The focus of the book is to demonstrate a feasibility study for detecting wormhole defects using the frequency spectrum, phase space, and time spectrum of feedback forces in real-time. It is asserted here that the oscillations of the feedback forces are related to the dynamics of the plasticized material flow and that the feedback forces can provide useful information for detecting wormhole defects. Two real-time feedback-force evaluation algorithms are developed for assessing the weld quality. A probability of detection analysis is conducted to compare the wormhole-detection performance of...