A Non-Invasive Flexible Glucose Monitoring Sensor Using a Broadband Reject Filter

In this paper, a novel, highly accurate, non-invasive glucose-monitoring sensor that is based on a flexible broadband reject filter is presented. The filter topology comprises a tapered feed line at a top layer that excites four open loop resonators on the bottom layer. The broadband reject response is achieved by relying on a modified log-periodic distribution of the open loop resonators. The embedded resonators are reduced in size and are designed to exhibit an enhanced sensitivity to track the variations of the glucose level across the 1.25-2.65 GHz frequency span. The proposed flexible filter is tested within in-vitro, ex-vivo and in-vivo setups. A high correlation between the scattering parameters of the proposed sensor and the variations in glucose levels is attained. Regression models are developed using experimental data obtained from healthy patients that are subjected to glucose tolerance tests. Results demonstrate less than 4% mean absolute relative difference between the reference and estimated glucose levels, and the predicted glucose levels lie 100% within the clinically acceptable zones as shown by the Clarke Error Grid analysis.

I. Introduction

During the past few decades, changes in lifestyle and nutrition made diabetes one of the most prominent diseases among chronic conditions. In 2019, the number of patients diagnosed with diabetes exceeded 425 million worldwide, resulting in more than 4 million deaths. This exponentially growing number is expected to reach 629 million by 2045 [1]. In fact, diabetes as a pandemic is one of the most common metabolic diseases. There are two main types of diabetes: type 1 and type 2, with type 1 being the most serious condition [2]. Although the underlying causes of these two categories are different, their consequences are dangerous and much alike [3]. To maintain a proper treatment, accurate determination of blood glucose levels (BGL) is a necessity. Currently, BGL is measured using a glucometer that is invasive and relies on finger pricking several times a day. On the long term, this increases the risk of infection and may damage the underlying tissue. More importantly, this measurement technique does not provide continuous monitoring, which can result in missing serious hypo/hyper-glycemic incidents [4].