A set of floating electrodes and a relatively thick buffer layer of low-dielectric constant is interspaced between the coplanar RF transmission line and the LiNbO3 substrate containing the optical wave-guide structure. The composite structure is designed to feature a 50-Ω characteristic impedance, to have an effective dielectric constant equal to that of the optical wave for close velocity match, and to have a 3 dB bandwidth of 40 GHz. The purpose of the floating electrodes is to optimize the modulation sensitivity resulting in an improvement of about 6 dB. As a result, the RF power required for full modulation is lower than heretofore reported changing over the range from below 2 GHz to 20 GHz, from 44 mW to less than 70 mW. The close agreement between the theoretical and experimental values of the design parameters demonstrates the usefulness of the quasistatic assumption in the analysis of the composite structure 相似文献
This paper describes a performance analysis of two open-cycle absorption systems for solar cooling. The working fluid is LiCl---H2O, where the water desorbs into the atmosphere and is replaceable. Both systems comprise a closed absorber and evaporator as in conventional, single-stage absorption chillers. The open part of the cycle is in the regenerator, used to reconcentrate the absorbent solution by means of solar energy. One of the systems under study has employed direct regeneration in a regenerating collector, exposing the solution simultaneously to the sun and to a stream of air. The other has employed indirect regeneration by contacting the solution with air heated elsewhere in a flat-plate collector. The analysis was performed using a code developed for modular simulation of absorption systems under varying cycle configurations and with different working fluids. The code has been modified to accommodate the features of the open-cycle systems, including the regenerating collector and the air-solution contactor. Based on specified design features, the code calculates the operating parameters in each system for a variety of conditions. The paper presents the performance curves obtained for both systems. Results indicate a definite performance advantage of the direct-regeneration system over the indirect-regeneration one. 相似文献
Large radomes are assembled from many panels connected together forming joints or seams. When the panels are type A sandwiches that are optimized for minimum transmission loss over moderately narrow bandwidths, the seams and joints introduce scattering effects that can degrade the overall electromagnetic performance. Tuning the dielectric seams with conductive wires and optimizing their geometry is, therefore, crucial to enhancing the electromagnetic performance of the radome. The authors address the problem of systematically tuning the dielectric seams and present both numerical and experimental results to illustrate the tuning procedure. Included are results showing the effect of the tuning of the radome on the radiation of an enclosed aperture of circular or elliptic shape 相似文献
A theoretical model to analyze a covered rectangular antenna with an arbitrary dielectric constant superstrate is developed. The antenna is simulated by the radiation of two magnetic dipoles located at the radiating edges of the patch. The Green's function of an elementary magnetic dipole in a superstrate-substrate structure, utilizing spectral-domain analysis, is formulated, and the surface-wave and radiation field are computed. An improved transmission line model, which considers the stored energy near the radiating edges and the external mutual coupling, is used to compute the input impedances and radiation efficiency. Design considerations on the superstrate thickness and its dielectric constant are discussed. Experimental data for a single element and a 4×4 microstrip array is presented to validate the theory 相似文献
Summary: Compacted fiber composites offer unique properties due to their lack of an extraneous matrix. The conditions of processing ultra‐high molecular weight polyethylene (UHMWPE) fibers were simulated in a heated pressure cell. In situ X‐ray diffraction measurements were used to follow the relevant transitions and the changes in the degree of crystallinity during melting and crystallization. The results strongly support the suggestion that the hexagonal crystal phase, in which the chain conformation is extremely mobile on the segmental level, constitutes the physical basis of compaction technologies for processing UHMWPE fibers into a single‐polymer composite. This report suggests that using a pseudo‐phase diagram outlining the occurrence of different phases during slow heating and the degree of crystallinity can provide valuable insight into the technological parameters relevant for optimal processing conditions.
Degree of crystallinity as a function of pressure and temperature in a region relevant to compaction processes. 相似文献
Observations show that, when a viscous fluid flows vertically through a bed of settled flocculated aggregates, particles are emerged from locations on the upper surface of the bed, as a volcano process, and hollow tubes are created in the bed though the latter remains basically stable. A theoretical model is presented to explain this odd phenomenon from the onset of particle motion to the development of the tubular cavities and the particles' deposits around them. Analytical and numerical calculations are performed to show fluid streamlines and particle trajectories. 相似文献
We present analytical solutions to the steady state nucleation-condensation-coagulation equation of aerosols in the atmosphere. These solutions are appropriate under different limits but more general than previously derived analytical solutions. For example, we provide an analytic solution to the coagulation limit plus a condensation correction. Our solutions are then compared with numerical results. We show that the solutions can be used to estimate the sensitivity of the cloud condensation nuclei number density to the nucleation rate of small condensation nuclei and to changes in the formation rate of sulfuric acid.
