Maximum length sequences in non-destructive material testing: application of piezoelectric transducers and effects of time variances

In this paper it is shown that even in the field of non-destructive material testing MLS has great advantages. The application of a correlation measuring technique promises a higher dynamic resolution in many acoustical measurements, especially when using maximum length sequences (MLS) as excitation signals. After a short introduction to the measuring principle, problems are described arising when relatively narrow banded piezoelectric transducers are applied. Piezoelectric transducers are common in non-destructive material testing. By means of a phase shift in sampling, effects of frequency aliasing can be used in a constructive way to improve the dynamic range of the system. After that the paper reports on experimental investigations of the effects of time variances on the measuring results, as may appear due to a sudden or continuous motion of the sample in testing practice.