Design of Coplanar Capacitive Sensors With Measurement Capability at Different Depths

A new type of coplanar capacitance sensor was designed to address the problem that coplanar capacitance sensors are difficult to use for measuring and characterizing defects at different depths in materials. Under different excitation modes, the sensor achieved a maximum penetration depth of 8 mm and a minimum penetration depth of 4 mm, successfully enabling the detection of defects at varying depths. Additionally, to resolve the discrepancy between the penetration depth calculated by traditional theoretical formulas and the actual penetration depth of the sensor, a new measurement method based on the liftoff technique was proposed. The penetration depth calculated using the theoretical formula derived from this method shows greater accuracy.