基于宽频激励电磁声谐振7075铝合金板厚检出概率

电磁超声换能器(EMAT)换能效率低、激发信号弱,而基于长周期激励信号以产生声波共振的电磁声谐振技术(EMAR)虽然可以提高接收信号的信噪比,然而可能导致主脉冲加宽并扩大超声波检测盲区,降低测量精度.本文应用一种宽频激励电磁声谐振技术(BE-EMAR)和一种Halbach阵列纵波EMAT,以单周期宽频激励作为EMAT输...

Probability of detection of 7075 aluminum alloy plate thicknessbased on BE-EMAR

The electromagnetic acoustic transducer (EMAT) has low energy conversion efficiency and weak excitation signal, althoughthe electromagnetic acoustic resonance (EMAR) technology based on long-period excitation signal for generating acoustic resonance canimprove the signal-to-noise ratio of the received signal, it may cause the main pulse widen, enlarge the blind area of ultrasonic detectionand reduce the measurement accuracy. In this paper, a broadband excitation electromagnetic acoustic resonance technology ( BEEMAR) and a Halbach array longitudinal wave EMAT are applied, a single-cycle broadband excitation is used as the EMAT inputsignal, and the EMAR method is used to measure the plate thickness of 7075 aluminum alloy specimens. The probability of detection(POD) model is used to characterize the measurement accuracy for micro metal plate thickness. The experiment results show that in thePOD curves obtained with BE-EMAR under three signal-to-noise ratios when the noise is not reduced, the corresponding maximumdifference of a50or a90/ 95is 0. 05 mm, while the maximum difference under the same signal-to-noise ratio before and after the noisereduction is 0. 07 mm. However, in the POD curve obtained with the time of flight (ToF) method the maximum difference is 0. 21 mm.Therefore, there is no significant difference between the results obtained with BE-EMAR before and after noise reduction, and thescheme is insensitive to conventional noise signals. Before and after noise reduction, in the POD curve obtained with BE-EMAR, a50anda90/ 95 both can be stabilized within 0. 55 mm, which proves that the BE-EMAR has better accuracy, stability and anti-noise ability thanToF method in thickness measurement.