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Bend loss from optical fibers can have positive applications, which need to be characterized and related to fiber curvature in a systematic approach to be useful. One potential application for optical fibers is a shape sensor for tracking flexible bodies in remote access environments, such as in endoscopy or boroscopy. We conducted a review of bend-loss characterization and evaluated several methods for characterizing bend loss in multimode optical fibers for an endoscopic shape-tracking application. Specifically, closed-form equation-based methods and numerical simulations were examined. Beam propagation method (BPM) simulations were determined to be the most applicable characterization tool. Results from simulations using BPM software were compared to experimentally obtained data. BPM simulation was sufficiently accurate for modeling 50 [micro]m fibers but impractical for larger, multimode fibers. OCIS codes: 060.2370, 280.4788, 170.2150, 080.1510.

Multilayer thin-film structures in butterfly wing scales produce a colorful iridescence from reflected sunlight. Because of optical phenomena, changes in the angle of incidence of light and the viewing angle of an observer result in shifts in the color of butterfly wings. Colors ranging from green to purple, which are due to nonplanar specular reflection, can be observed on Papilio blumei iridescent scales. This refers to a phenomenon in which the curved surface patterns in the thin-film structure cause the specular component of the reflected light to be directed at various angles while affecting the spectral reflectivity at the same time by changing the optical path length through the structure. We determined the spectral reflectivities of P. blumei iridescent scales numerically by using models of a butterfly scale microstructure and experimentally by using a microscale-reflectance spectrometer. The numerical models accurately predict the shifts in spectral reflectivity observed experimentally.

The link between the optical characteristics and temperature distributions in multilayer thin film structures exposed to thermalradiation was investigated. The results showed that film thickness, geometry and material characteristics determined the correlation. Variation in film thickness resulted in local minima and maxima in reflectivity and temperature distribution of these structures. This behavior was brought about by a cross correlation phenomenon that occurred when the optical thickness of the films was equal over a broad radiation spectrum.

The rapid growth of microelectromechanical systems (MEMS) industry has introduced a need for the characterization of thin film properties at all temperatures encountered during fabrication and application of the devices. A technique was developed to use MEMS test structures for the determination of the difference in thermal expansion coefficients (α) between poly-Si and SiO[sub 2] thin films at high temperatures. The test structure consists of multilayered cantilever beams, fabricated using standard photolithography techniques. An apparatus was developed to measure the thermally induced curvature of beams at high temperatures using imaging techniques. The curvatures measured were compared to the numerical model for multilayered beam curvature. The model accounts for the variation in thermomechanical properties with temperature. The beams were designed so that the values of Young’s moduli had negligible effect on beam curvature; therefore, values from literature were used for E[sub Si] and E[sub SiO[sub 2]] without introducing significant error in curvature analysis. Applying this approximation, the difference in thermal expansion coefficients between α[sub Si] and α[sub SiO[sub 2]] was found to increase from 2.9×10[sup -6] to 5.8×10[sup -6] °C[sup -1] between room temperature and 900 °C. These results suggest that the α for poly-Si thin films may be significantly higher than values for bulk, crystalline Si. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the use of multilayer thin-film structures with a radiant line heat source to recrystallize and improve the quality of specific films in the structure. Illustration of the silicon-on-insulator wafer being processed by zone-melting recrystallization with a graphite strip heater; Information on incident radiation; Heat conduction in the wafer.

Presents a study which developed a numerical model that considers changes in thermal and radiation properties during zone-melting-recrystallization processing of silicon-on-insulator film structures with a graphite strip laser. Discussion of the physical and numerical model; Effect of the strip size and distance from the strip to the wafer on temperature profile and melt-zone width in the silicon film; Conclusion.

A colonoscopy's near-blind navigation process frequently causes disorientation for the scope operator, leading to harm for the patient. Navigation can be improved if real-time colonoscope shape, location, and orientation information is provided by a shape-tracking aid, such as a fiber optic bend sensor. Fiber optic bend sensors provide advantages over conventional electromechanical shape-trackers, including low cost and ease of integration. However, current fiber optic bend sensors lack either the ability to detect both bending direction and curvature, or the ability to detect multiple localized bends. An inexpensive multifiber bend sensor was developed to aid users in navigation during colonoscopy. The bend sensor employs active-cladding optical fibers modified with fluorescent quantum dots, bandpass filters, and a complementary metal-oxide-semiconductor imager as key components. Results from three-fiber sensors demonstrate the bend sensor's ability to measure curvature (error of 0.01 mm), direction (100% accuracy), and location (predetermined distance) of a bend in the fiber bundle. Comparison with spectroscopy data further confirmed the accuracy of the bending direction measurement for a three-fiber sensor. Future work includes improvements in fiber manufacturing to increase sensor sensitivity and consistency. An expanded 31 fiber bundle would be needed to track the full length of a colonoscope. [ABSTRACT FROM AUTHOR]

Results of in situ measurements of the thermomechanical properties of polyimides used in the microelectronic packaging industry are presented. During the formation of polymer layers and their subsequent use, there are several thermomechanical effects which can affect the electronic packages performance. Specifically, thermal loading of the structure results in elastic and inelastic effects such as relaxation. The time and temperature dependent relaxation behavior of polyimides in multilayer structures were investigated to determine their thermomechanical properties. Both a numerical model and experimental analysis were used to determine the curvature change of multilayer structures during manufacturing. The numerical model, which is based on Maxwell's model, characterizes the stress relaxation behavior of thermoplastics. The changes in stress over time for quartz-polyimide-aluminum and quartz-polyimide-germanium heterostructures were obtained. From these observations, the relaxation time constant, activation energy, and viscosity-to-shear-modulus ratio were determined for the polyimide [ABSTRACT FROM PUBLISHER]

An innovative system was designed to optically measure the curvature of microelectromechanical system at high temperatures. The system takes advantage of the limited numerical aperture of the imaging system to detect the curvature of cantilever beams. Images of the beam are used to determine beam curvature at high temperatures of up to 850 °C by analyzing the apparent change in beam length as seen by the camera during an experimental trial. The system is designed to operate at very high temperatures, which is difficult in conventional microscale curvature measurement techniques such as scanning electron microscopy or stylus profilometry due to excess heating of peripheral equipment. The system can measure curvatures as small as 300 m-1, which corresponds to tip deflections of 1.5 μm for a 100 μm beam. The resolution of the system is limited by the image resolution of the charge-coupled device camera, and increases at large curvatures. The maximum curvature that can be measured by the system is limited by the increase in system resolution, and is estimated to be 4500 m-1, corresponding to 22 μm deflection for a 100 μm beam. The apparatus was demonstrated to measure the thermally induced curvature of multilayered thin-film cantilever beams. The beams bend at high temperatures due to mismatch in thermal expansion coefficients between the layers. One innovative application of such curvature measurement is the determination of thermophysical properties of thin films at elevated temperatures. This article presents the experimental setup and operational theory of apparatus, as well as curvature measurements obtained by the system. The thermal expansion coefficient of polycrystalline silicon, determined from the curvature measurements, are also discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article describes the design and operation of a new thermal analysis instrument which uses microwaves to simultaneously heat and detect thermally induced transformations in samples with masses in the range of 50 mg to 0.5 g. The data acquisition and control software developed for the instrument support a range of experimental techniques including constant power, linearly ramped power, linearly ramped temperature, and various modulated methods. Microwave thermal analysis utilizes the fact that physical or chemical alterations in a material, caused by processes such as melting, decomposition, or solid-solid phase changes, cause variations in its dielectric properties. These can be revealed by a variety of means including changes in the sample temperature, the differential temperature, or the shape of the power profile during linear heating experiments. The scope of the instrument is demonstrated with the decomposition of basic copper carbonate. The large temperature increase (∼100 °C) observed on the formation of the strongly coupling oxide indicates the potential sensitivity of using the thermal effects of dielectric changes as a means of detection. Further fine detail can be revealed by the use of derivative plots of either the applied power or the temperature. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

BACKGROUND: Patients with juxtarenal aortic aneurysms who are unfit for open repair may be considered for fenestrated endovascular repair (fenEVAR). We report our initial experience with fenEVAR. METHODS: We reviewed the data on all our patients receiving fenEVAR for juxtarenal aortic aneurysms. RESULTS: Eight patients, average age 75 years, underwent fenEVAR. Endografts were designed from details obtained from preoperative computed tomography angiography. There were 6 grafts with superior mesenteric scallops and bilateral renal fenestrations, 1 with bilateral renal scallops, and 1 with a single renal fenestration. All patients survived 30 days. There was no renal failure requiring dialysis. At 10 weeks, 1 patient died from acute intestinal ischemia and multisystem organ failure, and another died from respiratory failure. CONCLUSIONS: It is feasible to offer fenEVAR to patients who are poor candidates for open repair. However, these procedures are technically challenging. Early outcomes are less favorable than other aortic endovascular procedures. [ABSTRACT FROM AUTHOR]

Abstract: Background: Patients with thoracic aorta injuries (TAI) present a unique challenge. The purpose of this study was to review the outcomes of thoracic endovascular aortic repair (TEVAR) in patients with TAI. Methods: A retrospective chart review of all patients admitted for TEVAR for trauma was performed. Results: In a 5-year period, 19 patients (6 women and 13 men; average age, 42 y) were admitted to our trauma center with TAI. Mechanism of injury was a motor vehicle crash in 12 patients, motorcycle crash in 2 patients, automobile-pedestrian accident in 2 patients, 1 fall, 1 crush injury, and 1 stab wound to the back. A thoracic endograft was used in 6 patients and proximal aortic cuffs were used in 13 patients (68%). One patient (5%) died. There were no strokes, myocardial infarctions, paraplegia, or renal failure. Conclusions: TEVAR for TAI appears to be a safe option for patients with multiple injuries. TEVAR in young patients is still controversial because long-term endograft behavior is unknown. [Copyright &y& Elsevier]

Abstract: Background: An increasing number of elderly patients present for elective and emergent vascular procedures. The purpose of this study was to analyze the 30-day and long-term outcome of patients in their 10th decade of life undergoing vascular procedures. Methods: We reviewed the outcomes of all patients in the 10th decade of life included in our registry. Results: In a 15-year period, there were 176 patients, 102 women and 74 men, with a mean age of 92 (range 90–102) undergoing 196 vascular operations for acute and chronic limb ischemia, aortic and popliteal aneurysms, and carotid stenosis. Overall morbidity and mortality rates were comparable as well as the return to preoperative functional status. Conclusions: Patients in their 90s can safely undergo vascular procedures with reasonable early outcomes. Most patients return to their preoperative status. Age alone should not be a determinant in refusing surgery in this age group. [Copyright &y& Elsevier]