A non-contact Laser-EMAT integrated system (LEIS) that uses a pulse laser as a generator and an Electromagnetic acoustic transducer (EMAT) as a detector is proposed. To explain the LEIS could simultaneously measure the width and the depth of metal plate, the finite element model (FEM) of the LEIS, which can describe the entire process from laser generates ultrasound to EMAT receives ultrasound, is established. In detail, the intensity ratios of Rayleigh wave, Shear wave and Longitudinal wave excited by laser under the consideration of three components, the particle displacement, the particle vibration velocity in out-plane direction and particle vibration velocity in in-plane direction, are focused. Combining the characteristics of the ratio and the EMAT as a velocity sensor, the Rayleigh wave and Longitudinal wave in the case of the particle vibration velocity in out-plane direction are chosen as the using waveforms, and the changes of directivity of various waveforms with laser parameters are studied. Furthermore, after the coil structure parameters and magnetic field direction of EMAT were reanalyzed and reconsidered, it is decided to use the coil with the wire spacing of 0.1mm and a number of turns of 8 to combine with the transverse magnetic field to simultaneously detect the Rayleigh wave and Longitudinal wave generated by the laser. Finally, the signal-to-noise ratio of the two waveforms reach a balanced value, and can be clearly distinguished and extracted to achieve the purpose of measuring the depth and width of the metal plate at the same time.

In this article, the contributions are to further study and verify a bulk-wave electromagnetic acoustic transducer (EMAT) for the transverse crack detection of rail base and to propose an auxiliary method for achieving efficient detection. There is no verification for rail treated as a plate in the previous publication. For the verification, the wedge-like rail base is reasonably simplified into the front view and the side view to replace the 3-D finite-element model (FEM) simulation. In addition, the experiment to detect an artificial transverse crack of the standard rail specimen is carried out to verify the treatment of the wedge-like rail base. Both simulation and experimental results demonstrate that the wedge-like rail base can be inspected as a steel plate using a spiral-coil EMAT, but the only time of flight is hard to detect the transverse crack of the wedge-like rail base due to low SNR. For solving the problem of low SNR, this article proposes an auxiliary method of watching for the disturbances of the back-wall echo. Also, the limit condition of the auxiliary method is analyzed for practical applications.

The problem of poor coupling and wheel breakage is a critical issue in the rapid inspection of rails using contact piezoelectric ultrasonic technology for trolleys and vehicles. To overcome this shortcoming, a non-contact unidirectional Shear Vertical Wave EMAT (USV-EMAT) for rapid rail flaw detection with a larger emission angle is proposed and optimized. First, the core characteristics of the USV-EMAT and the Unidirectional Line-Focusing Shear Vertical Wave EMAT (ULSV-EMAT) are compared and analyzed, including emission angle, directivity, intensity, and detection scan distance. The results confirmed that the USV-EMAT is more suitable for rapid rail flaw detection. Secondly, the orthogonal experimental analysis method was used to optimize the structural parameters of the probe. This study systematically identified the key factors influencing the directivity and intensity of acoustic waves excited by the probe, as well as the detection blind zones. Finally, the structural parameters of the integrated 37° USV-EMAT probe were determined by comparing and analyzing the received signal characteristics of the transmit–receive racetrack coil and the self-transmitting–receiving meander coil. The results show that the optimized probe achieves a 14.3 dB SNR for detecting a 5 mm diameter, 50 mm deep transverse hole in the rail, and a 14.0 dB SNR for a 3 mm diameter, 25 mm long, 50 mm deep flat-bottomed hole. Additionally, this study reveals that as the burial depth of the transverse holes increases, the detection scan distance for such defects exhibits an “N”-shaped trend, with the minimum occurring at a depth of 90 mm.

With the increasing of operation speed and decreasing of interval time of train, high speed railway defect inspection method is required for rail transportation safety. In this paper, method of online electromagnetic rail defect inspection based on FPGA is proposed. This method, Use voltage demodulation algorithm to demodulate the information of amplitude of electromagnetic induction signal, and the results of demodulation are transmitted to host computer for storage and display through Ethernet. All algorithm, including generation of sinusoidal excitation signal, demodulation of amplitude, drive of Ethernet, et al, are implemented by using Field Programmable Gate Array (FPGA). Concept of pipeline and parallel are used when implementing the design, so that the efficiency of calculation is increased to fit the requirements of high speed online railway defect inspection. A real experiment system has been developed to simulate rail defect inspection with high speed condition. For this experimental system, a solid circular steel wheel with crack is used as rail sample and fast rotation of wheel is performed to simulate high speed operating condition. For experiment part, the surface speed of circular wheel is set as 20 km/h, 60 km/h, 120 km/h, 180 km/h, 240 km/h separately. When a certain surface speed option is selected, frequency of sample clock and system clock are both set at 20.48 MHz, 81.92 MHz and 122.88 MHz respectively to signal sampling and data processing for data analysis.