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-mu 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 e ' r and e'' r using the filter-based sensor with a VNA are -4.34% and 13.24%, respectively. At the same time, e ' r and e '' r 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.

Automated summary

A new RF liquid permittivity measurement system is proposed, which utilizes a filter-based microfluidic sensor to integrate with an RF source, power divider, and gain/phase detector (GPD). The filter-based sensor provides a stronger electric-field concentration in the sensing area and improves sensitivity. The proposed system achieves maximum errors of -4.34% and 13.24% for e ' r and e'' r when compared with a commercial dielectric probe kit, while errors of 8.28% and 14% are achieved for e ' r and e'' r using the proposed system. The flexibility of the proposed system makes it suitable for various microfluidic sensing scenarios.