Open Access
Superbackscattering antenna arrays
(IEEE, 2015) Liberal Olleta, Íñigo; Ederra Urzainqui, Íñigo; Gonzalo García, Ramón; Ziolkowski, Richard W.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa; Universidad Pública de Navarra / Nafarroako Unibertsitate Publikoa
This article discusses the theory, design and practical implementation of superbackscattering antenna arrays. In analogy with Uzkov’s maximal directivity theorem, it is demonstrated that the maximal backscattering cross-section, normalized to the wavelength squared, of a linear array of N isotropic scatterers whose separation tends to zero is N2(N + 1)2=(4pi). This analytical result is validated via numerical optimization of the excitation coefficients, and the same procedure is utilized to assess the maximal backscattering of arrays of electric Hertzian dipoles (EHDs). It is found that electrically small arrays of two and three EHDs can enhance the backscattering by factors of 6.22 and 22.01, respectively, with respect to the maximum value generated by a single element. In addition, physical realizations of arrays featuring comparable enhancement factors can be straightforwardly designed by using a simple procedure inspired by Yagi-Uda antenna concepts. The practical implementations of such arrays based on copper wires and printed circuit technologies is also addressed.
Open Access
Decoupling of multifrequency dipole antenna arrays for microwave imaging applications
(Hindawi Publishing Corporation, 2010) Sáenz Sáinz, Elena; Guven, K.; Ozbay, Ekmel; Ederra Urzainqui, Íñigo; Gonzalo García, Ramón; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
The mutual coupling between elements of a multifrequency dipole antenna array is experimentally investigated by S-parameter measurements and planar near-field scanning of the radiated field. A multifrequency array with six dipoles is analyzed. In order to reduce the coupling between dipoles, a planarmetasurface is placed atop the array acting as superstrate. Themutual coupling of the antenna elements in the absence and presence of the superstrate is presented comparatively. Between 3 and 20 dB mutual coupling reduction is achieved when the superstrate is used. By scanning the field radiated by the antennas and far-field measurements of the radiation pattern, it is observed that the superstrate confines the radiated power, increases the boresight radiation, and reduces the endfire radiation.
Open Access
A multipolar analysis of near-field absorption and scattering processes
(IEEE, 2013) Liberal Olleta, Íñigo; Ederra Urzainqui, Íñigo; Gonzalo García, Ramón; Ziolkowski, Richard W.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
A multipolar formulation is adopted to investigate the absorption and scattering processes involved in near-field interactions. This approach allows one to determine the upper bounds for the absorbed and radiated powers that would be achieved by an ideal lossless sensor, which are of particular interest, for example, to wireless power transfer (WPT), wireless sensors and near-field coupled radiators. The multipolar formulation also helps to extricate the fundamental compromises that must be addressed in the design of such systems, as well as to identify strategies that could approach their best possible performances. The general theory is illustrated with an example consisting of a coated sensor illuminated by a Hertzian dipole, which is a representative example of any scattering or radiating system based on small resonators. The example also serves to compare the performance characteristics obtained with different phenomena such as multipolar resonances, phaseinduced interference effects and cloaking.
Open Access
A water content continuous monitoring of grapevine xylem tissue using a portable low-power cost-effective FMCW radar
(IEEE, 2019) Quemada Mayoral, Carlos; García González, Cebrián; Iriarte Galarregui, Juan Carlos; Marín Ederra, Diana; Gastón Beraza, Diego; Miranda Jiménez, Carlos; Gonzalo García, Ramón; Maestrojuán Biurrun, Itziar; Santesteban García, Gonzaga; Ederra Urzainqui, Íñigo; Agronomia, Bioteknologia eta Elikadura; Ingeniaritza Elektrikoa, Elektronikoaren eta Telekomunikazio Ingeniaritzaren; Institute of Smart Cities - ISC; Agronomía, Biotecnología y Alimentación; Ingeniería Eléctrica, Electrónica y de Comunicación; Gobierno de Navarra / Nafarroako Gobernua, PI025 VITHZ; Gobierno de Navarra / Nafarroako Gobernua, 0011-1365-2016-000084 RAFF
This paper presents the real-time monitoring of a grapevine’s water content that flows up through the xylem tissue by means of a frequency-modulated continuous-wave (FMCW) radar. The application of an optimization process, based on the super-resolution multiple signal classification (MUSIC) algorithm, has enabled the reduction of the bandwidth required to discern the xylem water content, and thus the operating frequency, achieving a depth resolution of at least 3 mm. This design advantage has resulted in a significant step forward towards a real life application, allowing the use of fully-integrated off-the-shelf components in order to implement a completely portable low-power cost-effective radar at 23.1 GHz with a 3.4 GHz bandwidth. The sensor performance has been evaluated by means of three different experiments: irrigation cycles, day/night cycles and comparison between irrigation cycles at different temperatures. From the experimental results, it is possible to assert that the contactless sensor presented in this work is very sensitive to changes in the plant’s water content, differentiating between daytime and nighttime. In addition, it has been proved that temperature has a noticeable influence over the evapotranspiration, observing negative drying slopes of 5.62 mV/cycle and 6.28 mV/cycle at 23ºC and 26ºC respectively.
Open Access
Design of a multifrequency antenna array with the use of left-handed superstrates
(2005) Sáenz Sáinz, Elena; Gonzalo García, Ramón; Ederra Urzainqui, Íñigo; Maagt, Peter de; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this paper, the radiation performances of different antenna configuration based on Left-Handed superstrates are presented. First of all, the behaviour of a Left- Handed (LH) unit cell is analysed, showing a resonant response with pass band and stop band frequencies. In order to improve the radiation performances of a single dipole, ie., to increase the directivity and efficiency and to reduce the back radiation, diverse LH superstrates working at the resonant frequency of the dipole are analysed. With these configurations, improvements in terms of directivity higher than 6 dB with efficiency closer to 100 % have been obtained.
Open Access
Planar DNG superstrate for dipole antenna gain enhancement
(2007) Sáenz Sáinz, Elena; Gonzalo García, Ramón; Ederra Urzainqui, Íñigo; Ikonen, Pekka; Tretyakov, Sergei A.; Maagt, Peter de; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
In this paper, a volumetric double-negative (DNG) superstrate based on grids of dipoles and wires for dipole antenna applications is proposed.
Open Access
Sub-millimetre wave imaging array configurations using EBG technology
(2004) Ederra Urzainqui, Íñigo; Gonzalo García, Ramón; Martínez Pascual, Beatriz; Río Bocio, Carlos del; Azcona, L.; Alderman, B.; Huggard, P.G.; Hon, B.P. de; Beurden, M.C. van; Marchand, L.; Maagt, Peter de; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Open Access
Domain integral equations for electromagnetic band-gap slab simulations
(2004) Hon, B.P. de; Beurden, M.C. van; Gonzalo García, Ramón; Martínez Pascual, Beatriz; Ederra Urzainqui, Íñigo; Río Bocio, Carlos del; Azcona, L.; Alderman, B.; Huggard, P.G.; Maagt, Peter de; Marchand, L.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
Electromagnetic band-gap substrates o er advantages regarding cross-coupling in sub-mm range imaging array applications. Electromagnetic scattering by such substrates may e ectively be formulated in terms of integro- di erential equations. The scattered elds are evaluated via the spectral domain in which the 3-D problem reduces to an in nite system of coupled 1-D integro-di erential equations. The associated matrix-vector products are dominated by FFTs. For moderate frequencies an elementary preconditioner in combination with a prudent initial estimate usually su ces to reach rapid convergence using the transpose-free quasi-minimal residual method.
Open Access
Least upper bounds of the powers extracted and scattered by bi-anisotropic particles
(IEEE, 2014) Liberal Olleta, Íñigo; Ra'di, Younes; Gonzalo García, Ramón; Ederra Urzainqui, Íñigo; Tretyakov, Sergei A.; Ziolkowski, Richard W.; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
The least upper bounds of the powers extracted and scattered by bi-anisotropic particles are investigated analytically. A rigorous derivation for particles having invertible polarizability tensors is presented, and the particles with singular polarizability tensors that have been reported in the literature are treated explicitly. The analysis concludes that previous upper bounds presented for isotropic particles can be extrapolated to bianisotropic particles. In particular, it is shown that neither nonreciprocal nor magnetoelectric coupling phenomena can further increase those upper bounds on the extracted and scattered powers. The outcomes are illustrated further with approximate circuit model examples of two dipole antennas connected via a generic lossless network.
Open Access
Fe-rich ferromagnetic wires for self-sensing materials
(IEEE, 2012) Liberal Olleta, Íñigo; Ederra Urzainqui, Íñigo; Gonzalo García, Ramón; Ingeniería Eléctrica y Electrónica; Ingeniaritza Elektrikoa eta Elektronikoa
The possibility of using Fe-rich wires in mechanical stress self-sensing materials is investigated. To this end, a retrieval technique aimed to characterize the high-frequency magnetoimpedance effect in ferromagnetic wires under mechanical stresses is proposed. The technique is based on the measurement of the wires inside a metallic rectangular waveguide, and it is validated through numerical simulations and tested with already published experimental data. In addition, the studied Fe-rich wires are characterized by the occurrence of the natural ferromagnetic resonance, whose frequency position increases from 7 GHz to 8.25 GHz for elongations ranging from 0 μm to 60 μm.