Modeling of Coplanar Interdigital Capacitor for Microwave Microfluidic Application

• Published in: IEEE transactions on microwave theory and techniques 2019-07, Vol.67 (7), p.2674-2683
• Main Authors: Bao, Xiue, Ocket, Ilja, Bao, Juncheng, Liu, Zhuangzhuang, Puers, Bob, Schreurs, Dominique M. M.-P., Nauwelaers, Bart
• Format: Article
• Language: English
• Subjects: Capacitance; Capacitors; Complex permittivity; Computer simulation; Conformal mapping; Coplanar waveguides; Dielectric properties; Dielectrics; Electrodes; Finite element method; interdigital capacitor (IDC); Mathematical models; microfluidic; Microfluidics; microwave; Microwave theory and techniques; Multilayers; Nonhomogeneous media; Permittivity; Resistance; sensor; Sensors; Substrates
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2019.2916871

Due to its noninvasive property, the interdigital capacitor (IDC) has been applied in dielectric liquid detection and characterization. In order to integrate the IDC sensor on a lab-on-chip, it is often required to minimize and optimize the sensor for sensitive and efficient performance. However, the conventional numerical simulation approach is quite time-consuming. Therefore, an efficient analytical method is proposed herein, leading to accurate capacitance and conductance expressions of an arbitrary multilayer-structured IDC. The model is validated with practical measurements of a series of coplanar waveguide (CPW) structure-based IDCs. In addition, an accurate characterization function, which relates the IDC capacitance and conductance to the complex permittivity of a material loaded on the top of the IDC sensing area, is obtained. The characterization function shows good agreement with the finite-element method (FEM) simulation results, which demonstrates the capability of the IDC sensor in dielectric spectroscopy measurements of \mu \text{L} and even nL liquids.