Wide-Focus Imaging for Industrial Metal Workpieces Using Tower-Type Transmitting Coils

Metal workpiece imaging is of great significance for industrial nondestructive testing. However, current methods, such as radiographic or electromagnetic induction, are easily influenced by background noise, which leads to a short detection range and a high false detection rate. To overcome this issue, this article proposes a wide-focus imaging method for industrial metal workpieces using a tower-type transmitting coil and a magnetic sensing array. First, a single-loop coil excitation model is established to analyze the effects of transmitting current, coil radius, and other parameters on the radiation magnetic field. Second, a coaxial noncoplanar tower-type coil is designed, and a wide-focus optimization is achieved using a particle swarm algorithm, reconciling the conflict between high uniformity and high focusing degree requirements. Third, a wide-focus imaging system is developed, which combines a magnetic sensing array with cubic convolution interpolation algorithms to achieve 3-D imaging of metal workpieces. Experimental results demonstrate that the magnetic field uniformity achieved by the tower-type transmitting coil reaches 98.02%, representing a 43.82% improvement over the conventional single-loop coil. The proposed wide-focus imaging method leads to an average enhancement of 16.18% in imaging contrast and an average improvement of 37.33% in detection distance under various conditions, which increases the environmental adaptivity and decreases the false detection rate.