Characterization of ultrasonic signals generated by concealed insects

It is shown that concealed insect infestations in stored grain and wood products can be detected and identified from the ultrasonic emissions generated by the feeding activity of the insects. The signal is characterized by bursts of energy in the frequency range of 5 to 75 kHz. The number of ultrasonic events increases as a function of the number of insects present, and as a function of the stage of development of an individual insect. By use of the statistical distributions of the emissions, the stage of development of the insect concealed in the medium can be determined. The method chosen to couple the transducer with the medium housing the insect is critical because of the low signal power. Owing to the complex geometrical configuration of the medium, the sonic propagation properties of the medium must be understood to characterize the signal generated by the insects