Discrimination of Added Water Content of Milk by Ultra‐Wideband Non‐Contact Time Domain Dielectric Spectroscopy

ABSTRACT Recently, frequency‐domain and time‐domain (TD) wideband dielectric spectroscopy have been used for identifying the real and imaginary parts of material permittivity. High‐cost contact‐based method using a large form factor vector network analyzer (VNA) is a standard method for measuring the permittivity of liquids. In this paper, a non‐contact TD dielectric spectroscopy method based on a small‐form‐factor UWB system is presented for measuring the real part of the permittivity of highly dispersive liquids. The material under test is milk with different added water content. The measurements are performed using a maximum‐length sequence (m‐sequence) transceiver and Vivaldi antennas in a quasi‐monostatic free‐space dielectric spectroscopy setup. The reflection coefficient of a two‐layered heterogeneous medium is obtained using the Fast Fourier Transform of received reflected time domain signals. Finally, the real part of permittivity is calculated using the reflection coefficient. The calculated permittivity is compared against the measured permittivity using a classical coaxial probe and VNA. The mean square error in permittivity for milk with different added water content is below 0.043%.