1 Abstract-Limited sensitivity and sensing range are arguably the greatest challenges in microwave sensor design. Recent attempts to improve these properties have relied on metamaterial-(MTM-) inspired open-loop resonators (OLRs) coupled to transmission lines (TLs). Although the strongly resonant properties of the OLR sensitively reflect small changes in the environment through a shift in its resonance frequency, the resulting sensitivities remain ultimately limited by the level of coupling between the OLR and the TL. This work introduces a novel solution to this problem that employs negative-refractiveindex TL (NRI-TL) MTMs to substantially improve this coupling so as to fully exploit its resonant properties. A MTM-infused planar microwave sensor is designed for operation at 2.5 GHz, and is shown to exhibit a significant improvement in sensitivity and linearity. A rigorous signal-flow analysis (SFA) of the sensor is proposed and shown to provide a fully analytical description of all salient features of both the conventional and MTM-infused sensors. Full-wave simulations confirm the analytical predictions, and all data demonstrate excellent agreement with measurements of a fabricated prototype. The proposed device is shown to be especially useful in the characterization of commonly-available high-permittivity liquids as well as in sensitively distinguishing concentrations of ethanol/methanol in water.
This paper reports a highly sensitive, non-invasive sensor for real-time glucose monitoring from interstitial fluid. The structure is comprised of a chip-less tag sensor which may be taped over the patient’s skin and a reader, that can be embedded in a smartwatch. The tag sensor is energized through the established electromagnetic coupling between the tag and the reader and its frequency response is reflected on the spectrum of the reader in the same manner. The tag sensor consumes zero power as there is no requirement for any active readout or communication circuitry on the tag side. When measuring changes in glucose concentrations within saline replicating interstitial fluid, the sensor was able to detect glucose with an accuracy of ~ 1 mM/l over a physiological range of glucose concentrations with 38 kHz of the resonance frequency shift. This high sensitivity is attained as a result of the proposed new design and extended field concentration on the tag. The impact of some of the possible interferences on the response of the sensor’s performance was also investigated. Variations in electrolyte concentrations within the test samples have a negligible effect on the response of the sensor unless these variations are supra-physiologically large.
A novel flow sensor is presented to measure the flow rate within microchannels in a real-time, noncontact and nonintrusive manner. The microfluidic device is made of a fluidic microchannel sealed with a thin polymer layer interfacing the fluidics and microwave electronics. Deformation of the thin circular membrane alters the permittivity and conductivity over the sensitive zone of the microwave resonator device and enables high-resolution detection of flow rate in microfluidic channels using noncontact microwave as a standalone system. The flow sensor has the linear response in the range of 0-150 µl/min for the optimal sensor performance. The highest sensitivity is detected to be 0.5 µl/min for the membrane with the diameter of 3 mm and the thickness of 100 µm. The sensor is reproducible with the error of 0.1% for the flow rate of 10 µl/min. Furthermore, the sensor functioned very stable for 20 hrs performance within the cell culture incubator in 37 °C and 5% CO 2 environment for detecting the flow rate of the culture medium. This sensor does not need any contact with the liquid and is highly compatible with several applications in energy and biomedical engineering, and particularly for microfluidic-based lab-on-chips, micro-bioreactors and organ-on-chips platforms.Microfluidic techniques have been extensively used for efficient manipulation of fluid flow in microscale for biomedical research and analytical chemistry. The control of flow in microfluidic networks is crucial for cell sorting, cell collection, flow mixing, cell adhesion and culture, droplet manipulation and flow driving 1 . Moreover, the flow rate needs to be accurately quantified to determine the concentration of cells 2 , and production of hollow microspheres . A slight change in flow rate may lead to a size variation in the products. To precisely handle fluids at the microscale, the real-time detection of flow rate in microfluidic environment is essential and urgently needed though challenging.Organ-on-a-chip (OOC) technology, in particular, aims to build biomimetic in vitro physiological micro-organs to compliment animal models in biological systems and benefit the pharmaceutical industry for drug discovery 7,8 . Many groups including ours have developed OOC platforms made of microbioreactors and integrated sensors for long-term and real-time monitoring the microenvironment, screening the status of miniaturized organs, and characterizing the response of micro-tissues to drugs [9][10][11][12][13] . The real-time measurement of heat transfer 14 , differential pressure 15 , pH and oxygen 11 and biomarkers 10 are central to biomimetic performance of OOC systems. Miniaturized biosensors provide favorable features like low-cost reagents consumption, decreased processing time, reduced sample volume, laminar flow to cells, parallel detection for multiple samples as well as portability 12,13,16 . However, the OOC systems still need on-chip integrated flow sensors compatible with their fabrication processes and functions 17. The OOC platforms require the...
Steady-state (SRMC) and time-resolved microwave photoconductivity (TRMC) are key techniques used to perform the contact-less determination of carrier density, transport, trapping, and recombination parameters in charge transport materials such as organic semiconductors and dyes, inorganic semiconductors, and metal−insulator composites, which find use in conductive inks, thin film transistors, lightemitting diodes, photocatalysts, and photovoltaics. We present the theory, design, simulation, and fabrication of a planar microwave ring resonator operating at 5.25 GHz with a quality factor of 224, to perform SRMC and TRMC measurements. Our method consists of measuring the resonance frequency (f 0 ) and Q-factor of the microwave resonator with the sample to be probed placed in a defined sensitive region of the resonator where the microwave field is highly concentrated. We also provide proof of concept measurements of the time-resolved microwave photoresponse of anatase-phase TiO 2 nanotube array membranes (TNTAMs) using the planar microstrip resonator. An unusual observation was the persistence of charged pair states in TNTAMs for several hours at room temperature under ambient conditions. Fast (120−220 s), slow (1300−2850 s), and very slow (6−26 h) components were extracted from the long-lived photoconductive decays of TNTAMs in response to 365, 250, and 405 nm illumination and assigned to various trap-mediated processes in TiO 2 nanotubes.
A novel approach with a new configuration is introduced to design an ultra-wideband (UWB) band-pass filter (BPF) that demonstrates double/single notch-bands using micro-strip transmission lines without using any via-hole. The proposed approach is established using two parallel stepped-impedance resonators (SIR) that provide two paths with different electrical lengths. The mechanism of realising notch-bands within the pass-band of the UWB BPF is developed based on the waves' cancellation theory. To realise single or double notch-bands (DNBs) within the pass-band of a UWB BPF, the conventional tri-section stepped-impedance resonator (TSSIR) is adopted and its fundamental and first spurious resonance frequencies are chosen either to be suppressed or supported. New parallel dual-section T-shaped and TSSIRs are proposed, optimised and fabricated to provide single and DNBss, respectively. The proposed concept avoids using via holes, which is conventionally used in notch filters. In addition, a size reduction of about 75% is reported in comparison with the conventional BPF with a single notch-band accompanied by two transmission zeroes at the lower and upper stop-bands. Moreover, our proposed DNBs BPF demonstrates a comparable performance while being smaller in size (up to a 12.6% size reduction) to that of the latest UWB BPF design that used complicated and expensive multilayer liquid crystal polymer (LCP) technology.
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