Publications

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The purpose of this LDRD was to study the effect of steady-state neutron and gamma irradiation on the transmission of waveguides designed to operate well in the near- or mid-IR region of the electromagnetic spectrum. In this context, near-IR refers to the region between 1.3 {mu}m and about 2.4 {mu}m, and mid-IR between 3.0 {mu}m and 4.5 {mu}m. Such radiation environments could exist in nuclear power plants or nuclear weapons. Pulsed and steady-state radiation effects had been extensively studied on silica-based optical fibers because they have been the most readily available, most widely used in communications and sensing, and the least expensive. However, silica-based fibers do not transmit well beyond about 1.8 {mu}m and they are virtually opaque in the mid-IR. The mid-IR, as defined above, and beyond, is where vibrational spectroscopy is carried out. This type of sensing is one important application of infrared optical fibers.

Like microelectronic circuits, microelectromechanical systems (MEMS) devices are susceptible to damage by electrostatic discharge (ESD). At Sandia National Laboratories, polysilicon electrothermal MEMS actuators have been subjected to ESD pulses to examine that susceptibility. Failures, in the form of cracks at points of high stress concentration, occurred that could not be explained by thermal degradation of the polysilicon caused by excessive heating, or by excessive displacement of the legs of the actuator of the same nature that occur in normal operation. One hypothesis presented in this paper is that the internal magnetic forces between the legs of the actuator, resulting from the ESD-associated high current pulses, might produce vibrations of amplitude sufficient to produce these cracks. However, a dynamic analysis based on simple beam theory indicated that such cracks are unlikely to occur, except under rather extreme conditions. On the other hand, these same current pulses also cause resistive heating of the legs and, therefore, thermally induced compression that can lead to buckling. Buckling stresses, particularly when augmented by magnetic forces, can readily explain failure. Both the magnetic and thermal analyses were performed using the human body model and the machine model of ESD. A justification for ignoring shuttle motion and eddy currents induced in the substrate during the ESD pulse is presented, as well. Copyright © 2007 by ASME.

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In this paper, we discuss the primary characteristics and pitfalls associated with the use of Bragg Gratings for distributed temperature sensing, with particular attention to time-division multiplexing (TDM). Two pitfalls are intrinsic to a serial array of such gratings that use TDM: spectral shadowing and crosstalk. Two others involve strain in the fiber that masquerades as temperature and that could affect other methods of interrogating the gratings, in addition to TDM.

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This report describes work performed for the development of a fiber-optic shock position sensor used to measure the location of a shock front in the neighborhood of a nuclear explosion. Such a measurement would provide a hydrodynamic determination of nuclear yield. The original proposal was prompted by the Defense Nuclear Agency`s interest in replacing as many electrical sensors as possible with their optical counterparts for the verification of a treaty limiting the yield of a nuclear device used in underground testing. Immunity to electromagnetic pulse is the reason for the agency`s interest; unlike electrical sensors and their associated cabling, fiber-optic systems do not transmit to the outside world noise pulses from the device containing secret information.