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Over the years extensive studies have been carried out to apply coherent optics methods in real-time communications and image transmission. This is especially true when a large amount of information needs to be processed, e.g., in high-resolution imaging. The recent progress in data-processing networks and communication systems has considerably increased the capacity of information exchange. However, the transmitted data can be intercepted by nonauthorized people. This explains why considerable effort is being devoted at the current time to data encryption and secure transmission. In addition, only a small part of the overall information is really useful for many applications. Consequently, applications can tolerate information compression that requires important processing when the transmission bit rate is taken into account. To enable efficient and secure information exchange, it is often necessary to reduce the amount of transmitted information. In this context, much work has been undertaken using the principle of coherent optics filtering for selecting relevant information and encrypting it. Compression and encryption operations are often carried out separately, although they are strongly related and can influence each other. Optical processing methodologies, based on filtering, are described that are applicable to transmission and/or data storage. Finally, the advantages and limitations of a set of optical compression and encryption methods are discussed.

http://jap.aip.org/The randomness in the structure of two-component dense composite materials influences the scalar effective dielectric constant, in the quasistatic limit. A numerical analysis of this property is developed in this paper. The computer-simulation models used are based on both the finite element method and the boundary integral equation method for two- and three-dimensional structures, respectively. Owing to possible anisotropy the orientation of spatially fixed inhomogeneities of permittivity epsilon(1), embedded in a matrix of permittivity epsilon(2), affects the effective permittivity of the composite material sample. The primary goal of this paper is to analyze this orientation dependence. Second, the effect of the components geometry on the dielectric properties of the medium is studied. Third the effect of inhomogeneities randomly distributed within a matrix is investigated. Changing these three parameters provides a diverse array of behaviors useful to understand the dielectric properties of random composite materials. Finally, the data obtained from this numerical simulation are compared to the results of previous analytical work

Interest in filled polymers has expanded in recent years as investigators have recognized the great flexibility allowed by these materials to suit particular properties such as electrical, mechanical, and/or coupling between these properties. This article describes the work undertaken to investigate the microwave response of two different types of samples: one with carbon black or silica particles embedded in a linear low-density polyethylene, and the other with carbon black particles or carbon fibers embedded in an epoxy resin. We report broad-band (30 MHz–14 GHz) measurements of the complex permittivity of these materials obtained by measuring the scattering parameters (S parameters) of a microstrip line loaded with a rectangular sample of the test material. The experimental results presented give access to data which can be rationalized in terms of a combination of Bruggeman’s self-consistent model with Jonscher’s phenomenological analysis. This analytical approach yields data that are in good correspondence with experimental data in terms of the concentration dependence of inclusions within the polymeric matrixes and demonstrates large practical capabilities for analyzing the electromagnetic properties of these materials at microwave frequencies because it allows one to make an explicit connection between these properties and the experimentally accessible parameters.

Basic physical concepts and theoretical ideas concerning dielectric heterostructures are reviewed from a historical perspective. This background for today's theory of dielectric heterostructures is discussed in some detail because the guiding principles for our understanding can be traced to the earliest developments in electromagnetism. To give an impression of the accelerating progress, I shall distinguish five stages in the development of our understanding of the dielectric properties of heterostructures. Historical remarks are included and technical concepts are introduced informally. For each stage, I call attention to synthetic works or compendia created during the interval. The first stage was reached towards the second half of the 19th century with the work of James Clerk Maxwell. Next the second stage was initiated by Bruggeman through the concept of an effective medium. Bounding methods form the third stage, with many investigators involved, beginning with the work of Wiener; the importance and ingenuity of these methods cannot be overstated. The fourth stage was the introduction of the crucial concept of percolation through an infinite cluster of connected particles and the modern approach to criticality which began in the mid-20th century with the work of Broadbent and Hammersley. Finally, the fifth stage we have experienced in the last decades involves the rapidly developing subject of computational electromagnetics: computers have moved the emphasis away from the general theory of macroscopic electromagnetism towards a better look at the detailed features of the randomness and connectedness of heterostructures. It is concluded that computational techniques provide a versatile tool for studying the dielectric properties of complex composite materials and that considerable progress can be achieved by comparing numerical results against analytical predictions for the properties of these models. As the capabilities for performing realistic simulations increase, it might become possible to routinely design on a computer, at least in part, a combination of materials chosen specifically to achieve a desired response to an incident electromagnetic wave for a variety of technological and industrial processes ranging from electromagnetic shielding and capacitive video disk units to mammalian tissue simulants.

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We present computer simulation data for the effective permittivity (in the quasistatic limit) of a system composed of discrete inhomogeneities of permittivity epsilon(1), embedded in a three-dimensional homogeneous matrix of permittivity epsilon(2). The primary purpose of this paper is to study the related issue of the effect of the geometric shape of the components on the dielectric properties of the medium. The secondary purpose is to analyse how the spatial arrangement in these two-phase materials affects the effective permittivity. The structures considered are periodic lattices of inhomogeneties. The numerical method proceeds by an algorithm based upon the resolution of boundary integral equations. Finally, we compare the prediction of our numerical simulation with the effective medium approach and with results of previous analytical works and numerical experiments