Multifrequency Coupled-Resonator Sensor for Dielectric Characterization of Liquids

A six-band microstrip sensor, based on a pair of electrically coupled resonators (ECRs), is proposed to perform multifrequency dielectric characterization of liquids. A pocket is milled through the substrate bottom of the sensor to contain the fluid sample, avoiding the need for a sample holder. The pocket has been designed to achieve a higher electric field magnitude in the sensing region and a mechanism to separate the resonant frequencies, which helps to ensure a high span between the first and the last resonant frequency. The microstrip sensor is implemented on a 1.905-mm-thick substrate with
$\varepsilon ^{\prime }_{r} = 12.2$
and
$\tan \delta = 0.0019$
. The sensor’s six resonance frequencies span the range between 1 and 3.5 GHz. Experimental tests show that the sensor can measure a wide range of
$\varepsilon ^{\prime }_{r}$
values between 2 and 79 resulting in close similarities to the dielectric constants published in previous works.