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Saranraj Karuppuswami won Best of Session at the 2018 International Symposium on Microelectronics (IMAPS) for his paper "A Reusable 3D Printed Cavity Resonator for Liquid Sample Characterization" for the session RF/Wireless Components. Congrats Saran!



Liquid sample identification and quantification is of significant interest for many practical quality control applications in food, petroleum, oil, biomedical, and pharmaceutical industries. For example, in food industry, accurate estimation of properties of liquid food such as dielectric constant discourages adulteration and promotes consumption of high quality food products. A number of standard microwave techniques have been developed for characterizing liquid samples such as waveguides, open-ended coaxial line, and microwave resonators. Among these, resonant perturbation methods such as perturbed cavity resonators are preferable for small volume samples (< 1mL) due to their simplicity and accuracy. Perturbation techniques are based on the change in resonance frequency or quality-factor (Q-factor) of the resonant structure due to the influence of the sample under test In this paper, a 3D printed (additive manufacturing) reusable microfluidic coupled rectangular cavity resonator is fabricated and demonstrated for characterizing liquids in small volumes. The designed cavity operates in the fundamental TE101 mode and resonates at 4.12 GHz. The resonance of the cavity is perturbed by the sample placed in a small volume sample holder in a slot in the top cover. The sample holder is loaded with different solvents and the shift in the resonance frequency and the Q-factor is monitored. Based on these changes, the dielectric constant of the solvent is theoretically estimated and compared to standard values. Two different perturbation configurations are investigated: i) liquids with low to medium dielectric constants (strongly coupled), and ii) liquids with medium to high dielectric constant (weakly coupled). The reusable liquid sensor holds significant potential in identifying and quantifying unknown liquid samples in the supply chain. The details of design, fabrication, theory, and measurements are presented in this paper.