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.

Planar microwave sensors are considered an attractive choice to non-invasively probe the dielectric attributes of biological tissues due to their low cost, simple fabrication, miniature scale, and minimum risk to human health. This paper develops and measures a novel microwave biosensor for non-invasive real-time monitoring of glucose level. The design comprises a rectangular plexiglass channel integrated on a triple-pole complementary split ring resonator (TP-CSRR). The proposed sensor operates in the centimeter-wave range 1 — 6 GHz and is manufactured using PCB on top of an FR4 dielectric substrate. The sensor elements are excited via a coupled microstrip transmission-line etched on the bottom side of the substrate. The integrated CSRR-based sensor is used as a near-field probe to non-invasively monitor the glucose level changes in the blood mimicking solutions of clinically relevant concentrations to Type-2 normal diabetes (70 — 120 mg/dL), by recording the frequency response of the harmonic reflection and transmission resonances. This indicates the sensor's capability of detecting small variations in the dielectric properties of the blood samples that are responsive to the electromagnetic fields. The proposed sensor is verified through practical measurements of the fabricated design. Experimental results obtained using a Vector Network Analyzer (VNA) demonstrate a sensitivity performance of about 6.2 dB/(mg/ml) for the developed triple-pole sensor that significantly outperforms the conventional single-pole and other proposed sensors in the literature in terms of the resonance amplitude resolution.

This paper presents a high-sensitive planar microwave sensor based on the metamaterial technology, integrated with a microfluidic channel to be used for liquid sensing in a variety of biomedical applications. The sensor design comprises three cells of circular complementary split ring resonators (CSRRs) engraved on the ground plane of a dielectric substrate in a cascaded configuration. The sensing cells are excited with a time-varying electric field coupled from a planar microstrip-line (MTL) etched on the bottom side of the substrate. The proposed design of multiple coupled resonators would enhance the electric field intensity over a larger sensing region through the inter-resonator coupling, thus improving the overall sensitivity for detecting liquid samples of high permittivity and dielectric losses. The sensor exhibits a reject (band stop) filter behaviour with multiple resonances in the centimeter-wave band 1 – 6 GHz when loaded symmetrically with liquid samples. The sensor is fabricated on an FR4 dielectric substrate with a biocompatible microfluidic channel aligned appropriately over the sensing area to enable consistent and intact sensing of the liquid samples. The CSSR-sensor is numerically modeled and compared in performance to the single-cell CSRR for detecting small variations in the dielectric properties. The sensitivity, reliability, and repeatability of the proposed sensor are practically demonstrated by the in-lab measurements for different liquid samples using a Vector Network Analyzer (VNA) setup where distinctive resonant features (amplitude and frequency) are extracted from multiple resonance modes in the reflection and transmission responses. A high sensitivity is also demonstrated for monitoring glucose level variations in synthetic blood samples of concentrations (70 – 150 mg/dL) which are clinically-relevant to diabetes conditions. Beside its impressive capability in detecting small dielectric variations, the developed sensor features other favorable attributes including compact size, simple fabrication, affordable cost, non-ionizing nature, and minimal health risk or impact. Such key advantages could potentially promote the proposed sensor for integration with other microwave components in an embedded device for non-invasive monitoring of blood glucose for diabetes.

In this article, a novel sensing approach is presented for glucose level monitoring where a robust low-power millimeter(mm)-wave radar system is used to differentiate between blood samples of disparate glucose concentrations in the range 0.5 to 3.5 mg/mL. The proposed radar sensing mechanism shows greater capabilities for remote detection of blood glucose inside test tubes through detecting minute changes in their dielectric properties. In particular, the reflected mm-waves that represent unique signatures for the internal synthesis and composition of the tested blood samples, are collected from the multi-channels of the radar and analyzed using signal processing techniques to identify different glucose concentrations and correlate them to the reflected mm-wave readings. The mm-wave spectrum is chosen for glucose sensing in this study after a set of preliminary experiments that investigated the dielectric permittivity behavior of glucose-loaded solutions across different frequency bands. In this regard, a newly-developed commercial coaxial probe kit (DAK-TL) is used to characterize the electromagnetic properties of glucose-loaded samples in a broad range of frequencies from 300 MHz to 67 GHz using two different 50 Ω open-coaxial probes. This would help to determine the portion of the frequency spectrum that is more sensitive to slight variations in glucose concentrations as indicated by the amount of change in the dielectric constant and loss tangent parameters due to the different concentrations under test. The mm-wave frequency range 50 to 67 GHz has shown to be promising for acquiring both high sensitivity and sufficient penetration depth for the most interaction between the glucose molecules and electromagnetic waves. The processed results have indicated the reliability of using mm-wave radars in identifying changes in blood glucose levels while monitoring trends among those variations. Particularly, blood samples of higher glucose concentrations are correlated with reflected mm-wave signals of greater energy. The proposed system could likely be adapted in the future as a portable non-invasive continuous blood glucose level monitoring for daily use by diabetics.

A newly-developed commercial coaxial probe kit (DAK-TL) is used to characterize the electromagnetic properties of glucose-loaded samples prepared at a range of concentrations 0.7 – 1.2 mg/ml similar to Type-2 normal diabetics in a broad range of frequencies from 300 MHz to 67 GHz using two different 50 Ω open-ended coaxial probes. The objective is to determine the spectrum portion of the most sensitivity to slight variations in glucose concentrations and to identify the amount of change in the dielectric permittivity and loss tangent due to different concentrations of interest. The millimeter-wave range 50 – 67 GHz has shown to be promising for acquiring both high sensitivity and sufficient penetration depth for the most interaction between the glucose molecules and electromagnetic waves. Subsequently, the relative permittivity of the glucose-water mimicking samples are modeled in this mm-wave band using a single-pole Debye model with independent coefficients. The fitted Debye model is used to design a simple low-cost highly-sensitive integrated mm-wave sensing structure that utilizes the travelling-wave Whispering Gallery Modes (WGMs) launched in a dielectric disc resonator (DDR) when coupled to a dielectric image waveguide (DIG). The proposed sensor is used for continuous monitoring of glucose levels in blood mimicking aquatic solutions by tracking the variations in the magnitude and phase of the WGM transmission resonances in the mm-wave spectrum. This happens in reaction to the strong interactions of the coupled WGM evanescent field with the glucose samples loaded on top of the DDR inside a container. The sensor exhibits a high sensitivity performance (2.5 – 7.7 dB/[mg/ml]) for the two proposed DIG layouts, straight and curved, at the lower-order modes WGH600 and WGH700 of its five pure WGH modes supported in the frequency range 50 – 70 GHz as demonstrated by numerical simulations in a 3D full-wave EM solver and validated through proof-of-concept measurements.

In the article, we propose an integrated millimeter-wave radar system to detect different glucose concentration levels in fake blood samples prepared in the laboratory. This research aims at validating the suitability of using mm-wave radars for noninvasively monitoring glucose levels of patients with diabetes. The proposed concept benefits from the applied signal processing approaches to identify different glucose concentrations and to correlate them to the reflected mm-wave readings.