Comparison of continuous-wave (CW) and tone-burst (TB) excitation modes in vibro-acoustography: Application for the non-destructive imaging of flaws

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• 作者：F.G. Mitri ; J.F. Greenleaf ; M. Fatemi
• 关键词：Dynamic radiation force ; Flaw detection ; Non-destructive imaging ; Vibro-acoustography
• 刊名：Applied Acoustics
• 出版年：2009
• 出版时间：February 2009
• 年：2009
• 卷：70
• 期：2
• 页码：333-336
• 全文大小：309 K

文摘

This paper describes the application of continuous-wave (CW) and tone-burst (TB) vibro-acoustography (VA) experiments for imaging a flawed composite plate. For both modes, the ultrasound frequency is set at f₁ = 3 MHz and f₂ = 3 MHz + Δf. The plate was placed at the focus of the transducer and scanned point-by-point over an area of 60 mm by 50 mm on its frontal face with an increment step equal to 0.25 mm/pixel. The resulting acoustic emission amplitude at Δ f is recorded. For the CW mode the difference frequency was set at Δf = 12.9 kHz. For the TB mode, the burst-emitted signal was 100 μs long at a pulse repetition frequency (PRF) of 100 Hz corresponding to bursts of 300 cycles at 3 MHz, and the difference frequency was set at Δf = 44 kHz. The resulting VA images readily show the shape of the flaws. The images also reveal considerable detail of internal substructures such as the fibers used to reinforce the plate. However, the CW VA image shows an artifact caused by the effect of ultrasound standing waves established between the plate and the concave surface of the transducer, resulting in masking some of the flaws. On the other hand, the TB–VA image is free from such artifact. Despite some advantages of using TB–VA, there are some limitations related to this mode. Advantages and limitations of using the two modes are discussed.