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Title: Noise shielding of acoustic devices for insect detection

item Mankin, Richard
item Shuman, Dennis
item COFFELT, JAMES - Retired ARS Employee

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/1996
Publication Date: N/A
Citation: Mankin, R.W., Shuman, D., Coffelt, J.A. 1996. Noise shielding of acoustic devices for insect detection. Journal of Economic Entomology. 89:1301-1308.

Interpretive Summary: There is a need for new techniques to detect hidden insects like stored product pest larvae that feed inside kernels of grain. Earlier detection can lead to improved quality control and to reductions in the use of pesticides. Whenever foreign bulk grain purchases are transacted, USDA Federal Grain Inspection Service personnel examine and grade samples of the grain. One of the tests performed involves manually sieving a standardized sample of grain to determine the number of insects present. A system that can automatically determine the number of live larvae in a sample of grain has been developed by scientists at the Insect Attractants, Behavior, and Basic ;biology Research Laboratory in Gainesville, Florida. The Acoustic Location Fixing Insect Detector (ALFID) system detects sounds produced by insects as they feed and move among the kernels of grain. The sounds are of low intensity relative to the background noise in a commercial grain elevator. consequently, devices like ALFID require acoustical shielding. This report describes the design and testing of an effective shield for ALFID and other acoustic insect detection devices in a commercial grain elevator environment

Technical Abstract: Electronic devices that detect insect-generated sounds must amplify and filter signals that have a low signal-to-noise ratio. The mean sound pressure level (SPL) generated by Sitophilus oryzae (L.) (Coleoptera: Curculionidae) larvae in wheat kernels is only 23 dB//ref: 20 uPa (i.3., 23 dB relative to the 20 micropascal threshold of human hearing), measured by a microphone 3 cm from a larva inside a grain sample. To reduce background noise below these levels, a multi-layered sound- insulated box was constructed that attenuates sound by 70-85 dB between 1-10 kHz. Its noise-shielding characteristics were evaluated at Federal Grain Inspection Service Offices in two commercial grain elevators. Noise levels inside the offices ranged from 50-80 dB SPL between 0.1-10 kHz. The box effectively shields acoustic detectors in the frequency range between 2-6 kHz where signals generated by S. oryzae have the greatest energy