Low-cost portable microwave sensor for non-invasive monitoring of blood glucose level: novel design utilizing a four-cell CSRR hexagonal configuration

Abstract

This article presents a novel design of portable planar microwave sensor for fast, accurate, and non-invasive monitoring of the blood glucose level as an effective technique for diabetes control and prevention. The proposed sensor design incorporates four cells of hexagonal-shaped complementary split ring resonators (CSRRs), arranged in a honey-cell configuration, and fabricated on a thin sheet of an FR4 dielectric substrate.The CSRR sensing elements are coupled via a planar microstrip-line to a radar board operating in the ISM band 2.4–2.5 GHz. The integrated sensor shows an impressive detection capability and a remarkable sensitivity of blood glucose levels (BGLs). The superior detection capability is attributed to the enhanced design of the CSRR sensing elements that expose the glucose samples to an intense interaction with the electromagnetic fields highly concentrated around the sensing region at the induced resonances. This feature enables the developed sensor to detect extremely delicate variations in the electromagnetic properties that characterize the varying-level glucose samples. The desired performance of the fabricated sensor is practically validated through in-vitro measurements using a convenient setup of Vector Network Analyzer (VNA) that records notable traces of frequency-shift responses when the sensor is loaded with samples of 70–120 mg/dL glucose concentrations. This is also demonstrated in the radar-driven prototype where the raw data collected at the radar receiving channel shows obvious patterns that reflect glucose-level variations. Furthermore, the differences in the sensor responses for tested glucose samples are quantified by applying the Principal Component Analysis (PCA) machine learning algorithm. The proposed sensor, beside its impressive detection capability of the diabetes-spectrum glucose levels, has several other favorable attributes including compact size, simple fabrication, affordable cost, non-ionizing nature, and minimum health risk or impact. Such attractive features promote the proposed sensor as a possible candidate for non-invasive glucose levels monitoring for diabetes as evidenced by the preliminary results from a proof-of-concept in-vivo experiment of tracking an individual’s BGL by placing his fingertip onto the sensor. The presented system is a developmental platform towards radar-driven wearable continuous BGL monitors.

Radio-Frequency Biosensors for Real-Time and Continuous Glucose Detection

“…In addition, many glucose sensors have been reported for the detection of glucose concentration based on resonant frequency shifts [ 9 , 10 , 52 , 57 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 ], variations in the Q-factor [ 114 , 115 , 116 ], magnitude and phase variations in the reflection and/or transmission coefficient [ 10 , 108 , 114 , 117 , 118 , 119 , 120 , 121 ], and changes in input impedance [ 54 ]. The important parameters of various glucose sensors, such as sensor type, operating frequency, the detection range for glucose concentration, sample volume, sample type, sensing parameters, sensitivity, and continuous monitoring capability, are summarized in Table 3 .…”

“…The possibility of using RF or microwave sensing for blood glucose level characterization has also been investigated. In recent years, with the development of wireless technologies, an increased interest in noninvasive, noncontact, and continuous RF glucose detection has emerged [ 9 , 10 , 11 , 12 ].…”

First Microwave Tomography Approach Towards a Truly Noninvasive, Pain-Free and Wearable Blood Glucose Monitoring Device

“…However, measurements of ISF glucose level suffer from serious time delay compared to the blood glucose level. A recent study has provided a portable prototype of a microwave sensor, operating in the 2.4 GHz ISM band, to non-invasively measure glucose level variations of 70 to 120 mg/dl in blood [14]. The sensor showed frequency shifts of approximately 0.94 MHz/(mg/dl) in response to glucose level variation in blood samples.…”

Characterization of Dielectric Substrates Using Dual Band Microwave Sensor

“…Several characteristics make microwave sensors standout among other available options. These attributes include low-cost [15], high sensitivity [16], label-free [17], and non-intrusive evaluation [18]. In recent years, scientists have developed microwave sensors based on metamaterials because they are very sensitive to the ambient mediums' changes in electromagnetic properties [19,20].…”