E. Saenz

Universidad Pública de Navarra, Iruña, Navarre, Spain

Are you E. Saenz?

Claim your profile

Publications (34)24.26 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: A detailed broadband analysis of energetic materials using THz time-domain spectroscopy with a bandwidth from 0.2 to 6.4 THz is presented. Dependencies of the resonance features on different sample parameters are evaluated via spectroscopic investigation of several energetic materials (TNT, C4, RDX, PETN, AN) in transmission and reflection experiments. A strong dependency of the resonance features on the manufacturing process of an explosive is observed especially with TNT. The THz measurements of the TNT samples are compared to powder X-ray diffraction measurements. Furthermore, it is observed that additive compounds with a flat frequency response offset the THz reflection of an explosive, but the recognition capability of a resonance feature is not influenced.
    Terahertz Science and Technology, IEEE Transactions on. 01/2013; 3(5):649-655.
  • [show abstract] [hide abstract]
    ABSTRACT: The design of dual-optics circular-polarization offset reflectors has been addressed by using circular polarization selective surfaces (CPSS). A novel design of CPSS based on Pierrot's cells is proposed, and design guidelines and limitations of this technology are given. Manufacture constraints are discussed and a more reliable fabrication process is developed. A 29×29 array has been constructed and measurements are ongoing.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
  • [show abstract] [hide abstract]
    ABSTRACT: A detailed broadband analysis of the resonant absorptions of different common explosives in the range from 0.1-6 THz is presented. Dependencies of the resonance features on different sample parameters are evaluated via spectroscopic investigation of transmission and reflection. A significant dependency on the manufacturing process is observed.
    Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2012 37th International Conference on; 01/2012
  • [show abstract] [hide abstract]
    ABSTRACT: In this paper accurate material measurements at sub-millimetre wave frequencies performed with two different systems are compared. Transmission and reflection results of high quality samples measured with a quasi-optical open resonator and a quasi-optical free-space bench are presented. Based on the comparison between the two results, an accuracy assessment of the transmission set-up is performed.
    Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
  • [show abstract] [hide abstract]
    ABSTRACT: The field of antenna measurements is lacking a Golden Standard, i.e. an antenna of which the pattern is known by definition. To gain confidence in the performance of a range, including the procedures and skills of the operators, range comparison has been a popular tool for over three decades. In the beginning, ad-hoc available antennas were shipped around the various ranges. Soon it became clear that the comparisons were restricted by the properties of the antenna. The European Space Agency (ESA) stimulated and supported the development of a dedicated VAlidation STandard (VAST) antenna, specifically designed for validation campaigns of antenna measurement ranges. The driving requirements of VAST antennas are their mechanical stability over a given operational temperature range and with respect to any orientation of the gravity field. The mechanical design shall ensure extremely stable electrical characteristics allowing frequent travel and shall ease the handling of the VAST antenna (practical electrical and mechanical interfaces, well-defined alignment tools, low mass, attachment points for lifting, etc). The widespread use of the so-called VAST-12 antenna demonstrates the long-term value of dedicated test antennas. Currently, ESA is considering expanding its set of validation elements developing a VAST antenna at mm-waves. The frequencies considered are application driven: 20/30 GHz as up/down link of Ka-Sat, 38/48 GHz as up/downlink of Alphasat, thus, covering the Ku/Ka-band and the upcoming Q/V-band of telecom satellites. The paper will address requirements for future VASTs and possible architecture for multi-frequency Validation Standard antennas.
    Antennas and Propagation (EUCAP), Proceedings of the 5th European Conference on; 05/2011
  • [show abstract] [hide abstract]
    ABSTRACT: In this paper the material characterization at sub- millimetre wave frequencies facility recently developed at the European Space Research and Technology Centre (ESA-ESTEC) to complement existing antenna ranges is presented. By means of a Quasi Optical test bench, transmission/reflection measurements from 50 to 500 GHz are performed. Complex material parameters are then calculated from transmission measurements. As a first experimental campaign and in support to industry the transmission properties of several energetic materials (C4, RDX, TNT, PETN and Semtex-H) and barrier materials have been measured and material parameters extracted.
    Atmospheric Environment - ATMOS ENVIRON. 01/2011;
  • [show abstract] [hide abstract]
    ABSTRACT: This contribution analyzes several multi-frequency antenna systems based on meta-surfaces. As it is demonstrated, there is a synergy between the frequency-domain behavior of the meta-surface and multi-frequency antenna architectures. Therefore, the use of the meta-surface is not restricted to enhance the radiation properties of the single-antenna element, but also contributes at system level aspects such us isolation and compactness.
    Antenna Technology (iWAT), 2011 International Workshop on; 01/2011
  • [show abstract] [hide abstract]
    ABSTRACT: We investigate the application of a metamaterial that is formed by the sparse distribution of spiral resonators as an optical transformation medium is in order to achieve electromagnetic cloaking. The well-known Clausius-Mossotti formula relates the microscopic polarizability of a single resonant particle to the macroscopic permittivity and permeability of the effective medium. By virtue of transformation optics, the permittivity and permeability of the medium, in turn, can be designed according to a coordinate transformation that maps a certain region of space to its surrounding. As a result, the mapped region can be cloaked from electromagnetic waves. In this study, the spirals are optimized to exhibit equal permittivity and permeability response so that the cloak formed by these spirals will work for both the TE and TM polarizations. An experimental setup is developed to visualize the steady state propagation of electromagnetic waves within a parallel plate waveguide including the cloaking structure. The measured and simulated electromagnetic field image indicates that the forward scattering of a metal cylinder is significantly reduced when placed within the cloak.
    Proc SPIE 04/2010;
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: 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 planar metasurface is placed atop the array acting as superstrate. The mutual 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.
    International Journal of Antennas and Propagation 01/2010; · 0.68 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: A comparison is made between the two standard methods to characterise the quiet zone in a CATR and the applicability to mm-wave frequencies. The aspects considered are positioner accuracy requirements, dynamic range and measurement times. Typical numbers are given for the ESTEC ranges as representative examples.
    Antennas and Propagation, 2009. EuCAP 2009. 3rd European Conference on; 04/2009
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: The mutual coupling between dipole antenna array elements using a planar meta-surface as superstrate is experimentally investigated. The meta-surface is based on grids of short metal strips and continuous wires. A comparison between the mutual coupling when the dipoles are radiating in free space and in presence of the superstrate is presented. On average, between 3 to 14 dB reduction of the mutual coupling is achieved when the superstrate is used. The effect of the mutual coupling on the radiation performance of the array is studied by spherical near-field measurements of the radiation pattern when one driven dipole is fed and the others are matched with 50 Omega loads. The back-projected field on the aperture and on the E-plane is shown.
    IEEE Transactions on Antennas and Propagation 03/2009; · 2.33 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We report an electromagnetic cloaking structure that is composed of identical canonical spiral particles. By using the Clausius–Mosotti formula, the electric and magnetic polarizabilities of a single spiral particle are related to the relative permittivity and permeability of the sparse distribution of particles. The permittivity and permeability of the distribution are, in turn, defined according to the coordinate transformation, which leads to the cloaking effect. Spirals are optimized to exhibit equal permittivity and permeability response so that the cloak consisting of these spirals will work for both transverse electric (TE) and transverse magnetic (TM) polarizations. Measurement of the cloaking device surrounding a metal cylinder inside a parallel waveguide was performed. The steady-state propagation of an electromagnetic wave was reconstructed from the amplitude and phase data, which demonstrates that the field largely restores to a free-space propagation pattern after the cloak.
    New Journal of Physics 11/2008; 10(11):115037. · 4.06 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: The design of a multifrequency dipole antenna array based on a resonant meta-surface superstrate is proposed. The behavior of a single element that is closely placed to a meta-surface is experimentally investigated. The proposed meta-surface is based on resonating unit cells formed by capacitively loaded strips and split ring resonators. By tuning a dipole antenna to the pass band of the meta-surface, the physical area is effectively illuminated enhancing the radiation performance. The gain, radiation efficiency and effective area values of the whole configuration are compared to the ones obtained with a single dipole without superstrate. Radiation efficiency values for the proposed configuration of more than 80% and gain values of more than 4.5 plusmn 1 dB are obtained. Based on this configuration, simulated results of a multifrequency antenna array are presented. Distinctive features of this configuration are high isolation between elements (20 dB for a distance of lambda<sub>0</sub>/4), and low back radiation.
    IEEE Transactions on Antennas and Propagation 05/2008; · 2.33 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: In this paper, the uniform illumination of a meta-surface that is fed by a single dipole antenna or an array is experimentally investigated by means of near-field measurements. The results of the scanned field, when the dipoles are radiating in free space and when the meta-surface is placed atop them are presented. By means of this measurement, the coupling reduction between dipoles of an array due to the presence of the meta-surface is observed.
    Antennas and Propagation Conference, 2008. LAPC 2008. Loughborough; 04/2008
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: The enhanced directed emission from a metasurface which is illuminated at its resonance frequency by a dipole source is experimentally demonstrated. The metasurface consists of two cutwire layers and a continuous wire layer in between, which exhibits strong magnetic dipole resonance under excitation normal to the plane. The scanned near-field patterns show the confinement of the field in the presence of metasurface, which, in turn, provides an enhanced and directional radiation in the far field. The far-field patterns are obtained by direct measurement and by a far-field transformation of the scanned near field, which are found to be in good agreement. © 2008 American Institute of Physics. DOI: 10.1063/1.2931027 Artificial dielectrics, implemented, e.g., as arrays of wires, have been used for decades as lightweight beam shap-ing elements. It is nowadays well understood that some elec-tromagnetic photonic crystals simulate the behavior of ho-mogeneous materials with ultralow refractive index near stop-band edges. 1,2 This observation has led to several stud-ies concerning directive radiating source design using such periodical structures to shape the beam of a low-gain primary radiator. 3 It is also known that a slight local change in the period of electromagnetic crystals leads to localized resonant modes which can be used for the realization of devices radi-ating energy in a very narrow angular range. 4 Typically, ra-diating sources are placed inside Fabry–Perot resonant cavi-ties formed by removal of rows of wires or dielectric rods in a periodical lattice. 5,6 Similarly, partially reflective surfaces in combination with ground planes have been used to create Fabry-Perot-like cavities 7 for enhanced radiation purposes. The use of superstrates on top of radiating sources is another well-known gain enhancement tool. 8 As in the case of de-fected electromagnetic crystal structures 5,6 one of the key ideas of different superstrates is to allow radiation from a primary source to spread over a larger radiating aperture, and therefore enhancing the directivity. Recently, very exotic structures such as material covers or superstrates aimed to possess double-negative behavior 9–12 have been proposed for this aim. 13–16 The solution proposed herein is based on the property of metamaterials for enhancing the radiation performance of sources by virtue of their ability to control the propagation and suppression of electromagnetic waves. It is conceptu-ally different from the previous topologies, since no cavity or ground plane are required. We employ the metamaterial in the form of a multilayer metasurface that is placed in close proximity to the radiating source acting as superstrate. When working at the transmission pass band of the metasurface, magnetic dipole moments are induced in the superstrate in-clusions which enhance the emission. 14–17 The metasurface that was used in this work is schemati-cally shown in Fig. 1 and has been described in detail in Refs. 14–16. It based on the so-called cutwire/wire elements used in planar left-handed metamaterials, 9–12 where the cutwire and wire layers provide negative permeability and negative permittivity, respectively, so that the composite me-dium acts as an effective medium with negative index of refraction. The operation of the metamaterial can be heuris-tically explained in the following manner: 16,17 Under normal incident plane-wave excitation, at the resonant frequency f r , out-of-phase currents are induced in the pairing dipoles that are seated in layers 1 and 3. Therefore, a compensation of the total current in the slab is obtained allowing the inci-dent wave to propagate through the grids. Since the distance h between the layers is very small compared to the wave-length, a closed current loop is formed that creates a strong magnetic dipole moment that produces radiation, i.e., a trans-mission window appears see Fig. 1a BW S 11 =−10 dB = f / f 0 =4%. To widen the pass band, a grid of solid wires is placed in between the dipole grids. 16 In this case, two modes appear due to the capacitances and mutual coupling between the cutwires and the continuous wires. Since the wires are in the symmetry plane of the cutwires but shifted, the first mode is not disturbed. There are now two possibili-ties for the currents in the grids to cancel each other and by properly choosing the unit cell dimensions both transmission bands can be merged together enlarging the pass band 8.8– 10.3 GHz see Fig. 1b BW S 11 =−10 dB = 16%.
    Applied Physics Letters 01/2008; 92. · 3.79 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: In this article, we study spiral particles with optimized design parameters, which can make possible the realization of media with equal dielectric, magnetic, and chiral susceptibilities. Two different spiral structures are investigated: the canonical spiral (which consists of a split loop with two straight-wire sections, orthogonal to the loop plane and connected to the edges of the gap) and the true helix (which is obtained by bending a wire with a constant pitch angle). The transmission and reflection coefficients of arrays of spiral particles are obtained under plane wave excitation by numerical simulation. The properties of slabs formed by periodic chiral and racemic arrays of spirals are investigated. Good agreement is found between the presented results and the previously reported theoretical and experimental studies.
    Electromagnetics 01/2008; 28(7):476-493. · 0.73 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: The radiation performance of a planar meta-surface based on dipoles and wires are experimentally investigated. Transmission and reflection coefficients are presented for normally incident plane wave excitation. A dipole antenna closely placed to the meta-surface is also used as a feeding source of the meta-surface in order to enhance its radiation performance. Due to the uniform illumination of the superstrate, an enhancement of the gain up to 6.8 dBi is obtained being the thickness of the whole system 0.135 lambda<sub>0</sub> and the aperture efficiency 82%.
    Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on; 12/2007
  • [show abstract] [hide abstract]
    ABSTRACT: The radiation performance of a planar meta-surface based on dipoles and wires are experimentally investigated. A dipole antenna closely placed to the meta-surface is used as a feeding source of the meta-surface obtaining a gain value of 6.8 dBi; the thickness of the whole system is 0.135 lambda<sub>0</sub> and the aperture efficiency 82 %. A study of the mutual coupling between dipole antenna array elements is also presented. On average, between 3 and 14 dB reduction of the mutual coupling is achieved when the meta-surface is used.
    Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on; 12/2007
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We study the characteristics and radiation mechanism of antenna superstrates based on closely located periodical grids of loaded wires. An explicit analytical method based on the local field approach is used to study the reflection and transmission properties of such superstrates. It is shown that as a result of proper impedance loading there exists a rather wide frequency band over which currents induced to the grids cancel each other, leading to a wide transmission maximum. In this regime radiation is produced by the magnetic dipole moments created by circulating out-of-phase currents flowing in the grids. An impedance matrix representation is derived for the superstrates, and the analytical results are validated using full-wave simulations. As a practical application example we study numerically the radiation characteristics of dipole antennas illuminating finite-size superstrates.
    IEEE Transactions on Antennas and Propagation 11/2007; · 2.33 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: In this paper, the analysis and design of a planar meta-surface based on dipoles and wires is presented. The unit cell is formed by three layers, two parallel dipoles and one continuous wire. The transmission response and dispersion diagram of the unit cell are analysed step by step in order to determine the effect of each element; one dipole, two parallel dipoles and finally the two dipoles and wire unit cell. For a normally incident plane wave excitation with the E field parallel to the wires and the H field axial to the dipoles, a strong magnetic dipole moment is induced which produces a pass band around the resonant frequency and a stop band at higher frequencies. This cell is used to create meta-surfaces for antenna gain enhancement. Two configurations are analysed; the first one is a superstrate of a dipole antenna with the pass band tuned to the resonant frequency of the dipole. Due to the resonance of the superstrate inclusions, a uniform illumination is achieved, which produces high aperture efficiency and an increase of the directivity up to 6.31. By adding a meta-substrate with the stop band tuned to the resonant frequency of the dipole, an enhancement versus the conventional dipole of five times in the boresight radiation and 795 times in the front–back ratio is obtained.
    Journal of Optics A Pure and Applied Optics 08/2007; 9(9):S308. · 1.92 Impact Factor