Showing papers by "Constantine A. Balanis published in 1981"
16 Jun 1981
TL;DR: In this article, it was shown that very minor differences between patterns of antennas mounted on perfectly conducting and composite ground planes appear for conductivities equal to 104s/m. The computed patterns agree extremely well with measurements.
Abstract: Geometrical theory of diffraction methods have been used to develop models and to predict the patterns of communications, navigation, and identification (CNI) blade antennas mounted on finite size composite ground planes. The computed patterns agree extremely well with measurements. It has been shown, both analytically and experimentally, that very minor differences between patterns of antennas mounted on perfectly conducting and composite ground planes appear for conductivities equal to 104s/m.
22 citations
TL;DR: In this article, an imaging scheme that explicitly incorporates refraction and first-order reflection in the reconstruction process is developed, and several examples of successful reconstruction of multicell underground environments are presented to demonstrate its accuracy.
Abstract: An accurate technique for remotely determining the internal structure of an object or underground environment would have a significant impact in mining, geoexploration, ultrasonics, and the life sciences. This process of resolving the intrinsic properties of an object or environment by the transmission of radiation or ultrasound through the unknown anomaly is known as reconstructive imaging or tomography. Several efforts have been made to apply imaging (reconstruction) methods to measurements taken between two boreholes on either side of an unknown geophysical structure. However, it became necessary, because of the nature of existing reconstruction methods, to assume a straight-line propagation path from source to receiver. This assumption is not valid in many important applications of geophysical imaging; thus it is desirable to develop a method to account for the radiation mechanisms of refraction and reflection in the unknown medium. An imaging scheme that explicitly incorporates refraction and first-order reflection in the reconstruction process is developed. Several examples of successful reconstruction of multicell underground environments are presented to demonstrate its accuracy.
17 citations
01 Feb 1981
TL;DR: In this paper, the authors used a two-path interferometer at microwave frequencies (?9 GHz) to test the electrical properties of coal samples as a function of polarization and direction of travel of the electromagnetic wave.
Abstract: The development of electromagnetic systems to detect and monitor coal‐related processes requires a thorough knowledge of the electrical properties (dielectric constant and conductivity) of coal. Using a two‐path interferometer at microwave frequencies (?9 GHz), samples of solid eastern bituminous and eastern anthracite coals were tested as a function of polarization and direction of travel of the electromagnetic wave. Temperature moisture, and pyrite distribution tests were performed on eastern bituminous coal samples. In general there were slight decreases in the values of the dielectric constant and conductivity as a function of temperature, from ambient to 700° F, and as the moisture content decreased through drying. Pyrite layers along the bedding planes cause a general increase in the conductivity. The anthracites (higher rank coals) have larger values of conductivity (about a factor of 10) and permittivity (about a layer of 2 and 3) than bituminous (lower rank) coals. No distinct relationship was found between the direction of propagation and the electrical properties. Recommendations are made for orienting electromagnetic radiators to improve efficiencies of systems which are designed for coal‐related detection, monitoring and mapping applications.
3 citations
05 Apr 1981
TL;DR: In this article, a microwave system was designed and evaluated to measure the return-to-transmitted power ratio, which may be used to characterize the reflecting properties of the fluidized-bed surface.
Abstract: reflecting properties of the bed-level s urface. 26506 Presently, there exists no reliable techThis paper desnique to sense the height of the bed-level s urface in a fluidized bed combustor. cribes t he design and evaluation of a microwave system built t o detect t he height of the fluidized bed within a combustion chamber. In addition, a system has been designed, built, and evaluated to measure the return-totransmitted power ratio which may be used to characterize the reflecting properties of the fluidized-bed surface. Measurements by this system have been compared with Computations from an analytical model.