Highly Sensitive Microwaves Sensors for Fluid Concentration Measurements

Abstract

Although electromagnetic-stored energy of planar electrically-small resonators is mostly concentrated in an electrically small volume, most of the energy, however, is concentrated in the host substrate, thus limiting the sensitivity to detect changes in the material under test which is different from the host substrate. In this letter, a sensor design for enhancing the electromagnetic stored energy in the sensing volume is presented. The design concept is based on using a 3-D parallel-plate capacitor to enhance the stored electric energy in the sensing volume that is exposed to the material under test. For validation, a resonator based on a complementary electric-LC resonator was utilized to design the sensor. Using simulations, the sensor demonstrated a sensitivity enhancement of more than 400% when detecting changes in a dielectric material over the relative permittivity range of 1 to 1.2. To validate the concept experimentally, the sensor was utilized to detect changes in the concentration of two fluids, which makes it suitable for a host of emerging micofludic applications including lab-on-a-chip.