In recent years, the possibility of taking advantage of the unusual properties of the so-called metamaterial technology has led to a great deal of research activity. Metamaterial structures are created by assembling a periodic or nonperiodic structure composed of elements which are small compared to the wavelength of the propagating electromagnetic wave. As a consequence, the properties of these artificial materials no longer depend exclusively on the constitutive materials used, but rather they depend on the whole composite macrostructure thus formed. The resulting material can be engineered to realize novel electromagnetic properties and to achieve behaviors that are not found in naturally occurring materials. For instance, many efforts have been aimed at improving the performances of radiating antennas and novel propagating media with uncommon characteristics.

The principal goal of this special issue on metamaterials is to provide an in-depth description of the state of the art of research and development in this area. The special issue will highlight contributions intended to stimulate new metamaterial-inspired designs and practical applications. Potential topics include, but are not limited to:

• Beam steering
• Electromagnetic bandgap
• High-impedance ground planes
• Miniaturized antennas
• Frequency selective surfaces
• Reflectors
• Acoustic metamaterials
• Matching and bandwidth enhancement
• Tunable metamaterials
• Absorber
• Metamaterial cloaking

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