This open access book can be divided into three parts. In part 1, three articles are employed to introduce the RACFM technology. In part 2, two articles are introduced to explain the Multifrequency ACFM. In part 3, three articles are introduced to explain the visualization research in ACFM. With the development of ACFM detection technology, traditional single excitation frequency and single direction excitation structures cannot meet the requirements of multiple types of defect detection (such as cracks at different angles, and buried defects). New types of...