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- 3D antenna for wireless power transmission aperture coupled microstrip antenna with dielectric lensPublication . Dias, Gonçalo; Pinho, Pedro; Gonçalves, Ricardo; Carvalho, NunoNowadays 3D printers are useful for the development and rapid prototyping of dielectric structures for radiation manipulation and support of antennas. This is possible since the materials used in this machines are essentially dielectric. These can be used as radiating elements (dielectric resonators), as radiation handlers (lenses) or as a supporting base for applying conductive material to radiation (substrates). In this paper we explore 3D printing technology to develop a lens antenna for wireless power transfer operating at 20 GHz. The design, simulation and measurement of an aperture coupled microstrip antenna with dielectric lens is presented and discussed. The lens is used to focus the beam of lower gain feed antenna to produce a highly directive pattern with low side lobe.
- Flow of a periodic interfacial travelling water wavePublication . Cal, Filipe; Dias, GonçaloWe consider a symmetric periodic travelling wave propagating at the interface between two homogeneous, incompressible, irrotational and inviscid fluids bounded by horizontal planes. For interfacial waves of small amplitude, we present a formula for the interface wave depending on the pressure at the rigid lid and at the flat bottom, and, for the general non-linear case, we derive a lower bound for the interfacial wave height. Under certain conditions imposed on the horizontal component of the motion at the interface and supposing that the horizontal components of the velocity in each layer never reach the wave speed, we study the monotonicity of the horizontal component of the velocity field along the streamlines and also analyze the monotonicity of the pressure along horizontal lines throughout the fluid in both layers, and along the boundary of the domain, between the crest and the trough. Finally, based on the behavior of the velocity field components, we build a pictorial description of the particle paths in both layers.
- Trapped modes along periodic structures submerged in a three-layer fluid with a background steady flowPublication . Dias, Gonçalo; Pereira, Bruno M. M.In this study, we study the trapping of linear water waves by infinite arrays of three-dimensional fixed periodic structures in a three-layer fluid. Each layer has an independent uniform velocity field with respect to the fixed ground in addition to the internal modes along the interfaces between layers. Dynamical stability between velocity shear and gravitational pull constrains the layer velocities to a neighbourhood of the diagonal U1=U2=U3 in velocity space. A non-linear spectral problem results from the variational formulation. This problem can be linearized, resulting in a geometric condition (from energy minimization) that ensures the existence of trapped modes within the limits set by stability. These modes are solutions living the discrete spectrum that do not radiate energy to infinity. Symmetries reduce the global problem to solutions in the first octant of the three-dimensional velocity space. Examples are shown of configurations of obstacles which satisfy the stability and geometric conditions, depending on the values of the layer velocities. The robustness of the result of the vertical column from previous studies is confirmed in the new configurations. This allows for comparison principles (Cavalieri's principle, etc.) to be used in determining whether trapped modes are generated.