Research On Resonant Voltage Sensing Technology Of Piezoelectric Ceramics And Quartz Crystal Resonators

With the development of smart grids and smart Internet of Things(Io T),more and more smart electronic power devices are applied in daily production and life.The traditional voltage sensing technologies can no longer meet the new requirements of intelligence,miniaturization and easy to connect with devices,the new voltage sensing technologies have become the focus of current researches.The double-ended tuning fork(DETF)resonators can convert the measured physical quantity into frequency output,avoiding the error of amplitude measurement and being not easily interfered by environmental noise.Moreover,the frequency output can simplify the interface circuits,which are widely used in resonant accelerometers,gyroscopes,force sensors,and other sensors.In this paper,piezoelectric ceramics and DETF resonators are combined to form the resonant voltage sensors that can realize the "voltage/electric-field-force-frequency" conversion.The performance of the sensors have been investigated the means of theoretical analysis,finite element simulation,and experiment.And the major work is provided in the following:(1)The piezoelectric effect and the piezoelectric equation of piezoelectric materials are described.The piezoelectric actuators and the DETF resonator are introduced.The bending vibration modes of the DETF resonator are analyzed with COMSOL software,and the design,electrode arrangement and processing technologies of the DETF resonator are described in detail.The result shows that the quality factor(Q factor)value of the DETF resonator in the air is 3914.(2)The structure and working principle of parallel-connected resonant voltage sensor and series connected resonant voltage sensor are introduced,respectively.The stress/strain generated on the piezoelectric ceramics under the action of voltage is transferred to the longitudinal direction of the DETF resonator,which causes the resonant frequency of the resonator to change.Finite element software is used to simulate the voltage sensing characteristics of the resonant voltage sensors.The finite element simulation results demonstrate the feasibility of the resonant voltage sensor structure design and verify the theoretical analysis results,which is helpful for subsequent experiments.(3)The resonant voltage sensors are fabricated and the sensitivity,resolution,impedance characteristic and Q value of the resonant voltage sensors are tested and analyzed.The experimental results are little difference between the theoretical and simulation results.The sensitivity and resolution of the parallel-connected resonant voltage sensor are 3.5hz /V and0.02 V,respectively,and the Q value is about 3379(in air).The sensitivity and resolution of the series-connected resonant voltage sensor are 5.7Hz/V and 0.02 V,respectively,and the Q value is about 3023(in air).In addition,the resistance and static capacitance of the sensor is calculated to be > 50 G?,and > 850 p F,causes almost no influence on the DC voltage under test.(4)A differential resonant voltage sensor are developed by bonding two quartz crystal DETF resonators 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.The mathematical model of the sensor is established and the theoretical analysis and finite element simulation are carried out,respectively.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 Q value of the DETFs is about 3661(in air).The resistance and static capacitance of the sensor is calculated to be > 714 G?,and about 124 p F.The temperature characteristics of the differential resonant voltage sensor are tested,and the results show that the nonlinear temperature coefficient of the sensor in differential mode is about an order smaller than that of the individual DETF resonator,effectively reducing the influence of temperature drift.