Miniaturized Multiband Planar Sensor Based on Transmission Line Loaded With Pairs of Improved Resonators for Glucose-Aqueous Solution Sensing Applications

In this article, a novel miniaturized multiband microwave sensor is proposed for sensing applications of glucose-aqueous solutions. The sensor consists of a microstrip transmission line (TL) and two identical novel metamaterial structures, which is composed of homodromous multiple split-ring resonators (HMSRRs) with different dimensions. Field perturbation and symmetry can be used to detect variations in the permittivity of the liquid under test (LUT). When the device is in a symmetrical condition, four resonance frequencies can be obtained in a frequency range from 1 to 10 GHz. If the symmetry of the sensor is broken, frequency splitting occurs, and each resonance frequency is split into two. A comparison of the two test methods is given. Simulated results show that the sensor can ensure the strong electric field (E-field) to focus at a small region. This issue leads to a significant shifting in resonance frequency, and an increased sensitivity of the proposed sensor. Experiments illustrate that the designed sensor is well suited for sensing applications of liquids. The experimental results demonstrate a testing sensitivity of 0.4–1 MHz per mg/dL. Compared with multiple-cell microfluidic resonator sensor, the maximum sensitivity of the proposed sensor is increased by about $1.5\times $ under the condition of a requirement of a smaller volume.

I. Introduction

With the rapid development of microwave technology, especially electromagnetic metamaterials, various information components have ushered in the booming opportunity [1]. Microwave metamaterial-inspired sensors applied in dielectric property measurement domain have also emerged [2], [3]. Determination of the dielectric property or its minute variation is very important in medical and industrial processes for solid and liquid materials. For this reason, many techniques have been presented to detect the dielectric properties of the liquid under test (LUT), such as transmission, reflection, and cavity resonance methods [4], [5]. These methods are classified as nonresonance and resonance, and the latter usually has much higher sensitivity and accuracy. Thus, the resonance method is well suited to measure the dielectric property or its minute change of small samples (such as biosamples, cell cultures, particles, and microsomes) [6], [7], [8]. However, the traditional resonant method requires a circle resonator, which suffers from band-limited, is difficult to integrate with other microwave circuits, is expensive, and is nonplanar [5].