Yuan Libo

Characteristics of the guided modes in a two-dimensional three-component phononic crystal with linear defects

A two-dimensional (2D) phononic crystal (PC), including a type of linear defect that is composed of third component materials, is proposed in this paper. The sonic guided characteristics of the structure are investigated by combining the plane-wave expansion method and a supercell technique. The results show that there are guided modes in the original band gap when third material-based linear defects are introduced in the two-component PC. The frequency of the guided modes changes with the rotational angle and filling fraction of the linear defect. The frequency distribution is symmetric to the (0, 1) direction. The sonic waveguide characteristics of the PC do not change with the orientation and the type of cross-section of the defect cylinders when the filling fraction is very small. This property has potential application in controlling the guided modes in a 2D PC.

Photonic band gap structures in 2D tunable magnetic photonic crystals

The photonic band structures in 2D tunable hexagonal magnetic photonic crystals were investigated on the basis of plane wave expansion method. It was found that the photonic band gaps tended to exist in the magnetic photonic crystals, and magnetic permeability affected the photonic band gaps strongly. The width of two absolute band gaps was reduced gradually, then they vanished when magnetic permeability increased from 1.0 to 5.0 in photonic crystals with magnetic scatterers surrounded by air. However, as magnetic permeability continued to increase, an absolute band gap could appear in the lower frequency, and gap-mid-gap ratio increased and the optimal filling ratio changed lightly. Analogously, an absolute band gap also appeared in the lower frequency in photonic crystals with air scatterers surrounded by magnetic material. Further, the results revealed that the characteristic in photonic crystals with dielectric scatterers surrounded by magnetic material is similar to that in photonic crystals with magnetic scatterers surrounded by air.

Bandgap properties of phononic crystals with L-shape scatters

In this paper, we study the complete and directional bandgap properties of two-dimensional mercury/air phononic crystals (PnCs) with L-shape scatters based on the plane wave expansion method combined with a parallel shift scheme. As the symmetry of the scatters is lower than the symmetry of a square lattice, we scan the whole first Brillouin zone when performing the calculation. The relationships between the parameters (including geometry and filling fraction) of L-shape scatters and bandgaps are simulated in detail. The complete bandgap could be gained at a very low filling fraction (even below 0.076). The bandgap and directional bandgap width could be adjusted widely by changing its geometry and rotating the L-shape scatters, which could be useful for applications such as an acoustic directional filter or acoustic isolator.

Multi-ring compound fiber optic rotation measuring approach based on the Rayleigh Backscattering

A new structure of multi-ring compound fiber optic rotation velocity measurement approach was researched, in this paper, based on the single ring Rayleigh backscattering type fiber optic rotation sensing principle. N fiber optic ring cavities and N 2×2 single-mode optical fiber coupler were used in this new structure to build a model for measuring changes of scattering. The output signal of optical rotation sensor detected by optical time domain reflectometer was deduced and analyzed in digitization by MA TLAB software. And then the structure parameters of the multi-ring cavity lengths and coupling ratios were optimized according to the characteristic of output signal. When the system was constructed based on the optimization simulation results in the same condition that parameters setting were N=3, range of rotate speed measure 0-0.18rad/s and measurement accuracy 0.01rad/s, the feasibility of the system was verified by measuring the Rayleigh backscattering signal in different speed. The use of compound multiple ring cavities, compared with single ring, improved the measuring signal strength, increased the effective test data, which is helpful to identify.

Theoretical and experimental study on white light interferometric sensing network with double-ring topology

A white-light interferometric fiber-optic sensing network based on the double-ring topology is demonstrated, which can be applied to the measurements of quasi-distributed strain and temperature in a smart structure. In order to increase the multiplexing capacity, decrease the measurement cost of each sensor, and improve the ability of reliability of the sensor network, a double-port interrogating technology was used. The double-ring fiber optical sensing network based on the space division multiplexing (SDM) is further developed. The low coherent multiplexing principle in the double-ring network structure is analyzed. Based on the optical path matching condition of SDM, the intensity characteristic of the interference signal in the sensor is deduced. The characteristics of the double-ring sensing network connecting 9 sensors and its property of robust resisting destruction are verified by experiments, and the results are analyzed and discussed.

Study on fiber Bragg grating displacement sensor with angle steel structure

In this paper, two fiber reinforced polymer/plastic (FRP) encapsulated fiber Bragg grating (FBG) sensors were installed on the two sides of the angle steel beam, which was used to measure the displacement and direction of the diagonal steel beam, so as to realize the health inspection of the angle steel structure. The sensors were re-spectively installed on the different positions of angle steel beam, and the relationship between displacement and strain transmission of angle steel beam was simulated by the finite element analysis. The optimum design of sensors installation were discussed and the experimental verification was carried out. The simulation and experimental results show that the sensor has the capacity to discriminate the direction and measure the size of one side of the angle steel beam displacement when installed in a reasonable position. To realize the health monitoring by using optical fiber sensors on the structures composed by angle steel, such as bridges, electric towers and cranes, and so on, a basic research was provided.

The theoretical and experimental study on white light interferometric fiber optic sensors network based on Michelson and Mach-Zehnder interferometers

Based on the white light interferometric technology, a novel combination interferometer of Mach-Zehnder and Michelson system has been proposed and demonstrated. It consists of a Michelson interferometer and a series Mach-Zehnder interferometers which are linked to an arm of the Michelson interferometer, thus configuring a multi fiber optic sensors measuring network. It can be used to measure the distribution of strain or temperature, and it is especially suitable to monitor large-scale structural deformation, because its sensing gauge length is up to ten meters. Meanwhile, it could be used in temperature compensation mode with one arm of the Mach-Zehnder interferometer measuring the strain caused by the variation of deformation or temperature while another arm only measure the ambient temperature because it is in strain free state. Thus, this sensor arm could be used to compensate the variation of the refractive index of the fiber induced by temperature changes and the elongation of the fiber caused by thermal expansion.

The analysis of logarithm fitting method for measuring decay time of optical fiber fluorescence sensors

The logarithm fitting method, due to its simple principle, quick operational speed and accepted accuracy, is widely used to measure the decay time of the fluorescence temperature or pH value sensors. Using logarithm fitting method, the unavoidable random noise of the acquired signal causes the random fitting error of the decay time. In addition, we found that the random noise will lead a systemic deviation of the fitting decay time. The higher the noise level is, the smaller the fitting decay time is. Based on analysis and simulation, we explained the reason of systemic deviation of the decay time of a single-exponential decay with random noise and gave a modified method.

Electromagnetic Characterized Parameters of Negative Refractive Index Metamaterial

Two kinds of H-patterned unit structures are analyzed based on the equivalent homogeneous medium theory, the electromagnetic characterized parameters representing the effect of negative refractive index (NRI) are obtained, including wave impedance, refractive index, relative permittivity and relative permeability. Draw a comparison between the obtained parameters above, we find that the transmissivity and the frequency range with NRI are two aspects to be simultaneously considered in the process of NRI metamaterials constructing.