OAM multiple transmission using uniform circular arrays: numerical modeling and experimental verification with two digital television signals

In this work we present the outcomes of a radio-frequency OAM transmission between two antenna arrays performed in a real-world context. The analysis is supplemented by deep simulative investigations able to provide both a preliminary overview of the experimental scenario and a posteriori validation of the achieved results. As a first step, the far-field OAM communication link is tested at various frequencies and the corresponding link budget is studied by means of an angular scan generated by the rotation of the receiving system. Then, on the same site, two digital television signals encoded as OAM modes ($\ell$=1 and $\ell$=-1) are simultaneously transmitted at a common frequency of 198.5 MHz with good mode insulation.Comment: 16 pages, 14 figure

A New Approach to the Link Budget Concept for an OAM Communication Link

Following on from the increasing interest for electromagnetic waves carrying Orbital Angular Momentum (OAM), different configurations of antenna systems able to generate such beams have been proposed. However, in our opinion, a traditional radiation pattern approach does not provide the right picture of an OAM-based communication link. For this reason we propose a new general concept, the "OAM-link pattern", which takes into account the peculiar phase structure characterizing these waves. Focusing on OAM transmissions between antenna arrays, we introduce a formula for the link budget evaluation which describes the whole communication link and directly leads to a "classically shaped" main lobe pattern for a proper rephased reception in the case of uniform circular arrays.Comment: 4 pages, 3 figure

Left Ventricular Trabeculations Decrease the Wall Shear Stress and Increase the Intra-Ventricular Pressure Drop in CFD Simulations

The aim of the present study is to characterize the hemodynamics of left ventricular (LV) geometries to examine the impact of trabeculae and papillary muscles (PMs) on blood flow using high performance computing (HPC). Five pairs of detailed and smoothed LV endocardium models were reconstructed from high-resolution magnetic resonance images (MRI) of ex-vivo human hearts. The detailed model of one LV pair is characterized only by the PMs and few big trabeculae, to represent state of art level of endocardial detail. The other four detailed models obtained include instead endocardial structures measuring ≥1 mm2 in cross-sectional area. The geometrical characterizations were done using computational fluid dynamics (CFD) simulations with rigid walls and both constant and transient flow inputs on the detailed and smoothed models for comparison. These simulations do not represent a clinical or physiological scenario, but a characterization of the interaction of endocardial structures with blood flow. Steady flow simulations were employed to quantify the pressure drop between the inlet and the outlet of the LVs and the wall shear stress (WSS). Coherent structures were analyzed using the Q-criterion for both constant and transient flow inputs. Our results show that trabeculae and PMs increase the intra-ventricular pressure drop, reduce the WSS and disrupt the dominant single vortex, usually present in the smoothed-endocardium models, generating secondary small vortices. Given that obtaining high resolution anatomical detail is challenging in-vivo, we propose that the effect of trabeculations can be incorporated into smoothed ventricular geometries by adding a porous layer along the LV endocardial wall. Results show that a porous layer of a thickness of 1.2·10−2 m with a porosity of 20 kg/m2 on the smoothed-endocardium ventricle models approximates the pressure drops, vorticities and WSS observed in the detailed models.This paper has been partially funded by CompBioMed project, under H2020-EU.1.4.1.3 European Union’s Horizon 2020 research and innovation programme, grant agreement n◦ 675451. FS is supported by a grant from Severo Ochoa (n◦ SEV-2015-0493-16-4), Spain. CB is supported by a grant from the Fundació LaMarató de TV3 (n◦ 20154031), Spain. TI and PI are supported by the Institute of Engineering in Medicine, USA, and the Lillehei Heart Institute, USA.Peer ReviewedPostprint (published version

Characterization of an Open GTEM Cell with the COMSOL Multiphysics® Software

The Gigahertz Transverse Electromagnetic (GTEM) cell is a device used for generating known, homogeneous fields for calibration purposes and for studies on Electromagnetic Compatibility (EMC) on a wide frequency range. With the aid of the COMSOL Multiphysics® simulation software, we have analyzed the electromagnetic behavior of an existing open GTEM cell at different operating frequencies. This study allowed us to identify the region internal to the cell where the field is most purely TEM. Moreover, experimental values obtained using the real GTEM have been compared to the simulated results, providing a good agreement with them

Modeling Orbital Angular Momentum (OAM) Transmission in Waveguides with the COMSOL Multiphysics® Software

The recent years have witnessed a growing interest in the possibility of enhancing the information transfer per unit bandwidth by exploiting the Orbital Angular Momentum (OAM) of light in both free-space and guided scenarios. In the proposed paper, the propagation of suitable OAM superpositions of waveguide eigenmodes in guiding structures with a circular symmetry is analyzed both theoretically and with the aid of the software COMSOL Multiphysics®, leading to the estimation of the power attenuation constants due to the finite conductivity of the metallic guide walls

Full Simulative Approach to Orbital Angular Momentum (OAM) Transmissions between Antenna Arrays

The possibility of exploiting the Orbital Angular Momentum (OAM) of light as a means to simultaneously transmit radio signals at the same frequency led us to the experimental implementation of an OAM-based multiplexing scheme between antenna arrays. Within this framework, the realization of a full-wave simulation of the communication link with COMSOL Multiphysics® proved essential both as a guide to the experimental setting and as a numerical validation of the achieved results