Numerical modeling of two microwave sensors for biomedical applications

The purpose of this invited paper is to give readers a critical and comprehensive overview on how to extract dielectric properties of a bioliquid within a broad frequency range. Two sensors are used in the paper to characterize saline solutions by measuring the broadband complex permittivity. The two sensors are based on transmission line and interdigital electrodes designed for low- and high- frequency measurements, respectively, on the basis of the coplanar waveguide structure due to its convenience of fabrication and integration with microfluidic structures for liquid measurements. Different from traditional work where the finite element simulation method is used, the characterization theories of the two sensors are built based on a numerical modeling procedure, which can dramatically increase the device design efficiency, taking just a few seconds. Differently from the finite element method, the proposed numerical analysis utilizes a conformal mapping technique for both sensors. The characterization theories of the two sensors are validated by measuring de-ionized water. The platform is finally used to measure 0.1 and 0.5 mol/L saline solutions within a broadband frequency range going from 10 up to 50 GHz, with the repeatability error within 5%.