Electromagnetic techniques for moisture content determination of materials

Based on a short introduction to the dielectric properties of water and aqueous solutions, this review summarizes current techniques of electromagnetic aquametry. The techniques described here include time-domain and frequency-domain procedures, enabling moisture determination in a broad spectral range from millihertz to terahertz frequencies. In this review, quasi-static capacitance and impedance approaches as well as microwave and submillimetre wave reflection, transmission and resonant methods are presented. Sensor configurations and electronic measurement setups, including remote sensing, are discussed briefly. A broad spectrum of applications is introduced to show the extended usability of electromagnetic techniques of moisture content determination. The dielectric properties of some reference materials, suitable for the calibration of sensors and of electronic measurement devices, are tabulated. Reference is also made to some dielectric models of water-containing materials and to superior evaluation routines.