LFM激励信号在超声TOFD检测中的应用
Application of LFM excitation signals to ultrasonic TOFD test
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摘要: 对于大厚度焊接试件的超声衍射时差法检测(time of flight diffraction, TOFD),常规超声激励难以同时满足信噪比、检测距离以及检测分辨率的要求.文中将线性调频脉冲压缩技术应用在超声TOFD检测中,线性调频(linear frequency modulated, LFM)激励可综合改善检测信噪比(signal to noise ratio, SNR)与分辨率.首先对试验用10 MHz超声换能器进行了LFM信号参数测试,选择了合适的时宽和带宽.对埋藏3 mm高的横槽缺陷的钢板分别进行了超声LFM激励的TOFD检测及常规超声TOFD检测,对比发现超声LFM激励的TOFD检测精度高达0.01μs,可准确区分缺陷上下端衍射波.在较低的激励电压和系统增益下,实现了较高的检测信噪比及分辨率.Abstract: For ultrasonic TOFD test of weld specimen with large thickness, conventional excitation is difficult to satisfy the requirements of SNR(signal to noise ratio), detection distance and resolution. LFM(linear frequency modulation) pulse compression technique is applied to ultrasonic TOFD test in this paper. LFM excitation can improve both SNR and resolution. Firstly, appropriate pulse width and bandwidth for 10 MHz transducer were determined by LFM parameter test. Then, a slot defect hided in the depth of 3 mm in steel plate was tested by ultrasonic LFM-TOFD test and conventional ultrasonic TOFD test. The results show that LFM excitation can make diffracted waves separated obviously, and the precision reaches up to 0.01μs, compared with conventional excitation. In the case of lower exciting voltage and gain, higher SNR and resolution can be achieved.
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Keywords:
- TOFD test /
- LFM excitation /
- pulse compression /
- large thickness weld specimen
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