A New Radio-Frequency Microfluidic Injection-Locked Oscillator Sensor for Loss Tangent Measurement of Liquid Material

A new radio-frequency microfluidic injectionlocked oscillator (ILO) sensor is proposed in this paper for loss tangent measurement of the liquid material. The proposed sensor comprises a passive T-shape LC resonator (TLCR) sensing structure and an ILO. When an RF signal passes through the TLCR loaded by a test liquid, its amplitude will be decreased by the liquid's loss. The degraded signal is injected into an ILO to vary the output power. By loading different test liquids into the microfluidic channel, one can measure the ILO's output powers to relate the corresponding liquids' loss tangents. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$7.5-\mu \mathbf{L}$</tex> water-ethanol mixtures with ethanol volume fractions of 20 % to 80 % in increments of 20 % are used as the test liquids to evaluate the sensor performance. Compared with the results obtained from a dielectric probe, the maximum error of the loss tangent measured by the proposed sensor is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-3.8 \%$</tex>.