Coating quality nondestructive detection of metal materials using electromagnetic ultrasound

To solve the problem of low signal-to-noise ratio of received signals in the coating quality detection using ElectroMagnetic Acoustic Transducer(EMAT),ElectroMagnetic Acoustic Resonance(EMAR) technology is applied to improve the signal-to-noise ratio of received signals.The discrete resonance spectra and the time domain waveforms of resonance and non-resonance are obtained by simulation and the feasibility of coating quality detection by electromagnetic acoustic resonance is verified.The electromagnetic ultrasonic signal resonates in the coating and the resonant standing wave is collected as the detection signal.The amplitude of the resonant signal is about 2.5 times that of the reflected echo,and the signal-to-noise ratio is increased from 26 dB(reflected echo) to 34 dB(resonant signal).The coating thickness is detected by the resonant frequency difference of electromagnetic acoustic resonance signal.The detection error of specimens of 0.2-0.8 mm is within 5%.The larger the coating thickness is,the more resonant frequency is,the smaller the resonant frequency difference is,and the higher the detection accuracy is.The Power Spectral Density(PSD)is used to distinguish specimens with different adhesion degrees.The PSD ratio of different specimens was 61.17:4.15:1,which was significantly improved compared with the peak-to-peak ratio of 2.45:1.78:1.Experimental results show that the electromagnetic acoustic resonance technology can effectively improve the signal-to-noise ratio of electromagnetic ultrasonic echo signal and improve the precision of electromagnetic ultrasonic coating quality testing.