Research On Coaxial Cable Bragg Grating Characteristics

In recent years, fiber optic sensor has been widely used in the structure health monitoring systems. However, Fiber grating sensor is fragile and can't stand the large strain, so it can't meet the requirement of the measurement of the large tension. Based on the theory of the photonic crystal and the Fiber Bragg Grating(FBG), Coaxial Cable Bragg Grating(CCBG) that is grating structure fabricated by drilling holes into the coaxial cable is presented in the paper. Drilling holes in the coaxial destroy the impedance continuity, so the electromagnetic wave propagating in the cable will reflect, which is similar with the FBG. However, compared to the FBG, coaxial cable Bragg grating has a larger size,and can withstand a greater tension and can measure long gauge, which makes up shortcoming of the fragile fiber grating that can't measure large strain and long gauge.Coaxial Cable Bragg Grating has a similar grating transmission and reflection characteristics compared with FBG, even has the advantage that can measure large tension which FBC can't do. However there is few domestic and foreign theoretical studies and simulation about the Coaxial Cable Bragg Grating. First using the transmission line and the mode coupling theory to introduce the basic principle of the Coaxial Cable Bragg Grating, and analyze the mechanism of Coaxial Cable Bragg Grating. Then make an introduction of the structure of the Coaxial Cable Bragg Grating, besides deduce the reflection coefficient of Coaxial Cable Bragg Grating though the theory of the transmission line.Next, use the software electromagnetic simulation software Ansoft HFSS to carry out the coaxial cable Bragg grating modeling and simulation. Ansoft HFSS use the finite method as the base of the numerical solution of the electromagnetic field. Because of its friendly and simple design interface, powerful analytical performance and post-processor, it can carry out electromagnetic field analysis of arbitrarily shaped three-dimensional structure.First, establish the simulation on the uniform Coaxial Cable Bragg Grating, and compare the simulation result with the experimental result. Their frequency characteristic spectrums are same basically, so simulation result can be treated as the basis for the research of the Coaxial Cable Bragg Grating characteristics. Next, establish the simulation on the phase-shifted Coaxial Cable Bragg Grating, width of which is smaller than the uniform Coaxial Cable Bragg Grating when they are in the same structure parameters and better in the sensing application. Finally, establish simulation on the different structure parameters, such as numbers of the holes, depth of the holes and the diameter of the holes to study the relationship between the width and the structure parameters, so that we can optimize the parameters to reduce the width and improve the sensing accuracy.