Traditional permanent magnet or pulse electromagnet electromagnetic acoustic transducer(EMAT)has some problems,such as being easy to absorb ferromagnetic particles,resulting in the reduction of energy conversion efficiency and even functional damage,difficul-ty in achieving rapid separation or movement with ferromagnetic metal materials,a large volume of the probe,and being challenging to achieve the detection of the inaccessible areas of the probe such as small narrow areas.A technique realization and modeling method of coil-only electromagnetic ultrasonic testing is proposed to solve the above problems.A finite element model for field-circuit coupling analy-sis of the excitation equivalent circuit and the detection process of the coil-only EMAT is established.The mechanism of longitudinal wave excitation and reception of the coil-only EMAT is analyzed,and the effect of lift-off on the equivalent impedance of the EMAT coil,the high-frequency and DC-like components of the discharge current,and the amplitude and center frequency of the detection echo is also studied.A coil-only EMAT detection circuit is developed,and the lift-off effect is verified.The results show that the coil-only electromag-netic ultrasonic testing system can excite and receive longitudinal waves in an 80 mm thick aluminum alloy sample.The primary bottom wave's signal-to-noise ratio(SNR)is 28.10 dB at 0.1 mm lift-off.When the lift-off increases from 0.1 mm to 1.0 mm,the SNR of the second bottom wave decreases from 22.21 dB to 8.01 dB,and its center frequency decreases from 1.35 MHz to 1.27 MHz.
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