Use of resonating cavity to measure body volume

A technique to estimate the body volume of newborns has been developed using the principle of the Helmholtz resonator. The change in the resonance frequency of a small cavity after an infant is placed inside can be used to determine the body volume of the infant. A prototype system, termed an acoustic plethysmograph, was built and used to measure the volume of newborn miniature pigs. Results of the animal body volume measurements compare favorably (within an average of 1.1%) with body volumes measured by hydrostatic weighing.