| Ultrasonic is an important means to measure the rail stress. EMAT (Electromagnetic Acoustic Transducer) is a new type of ultrasonic transmitting and receiving devices, because it needs no couplant and contact, the EMAT gets more and more attention.This paper first discusses the EMAT technology development history and its application actuality, based on the deep research on the theory of EMAT, it divides an entire EMAT into three interconnected field: electromagnetic field, kinetic force field and ultrasonic field,deduces the corresponding physics equations and a complete set of EMAT acoustic equations are derived; In addition, it discusses several common types of ultrasonic and the relation between the stress and the surface wave propagation lag is given combined with the acoustoelasticity theory.Secondly, the structure and circuit model of EMAT system is designed. The characteristics of permanent magnet and two electromagnets are compared, and through analyzing different shapes of incentive coil derives, an EMAT detection probe is designed. A pulse bunch signal generator is designed by using phase-shift PWM controller UCC2895 and the power amplifier is also provided through full-bridge inverter circuit based on MOSFET. Among them, the MOSFET driving characteristics and driven parameters are introduced and proper drive circuit for MOSFET is given. In order to raise the launching efficiency and the SNR of received signal, EMAT impedance matching techniques are given in the dissertation.Finally, the detection system is optimized through a series experiments on the real rail, and the relation formula of rail stress and propagation time is provided by the experiment, and makes a foundation for future dynamic detection for rail stress based on electromagnetic ultrasonic.
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