This thesis presents an investigation of novel laser assisted micromachining processes that addresses the limitations of micromachining of hard-to-machine materials. Two different laser assisted approaches are used to machine hard metals and high strength ceramics. For hard metals, the basic approach involves localized thermal softening of the workpiece material by focusing a solid-state continuous wave near infra-red laser beam in front of the micro milling tool (end mills of 0.1 to 0.5 mm diameter). By suitably controlling the laser power, spot size and scan speed, it is possible to produce a sufficiently large reduction in the flow strength of the work material and consequently the cutting forces and tool deflections. A force model is developed to predict the cutting forces in Laser Assisted Micro Milling (LAMM) of hard metals. For high strength ceramics, the approach involves use of a two step process. In the first step, thermal cracks are generated in a confined volume by the steep thermal gradients generated by laser irradiation of the workpiece. In the second step, the weakened region is removed by a micro grinding tool. The characterization and modeling of the process serve as bases for users of the two approaches to select optimal process parameters.

Thesis (Ph. D.)--School of Electrical and Computer Engineering, Georgia Institute of Technology, 2004. Directed by Mark G. Allen. / Vita. Includes bibliographical references (leaves 155-166).

A novel technique of coupling near-field evanescent waves by means of variable period subwavelength gratings (1.2 ìm and 1.0 ìm), using a 1.55 ìm infrared semiconductor laser is presented for the use of an optical MEMS accelerometer. The subwavelength gratings were fabricated on both glass and silicon substrates respectively. Optical simulation of the subwavelength gratings was carried out to obtain the maximum coupling efficiency of the two subwavelength gratings; the grating thickness, grating width, and the grating separation were optimized. This was performed for both silicon and glass substrates. The simulations were used to determine the total system noise, including the noise generated from the germanium photodiode, sensitivity, and displacement detection resolution of the coupled subwavelength grating MEMS accelerometer. The coupled gratings were utilized as optical readout accelerometers. The spring/proof mass silicon accelerometer was fabricated using a four mask process, in which the structure was completed using two deep reactive ion etching (DRIE) processes. The designed serpentine spring styles determine the sensitivity of the accelerometer; when the springs are made longer or shorter, thicker or thinner, this directly attributes to the sensitivity of the device. To test function of the example of the devices, the accelerometer is placed on a platform, which permits displacement normal to the plane of the grating. The 1.550 ìm infrared laser is incident on the coupled subwavelength grating accelerometer device and the output intensity is measured using a geranium photodiode. As the platform is displaced, the grating separation between the two gratings changes and causes the output intensity to change. Using the coupled subwavelength grating simulations as a reference to the output intensity change with respect to gap, the mechanical and coupling sensitivity properties of as it relates to acceleration is presented.

Application of mechanical micromachining for fabricating complex three-dimensional (3D) micro-scale features and small parts on a broad range of materials has increased significantly in the recent years. In particular, mechanical micromachining finds applications in manufacturing of biomedical devices, tribological surfaces, energy storage/conversion systems, and aerospace components. Effectively addressing the dual requirements for high accuracy and high throughput for micromachining applications necessitates understanding and controlling of dynamic behavior of micromachining system, including positioning stage, spindle, and the (micro-) tool, as well as their coupling with the mechanics of the material removal process. The dynamic behavior of the tool-collet-spindle-machine assembly, as reflected at the cutting edges of a micro-tool, often determines the achievable process productivity and quality. However, the common modeling techniques (such as beam based approaches) used in macro-scale to model the dynamics of cutting tools, cannot be used to accurately and efficiently in micro-scale case. Furthermore, classical modal testing techniques poses significant challenges in terms of excitation and measurement requirements, and thus, new experimental techniques are needed to determine the speed-dependent modal characteristics of miniature ultra-high-speed (UHS) spindles that are used during micromachining. The overarching objective of this thesis is to address the aforementioned issues by developing new modeling and experimental techniques to accurately predict and analyze the dynamics of micro-scale cutting tools and miniature ultra-high-speed spindles, including rotational effects arising from the ultra high rotational speeds utilized during micromachining, which are central to understanding the process stability. Accurate prediction of the dynamics of micromachining requires (1) accurate and numerically-efficient analytical approach to model the rotational dynamics of realistic micro-tool geometries that will capture non-symmetric bending and coupled torsional/axial dynamics including the rotational/ gyroscopic effects; and (2) new experimental approaches to accurately determine the speed-dependent dynamics of ultra-high-speed spindles. The dynamic models of cutting tools and ultra-high-speed spindles developed in this work can be coupled together with a mechanistic micromachining model to investigate the process stability of mechanical micromachining. To achieve the overarching research objective,first, a new three-dimensional spectral- Tchebychev approach is developed to accurately and efficiently predict the dynamics of (micro) cutting tools. In modeling the cutting tools, considering the efficiently and accuracy of the solution, a unified modeling approach is used. In this approach, the shank/taper/extension sections, vibrational behavior of which exhibit no coupling between different textural motion, of the cutting tools are modeled using one-dimensional (1D) spectral-Tchebychev (ST) approach; whereas the fluted section (that exhibits coupled vibrational behavior) is modeled using the developed 3D-ST approach. To obtain the dynamic model for the entire cutting tool, a component mode synthesis approach is used to `assemble' the dynamic models. Due to the high rotational speeds needed to attain high material removal rate while using micro tools, the gyroscopic/rotational effects should be included in predicting the dynamic response at any position along the cutting edges of a micro-tool during its operation. Thus, as a second step, the developed solution approach is improved to include the effects arising from the high rotational speeds. The convergence, accuracy, and efficiency of the presented solution technique is investigated through several case studies. It is shown that the presented modeling approach enables high-fidelity dynamic models for (micro-scale) cutting-tools. Third, to accurately model the dynamics of miniature UHS spindles, that critically affect the tool-tip motions, a new experimental (modal testing) methodology is developed. To address the deficiency of traditional dynamic excitation techniques in providing the required bandwidth, repeatability, and impact force magnitudes for accurately capturing the dynamics of rotating UHS spindles, a new impact excitation system (IES) is designed and constructed. The developed system enables repeatable and high-bandwidth modal testing of (miniature and compliant) structures, while controlling the applied impact forces on the structure. Having developed the IES, and established the experimental methodology, the speed-dependent dynamics of an air bearing miniature spindle is characterized. Finally, to show the broad impact of the develop modeling approach, a macro-scale endmill is modeled using the presented modeling technique and coupled to the dynamics of a (macro-scale) spindle, that is obtained experimentally, to predict the tool-point dynamics. Specific contributions of this thesis research include: (1) a new 3D modeling approach that can accurately and efficiently capture the dynamics of pretwisted structures including gyroscopic effects, (2) a novel IES for repeatable, high-bandwidth modal testing of miniature and compliant structures, (3) an experimental methodology to characterize and understand the (speed-dependent) dynamics of miniature UHS spindles.

The three-dimensional (3-D) writing capability of a high repetition rate (1 MHz) fiber-amplified femtosecond laser with a wavelength of 522 nm was harnessed together with wet-chemical etching for laser-patterning of 3-D optofluidic microsystems in fused silica glass, by the method of Femtosecond Laser Irradiation followed by Chemical Etching (FLICE). Selective chemical etching of laser irradiated glass with dilute hydrofluoric acid (HF) enabled micro-fabrication of high aspect-ratio embedded micro-channels and fine-period 3-D glass meshes in a 3-D inverted woodpile (IWP) arrangement that permitted high density lab-on-a-chip (LOC) integration of flow channels, reservoirs, glass chromatography columns, and optical circuit devices. Optical waveguides, reservoirs, micro-channels, and IWP structures were first laser patterned and followed by selective wet etching controlled by the polarization orientation of the writing laser. With the laser polarization perpendicular to the scanning direction, the volume nanogratings were aligned perpendicular to glass surfaces to facilitate HF etching and thus created designer shaped micro-channels with the smoothest sidewall surfaces measured at present and terminated with open reservoirs. An array of vertical access holes spaced periodically apart facilitated etching of continuous and highly uniform buried channels of unrestricted length in the glass to interconnect flow channels and reservoirs. Alternatively, laser polarization parallel to the scan direction provided low-loss optical waveguides with nanograting walls resisting the acid etching, providing a convenient one-step laser scanning process of optofluidic microsystems prior to wet etching. For the first time, dual-channel capillary electrophoresis was demonstrated by simultaneous fluorescent detection of separating dyes in a 3-D microsystem having over- and under-passing crossed channels in fused silica. In addition, an on-chip particle counting device based on capillary force to drive analytes through an embedded micro-channel into a calibrated reservoir for particle counting was designed and demonstrated. Further, a new type of glass mesh structure is presented where a 3-D IWP micro-channel array with diamond-like symmetry was integrated inside a micro-channel for capillary electrophoretic chromatography. The FLICE technique thus enables rapid prototyping of fully integrated 3-D optofluidic systems in bulk fused silica glasses for numerous applications, and these provide the groundwork and open new 3-D design approaches for advanced microsystems in the future.

The three-dimensional (3-D) writing capability of a high repetition rate (1 MHz) fiber-amplified femtosecond laser with a wavelength of 522 nm was harnessed together with wet-chemical etching for laser-patterning of 3-D optofluidic microsystems in fused silica glass, by the method of Femtosecond Laser Irradiation followed by Chemical Etching (FLICE). Selective chemical etching of laser irradiated glass with dilute hydrofluoric acid (HF) enabled micro-fabrication of high aspect-ratio embedded micro-channels and fine-period 3-D glass meshes in a 3-D inverted woodpile (IWP) arrangement that permitted high density lab-on-a-chip (LOC) integration of flow channels, reservoirs, glass chromatography columns, and optical circuit devices. Optical waveguides, reservoirs, micro-channels, and IWP structures were first laser patterned and followed by selective wet etching controlled by the polarization orientation of the writing laser. With the laser polarization perpendicular to the scanning direction, the volume nanogratings were aligned perpendicular to glass surfaces to facilitate HF etching and thus created designer shaped micro-channels with the smoothest sidewall surfaces measured at present and terminated with open reservoirs. An array of vertical access holes spaced periodically apart facilitated etching of continuous and highly uniform buried channels of unrestricted length in the glass to interconnect flow channels and reservoirs. Alternatively, laser polarization parallel to the scan direction provided low-loss optical waveguides with nanograting walls resisting the acid etching, providing a convenient one-step laser scanning process of optofluidic microsystems prior to wet etching. For the first time, dual-channel capillary electrophoresis was demonstrated by simultaneous fluorescent detection of separating dyes in a 3-D microsystem having over- and under-passing crossed channels in fused silica. In addition, an on-chip particle counting device based on capillary force to drive analytes through an embedded micro-channel into a calibrated reservoir for particle counting was designed and demonstrated. Further, a new type of glass mesh structure is presented where a 3-D IWP micro-channel array with diamond-like symmetry was integrated inside a micro-channel for capillary electrophoretic chromatography. The FLICE technique thus enables rapid prototyping of fully integrated 3-D optofluidic systems in bulk fused silica glasses for numerous applications, and these provide the groundwork and open new 3-D design approaches for advanced microsystems in the future.

This thesis reports the development of high-performance symmetric and decoupled micromachined gyroscopes for tactical-grade inertial measurement applications. The symmetric structure allows easy matching of the resonance frequencies of the drive and sense modes of the gyroscopes for achieving high angular rate sensitivity / while the decoupled drive and sense modes minimizes mechanical cross-coupling for low-noise and stable operation. Three different and new symmetric and decoupled gyroscope structures with unique features are presented. These structures are fabricated in four different micromachining processes: nickel electroforming (NE), dissolved-wafer silicon micromachining (DWSM), silicon-on-insulator (SOI) micromachining, and silicon-on-glass (SOG) micromachining. The fabricated gyroscopes have capacitive gaps from 1.5&micro / m to 5.5&micro / m and structural layer thicknesses from 12&micro / m to 100&micro / m, yielding aspect ratios up to 20 depending on the fabrication process. The size of fabricated gyroscope chips varies from 1x1mm2 up to 4.2x4.6mm2. Fabricated gyroscopes are hybrid-connected to a designed capacitive interface circuit, fabricated in a standard 0.6&micro / m CMOS process. They have resonance frequencies as small as 2kHz and as large as 40kHz / sense-mode resonance frequencies can be electrostatically tuned to the drive-mode frequency by DC voltages less than 16V. The quality factors reach to 500 at atmospheric pressure and exceed 10,000 for the silicon gyroscopes at vacuum. The parasitic capacitance of the gyroscopes on glass substrates is measured to be as small as 120fF. The gyroscope and interface assemblies are then combined with electronic control and feedback circuits constructed with off-the-shelf IC components to perform angular rate measurements. Measured angular rate sensitivities are in the range from 12&micro / V/(deg/sec) to 180&micro / V/(deg/sec), at atmospheric pressure. The SOI gyroscope demonstrates the best performance at atmospheric pressure, with noise equivalent rate (NER) of 0.025(deg/sec)/Hz1/2, whereas the remaining gyroscopes has an NER better than 0.1(deg/sec)/Hz1/2, limited by either the small sensor size or by small quality factors. Gyroscopes have scale-factor nonlinearities better than 1.1% with the best value of 0.06%, and their bias drifts are dominated by the phase errors in the demodulation electronics and are over 1deg/sec. The characterization of the SOI and SOG gyroscopes at below 50mTorr vacuum ambient yield angular rate sensitivities as high as 1.6mV/(deg/sec) and 0.9mV/(deg/sec), respectively. The NER values of these gyroscopes at vacuum are smaller than 50(deg/hr)/Hz1/2 and 36(deg/hr)/Hz1/2, respectively, being close to the tactical-grade application limits. Gyroscope structures are expected to provide a performance better than 10 deg/hr in a practical measurement bandwidth such as 50Hz, provided that capacitive gaps are minimized while preserving the aspect ratio, and the demodulation electronics are improved.

In this study, the new predictive model for the micro-grinding process was developed by consolidating mechanical and thermal effects within the single grit interaction model at microscale material removal. The size effect of micro-machining was also included in the proposed model. In order to assess thermal effects, the heat partition ratio was experimentally calibrated and compared with the prediction of the Hahn model. Then, on the basis of this predictive model, a comparison between experimental data and analytical predictions was conducted in view of the overall micro-grinding forces in the x and y directions. Although there are deviations in the predicted micro-grinding forces at low depths of cut, these differences are reduced as the depth of cut increases. On the other hand, the optimization of micro machine tools was performed on the basis of the proposed design strategy. Individual mathematical modeling of key parameters such as volumetric error, machine working space, and static, thermal, and dynamic stiffness were conducted and supplemented with experimental analysis using a hammer impact test. These computations yield the optimal size of miniaturized machine tools with the technical information of other parameters.

Thesis (Ph.D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008. / Committee Chair: John Papapolymerou; Committee Chair: Manos Tentzeris; Committee Member: Gordon Stuber; Committee Member: John Cressler; Committee Member: John Z. Zhang; Committee Member: Joy Laskar

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 198-205).