A spectrum analyser for acoustic emission

Frequency analysis of acoustic emission (AE) involves the capture and analysis, or real-time analysis, of an impulsive or non-repetitive signal. The present ARL procedure involves the use of a transient recorder and conventional heterodyne spectrum analyser, and no more than one event per five seconds can be handled. Even with the adoption of a strict sampling procedure, much information is lost, particularly during the important periods of intensive AE activity. Upton (1977) discussed the use of the heterodyne analyser, of parallel analogue or digital filters, and of the FFT algorithm. Commercial equipment based on these principles is available but expensive. Clark and Mathieson (1977), and Graham (1979), used matched sets of band-pass filters whose centre frequencies were related by a fixed ratio. This method of spectral analysis is fast, provides an output suitable for handling by a computer and, by restricting the number of bands, suppresses much unwanted detail in the spectrum. It was chosen for laboratory development and was constructed from available cheap components.