Magnetic particle testing (MT) has the advantages of high sensitivity and adaptability. However, during the formation of magnetic particle indication (MPI) corresponding to surface opening defects, the defects are filled with magnetic particles, resulting in the weakening of the leakage magnetic field (LMF), a phenomenon that has been ignored in existing studies. In order to enhance the visual feature of MPI, this paper proposes an isolation strip-based magnetic particle testing method (ISMT), which can avoid the attenuation of LMF. Meanwhile, ISMT can isolate the surface conditions of the specimen to avoid the formation of pseudo-magnetic particle indication (PMPI). The enhancement principle of ISMT is analyzed by simulation. Comparative experiments between ISMT and traditional MT were conducted to verify the visual enhancement effect of ISMT on defects of multiple depths. The results show that the enhancement effect of ISMT is 1.51 times, 1.36 times, and 1.08 times for the standard test shims of 60/100, 30/100, and 15/100, respectively. In addition, the advantage of ISMT in detecting larger defects is verified by experiments on hole defects of different sizes, and the isolation effect against surface oil stains is discussed.

During electromagnetic ultrasonic testing, it is difficult to recognize small-size bottom cracks by time of flight (ToF), and the lift-off fluctuation of the probe affects the accuracy and consistency of the inspection results. In order to overcome the difficulty, a novel composite sensor of an electromagnetic acoustic transducer (EMAT) and pulse eddy current (PEC) is designed. We use the amplitude of a bottom echo recorded by EMAT to identify the tiny bottom crack as well as the amplitude of PEC signals picked up by the integrated symmetric coils to measure the average lift-off of the probe in real time. Firstly, the effects of lift-off and bottom cracks on the amplitude of bottom echo are distinguished by combining the theoretical analysis and finite element method (FEM). And then an amplitude correction method based on the fusion of EMAT and PEC signals is proposed to reduce the impact of lift-off on the defect signal. The experimental results demonstrate that the designed composite sensor can effectively detect a bottom crack as small as 0.1 mm × 0.3 mm. The signal fusion method can accurately correct the amplitude of defect signals and the relative error is less than ±8%.

In electromagnetic ultrasonic testing, it is difficult to recognize small-size bottom cracks by time of flight (ToF), and the lift-off fluctuation of the probe affects the accuracy and consistency of the inspection results. In order to overcome the difficulty, a novel EMAT (electromagnetic acoustic transducer)-PEC (pulse eddy current) composite sensor is designed. We use amplitude of bottom echo recorded by EMAT to identify the tiny bottom crack as well as the amplitude of PEC signals picked up by the integrated symmetric coils to measure the average lift-off of the probe in real time. Firstly, the effects of lift-off and bottom cracks on amplitude of bottom echo are distinguished combining the theoretical analysis and finite element method (FEM). And then an amplitude correction method based on the fusion of EMAT and PEC signals is proposed to reduce the impact of lift-off on the defect signal. The experimental results demonstrate that the designed composite sensor can effectively detect the bottom crack as small as 0.1mm* 0.3mm. The signal fusion method can accurately correct the amplitude of defect signal and the relative error is less than ±8%.

The conventional electromagnetic acoustic transducer (EMAT) testing method has inherent limitations, particularly in its detection range. Combining EMAT with other nondestructive testing (NDT) methods can expand the detection range and improve accuracy. Most EMAT-based dual testing methods can detect surface and backside defects, but cannot be applied in high-speed inspection conditions. Therefore, this article proposes a dual testing method that combines EMAT with motion-induced eddy current (MIEC), enabling the detection of defects on both the surface and backside of the specimen under high-speed conditions. The probe consists of a permanent magnet and a butterfly coil. First, the principles of EMAT and MIEC are analyzed, along with the interactions and interferences between the two methods. A signal separation technique is proposed based on spectral analysis of the individual EMAT and MIEC signals. A 2-D simulation model was developed to assess the detection range of both methods and evaluate the impact of the MIEC effect on EMAT detection. Experimental verification confirmed the effectiveness of the method, and the sensitivity and stability of the probe were also evaluated. The results show that the dual EMAT–MIEC testing method effectively detects millimeter-scale cracks on both surfaces and backsides at a speed of up to 21 m/s.

This study presents a novel, coil-only magnetostrictive ultrasonic detection method that operates effectively without permanent magnets, introducing a simpler alternative to conventional designs. The system configuration is streamlined, consisting of a single meander coil, an excitation source, and a nickel sheet, with both the bias magnetic field and ultrasonic excitation achieved by a composite excitation containing both DC and AC components. This design offers significant advantages, enabling high-frequency Lamb wave generation in nickel sheets for ultrasonic detection while reducing device complexity. Experimental validation demonstrated that an S0-mode Lamb wave at a frequency of 2.625 MHz could be effectively excited in a 0.2 mm nickel sheet using a double-layer meander coil. The experimentally measured wave velocity was 4.9946 m/s, with a deviation of only 0.4985% from the theoretical value, confirming the accuracy of the method. Additionally, this work provides a theoretical basis for future development of flexible MEMS-based magnetostrictive ultrasonic transducers, expanding the potential for miniaturized magnetostrictive patch transducers.