Editor’s message: microwave processing of modern materials

Ancient technology was aimed to manufacture tools and other devices using materials chosen due to their good structural properties. Toughness was an important criterion, but with invention of new artefacts led to greater requirements so that new materials were sought. The problem was that available materials in nature did not fulfil such needs, hence it was no longer a matter of materials choice, but materials engineering. In some cases different materials can be joined to enhance the properties of the system, having composites such as the mud brick made of a mixture of mud reinforced with straw, or processing them, metallurgy for instance, so that new manufactured items were either added or replaced those made of stone and clay. The specifications of the material are higher with each new application and now there are cases where strength, refractoriness, corrosion resistance and density, among others, are required at the same time, exceeding by far the possibilities of traditional materials. Mechanical resistance, density and refractoriness are properties that can be recognized qualitatively, better known than electrochemical and functional properties of materials. The latter allows the construction of semiconductors that are an engineering challenge since intrinsic semiconductors found in nature exhibit properties below the electronic industry requirements, while enhance is not a matter of superposition of materials for having additive properties. The properties are modified by adding dopant agents and conduct thermal treatments. That is, they are designed to have properties that are beyond (meta in Greek) those found in natural occurring materials. Although the term metamaterial is a way to make a distinction from other advancements in materials science and engineering, the modern reference to them considers “exotic” interaction with electromagnetic waves. Metamaterials are designed in size, shape and combination of different materials that can be stacked to form periodical arrangements, smaller than the wavelength. The list of applications is long; one that seems like science fiction is the invisibility cloak, by bending the wave propagation around an object, and that has been proven with some degree of success. The possibility for metamaterials to manipulate electromagnetic, and mechanical, waves, according to their wavelength, makes them attractive for fabricating small, high gain antennas for communication purposes. The wavelength is in the order of centimeters, large enough to prepare metamaterials for this application by mechanical assembling of periodical arrangements of rings and wires based on theoretical designs. There is a great number of documents dedicated to metamaterials for small antennas in different applications. Although in many cases they are related to microwaves, those documents are often addressed to the design and tests, sometimes virtual, of the fabricated devices for communication applications. In the case of shorter wavelength mechanical building of a device is more difficult, such as if it is in the order of Armstrongs, like X-ray. There are materials, not necessarily