<title>Investigation of tunable structures with liquid dielectrics for the microwave range</title>

Abstract

Tunable electromagnetic wave absorbers for the microwave range comprise polymer-liquid composites, made up of structures of definite shape from low dielectric constant polymer dielectric, filled with polar liquids. Tuning of reflection coefficient is performed in several ways: filling or removal of liquid from the structure, changing composition or temperature of liquid, etc. Effective absorption of electromagnetic waves by these structures in a wide range of frequencies is realized in case frequency dependence of dielectric constant of the liquid is such that for the whole range the condition of resonance absorption is fulfilled.The advantages of polar liquid dielectrics as absorbing media are demonstrated. Absorbing properties of structures with polar liquids and solutions of different salts are compared. Reflection coefficients for several structures of "dielectric on metal" type were measured.

Multifunctional polymer composites for intelligent structures

“…These are processes of interface polarization, adsorption, and formation of double electrical layers [14,15]. This problem is a complex one, with no final solution found yet, as the full description of geometry of such systems demands knowledge of many parameters: porosity, specific surface, pore size (effective diameter and of pores size distribution), connectivity of pores, their shape, smoothness of the surface of pores, etc.…”

Electrodynamic equations for heterogeneous media and structures on the length scales of their constituents

“…Some aspects of a combined scaled approach were demonstrated by measuring and modeling the electrodynamic properties of liquid-impregnated porous materials consisting of ferrite powders encapsulated in polymer tubes [29,52,53]. The ferrite powders were used as porous magnetic media with natural magnetic resonance frequencies in the microwave range.…”

“…The volume of the liquid per unit surface area of the metallic diamagnetic substrate was the same in the two systems. Several approaches to theoretical analysis of such systems were developed by Ponomarenko et al [52] and Shevchenko et al [53], who compared measured and calculated reflectivities. The latter were obtained by solving homogeneous equations for the E and H fields in one phase (polymer foam) or in a two-phase absorbing composite made up of alternating layers of the polar liquid and polymer foam of the same thickness.…”

“…For an incident TE wave, the upper-scale VAT electric-field equation has the form (66) For a single-phase polymer foam (phase 2), the wave equation is (67) The techniques developed in [52,53] for measuring the relative reflection coefficient ( ) made it possible to obtain reflection coefficients averaged over some volume of the heterogeneous layer and time-average values [52,53]. Such characteristics correspond to upperscale VAT variables.…”