Antenna Shielding Research Articles

Влияние несущего винта и других элементов конструкции вертолета на качество функционирования размещаемой на нем аппаратуры потребителей спутниковых радионавигационных систем

We analysed how signal diffraction caused by the main rotor, signal reflection from helicopter components, and receiver antenna shielding by the main rotor blades affect the signal-to-noise ratio in the correlator band of satellite radionavigation system user equipment for GLONASS and GPS, its navigation precision and error probability when transmitting overhead information from navigation spacecraft to the helicopter. The investigation showed that the effect of helicopter design on the performance of user equipment mounted on it manifests as antenna shielding and diffraction waves appearing at the edges. The presence of diffraction waves and reduction in the original signal amplitude as a result of shielding the user equipment antenna leads to the Bit Error Rate in the overhead information transmission channel increasing by one or two orders of magnitude. Effect on navigation accuracy is negligible.

고속 UHF RFID 태그 검사 장비를 위한 전용 리더

RFIDs have not become widespread as expected partly due to the cost, size, read range, and reliability problems of tags. The success rate of reading must be improved in order for RFIDs to be widely adopted. Quality control of tags is crucial to meet this requirement. In this study, we designed and implemented a high-performance reader used in inspection equipment that conducts prior inspection of tags. To improve performance of the developed reader, the baseband modem and command processor (CP) were designed using H/W logic and implemented with FPGA. The inspection of small pitch inlays was made possible through the antenna shielding device and H/W command processor function. This equipment enables accurate evaluation of performance and identification of tags satisfying a given read range. By contributing to sort out defective tags, the results can ultimately lead to more stable RFID services.

Evaluation of trenching, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) for sinkhole characterization

ABSTRACTThis paper explores the suitability and advantages of combining the trenching technique with geophysical surveys [ground penetrating radar (GPR) and electrical resistivity tomography (ERT)] for sinkhole characterization in a mantled karst area. The approach is applied to two active sinkholes concealed by anthropogenic deposits and formed by contrasting subsidence mechanisms; collapse and sagging. The ERT section acquired across the collapse sinkhole images the clayey fill of the depression as an obvious low resistivity area, showing the approximate location of the sinkhole edges. Spatially dense GPR surveys provide information on the position of the boundaries of the concealed subsidence structures and their three‐dimensional (3D) internal geometry, revealing the dominant subsidence mechanism. We illustrate the impact of several factors on the quality of the GPR data such as sinkhole size, nominal frequency of the antennas, antenna shielding, and the presence of backfilled excavations and above‐surface objects. Trenches provided detailed information on the subsurface structure of the sinkhole, subsidence magnitude, partitioning of the strain, and the position of the sinkhole edges, especially when they are deep enough and excavated across the central sector and perpendicular to the boundaries. The stratigraphic and structural relationships observed in the trench were then used to infer the spatial evolution of the sinkholes (e.g. enlargement), their kinematic behavior (episodic versus progressive), and to differentiate discrete subsidence events and their associated magnitude. Numerical dates were used to estimate average subsidence rates and the recurrence of subsidence events. Such integrated data sets may be used as an objective basis to forecast the future behavior of potentially damaging sinkholes and to assess the associated hazard and risk. Copyright © 2013 John Wiley & Sons, Ltd.

Transformation Electromagnetics: An Overview of the Theory and Applications

The recently introduced transformation-electromagnetics techniques provide a new methodology for designing devices that possess novel wave-material interaction properties. They are based on the form invariance of Maxwell's equations under coordinate transformations. These methods provide an extremely versatile set of design tools that employ spatial-coordinate transformations, where the compression and dilation of space in different coordinate directions are interpreted as appropriate scalings of the material parameters. The most famous transformation-optics device is the cloak of invisibility. However, a wide variety of other devices are also possible, such as field concentrators, polarization rotators, beam splitters, beam collimators, and flat lenses. In this paper, an overview of transformation-electromagnetics device design techniques is presented. The paper begins by introducing the underlying design principle behind transformation electromagnetics. Several novel transformation-based device designs are then summarized, starting with electromagnetic cloaks that have spherical shell or cylindrical annular shapes, More general cloaking designs of noncircular annular geometries are treated, and the application of cloaking to RF/microwave antenna shielding is also discussed. Following this, device designs that employ transformations that have discontinuities .on the domain boundary are presented. Unlike those used for cloaks, this type of transformation is capable of modifying the fields outside of the device. Examples of this type of transformation-electromagnetics device are presented, which include flat near-field and far-field focusing lenses, wave collimators for embedded sources (e.g., antennas), polarization splitters and rotators, and right-angle beam benders.

An acoustic Doppler wind measuring system

A system using the Doppler shift of audible sound waves to measure atmospheric winds to heights of 1 km above the surface is described. Planned application of the device at a commercial airport required extensive transducer and antenna shielding to reduce the effect of ambient noise. Comparisons of winds measured by both the acoustic Doppler system and standard radiosondes indicate that high accuracy and resolution can be achieved, and that the wind profiles can be continually monitored with relatively simple ground based equipment.

Acoustic Doppler Wind Measuring System

A system using the Doppler shift of audible sound waves to measure atmospheric winds to heights of 1 km above the surface is described. Planned application of the device at a commercial airport required that optimum transducer and antenna shielding be provided in order to reduce the effect of ambient noise. A description of the antenna and shielding is followed by an outline of the remaining system components. Comparisons of winds measured by both the acoustic Doppler system and standard radiosondes are presented. These results indicate that a rather high degree of accuracy and resolution can be achieved and that the wind profiles can be continually monitored with relatively simple ground-based equipment.