A Miniaturized Active Dual SIW Re-Entrant Resonators for High-Resolution and Ultra-low-Limit-Concentration Detection to Glucose Solutions

Abstract

Two passive re-entrant cavity resonators (RECRs) in substrate integrated waveguide (SIW) configuration are vertically stacked to implement a miniaturized dual RECRs sensor. Only one negative resistance circuit (NRC) is innovatively proposed to be connected with these two RECRs in the common stacked metal layer between them and implement an active dual RECRs sensor, and the corresponding equivalent lumped circuit mode is proposed to analyze the dielectric sensing characteristics. Then, the compensated power obtained from the NRC is simultaneously fed into these two RECRs embedded with two microfluidics, and the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> -factor of either of these two RECRs can be greatly enhanced by simply changing the bias voltages of the transistor and varactor in the NRC. Finally, the active sensor is utilized to perform high-resolution detection to glucose solutions in high concentration range from 100 to 1000 mmol/L and low concentration range from 1 to 50 mmol/L. By gradually approximating the resonant frequency self-shift noise <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta f_{\mathrm {Aself}}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta f_{\mathrm {Bself}}$ </tex-math></inline-formula> ) of the active RECR-A (RECR-B) by the resonant frequency shift <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta f_{\mathrm {s}}$ </tex-math></inline-formula> determined by glucose solutions, minimum detectable glucose concentration of 1 mmol/L is experimentally achieved. The linear relationship between the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta f_{\mathrm {s}}$ </tex-math></inline-formula> and the glucose concentration is experimentally demonstrated, and shows good potential for glucose sensing.