Phased array electromagnetic acoustic transducers (EMATs) for surface detection
L Xiang, R S Edwards and S Dixon
A phased electromagnetic acoustic transducer (EMAT) system has been developed for fast detection of surface-breaking defects, generating and detecting Rayleigh waves on thick metal samples. An array of several linear coils that are individually controlled are used to emit a Rayleigh wave with an enhanced signal-to-noise ratio (SNR). The high-accuracy electronics, combined with the coil designs, enable the array to generate either narrowband or broadband signals and the phasing makes it possible to change the ultrasound wavelength.
A prototype EMAT consisting of four coils has been made, with an operating frequency range from 250 KHz to 1 MHz on aluminium samples. Experiments for detecting surface-breaking defects were performed using a pitch-catch set-up with a broadband EMAT detector to receive the Rayleigh signal. Machined surface cracks with different depths were used for technique validation. The results show that the phased EMAT design is sensitive to cracks that are deeper than 1 mm when used in the mode for high SNR. Additionally, a wider depth sensitivity range for surface-breaking defect sizing can be easily achieved by applying the proposed phasing method to tune the frequency of operation. A large increase in detection flexibility is immediately shown.
A prototype EMAT consisting of four coils has been made, with an operating frequency range from 250 KHz to 1 MHz on aluminium samples. Experiments for detecting surface-breaking defects were performed using a pitch-catch set-up with a broadband EMAT detector to receive the Rayleigh signal. Machined surface cracks with different depths were used for technique validation. The results show that the phased EMAT design is sensitive to cracks that are deeper than 1 mm when used in the mode for high SNR. Additionally, a wider depth sensitivity range for surface-breaking defect sizing can be easily achieved by applying the proposed phasing method to tune the frequency of operation. A large increase in detection flexibility is immediately shown.
