Implementation of a mobile device for complex permittivity measurement of liquids based on microwave resonant method

As a standard measurement instrument, a vector network analyzer (VNA) provides high measurement accuracy of signal reflection and transmission for various applications. For some applications, however, there are limitations of using a VNA in terms of cost and bulkiness. This work presents an alternative low-cost mobile instrument for complex permittivity measurement of liquid samples using resonant cavity method. With the proposed instrument, resonant frequencies and quality factors have been measured in cases of an empty cavity and cavity loaded with materials under test including distilled water (high dielectric loss), ethanol (moderate dielectric loss) and diesel fuel (low dielectric loss). From the measured resonant parameters, complex permittivity values have been derived. Good agreement of measurement results when using the proposed system and when using a VNA can be achieved. By using cavity perturbation method described in the literature, relative complex permittivity can be determined from the measured resonant parameters. The values agree well with theoretical ones from the table of material properties.