Optimized microwave excitation probe for general application in NDT of wall thinning in metal pipes of arbitrary diameter

highlights
• This study develops a long-range inspection of metallic pipe using microwave.
• This study proposes a new optimization parameter of microwave exciter probes.
• A probe with the large parameter introduces microwaves into pipes largely.
• The probe is optimized by numerical analysis on transmission characteristics.
• Experiment using pipes with diameter of 19, 39 and 57.5 mm validates the parameter.

Generalized approaches to developing a microwave NDT for flaws inside an arbitrary diameter pipe through optimizing a microwave-exciting probe were investigated. A microwave probe obtained from a parameter-optimizing scheme based on transmission characteristics is proposed. Three-dimensional finite element simulation of five microwave probes indicates that a larger optimization parameter enables reduced microwave reflection, as well as improved single-mode propagation inside the pipe as compared with conventional probes. Experimental verification, using straight brass pipes of various diameters confirmed that the optimized microwave probe exhibits a larger signal-to-noise ratio for internal flaws when compared with conventional probes, thereby validating the new optimization parameter.