However, the first application of electromagnetic wave was in
the long wave range. In the following decades, scientists tried to use shorter
radio waves and extend the optical wavelength range on both sides of the
visible light waves. Now, radio and light waves have met in the far-infrared
band, and the full electromagnetic spectrum has been connected together.
The wavelength range involved in this book covers microwave and part of
the optical waves. Microwave deals with wavelengths in the order from meters
to millimeters, the shortest part in the radio-wave spectrum. It was studied
only by few scientists before the World War II, followed by fast development
during the war as desired by applications in radar, then post-war applications
in communications, industrial and scientific research. On the other hand, op-
tical wavelengths involved in this book lie in the micrometer or near-infrared
range, mainly for information transmission experiencing rapid development
in the recent decades. In fact, this part of electromagnetic spectrum shifts to
