We operated focus ion beam instrument (FIB) to etch array of cylindrical holes, with the diameter smaller than the wavelength of visible, on the sliver film. The sample was probed with the tungsten light source and the transmission spectrum of visible-NIR range was recorded with traix550 spectrometer with a cooling CCD. The optical extraordinary properties, such as the light can be transmitted through the holes array with the diameter of the hole smaller than the wavelength of the incident light and the enhancement of the efficiency, of the transmission of the subwavelength holes array were discussed. In this study, the factors affected the transmission spectrum of the subwavelength hole array, e.g.: the arrangement of the holes array, the material of the thin film, the diameter of the hole¡Kand so on, were researched. Besides, we modulated the effective dielectric property of the cavity of the subwavelength holes with the thermal evaporation method. It was pointed out that effective dielectric property of the cavity also influenced the optical properties of extraordinary transmission spectrum. We believe that our research was helpful to understand the physical properties of the subwavelength holes array.

We have fabricated a laser array module using a passive self-aligned flip-chip bonding technique. Silicon optical bench was used as a submount with PbSn (Tm=183¢J) solder bump and V-grooves. A 4-channel laser array was flip-chip mounted with coupling efficiency of 56% to cleaved 62.5/125£gm multimode fiber ribbons. The optimum fabrication parameters were bonding time of 20 seconds and bonding load of 10g. The average misalignments were measured to be 1£gm and 5£gm for X and Y directions , respectively.

Over the last few years‚ the number of subscribers of wireless services has increased at an explosive rate. This ever growing demand for wireless communications services is constantly increasing the need for better coverage‚ improved capacity and higher quality service. Smart antennas system is an effective technology for the performance improvement of wireless communications. Switching-beam smart antennas use a number of fixed beams at an antenna site. The system provides a beam that offers the best signal enhancement and interference reduction. Using the approach of dynamic switching-beam antenna system‚ an intelligent sector beam synthesis of adjustable sector width can be established. By doing so‚ traffic load balancing can be achieved, and therefore, system capacity is increased. In this thesis, a beam-pattern synthesis algorithm proposed by M.H. Er is applied to shape array patterns with an adjustable mainlobe width and average sidelobe level reduction. Using an established database of weighting for circular arrays, the proposed smart antennas can adjust suitable sectors for the high dense subscribers not uniformly distributed. Simulation results demonstrate the proposed technique can dramatically improve the performance of traditional switching-beam antennas.

This thesis investigates the performance of pulse charging, which is believed to be superior to constant current charging in some respects, such as charging efficiency and charging speed. The investigation is focused upon the extensively used secondary batteries, lead-acid batteries. The consecutive orthogonal arrays method is applied to search for the optimum operating variables of pulse charging, including pulse amplitude, duty ratio and frequency of the charging current. Unfortunately, the experimental results of consecutive orthogonal arrays reveal that charging efficiency is not obviously affected by pulse amplitude, duty ratio or frequency. Instead, charging rate is dominantly influenced by average charging current. These results indicate that pulse charging scheme is not superior to constant current charging. To compare these two charging schemes further, a series of experiments are carried out to discuss the effects of each operating variables. Unfortunately, no evidence from the experimental results can prove the superiority of pulse charging to constant current charging as formerly documented.

The switched-beam antenna is one type of the smart antennas, which consists of the antenna array and the beamforming network. The four-beam smart antenna generates four beams to cover a 120¢X area, which can be used to improve the carrier-to-interference ratio and the frequency reuse of a cellular system. Due to the attractive features of microstrip antennas such as low profile, easy fabrication, and low cost, we use microstrip antennas as array elements. In this thesis, we propose a novel four-beam beamforming network which consists of a 4¡Ñ4 Butler Matrix and four 180¢X power dividers. This network is able to provide low side-lobe level. A modified Butler Matrix not only simplifies the circuit of the 8¡Ñ8 Butler Matrix, but also meet the requirement of the original Butler Matrix. From the result of measurement, the side-lobe level of each beam of the modified Butler Matrix is less than ¡V10 dB. We also show that this method is applicable to any Butler matrix.

Magnetic bearings use variable attractive forces generated by electromagnetic control coils to support rotating shafts with low friction and no material wear while providing variable stiffness and damping. Rotor deflections are stabilized by position feedback control along two axes using non-contacting displacement sensors. These sensor signals contain sensor runout error which can be represented by a Fourier series composed of harmonics of the spin frequency. While many methods have been proposed to compensate for these runout harmonics, most are computationally intensive and can destabilize the feedback loop. One attractive alternative is to increase the number of displacement sensors and map individual probe voltages to the two independent control signals. This approach is implemented using a circular sensor array and single weighting gain matrix in the present work. Analysis and simulations show that this method eliminates runout harmonics from 2 to n-2 when all sensors in an ideal n-sensor array are operational. Sensor failures result in reduced synchronous amplitude and increased harmonic amplitudes after failure. These amplitudes are predicted using derived expressions and synchronous measurement error can be corrected using an adjustment factor for single failures. A prototype 8-sensor array shows substantial runout reduction and bandwidth and sensitivity comparable to commercial systems. Nonlinear behavior in homopolar magnetic bearings is caused primarily by the quadratic relationship between coil currents and magnetic support forces. Governing equations for a permanent magnet biased homopolar magnetic bearing are derived using magnetic circuit equations and linearized using voltage and position stiffness terms. Nonlinear hardening and softening spring behavior is achieved by varying proportional control gain and frequency response is determined for one case using numerical integration and a shooting algorithm. Maximum amplitudes and phase reversal for this nonlinear system occur at lower frequencies than the linearized system. Rotor oscillations exhibit amplitude jumps by cyclic fold bifurcations, creating a region of hysteresis where multiple stable equilibrium states exist. One of these equilibrium states contains subharmonic frequency components resulting in quasiperiodic rotor motion. This nonlinear analysis shows how nonlinear rotor oscillations can be avoided for a wide range of operation by careful selection of design parameters and operating conditions.

Modern satellite, wireless communications, and radar systems often demand wideband performance for multi-channel and multi-function operations. Among these applications, phased array antennas play an important role. This dissertation covers two wideband phased array antennas, one produces linear polarization and one produces circular polarization. The main difference between these two phased array antennas is the antenna array. For the linearly polarized array, a wideband microstrip line to slotline transition is used to feed a Vivaldi antenna. For the circularly polarized array, a wideband microstrip line to parallel stripline transition is used to feed a spiral antenna. From 3 to 12 GHz, the linearly polarized beam is steered over ± 15º. Since the electromagnetic spectrum is limited and has to be shared, interference is getting serious as more and more wireless applications emerge. Filters are key components to prevent harmonic interference. The harmonic signals can be suppressed by cascading additional lowpass filters or bandstop filters. A bandstop filter combining shunt open stubs and a spurline is proposed for a compact size and a deeper rejection. Two lowpass filters with interdigital capacitors and slotted ground structures are also studied. Harmonic suppression can also be achieved with the modification of bandpass filters. Three conventional bandpass filters with spurious passbands are investigated. The first one is a dual-mode patch bandpass filter. The second passband of the proposed filter is at 2.88fo, where fo is the fundametal frequency. The second filter is an open-loop bandpass filter. Two open stubs are added to achieve high suppression in the second harmonic signal. The suppression of 35 dB at the second harmonic is obtained. For the third filter using half-wavelength open stubs, a T-shaped line is used to replace the quarter-wavelength connecting line. The T-shaped line has the same response with the connecting line in the passband. Furthermore, the T-shaped line works as a bandstop filter at the second harmonic. Finally, a new compact slow-wave resonator and bandpass filters are presented. A simple transmission-line model is used to predict the resonant frequency. Compared with the conventional uniform half-wavelength resonator, the slow-wave resonator shows a 25% size reduction.

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This paper presents a search method of coupling between the laser and fiber , search method to make up through the fiber and the laser inter-position deviation caused optical transmission loss , this search method is applied in the array-alignment is different from the traditional single-alignment , the advantage for the method is simple, through the rough alignment then blind search and angle search , for fiber array find the coupling of the greatest optical power position. In the experiment there are four degrees of freedom to use precise stage to fine-tune the location of fiber array , to reduce losses due to tools to reach precise alignment of purpose ,so we prove our method can achieve the objective of the fiber-optic alignment in our experiments.

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 124-135). Available also in a digital version from Dissertation Abstracts.