document: There are a number of avenues to explore for future work, in particular the use of other time–frequency analysis methods. The STFT spectrogram was utilised here, as it is the simplest to implement. Whilst all of the echoes could be clearly resolved in both time and frequency, the spectrogram suffers from a fixed resolution, i.e. an increase of time resolution necessarily leads to a decrease in frequency resolution. Other methods of time–frequency analysis, such as discrete wavelet analysis, benefit from advantage of multi-resolution analysis, which offers improved temporal resolution of the high frequency components, and frequency resolution of the low frequency components [25,18,19]. Also, whilst the current work has utilised SH waves that are generated by EMATs, the physics that describes the pulsed array system is universal to other types of waves. Future work will include demonstrating this phenomenon with a number of other systems, for example using longitudinal ultrasonic waves or electromagnetic waves.
doc_bio_tags: O O O O O O O O O O O O O O O O O B I O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O B I O O O O B I O O O O O O B I O O O B I O O B I I O O O O O O O O O B I O O O O O O B I O O B I I O O O O O O O O B I O O O O B O O O O O B I I O O O O O O O O O O O B I I I I I I I I O O O B I I O B I
extractive_keyphrases: demonstrating this phenomenon with a number of other systems discrete wavelet analysis electromagnetic waves emats fixed resolution frequency resolution longitudinal ultrasonic waves low frequency components pulsed array system sh waves spectrogram temporal resolution time–frequency analysis time resolution
abstractive_keyphrases: multi-resolution analysis stft spectrogram use of other time–frequency analysis methods