Highlights: Publications

Abstract: Most experimental RF/microwave glucose sensors have to operate in conjunction with a vector network analyzer (VNA). Not only is a VNA bulky and expensive, but the process of a VNA-based glucose measurement is extremely tedious. For the first time, a fully customized system has been developed to demonstrate the feasibility of contact-based glucose measurement without any VNA. Method: A sweeping RF synthesizer (LMX2595) was used for scanning a specific range of frequencies that covered the perturbed frequencies of a membrane-supported glucose sensing head (MSSH), which was around 1.3 GHz. During the frequency sweeping process, a gain–phase detector (AD8302) was used to capture the gain, which was one of the parameters for determining the MSSH’s reflection coefficients (S11). During the frequency sweeping process, the measured voltage gains and phases from the AD8302 module were serially sent to a computer, where the reflection coefficients were retrieved and smoothed with a Savitzky–Golay filter augmented with a multilevel neural network implemented in PyTorch 2.13.0. Results: The proposed system was able to conduct continuous measurements on glucose concentrations from 0 to 111 mg/dL with no VNA and no manual intervention. Moreover, it was able to generate highly reproducible results consistent with those of a commercial VNA. Conclusion: The proposed non-VNA glucose sensing system was able to continuously measure the concentrations of a glucose–water solution with results consistent with those of a VNA.

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Abstract: Long-range wireless power transfer (WPT) is difficult with unguided radio waves or magnetic coupling. In this work, a plasma-assisted quasi-parallel planar waveguiding medium is proposed for overcoming the transmission range issues. Method: A dielectric layer sitting on a conductive object or grid was used as a medium for WPT. At the transmitting end, a plasma ball shielded with a spark-gap activated hemispheric metal cap was used to ionize the air in the space, thereby forming the top cladding layer of the quasi parallel-plate waveguide. At the receiving end, the transmitted power was coupled out of the waveguide over the entire ultrasonic spectrum using Avramenko diode configurations. A Kretschmann-like configuration was used at both ends for conversion between a plasmonic current and the surface waves. Results: In the proposed experimental setups, the transmitted power was successfully harvested over a frequency range from near DC to 230 MHz, with the ratio of the received power to the transmitted power significantly surpassing the value predicted by the Friis’ two-ray ground reflection model. Conclusion: WPT based on surface waves is technically feasible with the help of Kretschmann-like configurations.

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Abstract: For the first time, a portable glucose sensor has been built for in-vitro glucose measurements without a vector network analyzer. The proposed glucose sensor is currently being extended to work at 9 GHz, whilst the key component of this system (i.e. the gain phase detector) can cope with a maximum of 2.7GHz. In this study, we addressed the hardware limitation issue of the gain phase detector by developing a highly compact image rejection mixer to down-convert the 9 GHz sensing signal to 500MHz without using any filter. Methodology: An image rejection mixer was initially designed without a power combiner, simulated using uSimmics, and photolithographically fabricated on a 0.25 mm thick Rogers Duroid substrate. After probing the in-phase and quadrature mixing outputs, these mixing products were combined using a modified lumped-element Wilkinson power combiner that completely ignored the even modes. Results: The final fabricated mixer occupies an area smaller than 3 cm × 2 cm. With an 8.6 GHz, 22 dBm local oscillator input, the image rejection mixer achieved a conversion loss of approximately 7.07 dB across the 8.5 GHz to 9 GHz frequency range. Conclusion: Overall, the outcomes of this study indicated how the lumped element Wilkinson power combiner can be advantageously changed and shrunk to reduce the physical size of the suggested image rejection mixer without significantly sacrificing the conversion efficiency. Keywords: COVID-19, Split-ring resonator, metamaterial, metasurface, hyperglycemia, hypoglycemia, image rejection mixer, Wilkinson power combiner

Abstract: This paper presents the design and validation of a robust 60 GHz quasi-optical radar system for biomedical sensing, culminating in the identification of an optimal antenna configuration for practical use. Through a systematic comparison of 3.0 mm and 3.5 mm dielectric waveguides, both with and without a novel protective ePTFE coating, the 3.5 mm coated rod was unequivocally identified as the superior design. This configuration achieves a narrow 26° beamwidth while, most critically, maintaining over 75% signal integrity under significant mechanical bending—a key requirement for clinical applications. The system demonstrates a +5 to +15 dB gain improvement over the baseline sensor. A key contribution of this work was a cost-effective biomedical sensing method which enabled the directivity to be measured with the radar sensor in the absence of an vector network analyzer (VNA). This research establishes a complete, theory-driven methodology for developing mechanically resilient, high-performance mmWave antennas suitable for clinical-grade diagnostic devices. Keywords: Millimeter-wave radar, biomedical sensing, dielectric waveguide, quasi-optical systems, 60 GHz, pulsed coherent radar

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Abstract: Nowadays, the operating principle of most of the experimental electromagnetic glucose sensors is based on the effect of an anomalous dispersion caused by a direct contact between an object under test and a two-dimensional metasurface. Due to the repeated uses, the metasurface will be subjected to a chemical attack over time. To avoid this problem, this work proposes a novel glucose sensor that is equipped with an interfacial dielectric layer of 0.254 mm thickness to separate the object under test and the metasurface. The results of our analysis suggest that, if the interfacial dielectric layer is sufficiently thin, there will be no shortage of sensitivity in the proposed sensor. Consistent with our theoretical prediction, the proposed sensor was found to resonate at 9–10 GHz, with its resonant frequency responding to the glucose concentration in a dose dependent manner. The correlation the resonant frequency shift and …

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Diabetes is currently a major public health concern, partly exacerbated by the recent outbreak of coronavirus. Most of the published EM-wave based glucose sensors of this date allow a glucose concentration to be determined through a resonance frequency shift, inevitably with a questionable accuracy. To overcome the accuracy problem, a dual-band glucose sensor with dimensions 50 mm × 20 mm is proposed in this work to enable a glucose concentration to be measured at one resonance frequency band and cross-checked at another. An array of split-ring resonators (SRRs) was fabricated at a rectangular sensing area on the top surface of a 0.3 mm thick PET substrate, forming a metasurface with dual resonance bands at 4.5 GHz and 9.2 GHz. The backside of the PET substrate was fabricated with a defected ground plane designed to suppress the Q-factor associated with 4.5 GHz while leaving the Q-factor associated with 9.2 GHz unchanged. During a glucose concentration measurement, a drop of glucose solution was applied to the rectangular metasurface sensing area. The glucose concentration was determined in the form of a resonance frequency shift of the reflection coefficient at 4.5 GHz and a magnitude change of the reflection coefficient at 9.2 GHz. Consistent with our theoretical prediction, the fabricated sensor has indeed exhibited a dual resonant band characteristics, with one resonance occurring at 4.5 GHz and the other at 9.2 GHz. By measuring the reflection coefficient near 4.5 GHz, a positive and linear correlation in the log scale was observed between the glucose concentration and the resonant frequency shift with a sensitivity of 0.6 . At 9.2 GHz, there was no significant resonant frequency shift with varying glucose concentrations, but the magnitude of the reflection coefficient changed with the glucose concentration nonlinearly in an amount-dependent manner, with a sensitivity of 16.6 dB per unit glucose concentration within the clinical diabetic range. Overall, the log scale of the glucose concentration has exhibited a positive and linear correlation within the clinical diabetic range with both the resonant frequency shift at 4.5 GHz and the magnitude change at 9.2 GHz, thereby allowing the glucose concentration to be measured at 4.5 GHz and further cross-checked at 9.2 GHz at the same time.

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Abstract: As a chronic disease, diabetes has impacted millions of individuals across the globe and is spreading at a very fast rate among adults mainly. Continuous observations of essential indicators like pulse rate, arterial pressure, and blood sugar levels, and oxygen saturation are crucial to maintain a healthy life and preventing severe complications associated with these. Using non-invasive method of blood glucose monitoring has paved its way to be one of the most prominent safest technique without harming the skin of the patients. This examination delves into the application of planar resonant sensors utilizing microwaves for quantifying glucose concentrations. The sensors based on RF EM waves mainly operating in the region from few MHz to GHz frequencies have garnered notable attention in the scientific community in recent years due to their significant contributions. They can detect alterations in dielectric properties caused by fluctuations in glucose concentrations. These sensors exhibit electrical reactions that rely on the dielectric properties of their surroundings. This review offers a current assessment of this sensing methodology, categorized by sensing parameters, and suggests typical non-invasive microwave sensor varieties for assessment. It further examines the key aspects of different sensor types, outlines potential future avenues, and addresses challenges in the field of glucose monitoring.

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Abstract: Glucose monitoring is a critically important issue of health care, particularly in the aftermath of the COVID pandemic. In the field of glucose sensing, the issues currently receiving major attention from the research community include the accuracy, sensitivity, ease of use, repeatablity of measurements, selectivity and portability. Most of the published electromagnetic-wave (EM) based glucose sensors of this date have reasonable degrees of accuracy, sensitivity, ease of use, repeatability and selectivity, but these sensors must be operated in conjunction with a vector network analyzer, which is not only an expensive but also bulky and difficult to use. At the time of this writing, there is hardly any sensor capable of differentiating glucose from other substances such as water, fat, bones and some other glucose like compounds. Only a small subset of experimental devices have been through the in-vivo trials. In this work, the background understanding as well as the current status of the research in glucose sensing are reviewed with particular reference given to the important findings contributing to improvement in terms of portability. Overall, more research is needed in the areas of in-vivo tests, portability and selectivity.

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Abstract: Surface electromagnetic waves (also known as surface plasmon polaritons or SPP’s) propagate in the form of a slow travelling waves along the interface between one dielectric material and one highly conductive material. Since the group velocity of SSP is always less than the speed of light, it has a tendency of sub-wavelength confinement of electromagnetic waves at frequency below the plasma frequency. The idea of SSP has been further extended to spoof surface plasmon polaritons (SSPP), allowing the slow-wave nature of metamaterials or the like to be integrated in RF/microwave circuits. This paper takes advantage of some of the already known but seemingly unrelated features of SSPP’s to explain the role of glucose sensing in a slow wave medium. Particular reference has been given to the evolution from SSPP’s to glucose sensing using an SSPP based antenna. The presentation of this work has been substantiated with a successfully replicated experiment.

Keywords — antenna, RF ground, capacitance, spark gap,current harmonics, transmission line input impedance, wireless power transfer, surface plasmon polaritons.

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Abstract: In the field of dielectric sensing using electromagnetic waves, most of the studies of this date currently focus excessively on in-vitro measurement of an dielectric object under test. However, what was more urgently needed in the aftermath of the COVID pandemic was a functional device appropriate for in-vivo sensing. This paper reviews the status of in-vivo sensing, followed by proposing an extension of the existing research coverage from the conventional in-vitro contact based sensing to a non-contact based in-vivo sensing. With the rising need for non-contact biomedical sensing, millimeter-wave radars have emerged as promising tools for detecting vital signs and dielectric contrasts in biological tissue. A 60 GHz coherent radar (Acconeer XM125) with quasi-optical components was adopted to investigate the detectability of shallow inclusions that mimic tumors. Four phantom conditions were prepared: a water box, flat metal surface, empty box (control), and phantom box with saline-soaked sponge (inclusion). Each condition was measured in three runs by recording radar returns, with analysis focused on amplitude variations across distance. A consistent amplitude difference was observed between the control and inclusion phantoms, confirming that the radar can detect shallow dielectric anomalies. This proof-of-concept experiment is an ongoing feasibility study that investigates the sensitivity of millimeter-wave radar to surface inclusions,. The future work can be directed at in-vivo sensing of blood glucose on the tongue, or sublingual gland, millimeter-wave imaging of mouth tumors, millimeter-wave glucose sensing without any VNA and improvement of phantom and exploration of lower frequencies for deeper penetration.

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