Papers by Author: Ladislau Matekovits

Abstract: In the present paper (1-x)Pb (Zr_1-yTi_y)O₃ – xPb (Mn_1/3Sb_2/3)O₃ – z at%E system, with E = Pr³⁺, Nd⁵⁺ and Gd³⁺ where x = 0.12; y = 0.48; z = 0 and 0.02 ceramic synthesized by solid state reaction technique is analysed. The investigation aims studying of the effect of dopants on the dielectric and piezoelectric properties of such piezoelectric ceramic. The prepared powders have been uniaxially pressed into discs with diameter of 10 – 12 mm and thickness of 1.2 mm. Sintering has been carried out in air atmosphere at temperatures of 1150^°C and 1200^°C, respectively, for 2 hours each, followed by a controlled cooling at a rate of 200^°C /h. The piezoelectric properties have been investigated after a suitable preparation, including polishing, metallization. The structure of the samples has been determined by X-ray diffractometry (XRD), while the morphology and grains size have been investigated by the scanning electron microscopy (SEM). The piezoelectric properties have been studied by the resonance - antiresonance method. XRD analysis reveals a perovskite tetragonal structure and, as expected for ceramic materials, SEM analysis indicates that the average grain size increases as sintering temperature increases. The dielectric and piezoelectric properties have been determined measuring the ceramic discs, and properties, as dielectric permittivity (ε_r), dielectric loss (tg δ), and the electromechanical coupling factor (k_p) have been obtained. The acquired results indicate a significant effect of the dopants on the dielectric and piezoelectric properties of such materials.

Abstract: Conformal metasurfaces are even more diffused in different fields from optics to electromagnetics. Advanced applications, as making object invisible to incident fields also known as cloaking, require high precision realizations, since the resonant answer of the system is very sensitive to geometry details. Practical realizations are provocative, since material characteristics and mechanical restrictions should also be considered. Multi- and inter-disciplinary interactions are mandatory to overcome such technological challenges. Due to its excellent esthetic characteristics, good physical and mechanical properties, Aluminium is widely used for deposition on different substrates: physical and chemical vapor depositions are very suitable for micro-metallization process and for the realization of multilayered structures. This paper presents some results about the behavior of a cylindrical-shape system realized by Al films deposition on flexible, polymeric organosilicon substrate.

Abstract: We introduce a metamaterial based parallel-plate waveguide, devised in microstrip technology that features two electromagnetic band-gaps. Since one of the band-gaps extends from zero frequency, the structure can be used as a band-pass filter. We perform a parametric study in view of facilitating design and optimisation.

Abstract: This work numerically explores the relations between the positions and the widths of the frequency bandgaps that occur in some shielded high impedance surfaces and the geometrical dimensions of the structures. The reported parameterized results are useful for design issues and for circuit models conception and validation.