Characteristics of acoustic emission signals generated by termite activity in wood

A series of experiments have been performed lo determine if acoustic emission (AE) monitoring can be used to detect termite infestations in wood. Results obtained with a computer-controlled measuring system indicate that termite activities in the wood generate a significant amount of acoustic emission which have frequency componenls extending to above 100 kHz. These emissions can be easily detected by commercially available AE sensors (50 kHz resonant sensors were used in these measurements). Spectral analysis of noise signals (including some deliberately generated) indicate that nearly all noise signals have most of their energy below 20 kHz. Thus it appears feasible to separate termite-generated signals from noise signals by filtering. The ultrasonic propagation characteristics of wood, especially the large and frequency dependent propagation losses, have a significant impact on the detection process. However by working below 100 kHz, termite-generated signals could be detected at least 2 meters away from the site of the infestation, as long as the sensor was on the same piece of wood. A practical hand-held, battery-powered detection system has been designed, fabricated, and tested successfully in the laboratory.