The Design And Application Of Fringing Electric Field Sensor

Fringing Electric Field Sensors(FEF)are capacitive sensors,and the required physical quantity information such as dielectric constant,humidity,viscosity,thickness,displacement,and damage are obtained by measuring and analyzing the variation law of capacitance values which are outputted by the measured object.The bipolar plates of the fringing electric field sensor are located in the same plane and constitute a working zone above the plates.Compared with the traditional parallel-plate capacitors,the electric field lines is distributed in an arc and scattered outwards,the electric field energy is mainly concentrated on the edge of the electrodes.They have the advantages of unilateral penetration,adjustable signal intensity,and tomography,and are widely used in the non-contact measurement of sample object properties.Firstly,the structure and principle of the parallel plate capacitor are analyzed.Based on this,the principle,design parameters and performance index of the fringing electric field sensor are studied.Through the theoretical analysis,finite element modeling and simulating and experimental verification,the application of large displacement measurement,coating thickness detection and nondestructive testing is studied in detail.1)The basic principle of measuring the displacement of the interdigital FEF sensor is analyzed,and the mathematical relationship between the sensor transconductance capacitance and measured target displacement is established by using the finite element simulation software Ansys Maxwell.A conditioning circuit is designed and implemented to convert the sensor transconductance capacitance into voltage.Finally,a measurement experiment was carried out.The results show that the FEF sensor can realize large-scale displacement measurement,providing a feasible research approach for displacement measurement.2)The principle of measuring the thickness of the coating by the FEF sensor is analyzed,and 5 sensor models with different penetration depths are established.The numerical simulation is performed in the finite element simulation software Ansys Maxwell,the relationship between sensor mutual capacitance and coating thickness variation was obtained.This verified its feasibility for composite' coating thickness measurement.A concentric annular fringing electric field sensor was designed and the different thicknesses gradients of PVC samples was measured in different measurement pattern by using the precision LCR digital bridges.The results showed that the fringing electric field sensor with graphite substrate can better detect the coating thickness.3)The working principle in defect detection of planar capacitive array sensor was analyzed,which is based on Electrical Capacitance Tomography(ECT),and the influence of sensor design parameters on performance was studied.In the finite element simulation software Ansys Maxwell,the planar capacitive array sensor was modeled in three dimensions,and the feasibility of its use in composite defect detection was verified by numerical simulation.A multi-channel signal acquisition circuit based on planar capacitance array sensor is designed and implemented,and the function is verified.The results meet the design requirements.