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Microstrips with the ground plane perturbed by a sequence of slots appropriately spaced to reproduce a Cantor fractal scheme exhibit spectral responses characterized by several transmission bands. The parameters of these bands (center frequency, bandwidth, minimum insertion loss) have been calculated for a fixed fractal scheme by varying both the substrate permittivity and the width of the slots. Data show that microstrips with the highest substrate permittivity have a lower number of transmission bands and lower insertion loss values.

Materials exhibiting refractive index significantly depending on temperature can be used as defect layers to obtain temperature-dependent defect modes (narrow transmission peak in forbidden band) in perturbed truncated-periodic multilayers. Here we consider Indium Antimonide (InSb), which in the terahertz frequency range, as the temperature increases, transforms from a lossy dielectric material to a lossy plasmonic material. Despite the dissipative behavior of InSb, high peak defect modes can be excited if the truncated-periodic multilayer is properly designed. As an example, we show that in a Silica/Polymethylpentene (SiO$_{2}/$TPX) truncated-periodic multilayers perturbed by a InSb layer a defect mode can be excited with a center frequency which can span a significantly large band by varying the temperature.

The microwave dielectric resonators that we consider are multilayered structures where two or more materials with appropriate refractive indices are arranged in a given sequence. Generally, the transmissivity spectrum of such a structure exhibits forbidden bands and narrow transmission peaks. At resonance frequencies corresponding to these peaks the field localization phenomenon occurs, causing in some regions of the multilayer the field intensity to reach values significantly greater than the incident field one.

We present a method to design quarter-wave multi-section lossless devices which, in principle, works whatever the requested reflection/transmission spectrum may be. Some examples are reported confirming that our method allows to obtain devices exhibiting a reflection spectrum which can be considered a valid approximation to the requested one for both cases of multi-band matching and bandgap behavior.

Pit and hillock textures enhance the light-coupling efficiency of silicon solar cells. In a bioinspired pit/hillock texturing scheme, inspired by the compound eye of the common housefly, the surface of the silicon solar cell is textured as an array of parallel and equally spaced grooves/prisms whose cross-section is a circular segment that is decorated further by smaller equally spaced circular grooves/prisms. Complementary examples of both textures had been recently analyzed over the wavelength range [400,1100] nm under the rubric of geometrical optics. Here, we consider a new bioinspired pit texture and show that it leads to a light-coupling efficiency significantly greater than that of a flat silicon surface but intermediate between those of the previously analyzed hillock and pit textures.

Analysis of the reflecting features of Cantor dielectric multilayers for oblique incidence shows that, for suitable values of the refractive indexes of the two constituent materials, they behave as an omnidirectional mirror. The Cantor multilayer still keeps the characteristics of omnidirectional mirror also for lossy materials. The main effect of the material dissipation is to increase the minimum value of the dips delimiting the reflecting band and, consequently, to broaden the rejected frequency band. Comparison with a periodic quarter-wave stack having the same constituent materials points out that the Cantor multilayer has an higher rejection level with a narrower bandgap.

Fractals are geometric structures which exhibit invariance property with respect to a change of scale. They can be obtained by repeating a basic operation (generator) on a smaller and smaller scale. Optical Cantor fractal multilayers are structures obtained by applying the fractal Cantor construction to the optical length of the layers of two different dielectrics. Their transmission spectrum can be evaluated using the transmission matrix method. It can be shown that the spectrum exhibits several stop-bands and very narrow transmission peaks and that the self-similarity of the multilayer reflects on the self-scaling property of its electromagnetic response. In this work we show that the stop-bands and the transmission peaks can be shifted by inserting a defect in the fractal structure. The defect is a layer of a dielectric different from the ones constituting the fractal. The extension of the shift of both stop-bands and transmission peaks depends on both the thickness and the refractive index of the defect layer