Development of a laser based inspection system for surface defect detection

The objective of this project was to design and develop a laser based inspection system for the detection of surface defects and to assess its potentiality for high-speed online applications. The basic components of this inspection system are a laser diode module as illumination source, a random access CMOS camera as detector unit, and an XYZ translation stage. Algorithms were developed to analyze the data obtained from the scanning of different sample surfaces. The inspection system was based on optical triangulation principle. The laser beam was incident obliquely to the sample surface. Differences in surface height were then detected as a horizontal shift of the laser spot on the sample surface. This enabled height measurements to be taken, as per the triangulation method. The developed inspection system was first calibrated in order to obtain a conversion factor that would render a relationship between the measured spot shift on the sensor and the vertical displacement of the surface. Experiments were carried out on different sample material surfaces: brass, aluminum <ind stainless steel. The developed system is able to accurately generate three-dimensional topographic maps of the defects presented to it in this work. A spatial resolution of approximately 70 pm and a depth resolution of 60 pm were achieved. Characterization o f the inspection system was also performed by measuring the accuracy of distance measurements

Analysis and preliminary design of optical sensors for propulsion control

A fiber-optic sensor concept screening study was performed. Twenty sensor subsystems were identified and evaluated. Two concepts selected for further study were the Fabry-Perot fiber-optic temperature sensor and the pulse-width-modulated phosphorescent temperature sensor. Various designs suitable for a Fabry-Perot temperature sensor to be used as a remote fiber-optic transducer were investigated. As a result, a particular design was selected and constructed. Tests on this device show that spectral peaks are produced from visible white light, and the change in wavelength of the spectral peaks produced by a change in temperature is consistent with theory and is 36 nm/C for the first order peak. A literature search to determine a suitable phosphor for implementing the pulse-width-modulated fiber optic temperature sensor was conducted. This search indicated that such a device could be made to function for temperatures up to approximately 200 C. Materials like ZnCdS and ZnSe activated with copper will be particularly applicable to temperature sensing in the cryogenic to room temperature region. While this sensing concept is probably not applicable to jet engines, the simplicity and potential reliability make the concept highly desirable for other applications

Formation of RDX nanoparticles by rapid expansion of supercritical solution : in situ characterization by laser scattering

Cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), a well-known energetic material, is highly explosive. Reduction of the sensitivity of RDX is desired for safe handling and storage in military applications. Data on the sensitivity of RDX in the 10-1000 µm crystal size range suggested that the impact sensitivity could be further reduced by reduction of the crystal size to the sub-micron or nano-scale (Armstrong, 1990). Recent research with nano-RDX obtained using Rapid Expansion of Supercritical Solutions (RESS) confirmed these expectations (Stepanov, 2005). RESS process appeared to be one out of a few techniques of production of nanoscale energetic materials free of the risk of explosion. Current research was aimed at the understanding of the fundamentals of the RESS process and the mechanism of nanoparticle formation via an in situ particle monitoring and characterization in the RESS jet combined with the characterization of the final product. In this research, nanoparticles of RDX generated by RESS using supercritical CO2 were characterized in situ by a pulse laser light scattering imaging technique using gated ICCD camera. The sensitivity was determined using Rayleigh scattering from air as well as light scattering from standard polystyrene spheres. The size distribution functions of the particles formed in the RESS jet were determined using the calibrated sensitivity. The final diameter of RDX particles at the pre-expansion pressure of 180 bar was 73 nm at the maximum of the size distribution function. Assuming that the particles near the nozzle consisted mainly of CO2 and the log-normal size distribution, the diameter of the particles near the nozzle (7.5 mm from the nozzle) at the distribution maximum was 3.3 µm at the pre-expansion pressure of 180 bar. The number densities of the particles in the RESS jet were determined by counting individual particles in the light scattering images. Based on the measured particle size distributions and the number density of particles along the RESS jet, the mechanism of particle formation in the RESS is discussed. The homogeneous nucleation mechanism is rejected as it fails to explain the large particle size experimentally observed. Instead, a modified spray-drying mechanism is suggested

Measurement techniques and instruments suitable for life-prediction testing of photovoltaic arrays

Array failure modes, relevant materials property changes, and primary degradation mechanisms are discussed as a prerequisite to identifying suitable measurement techniques and instruments. Candidate techniques and instruments are identified on the basis of extensive reviews of published and unpublished information. These methods are organized in six measurement categories - chemical, electrical, optical, thermal, mechanical, and other physicals. Using specified evaluation criteria, the most promising techniques and instruments for use in life prediction tests of arrays were selected

Far-field Super-resolution Chemical Microscopy

Far-field chemical microscopy providing molecular electronic or vibrational fingerprint information opens a new window for the study of three-dimensional biological, material, and chemical systems. Chemical microscopy provides a nondestructive way of chemical identification without exterior labels. However, the diffraction limit of optics hindered it from discovering more details under the resolution limit. Recent development of super-resolution techniques gives enlightenment to open this door behind far-field chemical microscopy. Here, we review recent advances that have pushed the boundary of far-field chemical microscopy in terms of spatial resolution. We further highlight applications in biomedical research, material characterization, environmental study, cultural heritage conservation, and integrated chip inspection.Comment: 34 pages, 8 figures,1 tabl

Mineralogy

The power of mineralogical analysis as a descriptive or predictive technique stems from the fact that only a few thousand minerals are known to occur in nature as compared to several hundred thousand inorganic compounds. Further, all of the known minerals have specific stability ranges in pressure, temperature, an composition. A specific knowledge of the mineralogy of a planets surface or interior therefore allows one to characterize the present or past conditions under which the minerals were formed or have existed. For the purposes of this paper, a slightly broader definition of mineralogy was adopted by including not only crystalline materials found on planetary surfaces, but also ices and classes that can benefit from in situ types of analyses. Both visual examination and the various spectroscopies available for robotic probes to planetary surfaces are discussed