IMPROVING THE SENSITIVITY OF ELECTRIC-FIELD SENSOR WITH LINBO3 ELECTROOPTIC CRYSTALS BY LOADING INDUCTANCE

Recently, with the diversification of electromagnetic compatibility(EMC) problems, the need for an electric field sensor to measure the electromagnetic pulses and the electric field near the equipment has increased greatly. An electric field sensor using LiNbO3, which has an electrooptical effect, has been used for such measurements; but the sensitivity is not satisfactory. However, the sensitivity can be improved by increasing the sensitivity of the optical modulator or by increasing the output of the optical modulator source. Here, we describe a method to improve the sensitivity at resonance frequency by loading inductance. First, an equivalent circuit representing the sensor with loading inductance is derived. Second, the frequency characteristics are analyzed theoretically by applying the moment method to this equivalent circuit and the improvement in sensitivity by loading inductance is demonstrated. Moreover, the validity of analysis is confirmed by performing the experiments using the GTEM-cell. As a result, it is found that the measured results show good agreement with the calculated results and the sensitivity can be improved by inductance loading. It has been confirmed that the sensitivity of the electric field sensor with element length of 150 mm could be improved by about 40 dB at 200 MHz by using the loading inductance of 600 nH.