Frequency Optimization of PZT-FBG Voltage Sensor Based on Temperature-Independent Demodulation Method

Fiber grating sensors have been widely used in industry and has been an important research topic in power systems due to their small size, satisfactory electric shielding ability, and high compatibility with optical fibers. Voltage is a crucial parameter that must be monitored in the power system. Existing PZT-FBG voltage sensors are small, inexpensive, and present acceptable linearity in the range of 50 Hz-20 kHz. However, voltages in power systems cover signals with a frequency from DC to MHz and the existing frequency range is insufficient. Finite element method is adopted to improve frequency characteristics of the PZT-FBG sensor and choose the optimal basic structure by initially calculating resonant frequencies. Structural parameters are then selected via dielectric spectrum analysis. The test platform is established to verify amplitude response, frequency response, three-wave response, temperature characteristics, and impulse voltage response of the frequency-optimized PZT-FBG sensor. Test results showed that the sensor presents satisfactory linearity and the temperature-independent demodulation method improves its stability with temperature changes. Impulse voltage tests indicated that the sensor can respond to impulse waveforms with a wave front time of 250 and 10 \mu \text{s} . Hence, the sensor can respond to a voltage signal of 100 kHz with acceptable consistency. The optimization achieved in this study can provide a reference for further improvement of this sensor and other similar sensors with PZTs.