Measurement of cereal moisture content with an experimental acoustic device

An acoustic device was developed and tested that relates the moisture content of cereal grains to the sound spectrum generated by the fall of kernels over a rigid surface of known characteristics (a glass plate). Samples of wheat, parboiled rice, and corn were tested by recording the overall sound pressure level and conducting an octave band frequency analysis. The moisture content of the samples was determined with an infrared thermobalance. The results showed a good linear correlation between the moisture content of the cereal and the sound pressure level produced by kernels falling on a rigid surface. In the general range of 11% to 23% moisture content, the overall sound level decreased by approximately 0.4 dB for each percentage point of humidity for parboiled rice, whereas for both wheat and corn, the decrease was 0.3 dB. Octave band analysis clearly showed that the highest sound levels were obtained at high frequencies. The most sensitive bands, which are highly related to humidity variation, ranged from 2 to 16 kHz; therefore, inexpensive sound level meters, which could be designed and built on an ad hoc basis, could be profitably used.