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A simple method of superimposing multiple near field scans using a single horn antenna in different configurations to characterize a planar electromagnetic metasurface is proposed and numerically demonstrated. It can be used to construct incident fields for which the metasurface is originally designed for, which may otherwise be difficult or not possible to achieve in practice. While this method involves additional effort by requiring multiple scans, it also provides flexibility for the incident field to be generated, simply by changing the objective of a numerical optimization which is used to find the required horn configurations for the different experiments. The proposed method is applicable to all linear time-invariant metasurfaces including space-time modulated structures., Comment: 7 pages, 4 figures

A methodology for determining the scattered Electromagnetic (EM) fields present for interconnected regions with common metasurface boundaries is presented. The method uses a Boundary Element Method (BEM) formulation of the frequency domain version of Maxwell's equations - which expresses the fields present in a region due to surface currents on the boundaries. Metasurface boundaries are represented in terms of surface susceptibilities which when integrated with the Generalized Sheet Transition Conditions (GSTCs), gave rise to an equivalent configuration in terms of electric and magnetic currents. Such a representation is then naturally incorporated into the BEM methodology. Two examples are presented for EM scattering of a Gaussian beam to illustrate the proposed method. In the first example, metasurface is excited with a diverging Gaussian beam, and the scattered fields are validated using a semi-analytical method. Second example concerned with a non-uniform metasurface modeling a diffraction grating, whose results were confirmed with conventional Finite Difference Frequency Domain (FDFD) method., Comment: 9 pages, 7 figures

We model, demonstrate and characterize Dispersion Code Multiple Access (DCMA) and hence show the applicability of this purely analog and real-time multiple access scheme to high-speed wireless communications. We first mathematically describe DCMA and show the appropriateness of Chebyshev dispersion coding in this technology. We next provide an experimental proof-of-concept in a 2 X 2 DCMA system. Finally,we statistically characterize DCMA in terms of bandwidth, dispersive group delay swing, system dimension and signal-to-noise ratio.

Space-time modulation induced non-reciprocity in EM metasurfaces is proposed and numerically demonstrated using rigorous Generalized Sheet Transitions Conditions (GSTCs) under oblique plane-wave incidence. It is phenomenologically shown that the space-time modulation of surface susceptibilities create an inherent asymmetry with respect to the directional perturbation on the metasurface and the transverse wave momentum of the input wave, between forward and backward propagations, resulting in non-reciprocal wave transmission. Exploiting the periodicity of the surface susceptibilities in both time and space, Floquet mode expansion method is used to rigorously compute the scattered fields from, inherently dispersive metasurfaces, by solving GSTCs in combination with causal Lorentzian surface susceptibilities. Various harmonic solutions are shown and the non-reciprocal wave transmission has been confirmed under oblique plane-wave incidence., Comment: 6 pages, 6 figures

A finite-difference time-domain (FDTD) simulation of broadband electromagnetic metasurfaces based on direct in- corporation of Generalized Sheet Transition Conditions (GSTCs) inside a conventional Yee-cell region has been proposed, for arbitrary wave excitations. This is achieved by inserting a zero thickness metasurface inside bulk nodes of the Yee-cell region, giving rise to three distinct cell configurations - Symmetric Cell (SC), Asymmetric Cell (AC) and Tight Asymmetric Cell (TAC). In addition, the metasurface is modelled using electric and magnetic surface susceptibilities exhibiting a broadband Lorentzian response. As a result, the proposed model guarantees a physical and causal response from the metasurface. Several full- wave results are shown, and compared with analytical Fourier propagation methods showing excellent results, for both 1D and 2D fields simulations. It is found that the TAC provides the fastest convergence among the three methods with minimum error., Comment: 11 pages, 8 Figures

An explicit time-domain finite-difference technique for modelling zero-thickness Huygens' metasurfaces based on Generalized Sheet Transition Conditions (GSTCs), is proposed and demonstrated using full-wave simulations. The Huygens' metasurface is modelled using electric and magnetic surface susceptibilities, which are found to follow a double-Lorentz dispersion profile. To solve zero-thickness Huygens' metasurface problems for general broadband excitations, the double-Lorentz dispersion profile is combined with GSTCs, leading to a set of first-order differential fields equations in time-domain. Identifying the exact equivalence between Huygens' metasurfaces and coupled RLC oscillator circuits, the field equations are then subsequently solved using standard circuit modelling techniques based on a finite-difference formulation. Several examples including generalized refraction are shown to illustrate the temporal evolution of scattered fields from the Huygens' metasurface under plane-wave normal incidence, in both harmonic steady-state and broadband regimes. In particular, due to its inherent time-domain formulation, a significant strength of the methodology is its ability to model time-varying metasurfaces, which is demonstrated with a simple example of a pumped metasurface leading to new frequency generation and wave amplification., Comment: 11 pages, 10 figures

A finite-difference time-domain (FDTD) modelling of finite-size zero thickness space-time modulated Huygens' metasurfaces based on Generalized Sheet Transition Conditions (GSTCs), is proposed and numerically demonstrated. A typical all-dielectric Huygens' unit cell is taken as an example and its material permittivity is modulated in both space and time, to emulate a travelling-type spatio-temporal perturbation on the metasurface. By mapping the permittivity variation onto the parameters of the equivalent Lorentzian electric and magnetic susceptibility densities, $\tilde{\chi}_\text{ee}$ and $\tilde{\chi}_\text{mm}$, the problem is formulated into a set of second-order differential equations in time with non-constant coefficients. The resulting field solutions are then conveniently solved using an explicit finite-difference technique and integrated with a Yee-cell based propagation region to visualize the scattered fields taking into account the various diffractive effects from the metasurface of finite size. Several examples are shown for both linear and space-time varying metasurfaces which are excited with normally incident plane and Gaussian beams, showing detailed scattering field solutions. While the time-modulated metasurface leads to the generation of new collinearly propagating temporal harmonics, these harmonics are angularly separated in space, when an additional space modulation is introduced in the metasurface., Comment: 12 pages, 9 figures

A novel time-reversal subwavelength transmission technique, based on pulse shaping circuits (PSCs), is proposed. This technique removes the need for complex or electrically large electromagnetic structures by generating channel diversity via pulse shaping instead of angular spectrum transformation. It is shown that, compared to our previous time-reversal system based on chirped delay lines, the PSC approach offers greater flexibility and larger possible numbers of channels, i.e. ultimately higher transmission throughput. The PSC based time-reversal system is also demonstrated experimentally., Comment: 6 pages,9 figures. arXiv admin note: substantial text overlap with arXiv:1407.7085

A passive chipless Radio-frequency identification (RFID) tag based on log-periodic (LP) dipole array is proposed, where the tailorable band-rejection property of the LP aperture is utilized to realize large number of codes. The proposed tag principle is successfully validated using measurements, where the absence and presence of the band-rejection, is shown to carry the bit information. Its fabrication simplicity is also demonstrated by its implementation on a flexible substrate. Finally, two different tag formation schemes, based on specific set of resonance suppressions, are discussed in detailed., Comment: 2 pages, 6 figures

A novel tunable microwave broadband resonator, inspired from optical laser systems, is presented. In contrast to usual harmonic resonators, the proposed device is based on broadband composite right/left-handed (CRLH) metamaterial lines. This line, configured as a resonator, provides nonuniform spectral resonances due to the nonlinear nature of its dispersion curve. This is exploited in the impulse-regime, where the input pulse spectrum is discretized inside the resonator, with different spectral separation as a function of the carrier frequency. This discretization leads to a pulse periodicity in time, with a tunable output time period. Based on the new broadband resonator features, a pulse rate multiplication device is proposed. This device provides an increase in the repetition rate of a periodic input pulse, with the additional advantage of repetition rate tunability. Este trabajo ha sido cofinanciado por el Ministerio de Educación y Ciencia (Proyecto: TEC2007-67630-C03-02, Beca: FPU-AP2006-015).

A new time-domain Green’s function approach is used to characterize a composite right/left handed (CRLH) leakywave structure as a function of time under ultra-short modulated pulse excitation. This analysis is efficiently performed in the far-field region for both, a single CRLH element and for an array. Several novel broadband applications, such as a real-time spectrum analyzer (RTSA) (which exploits the unique frequencyspace mapping conversion of the CRLH) or an instantaneous radar scanning (based on the time-frequency relation of chirpmodulated pulses), are presented and discussed. Full-wave simulations and measurements are provided to validate the results. The semi-analytical formulation developed is compact, flexible and fast, avoiding stability conditions as in other completely numerical time-domain methods. Este trabajo ha sido cofinanciado por el Ministerio de Educación y Ciencia (Proyecto: TEC2007-67630-C03-02, Beca: FPU-AP2006-015).

Several novel dispersion-engineered CRLH TL metamaterial analog signal processing systems, exploiting the broadband dispersive characteristics and design flexibility of CRLH TLs, are presented. These systems are either guided-wave or radiated-wave systems, and employ either the group velocity or the group velocity dispersion parameters. The systems presented are: a frequency tunable impulse delay line, a pulse-position modulator, a frequency discriminator and real-time Fourier transformer, pulse generators, an analog real-time spectrum analyzer, a frequencyresolved electrical gating, a spatio-temporal Talbot effect imager, and analog true-time delayer. They represent a new class of impulse-regime metamaterial structures, while previously reported metamaterials were mostly restricted to the harmonic regime.