Millimeter wave measurement of high loss liquids permittivity

Abstract

Numerous techniques are applied to the complex permittivity (CP) measurement of liquids at microwave frequencies. It is well known that both resonator and waveguide methods used for the CP measurement of high loss liquids. The resonator methods apply the complex resonant frequency to obtain CP of liquid. And the waveguide methods use the complex propagation factor in the waveguide segment with liquid that under study. The significant limitation of the above-mentioned methods is a high attenuation observed in the high loss liquid measurements. Moreover, the high loss liquid has large real and imaginary CP parts (far more greater than 1, specifically, for water) and these values are of the same magnitude. Therefore, measured parameters (the resonant frequency and Q-factor in the resonator or the wave phase and attenuation in the waveguide) are simultaneously dependent both on real and imaginary CP parts. Owing to this fact the CP determination becomes considerably complicated while using measured parameters. For the resonator method the Q-factor is rather small (it is on the order of 10-100) and as a result it is difficult to determine the resonant frequency value. As to the waveguide method, the wave attenuation is high during the propagation of the wave even via a small waveguide section in the presence of high loss liquid.