A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Hypersonic Application of Focused Schlieren and Deflectometry(2010) VanDercreek, Colin Paul; Yu, Kenneth H; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A non-intrusive diagnostic capability for determining the hypersonic shock and boundary layer structure was developed, installed, and successfully tested at the AEDC Hypervelocity Tunnel 9. This customized diagnostic involves a combination of a focused schlieren system, which relies on creating multiple virtual light sources using a Fresnel lens and a source grid, and a deflectometry system, which uses the focused schlieren and a photomultiplier tube. It was used for obtaining spatially resolved images of density gradients with a depth of focus less than one centimeter, while allowing high frequency measurements of density fluctuations. The diagnostic was applied in investigating the second-mode instability waves present in the boundary layer of a sharp-nosed cone submerged in a Mach 10 flow. The waves were successfully imaged and their frequencies were measured even though the flow density was below 0.01 kg/m^3 and the frequencies over 200 kHz. This adds a new capability to hypersonic testing.Item OPTIMAL CONTROL OF OBJECTS ON THE MICRO- AND NANO-SCALE BY ELECTROKINETIC AND ELECTROMAGNETIC MANIPULATION: FOR BIO-SAMPLE PREPARATION, QUANTUM INFORMATION DEVICES AND MAGNETIC DRUG DELIVERY(2010) Probst, Roland; Shapiro, Benjamin; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis I show achievements for precision feedback control of objects inside micro-fluidic systems and for magnetically guided ferrofluids. Essentially, this is about doing flow control, but flow control on the microscale, and further even to nanoscale accuracy, to precisely and robustly manipulate micro and nano-objects (i.e. cells and quantum dots). Target applications include methods to miniaturize the operations of a biological laboratory (lab-on-a-chip), i.e. presenting pathogens to on-chip sensing cells or extracting cells from messy bio-samples such as saliva, urine, or blood; as well as non-biological applications such as deterministically placing quantum dots on photonic crystals to make multi-dot quantum information systems. The particles are steered by creating an electrokinetic fluid flow that carries all the particles from where they are to where they should be at each time step. The control loop comprises sensing, computation, and actuation to steer particles along trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. I address following aspects of this technology. First I explain control and vision algorithms for steering single and multiple particles, and show extensions of these algorithms for steering in three dimensional (3D) spaces. Then I show algorithms for calculating power minimum paths for steering multiple particles in actuation constrained environments. With this microfluidic system I steer biological cells and nano particles (quantum dots) to nano meter precision. In the last part of the thesis I develop and experimentally demonstrate two dimensional (2D) manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets, with a view towards enabling feedback control of magnetic drug delivery to reach deeper tumors in the long term. To this end, I developed and experimentally demonstrated an optimal control algorithm to effectively manipulate a single ferrofluid droplet by magnetic feedback control. This algorithm was explicitly designed to address the nonlinear and cross-coupled nature of dynamic magnetic actuation and to best exploit available electromagnetic forces for the applications of magnetic drug delivery.Item Application of porous silicon in terahertz technology(2010) Lo, Shu-Zee Alencious; Murphy, Thomas E; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis, we discuss our efforts in developing porous silicon based devices for terahertz signal processing. In the first stage of our research, we demonstrate that porous silicon samples fabricated from highly doped p-type silicon can have adjustable refractive indices ranging from 1.5-2.1 and can exhibit a resistivity that is four orders of magnitude higher than that of the silicon wafer from which they were made. We show that the porous silicon becomes stable and relatively lossless after thermal oxidation. The partially oxidized porous silicon is shown to exhibit a smooth absorption spectrum, with low absorption loss of <10 cm^-1 over the entire terahertz spectrum. As a proof of concept, we fabricated, for the first time, a porous silicon based multilayered Bragg filter with reflectance of 93% and full-width at half-maximum bandwidth of 0.26 THz. Compared with other multilayered filtering techniques, porous silicon has the advantage that it can be easily fabricated, and offers the possibility of forming multilayer and graded index structures for more advanced filters. The large surface area of nanoporous silicon makes it an especially attractive platform for applications in biochemical detection and diagnostics As part of our effort in developing terahertz waveguide for biosensing, we reported the world's first porous silicon based terahertz waveguide using the principle of surface plasmon polaritons. The effect of porous silicon film thickness on the propagation of surface plasmons is explained theoretically in this thesis and is found to be in good agreement with experimental results.Item EFFICIENT SIMULATION OF ELECTRON TRAPPING IN LASER AND PLASMA WAKEFIELD ACCELERATION(2009) Morshed, Sepehr; Antonsen, Thomas M; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Plasma based laser Wakefield accelerators (LWFA) have been a subject of interest in the plasma community for many years. In LWFA schemes the laser pulse must propagate several centimeters and maintain its coherence over this distance, which corresponds to many Rayleigh lengths. These Wakefields and their effect on the laser can be simulated in the quasistatic approximation. The 2D, cylindrically symmetric, quasistatic simulation code, WAKE is an efficient tool for the modeling of short-pulse laser propagation in under dense plasmas [P. Mora & T.M. Antonsen Phys. Plasmas 4, 1997]. The quasistatic approximation, which assumes that the driver and its wakefields are undisturbed during the transit time of plasma electrons, through the pulse, cannot, however, treat electron trapping and beam loading. Here we modify WAKE to include the effects of electron trapping and beam loading by introducing a population of beam electrons. Background plasma electrons that are beginning to start their oscillation around the radial axis and have energy above some threshold are removed from the background plasma and promoted to "beam" electrons. The population of beam electrons which are no longer subject to the quasistatic approximation, are treated without approximation and provide their own electromagnetic field that acts upon the background plasma. The algorithm is benchmarked to OSIRIS (a standard particle in cell code) simulations which makes no quasistatic approximation. We also have done simulation and comparison of results for centimeter scale GeV electron accelerator experiments from LBNL. These modifications to WAKE provide a tool for simulating GeV laser or plasma wakefield acceleration on desktop computers.Item IN-SITU MEASUREMENT OF EPITHELIAL TISSUE OPTICAL PROPERTIES: DEVELOPMENT AND IMPLEMENTATION OF DIFFUSE REFLECTANCE SPECTROSCOPY TECHNIQUES(2009) Wang, Quanzeng; Wang, Nam Sun; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cancer is a severe threat to human health. Early detection is considered the best way to increase the chance for survival. While the traditional cancer detection method, biopsy, is invasive, noninvasive optical diagnostic techniques are revolutionizing the way that cancer is diagnosed. Reflectance spectroscopy is one of these optical spectroscopy techniques showing promise as a diagnostic tool for pre-cancer detection. When a neoplasia occurs in tissue, morphologic and biochemical changes happen in the tissue, which in turn results in the change of optical properties and reflectance spectroscopy. Therefore, a pre-cancer can be detected by extracting optical properties from reflectance spectroscopy. This dissertation described the construction of a fiberoptic based reflectance system and the development of a series of modeling studies. This research is aimed at establishing an improved understanding of the optical properties of mucosal tissues by analyzing reflectance signals at different wavelengths. The ultimate goal is to reveal the potential of reflectance-based optical diagnosis of pre-cancer. The research is detailed in Chapter 3 through Chapter 5. Although related with each other, each chapter was designed to become a journal paper ultimately. In Chapter 3, a multi-wavelength, fiberoptic system was constructed, evaluated and implemented to determine internal tissue optical properties at ultraviolet A and visible wavelengths. A condensed Monte Carlo model was deployed to simulate light-tissue interaction and generate spatially distributed reflectance data. These data were used to train an inverse neural network model to extract tissue optical properties from reflectance. Optical properties of porcine mucosal and liver tissues were finally measured. In Chapter 4, the condensed Monte Carlo method was extended so that it can rapidly simulate reflectance from a single illumination-detection fiber thus enabling the calculation of large data sets. The model was implemented to study spectral reflectance changes due to breast cancer. The effect of adding an illumination-detection fiber to a linear array fiber for optical property determination was also evaluated. In Chapter 5, an investigation of extracting the optical properties from two-layer tissues was performed. The relationship between spatially-resolved reflectance distributions and optical properties in two-layer tissue was investigated. Based on all the aforementioned studies, spatially resolved reflectance system coupled with condensed Monte Carlo and neural network models was found to be objective and appear to be sensitive and accurate in quantitatively assessing optical property change of mucosal tissues.Item An Optical MEMS Sensor for On-chip Catechol Detection(2008-12-08) Dykstra, Peter Hume; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis reports the successful design, fabrication and testing of an optical MEMS sensor for the detection of the toxic phenol, catechol. Catechol's presence in food and drinking water posses a health concern due to its harmful effects on cell respiration. By-products of catechol oxidation have demonstrated increased absorbance changes in a chitosan film in the UV and near UV range. Our reported sensor utilizes patterned SU-8 waveguides and a microfluidic channel to deliver catechol samples to an electrodeposited chitosan film for absorbance measurements at 472 nm. Concentrations as low as 1 mM catechol are detected while control experiments including ascorbic acid display no measurable response. By using optical detection methods, our device does not suffer from many of the problems which plague conventional electrochemical based sensors.Item Analysis and Experimental Demonstration of Conformal Adaptive Phase-Locked Fiber Array for Laser Communications and Beam Projection Applications(2008-10-07) Liu, Ling; Vorontsov, Mikhail A.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The primary goal of this research is the analysis, development, and experimental demonstration of an adaptive phase-locked fiber array system for free-space optical communications and laser beam projection applications. To our knowledge, the developed adaptive phase-locked system composed of three fiber collimators (subapertures) with tip-tilt wavefront phase control at each subaperture represents the first reported fiber array system that implements both phase-locking control and adaptive wavefront tip-tilt control capabilities. This research has also resulted in the following innovations: (a) The first experimental demonstration of a phase-locked fiber array with tip-tilt wavefront aberration compensation at each fiber collimator; (b) Development and demonstration of the fastest currently reported stochastic parallel gradient descent (SPGD) system capable of operation at 180,000 iterations per second; (c) The first experimental demonstration of a laser communication link based on a phase-locked fiber array; (d) The first successful experimental demonstration of turbulence and jitter-induced phase distortion compensation in a phase-locked fiber array optical system; (e) The first demonstration of laser beam projection onto an extended target with a randomly rough surface using a conformal adaptive fiber array system. Fiber array optical systems, the subject of this study, can overcome some of the drawbacks of conventional monolithic large-aperture transmitter/receiver optical systems that are usually heavy, bulky, and expensive. The primary experimental challenges in the development of the adaptive phased-locked fiber-array included precise (<5>microrad) alignment of the fiber collimators and development of fast (100kHz-class) phase-locking and wavefront tip-tilt control systems. The precise alignment of the fiber collimator array is achieved through a specially developed initial coarse alignment tool based on high precision piezoelectric picomotors and a dynamic fine alignment mechanism implemented with specially designed and manufactured piezoelectric fiber positioners. Phase-locking of the fiber collimators is performed by controlling the phases of the output beams (beamlets) using integrated polarization-maintaining (PM) fiber-coupled lithium niobate phase shifters. The developed phase-locking controllers are based on either the SPGD algorithm or the multi-dithering technique. Subaperture wavefront phase tip-tilt control is realized using piezoelectric fiber positioners that are controlled using a computer-based SPGD controller. Both coherent (phase-locked) and incoherent beam combining in the fiber array system are analyzed theoretically and experimentally. Two special fiber-based beam-combining testbeds have been built to demonstrate the technical feasibility of phase-locking compensation prior to free-space operation. In addition, the reciprocity of counter-propagating beams in a phase-locked fiber array system has been investigated. Coherent beam combining in a phase-locking system with wavefront phase tip-tilt compensation at each subaperture is successfully demonstrated when laboratory-simulated turbulence and wavefront jitters are present in the propagation path of the beamlets. In addition, coherent beam combining with a non-cooperative extended target in the control loop is successfully demonstrated.Item STUDIES OF THE OPTICAL PROPERTIES OF PLASMONIC NANOSTRUCTURES(2007-11-28) Hung, Yu-Ju; Davis, Christopher C; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Various properties of Surface Plasmon Polaritons (SPPs) at the interface between a layer of PMMA (polymethyl methacrylate) gratings and a 50 nm thick gold film have been studied. Gold has a negative dielectric constant at visible wavelength range which results in negative refraction phenomenon without medium of both permittivity () and permeability () constants negative. A direct observation of negative refraction has been demonstrated. It verifies our assumption that in the 1-D stripe PMMA gratings on top of a gold film, SPPs experience negative group velocity and positive phase velocity. With this criterion, negative refraction is the natural choice in Snell's Law. Correspondingly, it was previously claimed that with a highly anisotropic layered structure (metal/dielectric stack), the high spatial frequency k vectors scattered from an object can be preserved in an imaging system and the conventional diffraction limit is defeated. In this thesis, this kind of layered structure, a so-called "hyperlens" or "superlens", has been experimentally demonstrated and the results verify theoretical predictions. A proof of concept on corner resonators has also been demonstrated. Four squares with PMMA/Au and Air/Au are arranged so that SPPs are trapped in the corner. It shows the possibility of making a tiny resonator with zero phase paths in the cavity. An experiment utilizing the field enhancement of SPPs is designed. A surface field is excited on R6G(Rhodamine 6G, fluorophore)/PMMA gratings/Au substrate. The enhanced pumping light pushes up the emission intensity 10-fold or higher compared to a sample with a R6G/PMMA gratings/Glass platform, a transparent substrate. This device with a R6G/PMMA gratings/Au platform has the advantage that the emission light is converted to the normal direction; the collection efficiency is high and the directivity makes the examination easy under a commercial fluorescence optical microscope. This device shows the potential of R6G/PMMA/Au platforms in gene chip industry.Item Indium Phosphide MEMS Cantilever Waveguides with Integrated Readout for Chemical Sensing(2007-11-26) Siwak, Nathan Paul; Ghodssi, Reza; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents the development towards an integrated, monolithic, micro-electro-mechanical system (MEMS) cantilever waveguide resonator chemical sensor using the III-V semiconductor indium phosphide (InP). Waveguide cantilevers with resonant frequencies as high as 5.78 MHz, a quality factor of 340, and a sensitivity of 4.4x10^16 Hz/g are shown for the first time in this system. The first demonstration of vapor detection using the sensor platform is performed utilizing an organic semiconductor Pentacene absorbing layer. Vapors are measured from mass shifts of 6.56x10^-14 and 7.28x10^-14 g exhibiting a mass detection threshold of 5.09x10^-15 g. The design, fabrication, and testing of an integrated waveguide PIN photodetector with an In0.53Ga0.47As absorbing layer is reported. Dark currents as low as 8.7 nA are measured for these devices. The first demonstration of a resonating cantilever waveguide measurement is also performed using the monolithically integrated waveguide photodiodes with uncertainty of less than ± 35 Hz. Finally, a future outlook is presented for this monolithic InP sensor system.Item Generation of a CW Local Oscillator Signal Using a Stabilized Injection Locked Semiconductor Laser(2007-04-25) Pezeshki, Jonah Massih; Goldhar, Julius; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In high speed-communications, it is desirable to be able to detect small signals while maintaining a low bit-error rate. Conventional receivers for high-speed fiber optic networks are Amplified Direct Detectors (ADDs) that use erbium-doped fiber amplifiers (EDFAs) before the detector to achieve a suitable sensitivity. In principle, a better method for obtaining the maximum possible signal to noise ratio is through the use of homodyne detection. The major difficulty in implementing a homodyne detection system is the generation of a suitable local oscillator signal. This local oscillator signal must be at the same frequency as the received data signal, as well as be phase coherent with it. To accomplish this, a variety of synchronization techniques have been explored, including Optical Phase-Lock Loops (OPLL), Optical Injection Locking (OIL) with both Fabry-Perot and DFB lasers, and an Optical Injection Phase-Lock Loop (OIPLL). For this project I have implemented a method for regenerating a local oscillator from a portion of the received optical signal. This regenerated local oscillator is at the same frequency, and is phase coherent with, the received optical signal. In addition, we show that the injection locking process can be electronically stabilized by using the modulation transfer ratio of the slave laser as a monitor, given either a DFB or Fabry-Perot slave laser. We show that this stabilization technique maintains injection lock (given a locking range of ~1GHz) for laser drift much greater than what is expected in a typical transmission system. In addition, we explore the quality of the output of the slave laser, and analyze its suitability as a local oscillator signal for a homodyne receiver.
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