An acoustic plethysmograph intended to measure the body volume of premature infants has been developed using the principle of the Helmholtz resonator, in which the resonance frequency is dependent on the volume of the resonating cavity. A prototype system was built and used to measure the volume of inanimate objects and newborn miniature pigs. Results for inanimate objects agree within 1 percent with comparable measurements by water displacement. Results of the animal body volume measurements compare favorably (within an average of 1.1 percent) with those obtained using hydrostatic weighing.

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