Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 130 for “"directivity"”.
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Two dimensional control of metamaterial parameters for radiation directivity
This work examines the feasibility of using metamaterials to direct radiation. The limits of required index of refraction and the required material depth are explored using MATLAB simulations. A wedge of connected S-shape metamaterial is chosen and simulated in CST Microwave Studio. The incident …
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Analysis and Optimization of Reflector Antenna Systems (Pattern Calculation, Optimum Directivity, Sidelobe Reduction)
This thesis studies the secondary pattern of a perfectly conducting reflector antenna system being illuminated by an array feed with arbitrary location, polarization, and orientation. The methods of analysis used are physical optics (PO) and the application of the Fast Fourier Transform (FFT) to …
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Superdirectivity and the Application of Complementary Split Ring Resonators in Directivity Enhancement of Millimeter-Wave Antennas
… by this limitation, this work investigates superdirectivity for millimeter wave antenna designs. Superdirectivity happens when a radiating body exceeds its maximum theoretical directivity limit. Based on a comprehensive literature review, a recent redirection away from reactive loading and …
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A statistical ultra wideband indoor channel model and the effects of antenna directivity on multipath delay spread and path loss in ultra wideband indoor channels
… combination pairs. The effects of antenna directivity on path loss and multipath propagation in the channel were analyzed extensively for various omni-directional and directional antenna combinations. A statistical model of the path loss in the channel is presented, where the parameters in …
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Adjoint-based monopole synthesis of sound sources with complex directivities
… In contrast to frequency domain methods, the directivity pattern of sound sources cannot be analytically implemented in the time domain directly. The sound sources are rather approximated by the superposition of monopoles around the directive sound source. For that purpose, an adjoint-based …
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Orientation dependence of the acoustic backscatter for elongated zooplankton
… of the main lobe of the acoustic backscatter directivity pattern of decapod shrimp (Palaemonetes vulgaris) is examined versus acoustic frequency. Using the distorted wave Born approximation (DWBA) and the geometry of a prolate spheroid, an analytic formula for the backscatter cross section as …
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Inhomogeneous, Anisotropic Turbulence Ingestion Noise in Two Open Rotor Configurations
… of the sound show that the source has a complex directivity, different from that of a streamwise aligned dipole, due to the inhomogeneous unsteady upwash distribution. In addition, observers at different far field locations will perceive sources from different locations on the rotor disk. The …
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Low-Frequency Emission Enhancement by Resonant Acoustic Metamaterials
… Emission enhancement and controlling the directivity of an acoustic source is however restricted to the properties of the source. In particular, the size of the source, in comparison with the wavelength of the sound, plays a very dominant role in determining the quality of the emitted …
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Analysis and characterization of the integrated dielectric slab waveguide-wedge antenna using iterative mode-matching technique
… Longer length wedges are shown to produce higher directivity and smaller half-power beamwidths (HPBW). For TB polarization, wedges with larger values of dielectric constant yield smaller directivity and broader HPBW. In contrast, for TM polarization, wedges with larger values of dielectric …
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Sound from ultrasound : the parametric array as an audible sound source
… versatile manner, permitting concise, narrow directivity patterns otherwise possible only with physically very large transducer geometries. This thesis explores the use of the parametric array as an audible sound source, permitting audible sound to be generated with very high directivity …
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Numerical modelling and design of wideband electromagnetic structures at radio frequencies: Applications in cosmology and digital communications
… models. So in the context of a dipole antenna's directivity pattern, and corresponding antenna temperature, the use of a parameterized sum of basis functions is considered to remodel the directivity of a physically perturbed antenna. Through the use of physically based basis functions and per …
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Directive ultra wideband antenna for medical applications
… size antenna that possess a good gain and high directivity. Thus, the aim of this project is to design and develop a directive and miniaturized antenna for UWB applications. The antenna is designed and fabricated on a Flame Retardant (FR4) laminated substrate with dielectric constant, ԑr of 4.3 …
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Aeroacoustic measurement and analysis of transient supersonic hot nozzle flows
… Far-field narrowband spectra were obtained at directivity angles from 65 to 145 degrees and the data were extrapolated to full-scale flight conditions consistent with FAR-36 regulations. Nozzle pressure ratio and total temperature ratio were repeatable to within ± 1 percent of desired …
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Design And Analysis Of Adaptive And Reconfigurable Antennas For Wireless Communication
… with respect to the 3dB beamwidth and directivity. However the reconfigurable rectangular-spiral antenna is the most compact in size among all four antennas. It is (20 mm x 20 mm) in size. At 2.45 GHz it has a 3dB beamwidth of 87° and directivity of 6.47dB. As for the 5.78GHz frequency …
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Tunable Piezoelectric Transducers via Custom 3D Printing: Conceptualization, Creation, and Customer Discovery of Acoustic Applications
… selectively tunable sensitivity, resonance, and directivity pattern. These technology advancements are extended to enable a workflow for users to input polar coordinates and receive an acoustic element of a continuously tuned directivity pattern. Investigation into customer problem spaces via …
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New Designs for Wideband Hemispherical Helical Antennas
… improvement in bandwidth, while maintaining the directivity and half-power beamwidth of the basic design. In the basic design, a simple wire of circular cross section is wound on the surface of a hemisphere, whereas in the proposed new designs a metallic strip forms the radiating element. …
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Innovative techniques for seismic-resistant bridge columns under ground motion excitations
… motions, near-fault motions without forward-directivity, near-fault motions with forward-directivity, and near-fault motions with fling-step on full-scale column models were investigated. An analytical model for the design of post-tensioned columns was provided”--Abstract, page iv.
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Rectangular Waveguide Filled with Uniaxial Medium and Negative Resistance Enhanced Composite Right/Left-Handed Transmission Line
… the structure is followed by an example of high-directivity leaky-wave antenna (LWA). In contrast to the conventional CRLH unit cell with via terminated stubs, the NR-CRLH unit cell is designed with negative-resistance (NR) terminated stub that compensates the power loss from the orthogonal …
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The electromagnetic modelling and optimization of planar holographic antennas
… because of their potentially relatively high directivity and low profile. Most published design work on planar holographic antennas has been based on approximate expressions and experimental experience. Little attempt appears to have made to use some computational electromagnetics approach to …
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Miniaturized Antenna for Satellite Broadband Application
… of a high-speed satellite internet system. High directivity, broadband characteristics, and circularly polarized radiations are essential for a user antenna to maintain a reliable connection with the overhead LEO satellite constellation. For commercialization and portability, the antenna is …
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