Nondestructive testing and antenna measurements using UWB radar in industrial applications

Sammanfattning: Many industries are rapidly substituting the manual test operations and move towards automated operations using modern technologies.Modern technologies such as digital cameras, sonic sensors, infrared sensors, and radar and lidar systems are used for non-destructive testingoperations. Among all the different sensors, radar systems have theability to penetrate built structures (dielectric materials), which makes them flexible and suitable for a wide range of industrial and military applications in non-destructive sensing. Such examples are the detection of damages in goods manufacturing, monitoring the health of manystructures, object detection through the wall for security purposes, etc.In particular, ultra-wide-band (UWB) radar systems are beneficial inproviding high measurement accuracy and simultaneously reduced sensitivityto passive interference (such as rain, smoke, mist etc.), immunity to external radiation and noise.The objectives of this thesis are: I) to investigate electrically small concealed structures using synthetic aperture radar (SAR), II) to determinethe complex refractive index of objects using an UWB radar system,and III) to answer to the question how we can reduce the mutual coupling (cross talk) in an UWB radar system with collocated transmitand receive antennae. In objective I, the aim is non-destructive testing of built structures, such as in concrete slab manufacturing or for use in the renovation process. In addition electrically small periodic meshes,and their orientation, could not be distinguished in conventional SAR images. The proposed polarimetric analysis method demonstrates the usefulness of the singular value decomposition (SVD) using back projection algorithm (BPA) in extracting information about shape and for classifying an electrically small object. Further in this thesis for objective II, a new method for determining the complex refractive index (or equivalently the complex relative permittivity) of objects with planar interfaces is presented. The proposed method is relatively insensitive to hardware-impairments such as frequency-dependence of antennas and analog front end. 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. Hence, the method is designed for industrial in-line measurements onobjects on conveyor belts. Furthermore, in the following parts of this thesis −objective III− we investigate and show how a microwave metamaterial based absorber can be used to improve the performance of aradar system for short range applications, when positioned between the transmit and receive antennas. As results, the error in estimated target distance is reduced and clutter reduction is improved.