Generation of the ultrasonic helical guided waves in a pipe structure using Staggered EMAT

Ensuring the structural integrity of pipelines is essential for industrial safety, especially as these assets operate in harsh and corrosive environments. Inspecting regions with limited wave coverage, such as the lower surface of pipes beneath saddle supports, remains challenging. Helical guided waves offer an effective solution by enabling circumferential scanning and improving accessibility. Staggered Electromagnetic Acoustic Transducer (EMAT) consists of reconfigurable magnet rows that are shifted laterally rather than dynamic electronic steering, resulting in steering of guided waves at predetermined angles. In this paper, Staggered Periodic Permanent Magnet (PPM) and Halbach EMAT are studied and compared for the same magnet size in an aluminium pipe. Experimental results indicate that the maximum beam steering angles achieved with Staggered PPM and Halbach EMATs are 14° and 26°, respectively, when the second row of magnets is laterally displaced by half of a wavelength. These transducers are systematically compared using three key performance metrics: amplitude variation study (AVS), side‑to‑main‑lobe ratio (SMLR) and beam divergence study (BDS). Furthermore, the study examines the application of Staggered EMATs to generate helically propagating guided wave, thereby enhancing accessibility to hard-to-inspect areas. This capability holds significant potential for the advancement of pipeline inspection techniques.