Cristian Della Giovampaola

Efficient Algorithm for the Evaluation of the Physical Optics Scattering by NURBS Surfaces With Relatively General Boundary Condition

An adaptive integration algorithm is presented for the computation of the Physical Optics (PO) electric and magnetic field scattered by electrically large objects modeled by Non-Uniform Rational B-Splines (NURBS). The algorithm is the customization of a more general-purpose result that has been recently published. By using a unique formulation both impenetrable (e.g., impedance surfaces, coated conductors) as well as transparent thin sheet materials (e.g., thin dielectric panels, or frequency selective surfaces) are treated, via their Fresnel reflection and transmission coefficients. The PO radiation integral is evaluated over the NURBS parametric domain. Since most of the computer-aided geometric design (CAGD) tools are based on NURBS, the proposed algorithm allows a straightforward electromagnetic analysis of the structures by exploiting the standard available geometrical description, with no need of generating new geometrical models. Furthermore, the proposed adaptive sampling requires a number of integration points that is found to be drastically smaller than that resulting from standard Nyquist-based sampling integration algorithms. Such reduction of the sampling points is achieved by resorting to high-frequency technique concepts and allows a significant reduction of the CPU computational burden. Therefore the algorithm is efficient and particulary suitable for the electromagnetic characterization of real-life electrically large objects.

UHF-HF RFID integrated tag for moving vehicle identification

Radio Frequency Identification (RFID) is an emerging technology which finds useful applications in many practical areas such as automatic identification and object tracking, supply chain integration, security access to controlled areas, health care and bio-engineering [1]. Due to high flexibility of the RFID systems, in addition to the typical applications mentioned above there is a growing interest in non conventional applications such as the identification of moving vehicles for road-toll and access control purposes.

A Closed-Form Representation of Isofrequency Dispersion Curve and Group Velocity for Surface Waves Supported by Anisotropic and Spatially Dispersive Metasurfaces

A general closed-form representation is introduced for representing the isofrequency dispersion curve (IDC) of an anisotropic, spatially, and frequency dispersive metasurface (MTS) constituted by a dense periodic texture of metallic elements printed on a grounded substrate. The formulation is restricted to printed elements isolated from each other (namely, patches and not slots) whose geometry exhibits at least two axes of symmetry. The expression is valid for the dominant TM surface wave (SW) until the limit of the Floquet-Bloch (FB) region and generalizes our previous formulation to arbitrary direction of propagation. This generalization permits a closed-form representation of the IDCs and of the group velocity as a function of two parameters only; these are the equivalent quasi-static capacitances along the symmetry directions of the geometry. The limit of validity of the closed-form representation has been defined and the formulation has been tested by full-wave analysis. The present formulation simplifies the design of MTS antennas and flat transformation optics devices.

A Hybrid PO/Generalized-Scattering-Matrix Approach for Estimating the Reflector Induced Mismatch

A generalized network formulation using a spherical wave expansion is applied to the analysis of the perturbation induced at the input port of an antenna by nearby scatterers. The antenna is characterized by using the total scattering matrix; the scattering from the obstacles is studied through a physical optics approach, and the interactions are described in terms of radiated spherical waves. The resulting procedure is simple, has a moderate computational cost and can be directly interfaced with measurements. Results show a very good agreement with full-wave simulations.

Entire-Domain Basis Functions for Scattering From Large Curved Surfaces Formulated by Transformation Optics

A complete set of entire-domain basis functions are introduced for the analysis of scattering from bodies with curved surfaces; they are defined via the application of a generalization of the Shannon sampling theorem. These basis functions are defined for curved patches with arbitrary contours, via a three-step procedure. First, the curved patch is mapped, via Transformation Optics, onto a flat parametric domain surrounded by a virtual anisotropic inhomogeneous space. Next, linear-phase functions are defined on the parametric flat domain; the sufficient and non-redundant number of functions is found by using a spectral domain “completeness relationship” of the delta function. Finally, the back-transformation from flat anisotropic to curved isotropic space yields the basis functions for the curved patch. The number of basis functions so obtained matches the degrees of freedom of the field known in the literature. Numerical results show the effectiveness of the representation for both fields and currents.

Antenna mismatch induced by nearby scatterers through a spherical wave - Generalized scattering matrix approach

This paper presents a procedure based on a spherical wave (SW) formalism for the estimate of the perturbations induced on the input impedance of an antenna by a nearby obstacle like a reflector. The antenna is characterized by using the total scattering matrix; the scattering from the obstacle is studied through a physical optics approach, and the interaction between the two objects is described in terms of radiated spherical waves (SW). The main advantages of the proposed technique are simplicity, direct interfaceability with the output of measurement procedures and moderate computational cost.

Accurate and efficient evaluation of fields radiated at arbitrary distances by numerically-defined currents residing on arbitrarily shaped objects

In numerical solution of radiation and scattering problems, the evaluation of the electromagnetic field produced by a set of induced currents lying on the surface of an object is almost always needed. There are some special cases where the a priori information about the nature of the surface and the type of illuminating source enables us to use either analytical or asymptotic methods for fast computation of the electromagnetic radiation. However, this is not the typical scenario in most applications, since the geometry of the object might be completely arbitrary and it may not be possible to represent the source in a convenient analytical form. Furthermore, an analytical representation of the induced current distribution is seldom ever available when a numerical technique, such as the Method of Moments (MoM) [1], is used to derive a solution for the current. In addition, the computation of the radiated field in the near-field zone might encounter difficulties because the Greens function is highly oscillatory in this region. A typical situation where the field needs to be evaluated at observation points very close to the object arises when we are interested in estimating the reaction between the fields produced by a set of currents and the currents themselves. Such a procedure is typically needed for the computation of the self-terms in the reduced matrix when applying the Characteristic Basis Function Method (CBFM) [2],[3].

Efficient computation of the reaction terms to fill the interaction matrix in the Characteristic Basis Function Method (CBFM)

A technique to speed up the evaluation of the reduced matrix terms in the CBFM, for scatterers modeled by using a generically-shaped NURBS surface, has been presented in this work. The PO-based CBFs are computed by considering linear variations of both the amplitude and the phase of the PO integrand, defined over triangular basis functions in the NURBS parametric domain.

Design and analysis of a compact antenna for UWB RFID applications

We present an Ultra Wideband (UWB) antenna for RFID applications. The antenna is designed to comply with the European bandwidth requirements and to be integrated directly on the same board which is used by the UWB pulse generator. The proposed antenna has dipole-like characteristics concerning its radiation properties. Numerical results have shown good impedance matching without the need for any additional impedance matching sections, as well as good radiation properties which are suitable for UWB-RFID applications.

Hybrid methods based on generalized scattering matrices

A general hybrid technique based on the use of generalized scattering matrices is presented for the electromagnetic analysis of complex antenna and/or scattering problems. The analysis domain is decomposed into separate subdomains, which are independently studied through the most appropriate technique and characterized by a generalized scattering matrix (GSM), where the ports are associated with a proper set of wave objects. Finally, the interactions among the subdomains are described by imposing the proper subdomain connections. Two particular implementations of the general technique are illustrated. In the first one, the wave objects are complex point source (CPS) beams. Thanks to the angular selectivity of the CPS beams, only a small fraction of the beams are involved in the final system, thus, leading to an efficient numerical procedure. In the second one, spherical waves are used as wave objects. This choice offers the advantage of direct interfaceability with the output of spherical near-field measurements or numerical simulations.