The New High Sensitive Variant of Nonlinear Ultrasound Spectroscopy for Nondestructive Testing

Abstract

The nondestructive testing by ultrasound nonlinear modulation spectroscopy has two basic variants of realisation. The ultrasound excitation uses harmonic signals with relatively near or distant frequencies as using of mixing or modulation principle. This paper presents comparison of these two basic methods and it asks new possibilities for rising of sensitivity. Especially a necessary time for the exciting and sensing signals is compared. The second part discusses possibility of using of the burst-wave exciting mode for these methods. First, the excitation by phase coupled pulse signals is derived for obtaining of result long lime signal without waste of its useful energy. Nevertheless this output long time signal consists from time-separated pulses and therefore the analog prefiltration cannot be used for suppression of excitation signals. Therefore the new variant of mixing method is derived, where such exciting frequencies are used, that result signal with difference frequency has a relatively high frequency and a shorter period then the exciting signal. On the other hand, the frequency difference between this result component and exciting signal is sufficient for using of LC linear filters with sufficient attenuation of exciting signals.