Analysis for propagation characteristics of longitudinal mode and torsional mode guided waves in rod
Regarding the application of guided waves in one-dimensional structure, the propagation characteristics of the longitudinal guided wave and torsional guided wave are investigated. The dispersion equations of guided wave in the longitudinal and torsional modes in one-dimensional component are derived. Through programming numerical calculation in MATLAB, the frequency dispersion curves of the two modes are obtained, which imply that the engineering application of guided waves in detection of rod needs to choose an appropriate frequency and the corresponding propagation characteristics of the waves should be combined to get reliable results. The dispersion characteristics analysis results in different radius of rods show that it is feasible for detecting the defects in rod using L(0,1) mode of ultrasonic guided waves.
Multi-modal signal propagation model based on time reversal method
Aiming at the defect non-destructive testing problem for one-dimensional rod-like structure, a time reversal based defect signal multi-modal propagation model is developed and a new one-dimensional structure non-destructive testing method based on time-reversal and multi-modal is proposed. Through analyzing the dispersion effect of guide waves in steel leading to signal distortion which means a single mode waveguide is changed to multi-modal, a multi-modal transfer function of the structure is formatted which theoretically verifies the feasibility of time reversal for one-dimensional structure defect testing. The simulation results show that time reversal method can be applied well in one-dimension structure to eliminate the multi-modal of guided wave and emphasis defect signal.
Photoreflectance characterization of vanadium-doped GaAs layers grown by metalorganic vapor phase epitaxy
Abstract We characterized the vanadium-doped (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy. The conductivity of the samples is checked by the Hall effect measurements, and it is n type with electrons concentration ranging from 2×10 13 to 2×10 17  cm −3 . We used the photoreflectance technique (PR) to study the effect of vanadium doping on the optical properties of GaAs. Our experimental results show that the built-in electric field F and the broadening parameter Γ 0 increase with V-doping concentration. Furthermore, the temperature dependence of the built-in electric field and the broadening parameter of GaAs:V samples have been investigated by PR. It has been observed that these parameters increase with increasing temperature. The decrease of the built-in electric field with decreasing temperature is due to the photovoltage effect.We characterized the vanadium-doped GaAs (GaAs:V) layers grown on GaAs substrate by metalorganic vapor phase epitaxy.