Fig. 1. Experimental scheme

Fig. 2. EIT signal of main optical path and reference experimental systems

Fig. 3. Simulation results of electric field distribution between electrode plates using COMSOL Multiphysics software

Fig. 4. EIT spectral under the different intensities of radio frequency electric fields

Fig. 5. The relationship between the frequency shift of EIT signal and the electric field strength between the electrode plates

Fig. 6. EIT signal for different frequency of power frequency fields and fitting results of sine function

Fig. 7. Frequency measurement of power frequency electric fields