The Spectrum Analysis Of Voltage Noise Of Moving Vortex Lattice And Dynamic Phase Transition In Type Ⅱ Superconductors The Experimental Research Of Fiber-Optic Acoustic Sensor

My research work includes two parts. The first part is"the spectrum analysis of voltage noise of moving vortex lattice and dynamic phase transition in type II superconductors". Based on the GL phenomenological theory and Langevin flux flow model,we study the voltage noise spectrum and the dynamics phase in the mixed state to explore the reordering characteristic of the vortex lattice. In this work we use molecular dynamic method to study the voltage noise spectrum generated by current-driven vortices as a function of the magnetic field and current in a disordered pinning vortex system. First, we calculate four different V-I curves by changing the magnetic field strength ( Fv v0=0.03, 0.1, 0.5, 1.5). If we take a uniform driving force FL =0.8, it is found that the vortex system is in the critical depinning state and in the plastic flow state at Fv v0=0.03 and Fv v0=0.1, respectively. And the vortex system is in the critical smectic state and in the elastic flow state at Fv v0=0.5 and Fv v0=1.5 , respectively. Then we calculate the voltage noise spectrum in above circumstances, subject to a uniform driving force FL = 0.8. It is found that in plastic phase, the broad band noise (BBN) at low frequencies decreases with the increasing magnetic field, and it behaves 1/f form in low velocity. It decreases at the magnetic field near the vortex dynamic transition field FP ( Fv v0=0.5) and the Lorentze narrow band noise (NBN) at high frequencies appears. As the magnetic field increases near the melting field Fm ( Fv v0=1.5), the NBN peak goes up and shifts towards higher frequencies. The result is consistent with experiments entirely.We also calculate NBN in the elastic motion region of vortices with strong driving currents, finding that NBN exhibits the washboard-like shape. This behavior arisesfrom the periodic modulation of the translational velocity of vortices, suggesting that there is a Bragg glass phase with the translation order in the vortex lattices of the layered superconductors. And the ?f w( NBN) increases with the increasing Lorentze force. These results are consistent with experiments and can explain the microscopic dynamics behavior of vortex motion.The second part in my work is"the experimental research of fiber-optic acoustic sensor". Using the structure of Y type reflective multimode fiber sensing probe, we design a novel reflective fiber-optic acoustic sensor and the use of Y type fiber-optic coupler greatly predigests the configuration of the sensor probe. Optical intensity modulation function of the fiber-optic acoustic sensor can be got by using imaging principle. According to the oscillation theory of membrane, we obtain the inherence frequency and basic frequency of the configuration of the sensor probe. It is feasible in theory. Also, we design the system in experiment and have a test. By testing and analyzing we find that it is linear between the light intensity and the input current of the acoustic sensor. And the output waveform is in accord with that of input at 1KHz frequency. The responsibility and the sensitivity is as scheduled, the acoustic sensor is good at low and high signal. At last, we give the signal waveform when we are speaking. The expecting function of the fiber-optic acoustic sensor system has been realized in experiments.