726 M A T E R I A L S E V A L U A T I O N • J U L Y 2 0 2 1 in amplitude and velocity of the transmission of the Lamb ultrasound waves caused by the presence of defects. Further investigation is needed to evaluate the sensitivity of the designed EMATs to size and shape of cracks and corrosion. Conclusion The objective of this study was to design and test a modular robotic gripper with embedded EMATs as the main compo- nent of a versatile LTI robot. By integrating a couplant-free ultrasound sensing and friction-based mechanical component in a single robot, it eliminated the need for smooth surfaces and simple pipe geometries. Moreover, the proposed system removes the need for point-by-point scanning of tubular surfaces for crack and corrosion detection. The proposed modular robotic gripper embedded with EMATs consisted of three major mechanical components, including base plate, arch, and fingers. The designed gripper was attached to a robotic manipulator and its performance was tested on pipes with different outer diameters. The sensing process was accomplished using Lamb waves. To this end, the S0 mode was applied to evaluate the performance of the gripper. Preliminary tests were conducted to investigate the effect of curvature on the properties of the Lamb waves. The obtained results revealed that conforming of the coils with the sample surface did not necessarily increase signal amplitude. Therefore, a nonconformed configuration was applied in the gripper to inspect pipes with different curvatures. The received time-domain waveform generated by the EMATs indicated that group velocities in the conformed and nonconformed configura- tions were almost consistent, while there existed an inversely proportional relationship between sample curvature and group velocity. From the experimental results, it could be inferred that directly transmitted and received signals were successfully acquired in the time domain. An increase in sample diameter led to an increase in signal amplitude. Moreover, it could be verified that the robotic ultrasonic system integrated with EMATs gener- ated Lamb waves with acceptable SNR levels for inspecting tubular components. Finally, the sensing system’s efficacy in terms of cracks and corrosion detection was considered via experimental measurements on artificially induced defects. For the developed modular robotic gripper system, two sets of tests were carried out on both defect-free pipes and pipe with simu- lated defects. Two grippers were used to detect a surface crack and partial corrosion with a depth of 1 ± 0.1 mm. Reduction in amplitude and wave velocity were shown to be effective damage- sensitive features. 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