Design and Development of Dual-Band Integrated Network Analyzer For Water Solvent Based RF Bio Sensors

Abstract

The detection of analytes using Radio Frequency (RF) based sensors has gained immense popularity in recent times. The change in the sensor’s resonant frequency in the presence of different analytes is used as the basis for detection. Although, there have been plethora of advancements in developing RF biosensors, yet most of them have been designed and fabricated considering air all around them. However, in a practical scenario, a solute is mostly used with solvent for testing. The solvent alone produces huge shift in resonant frequency whereas, the shift due to solute and solvent together is significantly narrower (in MHz) when compared to the solvent alone. This indicates that the shift due to solute is narrowband in nature. Most of these sensors utilize traditional Vector Network Analyzers (VNAs) for measuring the s-parameters. However, traditional VNAs are broadband devices that are expensive, large and cumbersome to operate. These VNAs also have much larger bandwidths than the observed frequency shifts as mentioned above and often prove to be overkill. Thus, the optimal solution is to develop narrowband measurement platforms that precisely monitor the frequency shifts. This article tackles the challenge and presents a solvent specific integrated solution for the detection of materials having different permittivities. An Integrated Biosensing Network Analyser (IBNA) is designed and fabricated using microstrip line technology to detect different analytes (Glucose and Sucrose). IBNA primarily consists of a sensing and a measuring unit specifically designed for solvent like water. While the Interdigitated Capacitor based RF Bio Liquid Cavity resonating at 2.3 GHz performs the sensing operation, the Dual Band Six-Port Reflectometer (DBSPR), with an operating frequency of 1.1 GHz and 2.3 GHz, participates in the measurement of the s-parameters. Furthermore, to demonstrate the working of the design, the detection of 1 M Glucose and Sucrose is performed by EM-simulations and experiments. The sensing is carried out efficiently, with Glucose and Sucrose yielding frequency shifts of 15 MHz and 20 MHz at room temperature respectively. The results help in establishing the utility of IBNA and its superiority over traditional network analyzers