The effect of non-metallic material’s thickness and inhomogeneous distribution of relative permittivity to capacitance

and the effective detection range of three-electrode planar capacitive sensor in horizontal direction are analyzed.A new method of three-electrode planar capacitive sensor which is simple in construction and easy to operate is proposed to detect and locate the subsurface anomalies or damage of non-metallic materials.The effective detection range of sensor probe whose size is defined in horizontal direction is the distance of 50mm between probe’s center and damage’s edge by analyzing damage zone.