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Impedance loading is a common technique traditionally used in the RF to enhance the performance of an antenna, but its application in the optical regime is not as rigorously studied. This is mainly due to a lack of exact analytical expressions that can be used to rapidly predict the radiation properties of loaded nanoantennas. This paper will derive a set of useful analytical expressions for the far-field radiation properties of loop antennas loaded with an arbitrary number of lumped impedances that are valid from the RF to optical regimes. The analytical expressions will be validated with full-wave solvers and can be evaluated more than 100x faster. The ability to perform such rapid evaluations enables, for the first time, large-scale single- and multi-objective optimizations. A series of optimizations reveal that electrically small super-directive antennas can be achieved at a variety of far field angles through capacitive loading, paving the way for a pattern reconfigurable antenna. In addition, gains of greater than 3 dB can be achieved for electrically small antennas over a fractional bandwidth of 28%. Finally, it is shown that impedance loading can be used to achieve circularly polarized radiation from a single loop., Paper submitted for review on 03/20/2018. The authors would like to acknowledge the Spanish Ministry of Education - Commission Fulbright Program “Salvador de Madariaga” (PRX14/00320) for sponsoring the joint research collaboration. This work has also been partially financed by the Spanish and Andalusian research programs TEC202016-79214-C3-3-R and P12-TIC-1442 as well as by the Center for Nanoscale Science, an NSF Materials Research Science and Engineering Center, under the award DMR-1420620.

Modern aircrafts have become increasingly dependent on electronic equipment to control its systems. This has led to new safety concerns with respect to their immunity levels against EM hazards and, in consequence, their assessment by aircraft manufacturers. Besides, the variety of potential EMI sources are increasing dramatically due to the appearing of new artificial sources in addition to the natural ones. This situation is aggravated by the pervasive use of composite materials in aircraft structure: CFC, CFRC, CFRP, etc. These materials, lighter and stronger from the mechanical point of view, are poorer conductors than metals and therefore have lower shielding capabilities. From the EMC point of view, the main EM threats for an AV can be summarized as follows: • Lightning Indirect Effects (LIE): 0 to ~50 MHz: Indirect effects are caused by the electric current flowing through the structure and internal wiring as a consequence of the impact of a lightning strike. This is, undoubtedly, the most important threat to onboard electronic equipment, becoming critical for aircrafts mostly made of CFCs (Meyer et al., 2008) like, for instance, modern UAVs. • High Intensity Radiated Fields (HIRF): 0 to ~100 MHz: This threat is caused by artificial intentional or unintentional, external or internal RF sources. These are constantly increasing in number: TV, mobile networks (3G/4G/5G), radars, navigation satellite systems, etc. and may couple to cables and equipment, potentially causing malfunction for high field levels. • Electromagnetic Pulses (EMP) of Nuclear or Non-Nuclear Origin: 0-100 MHz: Most of current non-nuclear low-level electromagnetic pulse generators are not capable of radiating enough EM energy to produce a significant damage. However, novel devices are appearing, which are able to involve much higher power levels with extremely short durations. These modern weapons, also named E-bombs, are becoming cheaper and susceptible of being used in terrorist acts. They can wreak havoc on computers and networks, yielding temporary disruptive effects (Radasky et al., 2004; Radasky, 2014). In all these cases, as a result of the exposition to the EM hazard, transient currents will flow along the aircraft surface, creating EM fields which penetrate into the fuselage through apertures such as windows, or by diffusion through parts made of poorly conducting materials (Figure 1). Inside the aircraft, these transients induce currents to the EWIS, which, in turn, couple to equipment, potentially compromising their safe operation or even creating permanent damage. Several aviation incidents, reported in the last quarter of the past century, triggered the attention of aviation agencies to include strict EMC requirements for the airworthiness certification processes of AVs during their whole life-cycle. Before a newly developed AV model is permitted to operate, it must get a certificate of airworthiness issued by an aviation regulatory authority. For instance, in civil aviation, the regulatory authority is the EASA in the EU, or the FAA in the US. Within the EMC context, certification methods are mainly based on experimental tests and the guidelines provided in several standardized documents and certification guides: Eurocae ED-105/SAE-ARP5416; SAE-ARP5415; Eurocae ED-107/SAE-ARP5583; MIL-STD-202; MIL-STD-461;EUROCAE ED-14/RTCA/DO-160, MIL-STD-464, STANAG 4370, etc.. Electrical and electronic systems on board air vehicles are susceptible to electromagnetic interference (EMI). This has made the topic of electromagnetic compatibility (EMC), a major concern for aircraft safety. The use of composite materials worsens this situation, for their poor shielding and low conductive capabilities. Some of the main experimental E3 certification scenarios used in aeronautics are revisited in this chapter. Guidelines to achieve simple, yet accurate, numerical models of them are provided, with appropriate tradeoffs between computational simplicity and accuracy. The numerical method, endowed with extended capabilities, has been chosen for this task for its ability and efficiency to deal with complex problems of arbitrary materials. The feature selective validation (FSV) IEEE standard procedure, commonly used to quantify the comparison of data in electromagnetic problems, is also revisited. The simulation of three different air vehicles in several certification scenarios is finally described and the numerical results compared to experimental data. Peerreview

The increased use of carbon-fiber composites in unmanned aerial vehicles is a challenge for their EMC assessment by numerical solvers. For accurate and reliable simulations, numerical procedures should be tested not only for individual com- ponents, but also within the framework of complete systems. With this aim, this paper presents a benchmark test case based on experimental measurements coming from direct-current injection tests in the SIVA unmanned air vehicle, reproduced by a numerical finite-difference-time-domain solver that employs a new subgrid- ding scheme to treat lossy composite thin panels. Validation was undertaken by applying the feature selective validation method, which quantifies the agreement between experimental and numerical data., This work was supported by the Projects TEC2013-48414- C3- { 1,2,3 } -R, TEC2016-79214-C3- { 1,2,3 } -R, and TEC2015-68766-REDC (Spanish MINECO, EU FEDER), P12-TIC-1442 (J. de Andalucia, Spain), Alhambra-UGRFDTD (AIRBUS DS), and by the CSIRC alhambra.ugr.es supercomputing center.

A new nodal hybrid continuous-discontinuous Galerkin time-domain (CDGTD) method for the solution of Maxwell's curl equations is proposed and analyzed. This hy- bridization is made by clustering small collections of elements with a continuous Galerkin (CG) formalism. These cluste rs exchange information with their exterior through a discontinuous Galerkin (DG) numerical flux. This scheme shows reduced numerical dis- persion error with respect to classical DG formul ations for certain orders and numbers of clustered e lements. The spectral radius of the clustered semi-discretized operator is smaller than its DG counterpart allowing for larger time steps in e xplicit time integra- tors. Additionally, the continuity across the element boundaries allows us a reduction of the number of degrees of freedom of up to about 80% for a low-order three-dimensi onal implementation., This work was supported in part by the National Projects under Grant TEC2010-20841-C04-04, Grant TEC2013- 48414-C3-1-R, Grant CSD2008-00068, Grant P09-TIC-5327, and Grant P12- TIC-1442, the GENIL Excellence Network, and the National Science Founda- tion under Grant ECCE-1305838

This paper presents a computational procedure to simulate the time-domain behavior of photoconductive antennas made of semiconductor and metal materials. Physical modeling of semiconductor devices at terahertz regime can be achieved by applying joint electronic and electromagnetic procedures, e.g., solving a coupled system of equations inferred from Poisson’s drift-diffusion and Maxwell’s equations. A set of discrete equations are derived by applying a combined finite-difference methodology for the previous steady-state and the finite-difference time-domain procedure for the transient regime. The results for the radiated electric field at broadside direction show good agreement with the experimental results previously reported in the literature, This work was supported in part by the Spanish Ministry of Education under Project CSD2008-00068, the Junta de Andalucia Project P09-TIC-5327, the EU FP7/2007-2013, under grant 205294 (HIRF-SE project), and the Spanish National Project TEC2010-20841-C04-04

A novel implicit nodal Space-Time Discontinuous Galerkin (STDG) method is proposed in this paper. An eigenvalue analysis is performed and compared with that for a DG scheme solved with a 4th-Order Runge-Kutta time integrator. We show that STDG offers a significant improvement of dissipative and dispersive properties and allows larger time steps, regardless of the spatial hp-refinement. A domain-decomposition technique is used to introduce an explicit formulation of the method in order to render it computationally efficient., This work is partially funded by the National Projects TEC2010-20841- C04-04, TEC2013-48414-C3-01, CSD2008-00068, P09-TIC-5327, P12-TIC- 1442, and from the GENIL excellence network.

This letter explores the influence of the geometry of bias electrodes in the performance of terahertz (THz) photoconductive antennas (PCAs). To this end, a methodology is presented to calculate numerically the operational bandwidth and radiation efficiency of the PCAs. The procedure is validated through a comparison to experimental measurements. Also, results are depicted from numerical simulations of different PCAs under varying conditions of bias voltage, doping factor, and incident optical power. It is concluded that an appropriate con figuration of the electrodes may double the efficiency of the antennas, with a penalty in the bandwidth of the radiated pulse usually smaller than 10%., This work was supported in part by the Spanish Ministry of Education under Project CSD2008-00068, the Junta de Andalucia Project P09-TIC-5327, the EU FP7/2007-2013 under Grant 205294 (HIRF-SE project), and the Spanish National Project TEC2010-20841-C04-04

A new set of genetically generated electrically small thin-wire antennas with a better performance than that of several families of Sierpinsky prefractal monopoles of the same electrical size at resonance is presented

A multi-objective genetic algorithm (GA) has been applied in conjunction with the numerical electromagnetic code (NEC) to the optimization of wire pre-fractal Koch-like antennas in terms of bandwidth, efficiency, and electrical size. Their performance is compared to that of other nonfractal designs.

Tesis Univ. Granada. Programa Oficial de Doctorado en: Física y Matemáticas, The work described in this dissertation has been partially funded through the European Community's Seventh Framework Programme FP7/2007-2013, under grant agreement n. 205294 (HIRF SE project), and his work is partially funded by the National Projects TEC2010-20841-C04-04, TEC2013-48414-C3-01, CSD2008-00068, P09-TIC-5327, P12-TIC-1442, and from the GENIL excellence network.

Resumen y Conclusiones en inglés, Tesis Univ. Granada. Departamento de Electromagnetismo y Física de la Materia. Leída el 5 de junio de 2008

Tesis Univ. Granada. Departamento de Electromagnetismo y Física de la Materia. Leída el 9 de mayo de 2005

Tesis Univ. Granada. Departamento de Química Física, Este trabajo ha sido financiado por los siguientes proyectos "Terahertz technology for electromagnetic sensing applications", Ministerio de Ciencia e Innovación, y "Teralab: numerical laboratory for design and simulation of THz technology", Junta de Andalucía.