β Scribed by Robert Hickling; Wei Wei
No coin nor oath required. For personal study only.
The transmission of sound in stored grain was investigated to facilitate the use of sensitive microphones to detect insect infestations. Such infestations cause sign@cant loss (about 10(X, or a billion (10') dollars worth, annually in the USA), and early detection is an importunt ,factor in reducing such losses. The tests were conducted in a tank containing about 5 m-j of wheat. The phase velocity of sound and the absorption coeficient were measured as a.function of frequency using a two-channel analyzer system. Data were analyzed using sound-transmission theory in porous media. It is shown thut sound is transmitted principally through the air passages between the gruins and that, over u distunce of I m, grain is highly absorbing ut frequencies above about 1 kH. The theory provides a measure of the uverage spacing between grains, which ut a depth of 0.5 m was found to be clbout 0.6 mm.
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