A differential resonant voltage sensor with frequency output was developed by bonding two quartz crystal double-ended tuning forks (DETFs) on both sides of a piezo bimorph. The applied voltage induced tensile and compression deformation in the upper and bottom layers of the piezo bimorph, which caused the resonant frequency of the dual DETFs to increase and decrease, respectively. In this case, the differential output of the resonance frequencies of the dual DETFs greatly reduced the effect of temperature drift. In addition, the input resistance of the piezo bimorph reached a few hundred GΩ, which caused almost no influence on the DC voltage under test. The fabricated device showed a linear characteristic over its measurement range of ±700 V with a sensitivity of 0.75 Hz/V, a resolution of 0.007% (0.1 V) and hysteresis of 0.76% of the full range. The quality factor of the DETFs was about 3661 (in air). This novel resonant voltage sensor with its extremely low power consumption is promising for measuring or monitoring DC voltage in various fields.
Keywords: double-ended tuning fork (DETF); piezo bimorph; resonant sensor; voltage sensor.