Reserach On Fiber Electric Field Sensing Technology Based On Weak Electrostatic Force And Micro Interferometer

As the rapid growth of power system and all kind of strong electricity devices, electric field sensing attracts equally attention and has been developing fast. Current optical electric field sensors are primarily based on electro-optic materials or liquid crystals. The electro-optic methods are used for RF electromagnetic signal detection, whereas, the low frequency application are heavy disturbed due to the interference of low frequency effects of material such as inverse piezoelectric effect. Though the liquid crystal methods are applied for low frequency measurement, the sensitivity are barely satisfactory. Besides, the actual use of above materials requires optical polarization devices which make the cost and complexity of system to be unacceptable for widely spread. More important, the leakage resistance of material is restricted because of the size of it. High electrostatic charge conservation rate, which creates strong induction electric field within the sensor to modulate the input light signal, is not achievable when frequency of electric field is low. According to the theory of electric field force induced nanometer class vibration of fiber optic mechanical structure, we proposed a low frequency optical polarization independent electric field sensor based on nanometer thickness golden film and fiber Fabry-Perot interferometer, and a optical polarization independent high voltage sensor based on dielectrophoresis and charged particle mobility inside insulating oil. The frequency characteristic of the sensors is analyzed and the equations between electric field or voltage, and light signal are derived. At last, the methods to eliminate temperature or external stress disturbance are presented. The main content of this thesis are as followings(1) The coupling model between low frequency spatial electric field and sensor are illustrated. Calculating with finite element software, the distribution of electrostatic field is analyzed, especially the electric field inside sensor structure, or expressed as the voltage amplitude of inner gap within the sensor. Then, a pre-voltage drive test is executed to confirm the possibility of using the sensor for electric field detection, and to figure out the rough measurable range. Beside the principle derivation of using the electrostatic force to modulate optical parameter in air space for spatial electric field sensing, the internal electric field induced dielectrophoresis of neutral particles and movement of charged particles inside insulating oil under high voltage are analyzed, and a corresponding mechanism of high voltage sensing is also demonstrated.(2) A low frequency optical fiber electric field sensor based on weak electrostatic force and interferometer which consists of fiber and nanometer thickness golden film. To process the 120 nm golden film to a bent beam structure with a central section that the shape is similar to rhombus, as the core component of electro-optic converting, a high-precision femtosecond laser processing system(3?m spot diameter) is used. The electric field test is taken with frequency range from 30Hz-27 kHz, and amplitude range from 0-3600V/m. The result shows the relationship between electric signal and light signal is quadratic as we expected. The sensor's response has a peak at 19 kHz because of the mechanical resonance effect. But it is weak below 500 Hz, in which region the sensor is only be able to couple lesser electric field on account of impedance induced high-pass filtering effect, and the light signal is phase lead ahead of electric field. The measurable range of sensor can be easily adjusted, but in the case of our current structure and size, the range is from 200V/m to 3000V/m.(3) Based on dielectrophoresis and charged particles movement of insulting oil, a PMMA box packaged optical fiber high voltage sensor is made. The core component is a liquid force sensor head which consists of several fiber sections. The sensor is tested under high pulse voltages with different amplitudes, millisecond of duration time that primarily using dielectrophoresis. And also it is tested under 7kVrms power frequency voltage that using charged particles movement only. The main frequency component of measurable high pulse voltage should below 350 Hz. The received light waveform can be used, along with empirical parameters, to inversely calculate out the corresponding original pulse voltage waveform, but high frequency components are lost. In power frequency experiment, the light waveform follows voltage waveforms, but has 0.1ms delay. Therefore, the highest responsive frequency of periodic voltage is 700 Hz.