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 32 for “"Quarter wavelength"”.
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Archimedean spiral antenna embedded with frequency selective surface for wideband applications
… technique of the spiral antenna by placing it at quarter wavelength behind spiral arms. Despite, the effects of the ground plane on the antenna’s wideband properties, to enable the realization of a conformal antenna without the loss of the antenna’s broadband characteristics, a radian sphere …
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Methods to achieve wavelength selectivity in infrared microbolometers and reduced thermal mass microbolometers
… coated Salisbury Screen can improve both the wavelength selectivity and the speed of thermal response for microbolometers. These patterned resistive sheets and Modified dielectric coated Salisbury Screen are a modified form of classical Salisbury Screens that utilize a resistive absorber layer …
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Active, Passive and Active/Passive Control Techniques For Reduction of Vibrational Power Flow in Fluid Filled Pipes
… been demonstrated. Improved performance of the quarter wavelength tube and Helmholtz resonator was obtained on implementation of the rubber isolator on the experimental rig. Active control experiments using the side-branch actuator and 1/3 piezoelectric composite yielded significant dB …
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Finite difference time domain analysis of microstrip antenna-circuit modules
… amplifiers in a ring-like arrangement) and a quarter wavelength antenna was analysed. Coupling effects were identified and their impact on the radiation patterns was shown. Electronically tuneable microstrip patch antennas using varactor diodes were also studied. Tuning range and harmonic …
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Measurement of electromagnetic signal velocities in saturated fine-grained soils
… such as in finegrained soils. Therefore, Quarter-Wavelength Analysis was developed for measurements of velocities in fine-grained soils. The developed measurement cell was used to undertake velocity measurements in parallel with geotechnical index tests, in order to develop …
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Seismic scattering attributes to estimate reservoir fracture density : a numerical modeling study
… fracture zones are spaced greater than about a quarter wavelength of a P-wave in the reservoir we see 1) significant loss of amplitude and coherence in the base reservoir reflection and 2) a large increase in bulk scattered energy. Wavenumber spectra for integrated amplitude versus offset from …
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The design of a two-element radio interferometer using satellite TV equipment
… manufacture of narrowband hairpin filters and quarterwavelength stub filters which were used to isolate the IF band between 1.05 GHz - 1.15 GHz (corresponding RF between 10.80 GHz - 10.90 GHz). This also improved the interferometer's resolution. A series of filter-integrated Wilkinson power …
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Improving seismic site response analysis for non-standard sites
… Therefore, it is common to take advantage of the quarter-wavelength method to assess site amplifications for these profiles because it does not need a detailed shear-wave velocity profile. In this thesis, I develop a procedure to generate randomized profiles for use within the standard site …
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Optical properties of black silicon - an analysis
… reflectance of about 30% in the visible range of wavelengths. Standard Silicon solar cells are not entirely useful in the infrared spectrum region. In order to enhance the performance of Silicon solar cells, reflectance losses must be minimized and absorption must be maximized. In the solar cell …
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INVESTIGATION OF SMALL ANTENNAS FOR PERSONAL HANDY PHONE USE
… even more flexible. The gain is higher than a quarter-wavelength and half-wavelength monopole according to numerical results. The numerical results are found to agree well when compared with the measurement results. Finally, we have investigated the effects of parasitic wire elements (PWE) on a …
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Biomedical ultrasonics, cavitation, and sonoporation
… The microbubbles formed clusters at a quarter wavelength apart owing to radiation forces. We observed cluster coalescence and translation towards the capillary wall. To study acoustic cavitation, we designed and built a scientific instrument combining a pulsed laser and a high-intensity …
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Surface acoustic wave devices with low loss and high frequency operation
… 1%. Both designs can be implemented with one quarter wavelength transducer geometries at operating frequencies up to 1GHz. The SPUDT design utilised an existing impulse response model to provide analysis of ladder or rung transducers. A coupled resonator filter at 400MHz is demonstrated with a …
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An investigation of series LC resonant circuits within a sleeve balun to achieve wideband operation
… the sleeve balun, also known as bazooka balun or quarter-wavelength balun, are commonly used in antenna measurements. In general, baluns do perform well, but their performance is band-limited. Hence, for wider frequency bands, multiple baluns with different operating frequencies have to be used. …
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The physics of superconducting ring resonators
… research on linear distributed, either half-wavelength or quarter-wavelength, and lumped element superconducting resonators, has led to a better understanding of their underlying physics and substantially improved resonator performance. However, there is another possible resonator geometry, …
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Resonant Detection of Nano to Microscopic Objects Using Whispering Gallery Modes
… from the microsphere surface the distance of a wavelength into the surrounding medium. This thesis demonstrates how label-free molecules binding to the microsphere surface perturb the optical resonance by interaction with this evanescent field. The effect is demonstrated by surface adsorption of …
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Miter bend loss and higher order mode content measurements in overmoded millimeter-wave transmission lines
… at 170 GHz with a diameter of 63.5 mm and quarter-wavelength corrugations. The loss in a miter bend was found to be 0.022+0.08 dB. This measurement is in good agreement with theory, which predicts 0.027 dB loss per miter bend, and past measurements [18]. The SPR was used to measure the loss …
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Design and comparative performance evaluation of novel mobile handset antennas and their radiative effects on users.
… from the use of a handset equipped with quarter wavelength monopole antenna. A new measure referred to as the 3dB SAR volume is proposed. This measure provides better understanding of the absorbed power distribution in the operator's head.<br/><br/>Results obtained in the course of study …
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Modelling of a microfluid ultrasonic particle separator
… micro-engineered device and a device based on a quarter-wavelength, providing valuable insight into various trends observed.The novelty in this work is the application of macro-scale numerical techniques to microengineered ultrasonic particle manipulators and the execution of an extensive …
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Energy efficient radio frequency system design for mobile WiMax applications. Modelling, optimisation and measurement of radio frequency power amplifier covering WiMax bandwidth based on the combination of class AB, class B, and C operations.
… 90-degree 2-way power splitter at the input, quarter wavelength transformer at the output, and a new output power combiner. The frequency range for the amplifiers was designed to operate in the 3.4 - 3.6 GHz frequency band of Europe mobile WiMAX. The experimental results show that 30dBm output …
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Characteristic Modes for Impedance Matching and Broadbanding of Electrically Small Antennas
Antennas smaller than a quarter wavelength are fundamentally constrained in a variety of ways. One of the more problematic limitations is that the antenna's bandwidth declines sharply as the size of the antenna decreases. Myriad studies have sought antennas that perform close to the fundamental …
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