Semitransparent Reflectors Research Articles

Scattering of Toroidal Waves by Semitransparent Reflectors of Revolution in Application to Omnidirectional Antennas

Problems of radiation pattern synthesis, sidelobe suppression, or back radiation suppression appear when using antennas with reflectors or ground planes. The use of a semitransparent surface allows the required shape of a radiation pattern to be synthesized efficiently through the variation of reflection and transmission coefficients. Effective radiation pattern synthesis is possible when using analytical formulas designed for the radiation patterns of antennas with semitransparent reflectors. In this article, we present a model for the scattering of a toroidal wave of a general form by means of a semitransparent reflector of revolution. The model allowed us to simulate the radiation patterns of various kinds of axisymmetric antennas with semitransparent reflectors and ground planes. Two asymptotic expansions of the radiation pattern of the model were found in the physical optics approximation. The expansions allow the radiation pattern for the entire space to be determined. As an example of its application, we used the model to calculate the radiation patterns of a plane with Archimedean two-wire spiral antenna and a loop antenna above concave and convex reflectors, as well as an Archimedean slot spiral antenna with a ground plane. We synthesized the optimal profiles of perfectly conducting and semitransparent reflectors and ground planes to improve the front-to-back ratio of the antennas.

Stratigraphic and three-dimensional morphological evolution of the late Quaternary sequences in the western Bohai Sea, China: Controls related to eustasy, high sediment supplies and neotectonics

The Bohai Sea is a shallow, semi-closed gulf (basin) at the proximal position of the very wide (one to several thousand kilometers) eastern Chinese margin and was persistently impacted by tectonic frameworks. Its late Quaternary stratigraphy provides an excellent natural laboratory for research on the sedimentary processes and evolutionary patterns on flat proximal continental margins with high sediment inputs and how these processes respond to synsedimentary tectonic activity. However, due to the scarcity of comprehensive sequence stratigraphic studies, our understanding of the above processes is limited. Here, we conducted a high-resolution sequence stratigraphic study using boomer seismic data with pseudo-3D coverage. The seismic data revealed seven seismic units (SUs A-G) within the late Quaternary stratigraphy, including (1) three marine prodeltaic units (SUs A, C, G) characterized by dipping/oblique internal reflections and/or lobate structures, (2) two terrestrial (fluvial/lacustrine) units (SUs B and E) dominated by heterogeneous reflections, (3) an erosional remnant unit (SUs D) with semitransparent reflectors and a lenticular geometry, and (4) a ravinement-attributed aggradational unit (SU F). Based on the extrapolation between the seismic stratigraphy and the onshore sedimentary architecture and well-established sequence stratigraphic models, our preferential interpretation for the four sets of SUs is that they correspond to the highstand, lowstand, falling-stage and transgressive system tracts, respectively. The seismic geomorphology suggests that the bulk of the accommodation is dominated by the former two, which is consistent with the alternative terrestrial-and-marine succession revealed by previous borehole studies. At such a proximal gulf, although the accumulation of thick highstand units is not surprising, the two thick lowstand units that are bounded above and below by two different subaerial unconformities are exceptional. Our interpretation indicates that abnormally thick accumulation occurred under subaerial environments during the lowstand period, which most likely corresponds to alluvial/floodplain progradation/aggradation given the western Bohai Sea is connected to the alluvial North China Plain. The lower subaerial unconformities of the lowstand units are associated with intensive subaerial (most likely fluvial) excavation. Erosion under SU E leads to the formation of incised and eroded areas that can be tens of kilometers wide and tens of meters deep, cutting into SU A or even into SU B, which are several times greater than the last glacial maximum incised valley at the top of SU E. Such intensive erosion appears to be a crucial contributor to the thick lowstand units, as it created more accommodation. The great scale of the subaerial incisions is presumably attributed to the fact that the bulk of them evolved from tectonically triggered depressions because their locations are consistent with the NE-SW- and NW-SE-striking fault populations. The tectonic forces also controlled the accumulation by resulting in high-relief basement blocks for the pre-Holocene sedimentation. However, despite such strong tectonic controls, the subsequent deposition filled and leveled the areas between the high-relief, steep-sided basement blocks and eventually resulted in a relatively flat substratum for post-LGM deposition, suggesting that the geomorphic threshold for geological control at such a proximal gulf was passed because of the high-supply environment.

Characterization of mass transport deposits using seismic attributes: Upper Leonard Formation, Permian Basin

The Permian Basin is a structurally complex sedimentary basin with an extensive history of tectonic deformation. As the basin evolved through time, sediments dispersed into the basin floor from surrounding carbonate platforms leading to various mass movements. One such mass movement is observed on a 3D seismic survey in the Upper Leonard interval (Lower Permian) of the Midland Basin that is characteristic of a mass transport deposit (MTD). The 350 ft thick MTD mapped in the study area is 5 mi wide, extends up to 14 mi basinward, and covers only the translational and compressional regime of the mass movement. A unique sedimentary feature, unlike those observed previously, is mapped and interpreted as gravity spreading. MTDs have been extensively studied in the Delaware Basin of Permian-aged strata; however, only a few works have been published on the geomorphological expression of MTDs using seismic and seismic attributes to delineate the shape, size, and anatomy of this subsurface feature. The MTD in the study area exhibits an array of features including slide, slump, basal shear surface, and MTD grooves. In cross section, the MTD is characterized as chaotic with semitransparent reflectors terminating laterally against a coherent package of seismic facies, or the lateral wall. Sobel filter-based coherence, structural curvature, dip magnitude, and dip azimuth attributes are used to map thrust faults within the discontinuous MTD. Kinematic evidence provided by the Upper Spraberry isopach suggests that this MTD was sourced north of the Midland Basin and deposited on the basin floor fairway. Slope strata are interpreted from well-log analysis showing MTD as a mixture of carbonates and siliciclastics with a moderate to high resistivity response.

Optical signal processing in nano nonlinear Fabry-Perot resonator containing negative index material

This paper investigates the issue of signal processing in a bistable Fabry-Perot (FP) resonator. FP resonator includes two one-dimensional photonic crystals (1DPCs) containing periodic structure of positive and negative index material (PIM-NIM) considering as two semi-transparent reflectors in nano scale which sandwiched a nanocavity. The transmitted intensity versus input intensity curve is obtained using the transfer matrix method which incorporates the bistability characteristics in some convenient conditions and parameters. We consider the bright soliton as an input pulse with nearly constant frequency and by changing its amplitude we investigate the output pulse in quasi-pulse regime. Such devices can practically be used as nano signal processing systems where it is illustrated that light can be controlled absolutely by light.

Absorption of Optical Microcavity in the Infrared Spectral Region

This paper describes an air Fabry-Perot (FP) cavity which is used in the infrared (IR) detector. When the distance of the FP cavity is wavelength-sized, it can store photons for almost a millisecond while they bounce up and down between the mirrors. Compared with another filled material, the air cavity not only gets high IR absorption when the cavity thickness is quarter wavelength, but also has much smaller thermal capacity and thermal time, which can improve the responsivity and detectivity of the IR detectors. An air FP cavity has been fabricated, with a thick metal mirror at bottom and a special sandwich film in the top served as absorption layer and semitransparent reflector. The materials and thickness are tested to optimize the absorption. According to the results, the best structure has been obtained, and the test results show that the IR absorption of this structure can reach to 85%.

Novel applications of bifacial solar cells

AbstractUtilizing the light reflected by simple means onto the rear surface of solar cells is an effective way of lowering the cost of solar electricity, since more power is generated per cell. Innovative bifacial photovoltaic modules have been introduced, such as a multi‐functional bifacial PV sun‐shading element which is based on bifacially sensitive solar cells in combination with a white semitransparent reflector back sheet. Not only is sunlight collected by its front and rear surface efficiently converted into electricity, but also diffuse glare‐free daylight is provided. Other applications include relatively narrow bifacial modules installed at a certain distance in front of a reflecting background. In all cases power gains of more than 50% can be achieved with little extra cost compared with monofacial modules. Copyright © 2003 John Wiley & Sons, Ltd.

Study of a combined millimeter-wave resonator

We present a theoretical investigation and measurements of a multielement open resonator composed of corrugated waveguides and plane semitransparent reflectors. A periodic-transmission-line model is used to analyze the transverse mode structure and the diffraction Q-factor of the proposed resonator. The setup containing the resonator (equipped with Bragg reflectors), mode converters, and an elliptical mirror is employed for measurements in Ka-band. Two- and three-waveguide-section resonators have been studied. The proposed resonators demonstrate good mode selectivity that permits one to utilize them in high-power millimeter-wave sources.

Broadband semitransparent dielectric reflectors with dispersion and absorption: design

The paper deals with the synthesis of dielectric multilayer systems that consist of materials with dispersion and absorption. Experience shows that for very good results, the dispersion of the refractive index and of the extinction coefficient should be introduced at the very beginning rather than in the final stages of the design. The numerical results quoted in this paper have been obtained with a previously developed method for the synthesis of broadband semitransparent reflectors that is based on the use of double layers. A new method for the synthesis of such systems, called the transient assemblies method, is also mentioned.