New Radio-Frequency Liquid Permittivity Measurement System Using Filter-Based Microfluidic Sensor

Abstract

A new radio-frequency (RF) liquid permittivity measurement system using a filter-based microfluidic sensor is proposed in this paper. Integrating the filter-based sensor with an RF source, a power divider, and a gain/phase detector can form a new permittivity measurement system without using a bulky and expensive vector network analyzer (VNA) to acquire measured data. Since two coupled resonators with a strong coupling synthesize the filter-based sensor, it can provide a stronger electric-field concentration in the sensing area and improve the sensor’s sensitivity. The 8-μL water-ethanol mixtures with ethanol volume fractions (EVF) ranging from 10% - 90% in 10% increments are used as the test liquids to evaluate the proposed sensor and system. Compared with the measured results using the commercial dielectric probe kit, the maximum errors of ε′ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and ε″ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> using the filter-based sensor with a VNA are -4.34% and 13.24%, respectively. At the same time, ε′ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and ε′ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> errors are 8.28% and 14%, respectively, using the proposed permittivity measurement system. Since the proposed permittivity measurement system can flexibly synthesize the sensing area size, control the electric-field intensity, and get rid of a VNA, it makes it easier to satisfy the requirements of various microfluidic sensing scenarios.