Interdigital(finger-like)electrodes are widely used for electrical impedance and capacitance tomography of composite dielectric materials and complex insulating structures.Because of their advantages,they are now effectively introduced as capacitance sensors into a variety of industrial branches,agriculture,medical science,biological engineering,military branches,etc.In order to effectively apply the so-called interdigital impedance sensors in practice,of great importance is to optimize the sensor design parameters such as the electric field penetration depth,signal strength and so on.The general design principles of the interdigital capacitance sensor have been discussed for a long time by many researchers.