Research On Optical Current Sensor And Microampere/nanoampere Galvanometer Based On MEMS

The measurement of high voltage current and microampere/nanoampere are two important application directions in the field of current sensor, the two types of current are difficult to be tested directly, so the input signal must be processed and transformed before accurate measurement. Compared to traditional current transformers, optical current sensors (OCSs) have many advantages, but they are restricted by many factors in practical application, especially the precision caused by temperature and aging of sensing head, so OCSs still stay at the stage of theory research and experiment. Amplifier circuit is mostly used in the measurement of microampere/nanoampere current, but noise and the input signal are synchronously amplified, which will bring the measurement errors.Based on optic fiber sensing technology and the characteristics of MEMS technology, such as mass production, high consistency and low cost, optical current sensor and microampere/nanoampere galvanometer (MNG) based on MEMS are researched in this thesis. The main contents are summarized as follows:(1) For the measurement of 50Hz high voltage current with peak value from hundreds to thousands ampere, the OCS sensing head composed of Rogowski coils, torsional micro-mirror and dual fiber collimator is proposed firstly. MEMS -OCS is a practical optical current sensor, which meets the requirement of 0.2%—0.6% precision and solves the problem of sensing head aging.(2) For the measurement of current within nanoampere to microampere, the galvanometer based on MEMS is studied firstly. The nanoampere current can be directly measured by the sensing head composed of torsional micro-mirror and dual fiber collimator, which eliminates the noise of the amplifier in the circuit, so MNG is a novel sensor for practical application. (3) With numerical calculation of Mathcad,Matlab and finite element analysis of ANSYS ,static analysis, dynamic response, heat expansion and stress of micro-mirror driven by induction current are analyzed and simulated, the optimized design and performance simulation of OCS and MNG are successfully finished.(4) The fabrication process of torsional micro-mirrors for OCS and MNG are detailedly explained. The most important process steps, such as the roughness improvement of silicon surface after etched by KOH, fabrication of lead wire, selection and etching of insulating layer, etching and protection of micrometer cantilever beam, are researched and improved, so the micro-mirrors with micrometer cantilever beam can be successfully fabricated.(5) The performance of OCS and MNG are tested in the laboratory. The results show: the sensitivity of OCS can reach 2.5 mV/A; the sensitivity of MNG is 0.81dB/μA, and the resolution of MNG can reach 6.5 nA. The experimental results are analyzed.