Control of the magnitude and spatial distribution of interference energy flows in near fields of systems of identical radiators

Abstract

The problem of active control for both the magnitude and spatial distribution of individual components of the interference component of the Poynting vector within the near zone of a system of radiators is studied. The characteristic size of this zone is on the order of the wavelength and is characterized by the presence of evanescent (nonpropagating) fields, which are formed due to the interference interaction of radiators. Using multipole expansions for fields and special summation formulas for such expansions allows one to obtain concise expressions convenient in carrying out numerical calculations. The results of calculations confirm the feasibility of the above-mentioned control in principle in solving problems of medium and object sensing.At the present time, the application area of nearfield microscopy, especially with the use of optical and infrared radiation, has been considerably expanded [1]. The possibility of breaking the diffraction limit was clearly experimentally shown for the first time in the microwave band [2]. This possibility was efficiently used, in particular, in problems of near-field microwave diagnostics of biological media [3]. At the same time, the results of some works (e.g., [4]) testify to the appropriateness of applying the technology in problems of radio tomography [5] with the use of evanescent (attenuating) fields of systems of identical radiators.The dynamics of total and interference energy flows in near fields of such systems was studied in part in [6]. Simultaneously, the presence of a nonradiative energy transfer between radiators and an additional increase or decrease in the radiation power were revealed. However, an important aspect related to the meaningful control in the near zone of a system of radiators by individual components of the real part of the interference component of the complex Poynting vector has not been studied. This topic is discussed in this work.The simplest model of a system of identical radiators is a pair of collinear electric dipoles with moments and (Fig. 1a).In a system of spherical coordinates connected in a conventional manner with Cartesian coordinates , components of their fields can be represented [7] in the form of the following expressions (under the assumption that the time dependence has the form ):(1)where is the imaginary unit, is the wavenumber, is the wave resistance of the ambient medium, are spherical Bessel and Hankel funcint S 1 p 2 p , , r θ ϕ , , x y z exp( ) i t ω ( ) ( ) ( ) ( ) ( ) ( ) ( ) [ ] ( ) ( ) ( ) (1) 1 0

Numerical Modeling and Experimental Investigation of the Breadboard Model of a Near-Field Interference Microscope

“…Moreover, the highest degree of localization is observed at ∆φ=90°. The results of modeling presented here agree quite well with conclusions of work [8]. In this work, the theoretical investigations of the structure of the near field for several elementary radiating systems revealed the feasibility of efficient control over the interference parameters of energy fluxes formed in near overlapping fields of the radiators.…”

“…Numerical modeling performed by us demonstrated that the sensitivity of the microscope with one probe was much worse. This can be explained by lacking of the additional interference energy flux formed in the counterpropagating evanescent fields of two probes [8] and providing deeper penetration into the examined medium as well as by the increased sensitivity in comparison with conventional technologies of measurements [10,11].…”

“…Previously we conducted theoretical research [8] showing the significant role of the interference of energy fluxes arising due to overlapping (superimposition) of near fields of several radiators. Some considerations concerning the method of control over these fluxes for sensing of media, materials, and objects were also presented.…”

Spatial structure of the phase state of the field generated by a system of closely spaced radiators

“…Известно [10][11][12][13], что в перекрывающихся эванесцентных полях, порождаемых распределенными в пространстве системами излучателей, имеют место интересные интерференционные эффекты, обусловливающие появление специфических интерференционных потоков энергии. В этой связи значительный интерес представляет исследование особенностей фазовой структуры поля в зоне перекрытия эванесцентных полей, а также и вне неё.…”

“…При моделировании нами были использованы мультипольные разложения произвольной системы электрических и магнитных токов в сферической системе координат [14] и специальные формулы суммирования типа представленных в [11,12]. Это позволило кардинальным образом упростить процедуру расчетов в силу того, что в ближней зоне исходные мультипольные разложения оказываются крайне медленно сходящимися.…”