నైరూప్య

Flaw Detection using Split Spectrum Technique

Gopika Syam, Sadanandan G.K.

Flaw detection is a common application of industrial ultrasonic testing. The propagation of sound waves through materials has been used to detect discontinuities within them. Sound waves reflect from flaws in a way that can produce distinguishable echo patterns. Thus the presence of flaw within materials can be determined. In addition to the flaw echo, reflections from microstructure contribute to reverberation, which interferes with the signal. Reverberation is expected to have complex interference structure. This interference pattern varies with the transmitted frequency. To take advantage of this phenomenon, a wide band signal is transmitted to effectively reduce the influence of reverberation. So it is assumed that the reflections from the flaw is insensitive to frequency and produces a steady output. This property has been utilized for flaw detection. Eliminating the unwanted reflections using conventional filtering techniques removes the flaw signal also, since both the received echo and reverberation are generated from the same transmitted signal itself and has similar spectral distributions. So, it has been proved that Split Spectrum processing algorithm followed by Order Statistic Filter can provide an optimized result. Multiple pulses will betransmitted and Order Statistic filters can be used for post processing of the received pulses. Thus, by processing the multiple echoes corresponding to a set of transmitted signals, the effect of microstructure reflections can be suppressed with respect to the flaw echo.