Improving the reliability of multiplexed fiber optic low-coherence interferometric sensors by use of novel twin-loop network topologies

Abstract

Novel twin-loop network topologies for multiplexing fiber optic low-coherence reflectometric sensors are proposed and theoretically analyzed. The sensing fibers are made by connecting segments of standard single-mode fibers with partial reflections at the fiber joints and are completely passive. Absolute length measurement can be made for each segment of the sensing fiber so that strain or temperature distribution along the entire sensing fiber can be derived. It is expected that novel topologies would help as to improve the reliability of the sensor network by providing multiple accesses to each of the sensing segment so that most of the sensing segments can still be interrogated even when one or more point breakages occur along the transmission fibers. A nine-sensor twin-loop sensing network was constructed and experimentally tested by use of a Michelson low-coherence interferometer, and the results obtained agree with our theoretical prediction. The novel network topologies may be used for large-scale smart structure applications where breakages of transmission fibers may occur during the stages of sensor imbedding, installation, and structure-in-service cycles.

A New Method for Total Fat Detection in Raw Milk Based on Dual Low-Coherence Interferometer

“…The proposed method is based on a dual low-coherence Fabry–Perot cavity [14,19,20]. The optical paths and light interaction are presented in Figure 2.…”

“…It is important to mention that the intensity variations of the electric vector are strongly related to the reflectivities in the EFPI cavity. The interferences generated false(Ir1 and Ir2false) are provided by the EFPI and the same cavity generates a dual response by the electric field directions [20]. However, when the interference signal is circulating into the loop, the light is once again affected by the milk solution.…”

Electroplated CoPt magnets for actuation of stiff cantilevers

“…Therefore, for optimizing the design with B 0 = B 0 z 0 , we need only consider the magnetic torque τ y with magnetization fixed in the x direction (M = M x x 0 ), i.e., Eq. (18). Values of the tip deflection for different cantilevers can be calculated using Eq.…”

“…Values of the tip deflection for different cantilevers can be calculated using Eq. (18) to reach the design criteria. In our case Silicon cantilevers were required having a spring constant ∼20 N/m or greater and a magnetically driven deflection of ∼1 nm with B 0 = 10 −3 T. Tabulated results (data not shown) showed that the criteria could be met using Silicon cantilever parameters of around t s = 4μm, w = 50 μm, and l s = 150 − 200 μm, and CoPt hard magnet films with M x ≈ 2 − 5 × 10 5 A/m, 20 l n ∼ 40 μm, and t n ∼ 10 μm ( Fig.…”

“…To date, magnetic force modulation of stiff AFM cantilevers has been achieved by gluing micrometer-size magnetic particles to the cantilever [15][16][17] and there are in general three different techniques currently used to attach micron sized particles, as recently reviewed by Yang. 18 However, attaching a magnetic colloidal particle to the cantilever requires manual manipulation using an optical microscope, is not suited to batch fabrication, is time consuming, and the particle geometry and hence the resultant magnetic force is variable.…”