Compact Size, and Highly Sensitive, Microwave Sensor for Non-Invasive Measurement of Blood Glucose Level

None-invasive blood glucose measurement enables effective diagnosis and treatment of diabetic patients. The existing microwave sensors suffer from low sensitivity and large size. This article presents a highly sensitive and compact size non-invasive microwave sensor for real-time blood glucose measurements. We have developed a new sensing technique using directly connected Branch Line Coupler and Split Ring Resonators. This technique significantly improves the sensitivity by mitigating the limited coupling between transmission lines and resonators. In addition, using Split Ring Resonators reduces the sensor size due to capacitive and inductive effects, which are loaded to the Branch Line Coupler. The proposed sensing function is based on shifting the transmission notch frequency in coupled arm of the Branch Line Coupler, which is caused by loading the Split Ring Resonators with varying glucose concentration. A prototype sensor is fabricated and successfully tested using several glucose concentrations in deionized water. Experimental results demonstrate 0.72 MHz/mgdL-1 measurement sensitivity, which is higher in comparison with available sensors in PCB technology. The prototype sensor size is 3.5× 3.5× 0.16 cm3.