Microwave moisture meter for in-shell peanut kernels

• Low-cost microwave meter for rapid moisture determination in-shell peanut kernel.
• Kernel moisture is determined from measurement of the dielectric properties of pods.
• Near-field free-space measurement of dielectric properties at 5.8 GHz.
• Novel algorithm for phase shift correction by using the attenuation is proposed.
• Moisture calibration equations with temperature compensation are given.

A microwave moisture meter built with off-the-shelf components was developed, calibrated and tested in the laboratory and in the field for nondestructive and instantaneous in-shell peanut kernel moisture content determination from dielectric properties measurements on unshelled peanut pod samples. The meter operates at a single frequency of 5.8 GHz and uses free-space transmission measurement principles for determining the dielectric properties of the peanut pods. From these properties, a dielectric-based algorithm provides peanut kernel moisture content from measurements on pods. Field tests at a peanut buying station showed that moisture content of peanut kernels can be determined with a standard error of performance of 0.82% when compared to the official moisture meter which required the pods to be shelled before kernel moisture content can be determined. When performance of both the microwave moisture meter and the official meter were compared to the oven-drying standard method, values of the standard errors of performance were 0.53% for the microwave moisture meter and 0.87% for the official moisture meter.