1. Introduction

Microwaves pervade the whole universe; this was discovered by quite an accident by R. W. Wilson and A. A. Penzias in 1964 [1–3]; microwaves seem to bathe the earth and the space from all directions. Microwaves, also, pervade today's world of high technology [4, 5]. They are of tremendous scientific interest, and they are, just, indispensable in today's communication [6], military [7], medical [8], domestic appliances, scientific instruments [9, 10] (electron spin resonance, ESR/ferromagnetic resonance spectroscopy, FMR), microwave passive instruments [11–15], radars, spaceships, satellites, and so forth; they are also found in many industries such as automobile, data, memory and computer processing, and microwave instrumentation [14, 15]; the signal processing in the range of 5–50 GHz is quite

## Electromagnetic Fields and Waves

interesting for security, military, and communication applications [15, 16]. Modern microwave communication especially mobile communication and satellites requires high performance band-stop filter having high frequency selectivity, smaller size, high stop band attenuation, and low insertion loss [15, 17]. A good account of different applications is found in [17].

Most impressive, they are already playing an important role in the development of smart cities along with smart transportation, smart energy, smart health care, and so forth [18]. Figure 1 shows an electromagnetic spectrum, making emphasis on the microwave region and the definition of its different bands. Figure 2 shows an assortment of pictorial representations of some of the modern applications of microwaves.

#### Figure 1.

The electromagnetic spectrum, making emphasis on the microwave region and its different bands.

#### Figure 2.

The microwaves in the electromagnetic spectrum range from 300 MHz (1 m) to 300 GHz (1 mm) [3]. There are microwaves present in: (a) and (b) the whole universe, a microwave view captured by the European Space Agency's Planck satellite [19]; (c) the digital technology [20, 21]; (d) biomedical use [22]; (e) controversial proposition to propel starships [23]; (f) in telecommunications, Wi-Fi antennas; and (g) in the development of smart cities [18].

The Interaction of Microwaves with Materials of Different Properties DOI: http://dx.doi.org/10.5772/intechopen.83675

#### Figure 3.

Microwaves as the signals coming in and out from magnetic microwire sensors implanted in injured-surgery patients in order to follow postoperatory recovery [8]. The transceiver houses, both, the microwave source and the microwave detectors. Probably with the capacity to detect anisotropic distribution of signals.

In Figure 3, we show one of the most impactful applications of microwaves as the signals coming in and out from magnetic microwire sensors implanted in injured-surgery patients in order to follow postoperatory recovery [8]. The microwave beam should penetrate a considerable section of tissue then "hit" the magnetic wire, film, or rod, reflecting in many directions. Some microwaves will get back to the horn entrance of the transceiver, then detected and processed. The technology already exists and is already in use in atmospheric sciences [21] and in gun radars to detect speedy objects. These applications cannot be carried out with laser, for example, as laser light cannot penetrate tissue as microwaves do. It should be noted that in all the above examples, microwaves and radar work in open spaces and "hit" a target, and then some of the reflected beams are detected. Absorption in the medium itself and by obstacles reduces the reading at the detectors. There are also a great number of uses of microwaves inside tubes, pipes, and cavities. More controlled energy flux is attained and precision measurements can be done. We treat them after we give the fundamentals of the physics involved.

But, why are they (microwave) everywhere in this world and out of this world? It is because of the peculiarity of their electromagnetic properties and the way they interact with matter. They started to propagate through the universe at the epoch of recombination in the cosmic evolution. The cosmic microwave background (CMB) is the most ancient relic we have today of the beginning of the universe in the form of a big bang [24, 25]. It is the oldest electromagnetic radiation, older than visible light [26]. When atoms and nuclei appeared for the first time in the universe, microwaves started to interact with them immediately. Microwaves interact with atoms, nuclei, protons, electrons, molecules, clusters of molecules, and so forth. At the macroscopic scale, microwaves interact with all kinds of matter: rocks, gases, clouds, liquids (water and oceans), dielectrics, plasmas, ionosphere, metals, magnetic matter, and so on. It gets reflected, transmitted, and very frequently absorbed. Microwaves make atoms rotate (rotational excitation) and make electric dipoles jiggle frenetically, and when electric dipoles are part of dielectric materials, microwaves heat them. Microwaves make magnetic dipoles rotate and jump up magnetic energy states. The free electrons in metallic objects absorb greatly microwaves.
