A New Microwave Oscillator-Based Microfluidic Sensor for Complex Permittivity Measurement

A new microwave oscillator-based microfluidic sensor is proposed in this paper for complex permittivity measurement. A modified coplanar strip resonator is proposed as the permittivity sensing device and frequency-selective element for the oscillator design. It can concentrate the sensing electric field with a distribution consistent with the microfluidic channel. As the test liquids are placed in the sensing region, the oscillation frequency and output power are measured for complex permittivity computation. The 23-μL water-ethanol mixtures with ethanol volume fractions of 10% to 70% in increments of 20% are used as the test liquids to evaluate the sensor performance. Compared with the results obtained from the commercial dielectric probe, the maximum errors of the dielectric constant and loss tangent measured by the proposed microfluidic sensor are 9.45% and −8.84%, respectively.