| Summary: | 碩士 === 逢甲大學 === 電機工程學系 === 106 === This thesis proposes a tunable sensitivity heterodyne interferometer for measuring magnetic field. Its consist of heterodyne light source, phase modulator, a magneto-optical glass, and a lock-in amplifier. A self-made U-shaped electromagnet is generated the different magnetic field. Therefore, when a heterodyne light source passes through a magneto-optical glass, the variation of phase difference can be generated. This phase difference variation can be precisely measured by lock-in amplifier. The magnetic field then can be obtained by the phase difference variation substituting into a specifically derived equation. In addition, in the apparatus, the phase modulator which consist of a half-wave plate and a quarter-wave plate can be modulated different sensitivity to adapt different measured field. The feasibility of this method was verified by experiment, and the results were quite consistent with the theoretical data. Because of applying the heterodyne interferometry and common-path structure, the proposed method has the merits of a simple optical setup, easy operation, non-destructive measurement, high accurately, and can avoid disturbances in the surrounding environment.
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