K. Tajima et al., IMPROVING THE SENSITIVITY OF ELECTRIC-FIELD SENSOR WITH LINBO3 ELECTROOPTIC CRYSTALS BY LOADING INDUCTANCE, Electronics & communications in Japan. Part 1, Communications, 77(10), 1994, pp. 39-48
Recently, with the diversification of electromagnetic compatibility(EM
C) problems, the need for an electric field sensor to measure the elec
tromagnetic pulses and the electric field near the equipment has incre
ased greatly. An electric field sensor using LiNbO3, which has an elec
trooptical effect, has been used for such measurements; but the sensit
ivity 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 inductan
ce. First, an equivalent circuit representing the sensor with loading
inductance is derived. Second, the frequency characteristics are analy
zed theoretically by applying the moment method to this equivalent cir
cuit and the improvement in sensitivity by loading inductance is demon
strated. Moreover, the validity of analysis is confirmed by performing
the experiments using the GTEM-cell. As a result, it is found that th
e measured results show good agreement with the calculated results and
the sensitivity can be improved by inductance loading. It has been co
nfirmed 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.