In the present study we use Argo float data, in-situ shipboard ADCP data,IFREMER wind stress curl data, QuikSCAT wind data and AVISO sea level anomaly data from 2006 to 2010 to investigate hydrographical characteristics and surface and deep currents in the seas surrounding Taiwan. The studied areas consist of the followings: the cyclonic eddy off the northeastern Taiwan coast, flow structure of the Luzon Strait, anticyclonic eddies off the southwestern Taiwan coast and east of Kuroshio. Our results found that some Argo floats drifting northward with the Kuroshio were occasionally intruded to the continental shelf off the northeastern Taiwan at 25¢XN-26¢XN,122¢XE-123¢XE. Statistics indicate that this phenomenon occurs most frequently in winter, and float profiling data reveal a marked upwelling above 150m depth. Temperature drops within this area can reach 5.1¢J and 8¢J, respectively at 50m and 100m depths. A deep southward current with a maximum speed of 30 cms can be found to exist between northeastern Taiwan and Kuroshio. On the other hand, Surface flows have strong seasonal variations in the Luzon strait, i.e., toward the southeastern side of Taiwan in the summer and intrude into the South China Sea (SCS) in the fall and winter. Deep currents in the Luzon Strait, however, flow mostly into the SCS regardless of seasonality. Maximum speed of deep current can reach 6 cms . Mixed-layer depth in the northern SCS is approximately 50m in the spring and summer, and about 110m depth in winter. The third part of this thesis concerns with the anticyclonic circulation off the southwestern Taiwan coast. Float observations show that this circulation exists almost all year round in 2009. Surface currents have a maximum speed in early May, reaching 104 cms , and the wind stress curl attains a maximum negative value. It is conjectured that this anticyclonic eddy is generated primarily due to the restriction of local coast and topography, and the wind stress curl is the secondary mechanism. Surface current derived from Shipboard ADCP is also consistent with the float results. The diameter of this eddy is about 110 km. T-S characteristics of Kuroshio can be observed at 150-210m depth, indicating a close link between this eddy and the Kuroshio. Finally, anticyclonic warm eddies east of Kuroshio are also investigated from the float data. It is found that the eddy flow structure in this region is more obvious in depths than in surface. Temperature distribution below the depth of 200 m also confirms the warm core structure. At an event during which when one float incidentally travelling through a cold eddy and an adjacent warm eddy, the temperature difference can reach 4.5 ¢J at 160m depth. The warm eddies are found to be more stable and more frequently observed than the cold eddies in this region.

This study investigates the accuracy of the wave products retrieved by a 12-MHz high-frequency (HF) phased-array radar, and establishes their potential to characterise wave-current interactions. The two stations composing the system were deployed in 2011 to overlook the Wave Hub, a test site for marine renewable energy devices located on the south-western coast of the United Kingdom. The system was conceived and configured to reduce the inaccuracies introduced by short time averaging and minimal overlap between stations, both associated with the most traditional HF radar deployments, whose primary activity is current measurement. Wave spectra were retrieved by two independent inversion algorithms, which were evaluated both independently and relative to each other. This process helped determining the errors associated to the algorithm used, and differentiated them from those inherent to the radar technology itself. The first method investigated was a semi-empirical algorithm distributed with Wellen Radars (WERA), which was calibrated using in situ measurements collected within the radar footprint. Evaluated through comparison against measurements acquired by three in situ devices, the results revealed estimates of significant wave height with biases below 9 cm, Pearson correlations higher than 0.9, and RMS errors that range from 29 to 44 cm. The relative error of wave energy period comparisons was within 10% for periods between 8 and 13 s, while both under- and overestimations were observed above and below that range, respectively. The validation demonstrated that when locally calibrated, the algorithm performs better than in its original form in all metrics considered. Observed discrepancies were mainly attributable to single-site estimations, antenna sidelobes, and the effect of the second-harmonic peaks of the Doppler spectrum. As opposed to the semi-empirical inversion, the second method evaluated in this work provides estimates of the full directional spectrum. Compared against the in situ measurements, the radar spectra were more spread over frequencies and directions, and had a lower energy content at the peak of the spectrum. In terms of parameter estimation, this was generally translated in a slight underestimation of wave periods, but accurate estimates of significant wave heights. Pearson correlations between these parameters and the in situ measurements for the bulk of the spectrum were higher than 0.9, and both types of measurements resulted in similar standard deviations. The inversion algorithm showed a high skill estimating mean wave directions, which revealed linear correlations higher than 0.8, when compared to the in situ devices. Overall, the inversion algorithm has shown to be capable of providing accurate estimates of directional spectra and the parameters derived from them, and at present the main drawback of the method is the data return, which due to the high data quality requirements of the algorithm, did not exceed 55% over the 8-month period studied here. In the second part of this work, the validated measurements were examined to determine their ability to reproduce the effects of wave-current interactions. The fine structure of the surface current was first evaluated, and revealed a circulation dominated by tides. The residual flow was seen to respond to the wind, as well as to the stratification present in the area during the spring and summer months. These data were then used to assess their contribution to wave refraction over the radar domain. The results show modulations in the wave phase parameters, which resulted from both the temporal and spatial derivatives of the surface current velocities. The evaluation of HF radar wave measurements provided in this work has shown that, properly configured, this technology can produce accurate estimates of several statistical descriptors of the wave field. Together with the highly accurate surface currents also measured by this device, the spatial wave data obtained has proved to have great potential for studying wave-current interactions; a skill that can be of support to coastal wave modelling.

Approved for public release, distribution is unlimited / High Frequency (HF) radar backscatter instruments are being developed and tested in the marine science and defense science communities for their abilities to sense surface parameters remotely in the coastal ocean over large areas. In the Navy context, the systems provide real-time mapping of ocean surface currents and waves critical for characterizing and forecasting the battle space environment. In this study, the performance of a network of four CODAR (Coastal Ocean Dynamics Application Radar) SeaSonde HF radars, using the Multiple Signal Classification (MUSIC) algorithm for direction finding, is described for the period between July to September 2003. Comparisons are made in Monterey Bay with moored velocity observations, with four radar baseline pairs, and with velocity observations from sixteen drifter deployments. All systems measure ocean surface current and all vector currents are translated into radial current components in the direction of the various radar sites. Measurement depths are 1 m for the HF radar-derived currents, 12 to 20 m for the ADCP bin nearest to the surface at the M1 mooring site, and 8 m for the drifter-derived velocity estimates. Comparisons of HF radar-M1 mooring buoy, HF radar-HF radar (baseline), and HF radar-drifter data yield improvements of - 1.7 to 16.7 cm/s rms differences and -0.03 to 0.35 correlation coefficients when measured antenna patterns are used. The mooring comparisons and the radar-to-radar baseline comparisons indicate angular shifts of 10Ê» to 30Ê» for radial currents produced using ideal antenna patterns and 0Ê» to 15Ê» angular shifts for radial currents produced using measured patterns. The comparisons with drifter-derived radial currents indicate that these angular biases are not constant across all look directions, even though the local antenna pattern distortions were taken into account through the use of measured antenna patterns. In particular, data from the SCRZ and MLNG radar sites show varied pointing errors across the range of angles covered. / Lieutenant Commander, Republic of Korea Navy

In this thesis, two types of handset antenna design respectively for dual-band GSM850/1900 operation and seven¡Vband LTE/WWAN operation are presented. The proposed antennas can achieve decreased antenna size and enhanced operating bandwidth by shaping the system ground plane of the handset. The seven-band LTE/WWAN antenna is printed on the system circuit board with good radiation characteristics and occupies a small size of 24.5 x 10 mm2. At first, we propose a half-loop antenna structure which integrates its facing edge of the system ground plane as the resonant path of the antenna. In this case, the required length of the half-loop antenna structure is only about a half compared with the traditional loop antenna. Next, to enhance the operating bandwidth of the antenna, a parasitic shorted monopole strip is added and a shaped system circuit board is used. The shaped system circuit board can integrate the battery with the circuit board to help reduce the thickness of handset. Also, much enhanced operating bandwidth for the lower band can be obtained, owing to the enhanced surface current excitation in the system ground plane resulting from properly shaping the system circuit board. Effects of the user¡¦s head and hand on the proposed antenna are studied, and the simulated SAR and HAC results are also analyzed for bio-compatibility issue.

In this dissertation, novel printed multiband antennas for slim mobile communication devices are presented. The design techniques on achieving decreased antenna size and enhanced operating bandwidth in different shaped system ground planes with the antennas printed thereon are proposed. At first, a WWAN antenna integrated with a U-shaped ground plane is presented. Two techniques are applied to achieve WWAN operation with a small antenna size. The first technique is to embed load a proper chip inductor at a proper position in the shorted strip monopole of the antenna. The second one is to use a band-stop matching circuit disposed on the main circuit board of the handset. For the second and third antenna designs, owing to the C-shaped ground plane, much enhanced operating bandwidth for their lower band can be obtained. The second antenna design can cover the LTE/WWAN eight-band operation without increasing the size of the antenna by using a reconfigurable circuit element. The third antenna design integrated with a battery element and a metal midplate for practical application to help reduce the thickness and enhance the robustness of handset. The antenna can cover seven-band LTE/WWAN operation with good radiation characteristics and occupy a small size of 35 x 8 mm2. Finally, the simulated SAR and HAC results are analyzed for bio-compatibility consideration.

No / An investigation of the surface current distribution in a normal-mode helical antenna (NMHA) is reported. This enables precise prediction of the performance of NMHAs, since traditional wire-antenna simulations ignore important details, such as non-uniform and transverse current distributions. A moment-method formulation is developed, using two-dimensional basis functions to represent the total non-uniform surface current distribution over the surface of the wire of the helix. Piecewise-sinusoidal basis functions are employed in two normal directions, with an exact kernel formulation and application of Galerkin's solution method. The numerical solution of the singular integrals associated with self-impedance terms was computed with a very low relative error. The surface current distribution was computed for different helix geometries. It was found that the axially-directed component of the current distribution around the surface of the wire was highly non-uniform and that there was also a significant circumferential current flow due to inter-turn capacitance, both effects that are overlooked by standard filamentary current representations.

Wearable technology has attracted global attention in the last decade and the market is experiencing an unprecedented growth. Wearable devices are designed to be low-profile, light-weight and integrated seamlessly into daily life. Comfort is one of the most important requirements for wearable devices. Fabric based antennas are soft, flexible and can be integrated into clothing. State of the art textile manufacturing techniques such as embroidery, combined with advanced conductive textile materials can be used to fabricate flexible fabric based on-body antennas. In this thesis, the feasibility of using computerised embroidery in the fabrication of wearable, flexible yet functional fabric based antennas have been examined. The fabric based antennas are embroidered using conductive threads. The most suitable materials for fabricating embroidered antennas have been identified. The embroidered fabric based antenna systems including transmission lines and low-profile detachable connectors have been fabricated and their RF performances have been tested. The optimal manufacturing parameters related to embroidery such as stitch direction, spacing and length have been examined. The repeatability of embroidered antennas, cost estimation, and complexity of manufacturing process have been clearly presented. The results can be used to inform and provide guidelines for the development of representative products that can be mass manufactured. A new simulation approach has been introduced to analyse the anisotropic properties of embroidered conductive threads. Simulations and measurements indicate that the performances of embroidered antennas are affected by the anisotropic surface current due to the embroidered stitches. Exploiting the current direction, a novel non-uniform meshed patch antenna has been designed. Representative results show that the non-uniform meshed structure can significantly reduce more than 75% of the usage of conductive materials for the microstrip antennas with negligible effect on the antenna performance.

Bandwidth enhancement of the LTE/WWAN handset antenna achieved by improving the excited surface current distribution in the system ground plane is presented. To achieve this goal, the system ground plane is shaped to be of a C-shape in this thesis. In this case, the longitudinal excited surface current in the system ground plane can have a smooth distribution. The proposed antenna is disposed at one edge of the C-shaped system ground plane, and the antenna comprises a driven monopole strip, a shorted monopole strip and a distributed parallel resonance (PR) circuit. By controlling the resonant frequency of the distributed PR circuit, it can result in dual-resonance excitation of the lowest resonant mode contributed by the shorted monopole strip to cover the LTE700/GSM850/900 operation. The antenna also occupies a small volume of 44 ¡Ñ 10 ¡Ñ 5 mm3 (about 2.2 cm3). Good radiation characteristics of the antenna are also obtained. For practical applications, effects of the electrical connection between the system ground plane and the surrounding metal elements such as the battery¡¦s metal casing and the handset metal midplate are studied. The simulated SAR (Specific Absorption Rate) and HAC (Hearing Aid Compatibility) results are also analyzed.

In this study, RF coil geometries are designed for MRI applications using inhomogeneous main magnetic fields. The current density distributions that can produce the desired RF magnetic field characteristics are obtained on predefined cubic, cylindrical and planar surfaces and Tikhonov, CGLS, TSVD and Rutisbauer regularization methods are applied to match the desired and generated magnetic fields. The conductor paths, which can produce the current density distribution calculated for each surface selection and regularization technique, are determined using stream functions. The magnetic fields generated by the current distributions are calculated and the error percentages between the desired and generated magnetic fields are found. Optimum conductor paths that are going to be produced on cubic, cylindrical and planar surfaces and the required regularization method are determined on the basis of error percentages and realizability of the conductor paths. The optimum conductor path calculated for the planar coil is realized and in the measurement done by LakeShore 3-Channel Gaussmeter, an average error percentage of 11 is obtained between the theoretical and measured magnetic field. The inductance values of the realized RF coil are measured / the tuning and matching capacitance values are calculated and the frequency characteristics of the system is tested using Electronic Workbench 5.1. The quality factor value of the tested system is found to be 162.5, which corresponds to a bandwidth of 39,2 KHz at 6,387 MHz (operating frequency of METU MRI system). The techniques suggested in this study can be used in order to design and realize RF coils on prede&macr / ned arbitrary surfaces for inhomogeneous main magnetic fields. In addition, a hand held MRI device can be manufactured which uses a low cost permanent magnet to provide a magnetic field and generates the required RF field with the designed RF coil using the techniques suggested in this study.

No description available.