Guided wave arrays for large plate structures inspection

Guided wave array provides a way to inspect large areas of plate-like structures quickly and has shown great potential in the industry. The problems with present methods to achieve this technology are that purity mode transducer is difficult to produce, operating frequency is high (usually above 200 kHz), distance between transducers need to be small and image algorithm can't achieve the same resolution in all directions. In this paper the pancake coil EMAT (Electromagnetic Acoustic Transducer) is employed to produce purity A0 mode in 15 kHz. A circular array assembled by 8 EMATs and TFM(Total Focus Method) imaging algorithm are used to execute inspection. The validity and efficiency of the proposed method are demonstrated experimentally using a 3 mm thickness aluminum plate with a 27mm hole in the center. Results illustrate that the system can inspect large plate with high stability and imaging resolution. The reason for dead zone is studied and a model to calculate it is also established.