Particle sensing with narrowband microwave split-ring resonators

Abstract

A new microwave sensor with concentric split-ring resonator (CSRR) topology is designed and integrated with microfluidics. While the resonator is being driven at its resonant frequency, cells passing through the channel shift this frequency. Information regarding the cell (or microparticle) can be extracted from the am-plitude of this shift. The design is based strongly on simulations and shows good agreement with the theory. Experiments are performed to evaluate the sensor’s performance with polystyrene particles. These experiments show that the sensor gives an outstanding SNR value: around 140kHz mean signal amplitude com-pared to a 1.2kHz average noise amplitude. To further evaluate the performance, single-cell experiments are performed. A target cell is selected and passed through the sensing region repeatedly. Frequency shifts are recorded. The mean frequency shift is 44kHz, and the signal-to-noise ratio is over 140. The ensemble standard deviation for the frequency shifts is 9.33kHz, and the variance in the results can be further improved with creative microfluidic designs. Work has been directed towards improving the measurement setup for split-ring resonators. A split-ring resonator sensor is designed and integrated into an oscillator loop, designed from scratch. The design criteria for this project are; faster acquisition times, control-loop parameter independence, and improved cost-effectiveness. It is shown that the new oscillator setup satisfies all the design criteria. The design process is once again simulation-driven. Real-life experiments are also performed with the oscillator boards for performance evaluation. Allan deviation experiments show promising results (1.49 × 10−6) regarding oscillator stability. Polystyrene experiments show a lower response compared to the CSRR sensors.