Quantifying the lowest remnant thickness using a novel broadband wavelength and frequency EMAT utilizing the cut-off property of guided waves

Thickness reduction arising due to corrosion or in any other ways can cause severe damages to structures. Hence regular inspection of structures is vital in many industries. One of the factors deciding the replacement of a structure is the minimum thickness remaining in the structure. A novel ultrasonic method is introduced in this paper to precisely evaluate the minimum remnant thickness of structures. This method utilized the cut-off property of SH1 guided wave mode. A continuous broadband SH1 wave mode was required for establishing this method. This was achieved by exciting a range of wavelength and a range of frequency corresponding to the desired SH1 generation region. The range of wavelength generation was achieved by appropriately selecting the magnet spacings in a Lorentz force EMAT. The range of frequency input was achieved using a linear frequency modulated chirp signal. Finite Element models and experiments were conducted to demonstrate the method. These results are in close agreement.