An electro-optic sensor capable of detecting electric fields with a high degree of sensitivity and linearity is fabricated using optical D-fiber. The slab coupled optical sensor utilizes weak coupling and long evanescent interaction with a lithium niobate waveguide. Transmission dips from mode resonances have a linewidth of 0.12 nm and a Q factor of approximately 13,000. These sharp resonances improve device sensitivity and are achieved due to the unique fabrication process possible with D-shaped fibers. The sensor deviates <0.1% from linearity while monitoring fields between 200 V/m and 20 kV/m and promises high sensitivity to fields well beyond that range.
One challenging need for inspection capabilities is in adhesively bonded joints between composite components, a common location of premature failure in aerospace structures. In this work we demonstrate that dynamic, full spectral scanning of FBG sensors embedded in the adhesive bond can identify changes in bond quality through the measurement of non-linear dynamics of the joint. Eighteen lap joint specimens were fabricated with varying manufacturing quality. Ten samples also included fiber Bragg grating (FBG) sensors embedded in the adhesive bond for real-time inspection during a simulated flight condition of these single-lap joints. Prior to testing, pulse phase thermography imaging of the pristine specimens revealed defects such as air bubbles, adhesive thickness variations, and weak bonding surface between the laminate and adhesive. The lap joint specimens were then subjected to fatigue loading, with regular interrogation of the FBG sensors at selected load cycle intervals. The FBG data was collected during vibration loading of the lap joint to represent an in-flight environment. Changes in the lap joint dynamic response, including the transition to non-linear responses, were measured from both the full-spectral and peak wavelength FBG data. These changes were correlated to initial manufacturing defects and the progression of fatigue-induced damage independently measured with pulse phase imaging and visual inspections of the failure surfaces.
We use a single surface relief fiber Bragg grating as a bend sensor with two degrees of freedom. By monitoring the Bragg efficiency and Bragg wavelength, an effective multi-axis bend sensor can be realized.
We use a surface relief fiber Bragg grating with a polydimethylsiloxane layer as a volatile organic compound chemical sensor. Sensitivity of ~4000 ppm is demonstrated of dichloromethane in a gas state.
Fiber Bragg gratings (FBGs) are widely recognized for their unobtrusive sensing character and multiplexing possibilities. Within this article, these advantages are fully exploited through the development of a high-speed full-spectral FBG interrogation system capable of simultaneously reading out a range of FBG sensors. For the first time, the full-spectra of multiplexed FBG sensors are dynamically interrogated up to 100 kHz with a spectral resolution down to 40 pm. The feasibility of this unique sensing system is demonstrated using carbon fiber integrally stiffened panels which are monitored for their structural health. Detailed analysis based on the full-spectral datasets is enabling the assessment of non-linear events involving non-uniform strain distributions, such as impact loading. Moreover, we show real-time visualization of these impact events based on the multiplexed FBG responses.
Since its introduction in 1992, silica has become a widely used filler in passenger tire treads. Compared to carbon black filled compounds, it brings about the benefit of lower rolling resistance and consequently lower vehicle fuel consumption: a global concern nowadays. But replacement of carbon black by silica is rather difficult, since the latter is a polar filler and has a low compatibility with non-polar rubbers. In order to solve the problem of low filler-polymer compatibility and interactions as well as to improve filler dispersion, coupling agents were introduced for silica-filled compounds. These coupling agents, predominantly bi-functional silanes, interact with the hydrophilic silica surface on one side and the hydrophobic rubber chains on the other side, thereby creating chemical coupling. Styrene butadiene rubber (SBR), which is functionalized with polar and/or reactive groups, enables the polymer to directly physically or chemically interact or bond with silica and has the potential to further improve the dispersion of the filler and reduce the hysteresis of the resulting material. In the present work, two functionalized SBRs, one backbone modified with carboxylate moieties and the other one modified with dithiol groups, are used. The effect on dynamic mechanical properties of a silica filled passenger car tire tread compound is studied. In addition, the effect of zinc oxide on the compound properties is discussed, since it can interfere with the silanization reaction and may also react with the functionalized polymers. The results show the significant potential of these modified SBRs to reduce rolling resistance while maintaining wet grip.
A novel system-level model describing a printed wiring board-level, high-fanout, curved aperture optical waveguide H-tree network using volume grating focusing couplers is presented. The intra-chip optical network globally distributes an optical signal to monolithic CMOS receivers for local clock distribution. An estimation for the available optical output power as a function of distribution fanout is presented. Assuming -2 dB optical loss per y-junction, a distribution fanout of 256 can be achieved for an optical input power of 1.23 W.
A new fiber sensor integrated monitor to be used in an embedded instrumentation system is proposed and its operating features are examined. The system integrates a fiber sensor together with a tunable MEMS filter, superluminescent light emitting diode and microcontroller creating a high-speed, low cost, low power smart sensor. The device has applications to a variety of fiber sensing technologies and, as an example, is integrated with a fiber Bragg grating for temperature sensing.
