The propagation velocity of terahertz wave in insulating medium is related to the refractive index.In the case of the known refractive index of the material

the thickness of the material can be measured via the time delay characteristic of the terahertz wave.Many insulation parts in power grid equipment are of irregular structures and cannot be destroyed

so their insulation thicknesses are difficult to be measured directly by conventional methods.In this paper

the superposition effect of multiple reflection waves in the propagation process of terahertz wave is analyzed with the propagation model

the transmission and reflection characteristics of silicone rubber and epoxy glass fiber plate with different thickness are measured

the relationship between the time delay and the dielectric thickness of the terahertz time-domain wave in the medium is analyzed

and a method for measuring the thickness of insulating material with two modes of transmission and reflection is presented.Research shows that terahertz wave has high accuracy in thickness measurement of insulating materials

and can be applied to thickness measurement and sheath uniformity test.