A Microwave and Microfluidic Planar Resonator for Efficient and Accurate Complex Permittivity Characterization of Aqueous Solutions

Abstract

A microwave resonator is presented as a microfabricated sensor dedicated to liquid characterization with perspectives for chemistry and biology. The nanolitter range aqueous solution under investigation is located on top of the planar resonator thanks to a microfluidic channel compatible with a future lab-on-a-chip integration. The interaction between the electric field and the liquid translates into a predictable relationship between electrical characteristics of the resonator (resonant frequency and associated insertion loss) and the complex permittivity of the fluid (real and imaginary parts). A prototype of the resonator has been fabricated and evaluated with de-ionized water/ethanol mixtures, with ethanol volume fraction ranging from 0 to 20 %. Good agreement has been reached between theoretical and measured electrical parameters of the resonator. The discrepancy on the resonant frequency is estimated to 0.5 %, whereas the one on the associated transmission coefficient is lower than 1 %. This translates into a maximum relative error on the real and imaginary part of the predicted relative permittivity of less than 6.5 % and 4 % respectively, validating the principle of this accurate permittivity characterization methodology.

Improved Split-Ring Resonator for Microfluidic Sensing

“…Planar interdigitated capacitor sensors suffer from similar disadvantages. That demonstrated in [37] has a quality factor two orders of magnitude lower than those presented here, resulting in reduced sensitivity as described in Section III-A. The second, non-planar SRR implementation typically utilises a much thicker ring, which means the capacitive region occupies a larger volume.…”

“…To measure the complex permittivity of a material, it must perturb the electric field within the loop gap. A planar interdigitated capacitor can be used as a resonant permittivity sensor in a similar way; this has been demonstrated using liquid-filled capillaries to perturb the capacitor electric field in [37].…”

Microwave-to-terahertz dielectric resonators for liquid sensing in microfluidic systems

“…Planar resonators, multiple resonator filter structures and even metamaterials are attractive because of their high electric fields within capacitive gaps, like in coplanar waveguides, lumped element LC resonators or split ring resonators [8,9]. Microfluidic fabrication technology enables the integration of metal electrodes within microfluidic channels.…”

Design of Rf Sensor for Simultaneous Detection of Complex Permeability and Permittivity of Unknown Sample

“…Since cavity resonator technique requires bulky and costly metallic cavity, the planar resonant sensors are preferred because of advantages such as low cost, easy fabrication and integration with other microwave circuits [11]. Designs of the planar resonant sensor are mostly based on various resonant structures such as split ring resonators (SRR) [12][13][14][15], complementary split ring resonators (CSRR) [16], substrate integrated waveguide (SIW) [17,18], slotline based RF sensor [19], stepped impedance resonator (SIR) [20], series resonators [21], fractal capacitors [22], spiral inductors [23] and interdigitated capacitor (IDC) [24]. Among these different resonant structures, the fractal capacitors, spiral inductors, IDC are easy to get fabricated on microstrip line and provide a reasonably high amount of sensitivity.…”