Characteristics of noise attenuators for use in acoustic emission studies

The background noise generated by servo-hydraulic machines commonly used in laboratory tests of materials prevents the extraction of the maximum amount of acoustic emission data during fatigue experiments. Some of the solutions for removing background noise during monotonic tests are not applicable, and modern acoustic emission (ae) monitoring systems cannot detect all ae generated in the presence of continuous background noise. The best technique for reducing the background noise appears to be the insertion of a noise attenuating barrier between the noise source and the test specimen.Multilayer sound transmission theory is outlined to show that noise attenuators must be designed for the particular frequency at which the ae system is to operate. The theoretical basis for obtaining (for a given application) the optimum attenuation from attenuators constructed on an acoustic impedance mismatch basis is provided. Finally, physical properties of materials suitable for use in attenuator construction are tabulated.