A Nondestructive Testing Method for the Determination of the Complex Refractive Index Using Ultra Wideband Radar in Industrial Applications

Abstract

An ultra-wide band radar reflection measurement technique for industrial applications is introduced. A new method for determining the complex refractive index (or equivalently the relative permittivity) of objects with planar interfaces is presented. The object thickness can also be obtained experimentally. The method is a combination of time and frequency domain techniques. The objects can be finite in size and at a finite distance. The limits in size and distance for the method to be valid are experimentally investigated. The method is relatively insensitive to hardware impairments such as frequency dependence of antennas and analog front end. The method is designed for industrial in-line measurements on objects on conveyor belts. Results are presented for solid wood and wood chips; the complex refractive index is determined in the frequency range 0.5 to 2.0 GHz for the moisture content of 3.6–10% for solid wood and 30–50% for wood chips. Polarimetric measurements are used; wood and wood chips are anisotropic.