Stereometric Design for Desk-Top SFF Fabrication

Solid Freeform Fabrication (SFF) technologies refer to the fabrication of physical parts directly from computer based solid models described by STL (Stereo Lithography) or VRML (Virtual Reality Modeling Language) files generated by Computer-Aided Design (CAD) systems. Most of the SFF processes produce parts by building them layer by layer using a row by row pattern, though it is possible to build the part using other patterns. The SFF technology represents a challenge to designers who, in addition to making decisions concerning optimum shape and functionality of the entire part, have'to take under consideration several other manufacturing factors. These factors cover a wide range of technical issues such as Computer-Aided Design model generation, part description and model slicing files, laser path files, precision of part design, rendering patterns, manufacturing tolerances, thermal expansion and residual stress phenomena. This paper investigates the effect of rendering patterns on the integrity, material characteristics and mechanical properties of the parts prepared by a desk-top SFF device using diode lasers. Fe - Bronze (Cu - Sn) premixed metal powders were used as the starting material. The particle size was about 100 /lm to 200 /lm. Density, tensile strength and microstructure of the parts prepared using different rendering patterns were characterized. The results were analyzed to seek optimal rendering patterns. It was noticed that the samples were strong along the laser scanning direction, while they were weak perpendicular to the scanning direction. These results suggest that the laser scanning patterns should be designed to minimize the warping and maximize the strength of the part in the direction depending on the part's function.Mechanical Engineerin

DEMONSTRATION OF THE EVOLUTION OF SPECTRAL RESOLVING POWER AS A SUPERPOSITION OF HIGHER ORDER DELAYED BEAMS

ABSTRACT Introductory textbooks on basic optics introduce gratings and Fabry-Perot spectrometers separately with the logic that they are based on (i) diffraction and interference or (ii) division of wavefront and division of amplitude. Since in modern classrooms, most of the experiments can be carried out with highly coherent and collimated laser beams, we propose to introduce that gratings and Fabry-Perots are equivaleni to each other by using a "pencil" He-Ne beam illuminating a plane-parallel Fabry-Perot at an angle. It produces a set of distinct and parallel pencil of beams by multiple reflection resembling a multiple slit illumination ' . When these beams are superposed by a focusing lens, a multiple slit diffraction grating like pattern is observed. One can use an appropriately spaced etalon and reflectivity to demonstrate the evolution of resolving power by allowing step-by-step an increasing number of beams to interfere at the focus and slowly resolve the longitudinal modes (or frequencies) ofthe He-Ne laser

Solid Freeform Fabrication at The University of Connecticut

Gas phase solid freeform fabrication research at The University of Connecticut focuses on two main procedures, Selective Area Laser Deposition (SALD) and Selective Area Laser Deposition Vapor Infiltration (SALDVI). A SFF research laboratory is under construction at UCONN, with two new operation systems. These systems possess temperature control, data acquisition capabilities, in-situ video monitoring, and the ability to fabricate SALDVI parts up to four inches wide by four inches long. The procurement of a harmonic generating Nd:YAG six watt laser, capable of producing output at 532, 355, and 266 nanometer wavelengths, as well as a coupled effort with the Photonics Center at the University providing laser diodes at a variety of wavelengths, presents the opportunity to explore interactions involved in gas reactions driven by lasers. Investigations of material systems will include ceramic carbides, nitrides, and their composites, as well as metals.Mechanical Engineerin

Omecamtiv mecarbil in chronic heart failure with reduced ejection fraction, GALACTIC‐HF: baseline characteristics and comparison with contemporary clinical trials

Aims: The safety and efficacy of the novel selective cardiac myosin activator, omecamtiv mecarbil, in patients with heart failure with reduced ejection fraction (HFrEF) is tested in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure (GALACTIC‐HF) trial. Here we describe the baseline characteristics of participants in GALACTIC‐HF and how these compare with other contemporary trials. Methods and Results: Adults with established HFrEF, New York Heart Association functional class (NYHA) ≥ II, EF ≤35%, elevated natriuretic peptides and either current hospitalization for HF or history of hospitalization/ emergency department visit for HF within a year were randomized to either placebo or omecamtiv mecarbil (pharmacokinetic‐guided dosing: 25, 37.5 or 50 mg bid). 8256 patients [male (79%), non‐white (22%), mean age 65 years] were enrolled with a mean EF 27%, ischemic etiology in 54%, NYHA II 53% and III/IV 47%, and median NT‐proBNP 1971 pg/mL. HF therapies at baseline were among the most effectively employed in contemporary HF trials. GALACTIC‐HF randomized patients representative of recent HF registries and trials with substantial numbers of patients also having characteristics understudied in previous trials including more from North America (n = 1386), enrolled as inpatients (n = 2084), systolic blood pressure < 100 mmHg (n = 1127), estimated glomerular filtration rate < 30 mL/min/1.73 m2 (n = 528), and treated with sacubitril‐valsartan at baseline (n = 1594). Conclusions: GALACTIC‐HF enrolled a well‐treated, high‐risk population from both inpatient and outpatient settings, which will provide a definitive evaluation of the efficacy and safety of this novel therapy, as well as informing its potential future implementation

Uncooled silicon carbide sensor producing optical signal

A novel approach will be discussed to design and fabricate sensors for a wide variety of wavelengths by selecting appropriate acceptor levels in a semiconductor material. An n-type 4H-SiC substrate has been doped with gallium using a laser doping method for sensing the MWIR wavelength of 4.21 mm. The incident MWIR photons change the electron densities in the valence band and the acceptor energy levels, modifying the reflectivity of the sensor. This change in the reflectivity is determined with a He-Ne laser as an optical signal and the sensor can be operated at room temperature. The effect of the photon collection optics on the sensor response has been studied. Also the dopant concentration has been found to affect the optical signal. © 2012 SPIE

Laser-Doped Sic As Wireless Remote Gas Sensor Based On Semiconductor Optics

An uncooled SiC-based electro-optic device is developed for gas sensing applications. P-type dopants Ga, Sc, P and Al are incorporated into an n-type crystalline 6H-SiC substrate by a laser doping technique for sensing CO 2, CO, NO2 and NO gases, respectively. Each dopant creates an acceptor energy level within the bandgap of the substrate so that the energy gap between this acceptor level and the valence band matches the quantum of energy emitted by the gas of interest. The photons of the gas excite electrons from the valence band to the acceptor level, which alters the electron density in these two states. Consequently, the refractive index of the substrate changes, which, in turn, modifies the reflectivity of the substrate. This change in reflectivity represents the optical signal of the sensor, which is probed remotely with a laser such as a helium-neon laser. Although the midwave infrared (3-5 μm) band is studied in this paper, the approach is applicable to other spectral bands. © (2012) Trans Tech Publications

Improved Optical Properties And Detectivity Of An Uncooled Silicon Carbide Mid-Wave Infrared Optical Detector With Increased Dopant Concentration

An n-type 4H-SiC substrate is doped with gallium using a laser doping technique and its optical response is investigated at the mid-wave infrared (MWIR) wavelength 4.21μm as a function of the dopant concentration. The dopant creates a p-type energy level of 0.3eV, which is the energy of a photon corresponding to the MWIR wavelength 4.21μm. Therefore, Ga-doped SiC can be used as an uncooled MWIR detector because an optical signal was obtained at this wavelength when the sample was at room temperature. The energy level of the Ga dopant in the substrate was confirmed by optical absorption spectroscopy. Secondary ion mass spectroscopy (SIMS) of the doped samples revealed an enhancement in the solid solubility of Ga in the substrate when doping is carried out by increasing the number of laser scans. A higher dopant concentration increases the number of holes in the dopant energy level, enabling photoexcitation of more electrons from the valence band by the incident MWIR photons. The detector performance improves as the dopant concentration increases from 1.15×1019 to 6.25×1020cm3. The detectivity of the optical photodetector is found to be 1.07×10 10cmHz1/2W1 for the case of doping with four laser passes. © 2012 IOP Publishing Ltd

Novel Sic Detector Based On Optical Signal Instead Of Electrical Signal

A novel SiC optical detector that produces optical signal in contrast to the electric signal generated by conventional electrical detectors. The optical detector is a remote sensor providing response to incident photons from a distant object. The incident photons modify the refractive index and, consequently, the reflectance of the doped SiC by altering the electron densities in the valence band and the acceptor energy levels. This variation in the refractive index or reflectance represents the optical signal as the sensor response, which can be determined with a probe laser such as a He-Ne laser or a light-emitting diode. The sensor can be applied to numerous remote sensing applications including high-temperature or harsh environments due to the optical read-out of the detector response with a probe laser. The effects of different dopants on the detector response for sensing different chemical species, or equivalently imaging in different MWIR wavelengths, have been studied and the dopant concentration has been found to affect the optical signal. These results indicate that a new class of SiC detectorsclassified as optical detectors can be produced for a variety of wavelengths using different dopants for numerous applications

Laser Fabrication Of Silicon Carbide Detector For Gas Sensing And Focal Plane Array Imaging

A Mid-Wave Infra-Red (MWIR) detector is developed by doping an n-type 4H-SiC with an appropriate dopant to create a dopant energy level that matches with a quantum of energy for the wavelength of interest. The detector absorbs the photons and the absorbed photon energy modifies the electron density in the semiconductor by the photoexcitation, leading to changes in the refraction index. Ga is known to have an energy level of 0.30 eV in n-type 4H-SiC substrates, which corresponds to the wavelength 4.21 μm. A detector was fabricated for the MWIR wavelength of 4.21 μm by doping n-type 4H-SiC with Ga. The dopant energy level was confirmed by optical absorption measurements in the wavelength range of 4 to 5 μm. The optical response of the detector to the wavelength 4.21 μm was determined by measuring the reflectivity of the detector using a He-Ne laser of wavelength 632.8 nm as the probe beam. The reflectivity data were used to calculate the variation in the refraction index of the detector at the MWIR wavelength of interest and the selectivity of the detector was established by testing the sensor response to that of an as-received sample. The comparison yielded a distinct change in the refraction index curve for the detector, indicating that the detector is suitable for applications at the wavelength 4.21 μm. © 2009 Copyright SPIE - The International Society for Optical Engineering