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

A new radio-frequency (RF) liquid permittivity measurement system using a filter-based microfluidic sensor is proposed in this article. Integrating the filter-based sensor with an RF source, a power divider, and a gain/phase detector (GPD) 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- μ L water-ethanol mixtures with ethanol volume fractions (EVF) ranging from 10% to 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 r' and r using the filter-based sensor with a VNA are -4.34% and 13.24%, respectively. At the same time, r' andr 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.