Microwave nondestructive sensing of moisture content in shelled peanuts independent of bulk density and with temperature compensation

Dielectric methods for rapid and nondestructive sensing of moisture content in shelled peanuts from free-space measurement of attenuation and phase shift, and their corresponding dielectric properties at temperatures ranging from 1 to 38 °C and frequencies ranging from 8 to 14 GHz, are presented. These methods provide moisture content independent of bulk density and compensated for temperature effects. Results of moisture prediction with three density-independent calibration functions (ψ₁, ψ₂, and ψ₃) are compared. For each function, the moisture calibration equation with temperature compensation is given along with corresponding standard errors of performance (SEP). For all three calibration functions, the SEP was less than 1% moisture content. Also, the frequency behavior of each of these calibration functions was examined in the frequency range between 8 and 14 GHz. Among the three density-independent calibration functions, calibration function ψ₃ showed the least variation with frequency.