Near and far field

About: Near and far field is a research topic. Over the lifetime, 15922 publications have been published within this topic receiving 220571 citations.

Axial slot antenna on dielectric-coated elliptic cylinder

Abstract: The radiation properties of an axial slot antenna on a conducting elliptic cylinder with a homogeneous dielectric coating are investigated. In the dielectric coating and in the exterior free-space region the field is expanded in elliptic waves using the Mathieu functions. The Mathieu angular functions are employed as basis and testing functions to enforce the boundary conditions at the interface between the dielectric and the free-space regions. The equations of continuity at the boundary are solved by Galerkin's method. Numerical results are presented in graphical form for the transverse electric (TE) and transverse magnetic (TM) polarizations to illustrate the far-field radiation patterns, the gain versus coating thickness, and the aperture conductance versus coating thickness. >

Adaptive processing using a single snapshot for a nonuniformly spaced array in the presence of mutual coupling and near-field scatterers

Abstract: This paper presents an adaptive technique to extract the signal of interest (SOI) arriving from a known direction in the presence of strong interferers using a single snapshot of data. The antenna elements in this method can be nonuniformly spaced and there can be mutual coupling between them. In addition, near-field scatterers can also be present. First, the voltages induced in the antenna elements of the array due to interferers, mutual coupling between the elements, and near-field scatterers is preprocessed by applying a transformation matrix to these voltages through a rigorous electromagnetic analysis tool. This electromagnetic preprocessing technique transforms the voltages that are induced in a nonuniformly spaced array containing real antenna elements to a set of voltages that will be produced in a uniform linear virtual array (ULVA) containing omnidirectional isotropic point radiators. In the transformation matrix we would like to include various electromagnetic effects like mutual coupling between the antenna elements, presence of near-field scatterers and the platform effects on which the antenna array is mounted. This transformation matrix when applied to the actual measured voltages yields an equivalent set of voltages that will be induced in the ULVA. A direct data domain least squares adaptive algorithm is then applied to the processed voltages to extract the SOI in the presence of interferers. Limited numerical examples are presented to illustrate the novelty of the proposed method.

System and method for near field communications having local security

Abstract: A system and method for near field communications is provided. The system includes a near field generator (106) configured to generate a near field detectable signal (108) comprising information, a near field detector (110) configured to receive the near field detectable signal (108) and output the information, and an Electro-Magnetic (EM) Radio Frequency (RF) jamming transmitter (116) configured to radiate an EM RF jamming signal (118), in order to jam reception of EM RF signals in the vicinity of at least one of the near field generator (106) and near field detector (110).

Electron diffraction by plasmon waves

Abstract: The properties of an electron beam can be manipulated by electromagnetic fields in vacuum via the ponderomotive force. Such an interaction is also at the core of the Kapitza-Dirac effect, which describes the diffraction of electrons by an optical standing wave. Here, the authors predict a new type of interaction between electrons and the electromagnetic field, opening up new possibilities for the manipulation of electron beams. If surface plasmon polaritons are tailored to interfere forming a periodic field pattern, it becomes possible to diffract electrons from such near field. With the proper manipulation of the plasmonic fields, orbital angular momentum can be imparted to the electrons, and even the phase of their wave functions can be manipulated. An additional degree of freedom is provided by the possibility to tailor the spatial properties of the light and the materials supporting the surface plasmons. This arbitrary control can be extended to different substrates such as graphene or layered systems and may open up a viable route to create tunable phase plates for electron microscopes.