Oscillation-Based Active Sensor on SIW Reentrant Cavity Resonator for Self-Sustained Ultralow Concentration Detection to Saline Solution
Jie Huang, Shiheng Hu, Hongtao Yue, Qian Zhao, Feng Ye, Xingchuan Liu, Ao Shen, Shuyan Zhu
Abstract
A back-to-back reentrant cavity resonator (BTB RECR) in substrate integrated waveguide (SIW) configuration is integrated with a negative resistance oscillation (NRO) circuit to implement an SIW BTB RECR NRO-based active sensor for self-sustained sensing application. The dependence of sensitivity on the polarization between the dielectric sample and the induced <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field of the passive SIW BTB RECR is investigated to obtain sensitivity as high as possible. A multitask LabVIEW-based real-time test system, which can avoid disassembly and ensure the reliability of the measured results, is built up to selectively measure for transmission coefficient <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{21}}$</tex-math> </inline-formula> and frequency spectrum through a microwave switch. During the process of real-time replacement of deionized (DI) water reference solution with NaCl solution in dielectric sensing channel, the in-between real-time recorded oscillation frequency is cleverly used as the frequency-modulated (FM) input signal to the delay-line-based frequency demodulator and is transferred to in-phase <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{\text{I}}}$</tex-math> </inline-formula> and quadrature <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{\text{Q}}}$</tex-math> </inline-formula> dc voltages. Then, the modulated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{\text{I}}}$</tex-math> </inline-formula> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</i> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{{\text{Q}}}$</tex-math> </inline-formula> dc voltages are postprocessed into phase angle by using arctangent algorithm, and the phase angle in stable convergence state is finally used as response parameter for self-sustaining measurement for the concentration of NaCl solution. The NRO-based active sensor demonstrates a phase angle self-shift noise of 7.8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> and a high-resolution detection to NaCl solution at low concentration level from 2.5 to 80 mM/L and high concentration level from 100 to 800 mM/L. The measured minimum detectable lower limit concentration is 2.5 mM/L, and maximum sensitivity is 40 kHz/mM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot$</tex-math> </inline-formula> L <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{-1}}$</tex-math> </inline-formula> (0.31 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> /mM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\cdot$</tex-math> </inline-formula> L <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{{-1}}$</tex-math> </inline-formula> ).