E. Saenz

Cardiff University, Cardiff, Wales, United Kingdom

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Publications (40)29.38 Total impact

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    The 8th European Conference on Antennas and Propagation; 04/2014
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    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.
    IEEE Transactions on Terahertz Science and Technology 09/2013; 3(5):649-655. DOI:10.1109/TTHZ.2013.2265602 · 4.34 Impact Factor
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    ABSTRACT: A prototype gradient index lens has recently been produced by using a stack of frequency selective surfaces, based on a square patch unit cell. The lens was modelled using a transmission line method(TLM) and HFSS. Additional measurements have been taken using a VNA which allows for detailed magnitude and phase information at precise frequencies. The lens has a broadband performance due to non resonating metamaterial structure used. A proposed solution is given to increase the performance of the GRIN lens by the use of antireflection coating built into the design of the lens.
    2013 7th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics (METAMATERIALS 2013); 09/2013
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    ABSTRACT: We recently showed (Savini 2012) the use of stacked graded photolithographic capacitive metal-mesh structures on polypropylene substrates to produce a thin flat Wood lens working in a wide (90%) bandwidth. Here an additional impedance-matched layer is designed to improve the original lens efficiency in a wide band around the central frequency of operation.
    2013 6th UK, Europe, China Millimeter Waves and THz Technology Workshop (UCMMT); 09/2013
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    ABSTRACT: A flat lens-filter (or lenster) has recently been produced using capacitive metal-mesh structures on polypropylene substrate. The prototype was designed using a combination of a transmission line method(TLM) and HFSS. Its performance was measured and compared to a standard polypropylene lens. We propose to perform further measurements, focusing on the phase, to give a deeper understanding on how the lens performs. This will allow to verify the tlm model used to design the lens, which will aid in designing future prototypes.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
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    ABSTRACT: The realization of a Circular Polarization Selective Surface (CPSS) exhibiting low Axial Ratio (AR) has been demonstrated experimentally in the X band, showing good agreement with the simulated response. The fabricated CPSS has been characterized using a free-space collimator system recently acquired by ESA. An AR below 1dB, which is comparatively smaller than previous results shown in the literature, has been achieved for more than 20% bandwidth.
    2013 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting; 07/2013
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    ABSTRACT: The use of capacitive metal-mesh structures on polypropylene substrates is routinely used in far infrared astronomy for the purpose of spectral low-pass filtering. The transmission of these filters well below their cut-off frequency follows the well known behavior of a Fabry-Perot etalon due to the fairly achromatic nature and finite thickness of the embedding substrate. We show how it is possible to reproduce to a good level of precision, the predicted transmission of an embedded stack of layers of a given square-geometry using Transmission Lines when compared to HFSS simulations. We then use the Fabry-Perot etalon model to invert their spectral behavior to extract an effective index of refraction corresponding to the mesh geometry and device thickness. This injective mapping allowed us to design a Gradient Index lens based on a fixed spacing (or grid) while varying the mesh filling factor. Measurements of such a flat lens-filter (or lenster) are shown.
    Antennas and Propagation (EuCAP), 2013 7th European Conference on; 01/2013
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    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
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    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
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    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
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    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
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    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.
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    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
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    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.
    Proceedings of SPIE - The International Society for Optical Engineering 04/2010; DOI:10.1117/12.855099 · 0.20 Impact Factor
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    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; DOI:10.1155/2010/843624 · 0.83 Impact Factor
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    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
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    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; DOI:10.1109/TAP.2008.2011249 · 2.46 Impact Factor
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    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. DOI:10.1088/1367-2630/10/11/115037 · 3.67 Impact Factor
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    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 09/2008; 28(7):476-493. DOI:10.1080/02726340802322528 · 0.77 Impact Factor
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    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. (C) 2008 American Institute of Physics.
    Applied Physics Letters 05/2008; 92(20). DOI:10.1063/1.2931027 · 3.52 Impact Factor