Gold-on-glass microwave split-ring resonators with PDMS microchannels for differential measurement in microfluidic sensing.

This paper describes a microwave resonator incorporating microfluidic lab-on-chip sensor system capable of performing simultaneous differential measurement based sensing of liquid samples. The resonators are split-ring resonator shapes made of gold on glass substrates. Directly bonded on glass substrates are polydimethylsiloxane microchannels. Sensor system design incorporates a pair of identical resonators, one of which performs reference reading from the background. Tracking the difference of the responses of both resonators simultaneously, rather than a single one, is used to obtain a more linear and noise-free reading. The sensor system was produced with conventional fabrication techniques. It is compatible with low-cost, simple, easy to handle sensing applications. Results indicate that reliable differential measurement was possible owing to a well-matched pair of sensors with a response error as low as 0.1%. It was also demonstrated that differential measurement capability enables sensing with improved linearity. Measurements were performed with glucose solutions in the range of 3.2-16.1 mM, achieving a sensitivity of 0.16 MHz/mM.

Note: Tunable overlapping half-ring resonator.

A unique tunable microwave resonator with a pair of half-rings is introduced and validated by experimental data. The capacitive gap between the overlapping areas can be controlled accurately using a magnetic actuator for tunability. The design geometry is scalable to cover different bands of electromagnetic spectrum. Transmission characteristics of the resonators have been modeled using finite-element analysis and have been measured. The experimental results indicate the resonant frequency can be controlled with a resolution of a few MHz in a tuning range of 38%. The resonator exhibits sharp transmission dips within the tuning range with measured quality factors larger than 2500.