Design of a dual-port, side-incident microwave probe for detection of in-pipe damage

This study reports on a dual-port, side-incident microwave probe dedicated to the non-destructive inspection of metal pipes. Two types of side-incident probes (LJ and JL) are proposed to emit TM01- and TM02-mode microwaves into the pipe under test, and each type of probe has two ports used to inspect in two opposite directions. Numerical simulations are conducted to study the dimensional parameters affecting the transmission characteristics of the probe and optimize the probe to obtain better mode purity and transmission directivity. The simulation results also suggest that the optimal probe dimensions for one inner pipe diameter can be applied to another diameter by multiplying the dimensions by a factor that is determined by the ratio of two diameters. Two LJ-type, side-incident probes, one with an inner diameter of 19 mm and one of 39 mm, are fabricated according to the simulation results. Experimental verification is subsequently carried out to test the detection directivity of the probes by detecting the short pipes with partially milled damage situated on both sides of both probes. Experimental results show that the proposed dual-port, side-incident probe can effectively detect the in-pipe damage on either side of the probe using the corresponding port and thus realize the directional pipe inspection. Furthermore, this method shows a potential to be applied to various inner pipe diameters.