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Herein, stacked films of WO3 separated by indium nanosheets are fabricated as quad‐band antennas suitable for high‐frequency applications. The amorphous WO3 films and indium nanosheets are coated onto each other using the thermal evaporation technique under a high vacuum pressure of 10−5 mbar. The stacked layers of Pt/WO3/In/WO3/Pt are structurally and electrically characterized. The tunneling‐type quad‐band antennas are tested in the driving frequency domain of 0.01–1.80 GHz and a low signal amplitude of 0.10 V. It is observed that the insertion of indium nanosheets between layers of WO3 remarkably increases the width of the tunneling barrier from 55 to 70 nm without altering the tunneling barrier height. This also enhances the cutoff frequency at a quad‐band frequency of 1.80 GHz from 10 GHz to 1.46 THz and increases the return loss values from ≈5 to 21 dB. A widely tunable cutoff frequency extending from 0.30 GHz to 1.46 THz can be obtained based on the selected driving signal frequency. The microwave‐controlling features of the Pt/WO3/In/WO3/Pt devices, with their high cutoff frequency and high power transmission ratios at the quad‐band frequency, make them attractive for 6G technology. [ABSTRACT FROM AUTHOR]

Microwave resonators are a technology with the potential to automate the rapid acquisition of vapour-liquid equilibrium data in multicomponent mixtures. However, the re-entrant resonators commonly used for fluid characterization have limited ability to mix or drain adequately due to the bulbs and narrow gaps used within the sample volume to spatially distribute the sensing regions with intense electric fields. This work describes a novel composite cavity combining two toroidal split-ring resonators and a cylindrical resonator, each sealed and partially filled with the polymer PEEK, to spatially separate sensing regions whilst maintaining an unobstructed sample volume. This unique design also allows for the total sample volume to be an order-of-magnitude smaller than conventional microwave cavities, without significantly increasing the resonant frequencies. Mass transfer between phases is facilitated by mechanical agitation, reducing equilibration time. Finite element analysis (FEA) is used to model how the dielectric interfaces within the cavity perturb electric field distributions. This model is used to interpret measurements of two-phase propane to quantify liquid volume fraction and phase dielectric permittivities. [ABSTRACT FROM AUTHOR]

Herein stacked layers of Nb2O5 coated onto Al substrates are fabricated as microwave resonators. Structural and morphological analyses on these stacked layers have shown the amorphous nature of growth of the stacked layers. Electrically, the resonators showed negative capacitance effect accompanied with series and parallel resonance at three well -distinguished notch frequencies. Additionally, the resonators exhibited bandstop filter characteristics with notch frequency ( f n) centered at 1.05 GHz, return loss ( R L) value of 9.0 dB and voltage standing wave ratios ( V S W R) of 2.12. To enhance the performance of the Nb2O5 microwave resonators, platinum nanosheets of thicknesses of 50 nm were inserted between layers of Nb2O5. Platinum nanosheets successfully decreased the surface roughness and increase the electrical conductivity by five orders of magnitude. Pt nanosheets additionally improved the values of f n, S 11, R L and V S W R to 1.16 GHz, 0.039, 30.3 dB and 1.12, respectively. The features of the microwave resonators comprising Pt nanosheets in its structure are promising for using them in communication technology.

Topological photonics has been widely investigated due to its profound physical significance and great number of potential applications. Microwaves have long wavelengths, so it is relatively easy to manufacture large-sized microwave photonic crystals, enabling researchers to observe and measure phenomena such as topological boundary states. Nevertheless, the quality factors (QFs) of most resonators composed of traditional materials in the microwave region are relatively low, leading to topological edge states with high decay rates. In this study, we present a one-dimensional topological photonic crystal in the microwave region based on coupled superconducting resonators. A topological state with a QF as high as 6000 is observed, which proves this to be a new platform for the investigation of topological photonics with low decay rates in the microwave regime. [ABSTRACT FROM AUTHOR]

Abstract A number of high‐sensitivity microwave sensors with compact resonators are designed, fabricated, and tested for non‐invasive blood glucose monitoring. In the first step, a split ring resonator (SRR)‐based sensor is designed, and then it’s sensing parameters, viz. the reflection coefficient magnitude and phase coupled with its input impedance, are extracted and calibrated by different glucose solutions. The results of this structure are subsequently saved as a reference sensor. During the second step, the swastika‐shaped and electric‐LC (ELC) geometries are substituted for the SRR to enhance the sensitivity of the reference sensor, and the sensing parameters of these structures, which are sensitive to the glucose solutions, are obtained. In the third step, the sensitivity of the three proposed designs is calculated and compared, using the reflection coefficient amplitude, phase, and input impedance. The comparisons typically demonstrate that the sensitivity of the swastika‐shaped structure is equal to 148.367 (Ω/mgmL−1) if the sensitivity is acquired from the imaginary part of the input impedance, which is better than the SRR and ELC geometries. On the contrary, the sensitivity of the SRR geometry is at a maximum and equal to 16.79 (deg/mgmL−1) if the sensitivity is calculated in terms of the reflection coefficient phase.

Abstract This study proposes a highly sensitive portable device that utilizes electromagnetic waves and data analytics for instantaneous Severe Acute Respiratory Syndrome CoronaVirus 2 (SARS‐CoV‐2) detection. The device consists of a Radio Frequency (RF) circuit that interprets reflected and transmitted electromagnetic waves to identify virus signatures in physiologically significant matrices, including human saliva and diluted nasopharyngeal swabs. The sensor's accuracy is validated in both pre‐clinical and clinical settings, where clinical measurements demonstrate an instantaneous detection accuracy of 94%, sensitivity of 95%, and specificity of 97.5% between the sensor's physical parameters and SARS‐CoV‐2 detection. The sensor's accurate real‐time response is due to its unique design and precise modeling techniques. In addition, the same sensing system is tested across different viruses and its ability to differentiate between influenza A, respiratory syncytial, and SARS‐CoV‐2 viruses is proven. Hence this work presents a holistic system that can predict the viral concentration of SARS‐CoV‐2, as well as differentiate between different viruses instantaneously and without adding any amplifying agent.

Herein, stacked layers of FeSe2 deposited onto ytterbium substrates using the thermal evaporation technique under a vacuum pressure of 10−5 mbar are observed to form nanowire bundles (NBs). Structural investigations on these NBs have shown the preferred growth of orthorhombic FeSe2 in addition to hexagonal ytterbium selenide as a minor phase in the structure of FeSe2. Impedance spectroscopy analyses conducted in the frequency domain of 0.01–1.80 GHz show that FeSe2 stacks can exhibit a negative capacitance effect and bandstop filter characteristics. For these bandstop filters, the refection coefficient (S11$S_{11}$), the voltage standing wave ratios (VSWR$\text{VSWR}$), and the return loss (Lr$L_{\text{r}}$) spectra display optimum values at a notch frequency of 0.87 GHz. In addition, computational analysis using Lorentz oscillator model has shown that the negativity of the capacitance is dominated by two oscillators centered at 0.08 and 1.25 GHz. On the other hand, the insertion of aluminum nanosheets between the stacked layers of FeSe2 has been observed to decrease the negativity of the capacitance, increase the values of S11$S_{11}$ and Lr$L_{\text{r}}$, and bring the VSWR$\text{VSWR}$ closer to ideality. FeSe2 nanowire bundles resulting from FeSe2 stacks comprising Al nanosheets are considered suitable for microwave communication technology. [ABSTRACT FROM AUTHOR]

In this letter, electromagnetically induced transparency (EIT) is implemented in the microwave region with an experimental system composed of two indirectly coupled high‐temperature superconducting resonators. The transition condition between EIT and Autler–Townes splitting is analyzed, giving a physical explanation of this transition based on the superposition of dressed modes in a three‐level system. Benefit from the ultra‐low loss of superconducting circuit, it is experimentally shown that either EIT or Autler–Townes splitting can be explicitly achieved through control of the detuning between the two resonators and a group delay as high as 5 μs is obtained for the EIT case. This work suggests that high temperature superconducting circuit is a concise and explicit platform for investigating indirectly coupled resonators with standing‐wave modes and the physical mechanism underneath coherence phenomena in the microwave region. [ABSTRACT FROM AUTHOR]

Triangular resonators re-shaped with Sierpinski geometry were designed, manufactured, and tested for potential applications in the K-Band. Prototypes of band-stop filters working around 20 GHz and 26 GHz, interesting for RADAR and satellite communications, were studied in a coplanar waveguide (CPW) configuration. Single and coupled structures were analyzed to give evidence for: (i) the tuning of the resonance frequency by increasing the internal complexity of the triangle and (ii) resonance enhancement when coupled structures are considered. The exploited devices were part of the more extended family of metamaterial-inspired structures, and they were studied for their heuristic approach to the prediction of the spectrum using experimental results supported by electromagnetic simulations. As a result, a Sierpinski resonator, not only fed into but also fully embedded into a CPW environment, had a frequency response that was not easily determined by classical theoretical approaches. [ABSTRACT FROM AUTHOR]

A number of high‐sensitivity microwave sensors with compact resonators are designed, fabricated, and tested for non‐invasive blood glucose monitoring. In the first step, a split ring resonator (SRR)‐based sensor is designed, and then it's sensing parameters, viz. the reflection coefficient magnitude and phase coupled with its input impedance, are extracted and calibrated by different glucose solutions. The results of this structure are subsequently saved as a reference sensor. During the second step, the swastika‐shaped and electric‐LC (ELC) geometries are substituted for the SRR to enhance the sensitivity of the reference sensor, and the sensing parameters of these structures, which are sensitive to the glucose solutions, are obtained. In the third step, the sensitivity of the three proposed designs is calculated and compared, using the reflection coefficient amplitude, phase, and input impedance. The comparisons typically demonstrate that the sensitivity of the swastika‐shaped structure is equal to 148.367 (Ω/mgmL−1) if the sensitivity is acquired from the imaginary part of the input impedance, which is better than the SRR and ELC geometries. On the contrary, the sensitivity of the SRR geometry is at a maximum and equal to 16.79 (deg/mgmL−1) if the sensitivity is calculated in terms of the reflection coefficient phase. [ABSTRACT FROM AUTHOR]

During cold start of vehicles with gasoline combustion engines, conversion of pollutants in the exhaust gas to inert products is very low due to low catalyst temperature. Only above the light-off temperature, significant conversion can be achieved. Previous strategies to reduce cold-start emissions have been focused on developing catalysts with a low light-off temperature. Electric catalyst heating systems have also been discussed repeatedly. A disadvantage of such systems is the required volume flow through the catalyst, which is necessary for heat transfer to the catalyst. In contrast, microwave-assisted heating allows direct introduction of thermal power into the catalyst due to dielectric losses of the catalyst materials. This work analyses simulation-based the influence of the material on the heatability by microwaves. The focus is on the substrate materials rather than the catalytically active coatings, since the substrate represents the part in the TWC where most of the dielectric losses occur. For this purpose, the temperature-dependent dielectric material properties of cordierite and silicon carbide (SiC) are investigated. The determined material properties are then transferred to a simulation model that calculates heat distribution and heat insertion based on the electromagnetic field distribution. The heat propagates better throughout the monolith due to the higher thermal conductivity of SiC compared to cordierite. In summary, SiC leads to a homogeneous heating of the entire catalyst material. The fact that dielectric losses of SiC decrease with temperature may help to self-limit the catalyst temperature. [ABSTRACT FROM AUTHOR]

The accumulation of snow and ice has the potential to have a negative impact on numerous industries if it is not accurately detected and processed in real-time. Microwave resonators have gained interest as durable and reliable ice detectors. To detect the thickness of clear ice slices on a horizontal cold plate surface, a capacitively coupled split-ring resonant sensor was experimentally investigated. To ascertain the efficacy of the sensor, plexiglass with similar relative permittivity to ice was firstly tested. The effect of the plexiglass plate thickness on the resonance amplitude of the transmission scatter parameter was found to be monotonic in the range of 16.8 mm thickness, thereby demonstrating the ability of the sensor to accurately measure plate thickness. Then, the effect of different thicknesses of clear ice slices within 17.0 mm on the resonance parameters was tested under constant temperature. The resonant amplitude decreased by 46.55% from −4.13 dB to −6.05 dB, as the thickness of the clear ice slice gradually increased from 2.5 mm to 17.0 mm. A model for the detection of ice thickness based on the analysis of theoretical principles and experimental data was developed. The ice thickness could be detected accurately within a range of 17.0 mm at temperatures between −3 and −20 °C, with a maximum deviation of 5.66% in the detection of ice thickness. This study validates the application of the sensor to detect ice thickness, such as on ships, roads and aircraft. • The relationship between the thickness of ice and microwave signal is revealed. • The thickness of clear ice on cold plate could be detected clearly in real-time. • The maximum thickness of clear ice that could be detected is 11.5 mm. • The relative deviation of the ice thickness detection sensor is less than 5.6 %. [ABSTRACT FROM AUTHOR]

Magnesium selenide thin films are coated onto glass and semitransparent Pt substrates (nanosheets) by the vacuum evaporation technique under a vacuum pressure of 10−5 mbar. The effect of Pt nanosheets of thicknesses of 100 nm on the structural, compositional, optical, and electrical properties of MgSe is explored. It is found that platinum nanosheets enhance the light absorbability in the visible and infrared ranges of light. They slightly redshift the energy bandgap and decrease the dielectric constant. The strong interaction between Pt and MgSe increases the electrical conductivity by five orders of magnitude. Pt forms shallow impurity levels in the energy bandgap of MgSe allowing the tunneling process at the Pt/MgSe interfaces. Practically, a Pt/MgSe/Pt tunneling type device is fabricated and tested by the microwave impedance spectroscopy technique. It is found that Pt/MgSe/Pt devices can exhibit resonance–antiresonance and negative capacitance effects which are important in electronic circuits as parasitic capacitance cancelers, signal amplifiers, and noise reducers. In addition, evaluation of the cutoff frequency spectra has shown the ability of using the Pt/MgSe/Pt devices as microwave resonators appropriate for 5G/6G technologies. A cutoff frequency larger than 70 GHz can be achieved by imposing ac signal of amplitude of 0.10 V. [ABSTRACT FROM AUTHOR]

U-shaped microwave resonators implemented by RF MEMS switches can be considered the result of a novel design approach for obtaining small-footprint tunable resonators, owing to the bent shape of the resonator and the microsystem solution for changing the frequency of resonance. In this paper, we discuss the design approach for potential configurations of U-shaped structures combined with ohmic RF MEMS switches. Owing to their prospective application in RADAR and satellite systems, the devices were assessed for K-Band operation, specifically for 15 GHz, 20 GHz, and 26 GHz. The ON-OFF states determined by an electrostatic actuation of metal beams composing the RF MEMS ohmic switches allow for selecting different path lengths corresponding to different frequencies. In this contribution, initial configurations were designed and manufactured as a proof-of-concept. The advantages and critical aspects of the designs are discussed in detail. [ABSTRACT FROM AUTHOR]

Non-invasive contactless simultaneous sensing and heating of individual droplets would allow droplet microfluidics to empower a wide range of applications. However, it is challenging to realize simultaneous sensing and heating of individual droplets as the resonance frequency of the droplet fluid, which is decided by its permittivity, must be known so that energy is only supplied at this frequency for droplet heating with one resonator. To tailor the energy transfer in real-life heating applications, the droplet has to be sensed first to identify its corresponding resonance frequency, which is used to dynamically tune the frequency for supplying the required energy for heating this particular droplet. To achieve this goal, two resonators are needed, with one for sensing and one for heating. Integrating multiple resonators into one typical microfluidic device limits placement of the resonators to be as close as possible, which would raise the concern of crosstalk between them. The crosstalk would result in inaccurate sensing and heating. This study focuses on numerically and experimentally investigating the effect of influencing parameters on the crosstalk between two adjacent resonators with the ultimate goal of providing guidance for multiplexing the resonators in a typical microfluidic device. ANSYS HFSS is used to perform the electromagnetic analysis based on the finite element method. Experimental studies are conducted on a microfluidic chip integrated with two resonators to validate the numerical results. An optimal distance between two resonators is suggested, with the recommendation for the resonator size and heating power towards simultaneous sensing and heating of individual droplets. [ABSTRACT FROM AUTHOR]

Abstract A dual‐path coupled‐line circular ring resonator filter synthesis is presented. The topology comprises identical coupled lines in series duplicated to form dual‐path coupled‐line interconnections. A bandpass response of nth order equal to (n/2) + 1, corresponds to controllable transmission zeros (TZs) found on both sides of the passband by varying the values of the even‐ and odd‐mode impedances of the coupled lines, denoted Zoe and Zoo, respectively. Concerning the efficiency of controllable electrical characteristics of the resonator filter, such as in‐band matching level, high selective response, and wide bandwidth, and fixing the position of the TZ frequencies, the proposed method using asymmetrical quarter‐wavelength coupled lines in a circular ring resonator filter is superior to existing methods. Ultimately, the proposed bandpass filter is implemented on contrast dielectric substrate FR‐4 and Taconic TRF‐45 substrates using a planar form of microstrip technology to verify the synthesis equation. The measurement results indicate that the filter achieved more than 40% fractional bandwidth with excellent in‐band matching levels and a controllable filter order. Both measurement and simulation results are in good agreement regarding return and insertion loss values, thus validating the proposed designs.

In this paper, a quasi‐optical resonator with new coupling method and parasitic‐mode‐suppressing in 110–170 GHz is proposed. The coupling of terahertz (THz) quasi‐optical resonator in this paper is realized by PCB substrate processing and pressurized flange. At the same time, the parasitic mode is effectively suppressed by slitting the plane mirror to reduce the influence on the main mode during the test. And the fused quartz sample was tested to verify the feasibility of the system for complex dielectric testing of materials in 110–170 GHz. [ABSTRACT FROM AUTHOR]

Herein, the structural, optical and electrical properties of band-aligned CdBr2/Ga2S3 interfaces in the presence and absence of Au nanosheets (10-20 nm) as interface spacers are reported. CdBr2/Au/Ga2S3 (CAG) stacked layers are grown by vacuum evaporation under a vacuum pressure of 10-5 mbar. It is observed that coating of amorphous Ga2S3 onto CdBr2 increases the crystallite size and decreases the microstrain, defect density and stacking faults in hexagonal CdBr2. Depositing Ga2S3 onto CdBr2 enhanced the light absorbability of Ga2S3 by more than 120 times. Insertion of Au nanosheets as spacers between the Ga2S3 and CdBr2 layers highly engineered the energy band gap of the CAG structure. In addition, the frequency-dependent capacitance, conductance and impedance spectroscopy analyses in the microwave frequency domain have shown the ability of the CAG structure to reveal negative capacitance effect and the ability to behave as microwave resonators displaying controllable (by Au nanosheets) resonance-antiresonance phenomena. CAG bilayers showed microwave band pass/reject characteristics with tunable and multiband features. The microwave cutoff frequency at the notch frequency of the band filters are found to suitable for the 5G mobile technologies. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a novel technique to design an ultra‐wideband bandpass filter (UWB BPF) based on fractal tree stub loaded multimode resonators. Two different topologies are opted to verify the relationships between resonant modes of the multimode resonators with different parameters of the fractal tree stub. UWB bandwidth is acquired by increasing iterations of the fractal tree without a significant effect on the filter's physical size. The proposed topologies provide design flexibility in terms of resonance and bandwidth, which are directly related to the iteration order of the fractal tree used. To verify all the features of fractal‐tree‐based UWB BPF, the proposed UWB BPF is parametrically studied using electromagnetic simulation, and a prototype is fabricated. The measured and simulated results are in close agreement. The actual size of the filters is 11.5 × 9.6 mm2. The proposed filter covers the whole band of UWB with a minimum insertion loss of 1 dB and return loss is better than 10 dB. The measured stopband extends up to 16 GHz.

Herein, MoO3/ZnS broken gap heterojunction devices are fabricated by thermal evaporation under a vacuum pressure of 10−5 mbar. The devices are characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, ultraviolet-visible light spectroscopy and impedance spectroscopy. Three channels composed of one Schottky arm (Ag/ZnS) and two ohmic arms (Au, C)/ZnS are formed on the epilayer of the amorphous (MoO3)/polycrystalline (ZnS) heterojunctions. Optical analyses show that the broken gap devices exhibit valance and conduction band offsets of 2.6 eV and 2.8 eV, respectively. Practical tests on the devices show that they can behave as abrupt electronic switches with biasing independent current rectification ratios of 2.7 × 103 at an applied voltage of 0.14 V. The Au/MoO3/ZnS/Ag channels displayed metal oxide field effect transistor characteristics as they are effective in the frequency domain of 3.0–20 MHz. In addition to its performance as a negative capacitance FET, the broken gap device can be employed as a radiowave/microwave cavity with notch frequency ( f n ) values of 0.86 GHz, 1.16 GHz, 1.69 GHz and 1.75 GHz. The ideality of the resonators was observed at 1.16 GHz for the Au/MoO3/ZnS/C channel. This channel displayed bandpass filter characteristics with voltage standing wave ratios of 1.0 and return loss values of 40.2 dBs. [ABSTRACT FROM AUTHOR]

Herein, cadmium bromide thin film devices are designed for possible use in communication technology. The 1.0 μ m thin layer of CdBr2 is sandwiched between two Au (1.0 μ m thick) layers using the thermal evaporation technique under a vacuum pressure of 10-5 mbar. The Au/CdBr2/Au devices are structurally morphologically and electrically characterized. It is observed that the hexagonal cadmium bromide exhibits large lattice mismatches with cubic Au substrates. The randomly distributed nano- rod like grains is accompanied with average surface roughness of ~26 nm. When an ac signal of low amplitude is imposed between the terminals of the Au/CdBr2/Au devices, a negative capacitance effect in the frequency domain of 10-1800 MHz is observed. In addition, analysis of the impedance spectra in the same domain has shown that the device behaves as band pass/stop filters suitable for 4G technology. The microwave based standard analysis of the Au/CdBr2/Au band filters have shown that it displays a notch ( f c o) frequency of 2.0 GHz. The cutoff frequency at f c o reaches 7.86 GHz. The features of the Au/CdBr2/Au devices nominate it for use as microwave resonators and as negative capacitance devices suitable for; 4G technology, noise reduction and for parasitic capacitance cancellation.

Herein, SiO2 nanosheets with thicknesses of 25−100 nm are used to enhance the performance of Au/CdBr2 Schottky barriers. The Au/CdBr2/SiO2/Au straddling‐type heterojunction devices are prepared by the thermal evaporation technique. It is observed that SiO2 layers enhance the crystallinity of CdBr2 through increasing the crystallite sizes and decreasing the defect density, stacking faults, and microstrain by 50%, 56%, 32%, and 34%, respectively. A work function of 6.38 eV is determined from the temperature‐dependent electrical resistivity measurements of p−type CdBr2. In addition, it is observed that, when coated with 50 nm‐thick SiO2, the Au/CdBr2/SiO2/Au straddling‐type transistors can reveal high current rectification ratios of 6.9 × 102 at low biasing voltages in the range of 0.06−0.30 V. The alternating current signals' analysis in the microwave range of spectra indicates that the current conduction mechanism is dominated by the correlated barrier hopping and quantum mechanical tunneling. It is observed that the Au/CdBr2/SiO2/Au devices exhibit a negative effect accompanied with resonance−antiresonance in the capacitance spectra. Moreover, the microwave cutoff frequency which reaches ≈165.1 GHz and the magnitude of reflection coefficient spectra show that the device under study can perform as multiband pass/stop filters suitable for wire/wireless communication applications including 3G/4G technologies. [ABSTRACT FROM AUTHOR]

This article explains the frequency limitation in designing microstrip circuits based on a complementary split-ring resonator (CSRR) and reports a novel technique for increasing its operating frequency, which makes the CSRR suitable for high-frequency applications. This study helps in synthesizing the dimensions of symmetric CSRR (SCSRR) and asymmetric CSRR (ACSRR) circuits, which shows the applicability of the proposed technique in designing mm-wave circuits. It is observed that the upper frequency limit of the microstrip-coupled SCSRR is mainly due to weak electric coupling. The weak coupling implicates radiation loss in the structure, and the frequency at which the SCSRR has maximum loss due to radiation is found to be much less than the cutoff frequency of the higher order mode of the microstrip line, thus effectively limiting the operating frequency range of the circuit. In this article, the type of coupling and associated electrical parameters, e.g., reflected power, transmitted power, radiated power, losses, quality factor, voltage standing wave ratio, and gain, are investigated in detail. The allowable bandwidth of the fundamental mode of the microstrip line can be utilized to design CSRR with improved coupling. It is found that the ACSRR enhances the coupling coefficient using the cross-coupling effect. At higher frequencies, where the electric coupling is becoming too weak for the SCSRR, it is possible to design a magnetically coupled ACSRR of the same dimensions as the SCSRR. Finally, the design profile for both the SCSRR and ACSRR is studied in detail, and the radiating condition is discussed as a function of the height and dielectric constant of the substrate. For practical-verification purposes, two circuit prototypes are fabricated on a 1.5-mm-thick Rogers RT5880 substrate, and the measured results are found to be in good agreement with the proposition. It is found that, for a given microwave substrate, the maximum allowable resonating frequency of the ACSRR structure is nearly twice that of the SCSRR structure. [ABSTRACT FROM AUTHOR]

We describe an algorithm capable of extracting the unloaded quality factor and the resonant frequency of microwave resonators from vector S-parameters. Both symmetrical (Lorentzian) and asymmetrical (Fano) transmission responses are supported. The algorithm performs an adaptive outlier removal to discard measurement points affected by noise or distortion. It removes the effects caused by imperfections in the device (such as modes with close resonance frequencies or stray coupling between the resonator ports) or the experimental setup (such as lack of isolation or dispersion in the test set and cables). We present an extensive assessment of the algorithm performance based on a numerical perturbation analysis and the evaluation of S-parameter fitting results obtained from network analyzer measurements and resonator equivalent circuits. Our results suggest that uncertainty is mainly caused by factors that distort the frequency dependence of the S-parameters, such as cabling and coupling networks, and is highly dependent on the device measured. Our perturbation analysis shows improved results with respect to those of previous publications. Our source code is written in Python using open-source packages and is publicly available under a freeware license. [ABSTRACT FROM AUTHOR]

A novel sensing method that uses the separate design of a sensitivity enhancer and sensing zone is reported. Unlike most resonance-based sensors, the flexible design of a sensing zone is beneficial to the increment of effective material-under-test volume. A novel technique to enhance sensitivity is proposed by engineering the −1/ $x$ -like function microwave transmission to slow the energy-flow velocity. The measured large group delay is up to $\sim 16~\mu \text{s}$ at 2.967 GHz. A lumped model is built to study the condition of the engineered transmission. Compared with a regular coplanar waveguide sensor, the sensitivity is improved up to ~227 times when it is connected to the slow microwave circuit. [ABSTRACT FROM AUTHOR]

Metamaterial‐based double‐slit complementary split rectangular resonator sensor is proposed for the characterisation of dielectric properties of the materials under test (MUTs). The proposed sensor is designed and simulated on the CST microwave studio software using a low‐cost substrate FR4. An array of three identical resonators is etched in the ground plane of the sensor to achieve a single and deep notch of −58.7 dB in the transmission coefficient (S21) at the resonant frequency of 7.01 GHz, which is the novelty of the proposed sensor. A deep and single resonant frequency band has a significant role in the precise measurement of the dielectric properties of the MUTs. The effective constitutive parameters are extracted from the S‐parameters. An equivalent circuit model is suggested that describes the overall behaviour of the sensor. The sensor is fabricated on the FR4 substrate and measured through the vector network analyser (N5224B) by placing the standard materials. The parabolic equation for the proposed sensor is formulated to approximate the permittivity of the MUTs. A very small percentage of error, 0.77, is found which shows high accuracy of the sensor. This methodology is efficient, simple in fabrication, and reduces cost and computational time also. [ABSTRACT FROM AUTHOR]

A new compact multilayer dual-band balanced-to-balanced filtering power divider (FPD) based on substrate integrated waveguide (SIW) resonator is proposed in this Letter. Originating from the field distributions of resonant modes in the square SIW cavity, TE201-mode and TE203-mode are utilised to achieve desired differential-mode (DM) transmission and high common-mode (CM) suppression. Meanwhile, dual DM passbands are generated by reasonably coupling two SIW resonators in the back-to-back form with the help of four coupling apertures etched on the middle-layer ground. Besides, a pair of isolated resistors is loaded at back-diagonal regions of the upper-layer SIW resonator, achieving high port-to-port isolation. For demonstration, a prototype dual-band balanced-to-balanced SIW FPD operating at 11.0 and 18.4 GHz is ultimately designed, fabricated and tested. Good agreement between simulated and measured results is obtained, verifying the feasibility and validity of the design concept. [ABSTRACT FROM AUTHOR]

Nitrogen‐vacancy (NV) colour centres in diamond have attracted extensive attention in quantum precision measurement, computation and communication. In these fields, microwave manipulation is a technology in which antenna is used to radiate special microwave to manipulate the quantum spin state of NV colour centres. In this work, high frequency structure simulator software is used to design a microstrip antenna with a resonance frequency of 2.8756 GHz. Based on simulation and experiments, near field radiation of antenna is optimised to improve its microwave manipulation quality. This antenna will be helpful in the development of hybrid quantum devices of NV centres. [ABSTRACT FROM AUTHOR]

In this Letter, a non-destructive microwave resonant sensor based on the modified complementary split-ring resonator has been proposed and analysed with respect to its sensitivity for detecting the aqueous biochemicals. This technique is based on the perturbation theory and only requires to measure resonant frequency and hence, achieving a substantial reduction in the computation time and cost. The proposed sensor is designed to achieve high sensitivity performance with a measured quality factor of the sensor in the bare state, QB = 631.5, at the centre frequency of fo = 6.31 GHz. The proposed sensor has a maximum sensitivity of S = 6.23 MHz with respect to a unit change in the dielectric constant value. A numerical model is developed for the dielectric constant of the biochemicals as a function of the resonant frequency. The proposed sensor, therefore, provides high sensitivity, simple structure layout and real-time response with cost effectiveness. The proposed structure can be a potential candidate for the non-intrusive sensing of aqueous biochemicals. [ABSTRACT FROM AUTHOR]

In this paper a design for a microwave sensor for the non-invasive measurement of blood glucose concentrations is proposed. The sensor is intended for usage as part of a non-invasive glucose-quantifying device. With this aim, three different microwave resonator structures are analyzed as possible candidates, and strengths and weaknesses are highlighted in each case. The chosen resonator is an open structure in which a finger of the patient is placed, fulfilling the role of a sample to be characterized by the sensor. The shape and size of the finger thus condition those of the resonator. Variations in the concentration of blood glucose modify the dielectric properties of the tissue, which is part of the microwave resonator-finger system, and as such, the changes translate to the resonance frequency of the whole structure. Among the three studied topologies, it was found that a single resonator designed using a coplanar structure with a ground plane showed the best trade-off in frequency sensitivity, stability and repeatability of the measurements. A notable correlation, between the resonance frequency of the proposed sensor and the blood glucose levels measured with a traditional glucometer, was found. This highlights a potential interchangeability of both glucose measurement methods. [ABSTRACT FROM AUTHOR]

This study presents a compact wide stopband microstrip diplexer which is designed based on a novel resonator structure. This novel resonator consists of a main hairpin cell loaded by a smaller hairpin and T‐shaped cells. The presented diplexer operates at 3.46 and 4.75 GHz for IEEE 802.16 worldwide interoperability for microwave access (WiMAX) and IEEE802.11a Wireless LAN applications, respectively. The main advantages of the proposed diplexer are its flat channels, two wide bandwidths, attenuated harmonics, low insertion losses better than 0.18 dB, several transmission zeros and sharp frequency response. From first up to fifth harmonics of the proposed diplexer are well attenuated with the maximum harmonic level −20 dB. Meanwhile, the simulation results show that the presented design can suppress harmonics up to 44 GHz. In other words, the harmonics from the 1st up to 12th are suppressed. The group delay at both channels is lower than 1.1 ns, which is good for a microstrip diplexer. This good performance is obtained, while the overall area of the designed diplexer is only 0.037λg2. Based on the comparison results, the proposed diplexer has a compact size, the minimum group delay and a wide stopband rejection. The proposed diplexer is fabricated and measured. Both simulation and measurement results are in good agreement. [ABSTRACT FROM AUTHOR]

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Niobium nitride (NbN) is a useful material for fabricating detectors because of its high critical temperature and relatively high kinetic inductance. In particular, NbN can be used to fabricate nanowire detectors and mm-wave transmission lines. When deposited, NbN is usually sputtered, leaving room for concern about uniformity at small thicknesses. We present atomic layer deposition niobium nitride (ALD NbN) as an alternative technique that allows for precision control of deposition parameters such as film thickness, stage temperature, and nitrogen composition. Atomic-scale control over film thickness admits a high degree of uniformity for films 4–30 nm thick; control over deposition temperature gives rise to growth rate changes, which can be used to optimize film thickness and critical temperature. In order to characterize ALD NbN in the radio-frequency regime, we construct single-layer microwave resonators and test their performance as a function of stage temperature and input power. ALD processes can admit high resonator quality factors, with ≥ 43 % of resonators above Q i = 10 6 , which in turn increase detector multiplexing capabilities. Furthermore, we find critical temperatures in the range of 7.5–10.9 K that vary as a function of cycle count and deposition temperature. [ABSTRACT FROM AUTHOR]

A soft and highly directive, proximity-coupled split-ring resonator fabricated with a liquid alloy, copper and polydimethylsiloxane (PDMS) is presented. The same was designed for sensing osteogenesis of calvarial bone. As dielectric properties of bone grafts in ossifying calvarial defects should change during the osteogenesis process, devices like this could monitor the gradual transformation of the defect into bone by differentiating changes in the dielectric properties as shifts in the resonance frequency. Computational Software Technology (CST) Microwave Studio®-based simulation results on computational head models were in good agreement with laboratory results on head phantom models, which also included the comparison with an in-vivo measurement on the human head. A discussion based on an inductive reasoning regarding dynamics’ considerations is provided as well. Since the skin elasticity of newborn children is high, stretching and crumpling could be significant. In addition, due to typical head curvatures in newborn children, bending should not be a significant issue, and can provide higher energy focus in the defect area and improve conformability. The present concept could support the development of soft, cheap and portable follow-up monitoring systems to use in outpatient hospital and home care settings for post-operative monitoring of bone healing after reconstructive surgical procedures.

An ultra-wideband (UWB) printed monopole antenna is designed from stepped-impedance resonator (SIR) geometry. An inductor which is loaded in series between the radiating strips combines the multiple resonance bands of a two-strip stepped-impedance printed monopole antenna into a single ultra-wide resonance band. The two-strip inductive-loaded stepped-impedance printed monopole antenna is theoretically analysed for its resonant frequencies with the proposed modified transmission line analysis of inductive-loaded SIR model. The proposed analysis is validated by comparing the resonances with the electromagnetic simulation results and real-time measured results from the fabricated prototype of the antenna. The prototype of the two-strip inductive-loaded stepped-impedance printed monopole antenna fabricated on the low-cost FR4 substrate, resonated for the ultra-wide frequency range from 2.58 to 10 GHz.

An ultra-wideband (UWB) printed monopole antenna is designed from stepped-impedance resonator (SIR) geometry. An inductor which is loaded in series between the radiating strips combines the multiple resonance bands of a two-strip stepped-impedance printed monopole antenna into a single ultra-wide resonance band. The two-strip inductive-loaded stepped-impedance printed monopole antenna is theoretically analysed for its resonant frequencies with the proposed modified transmission line analysis of inductive-loaded SIR model. The proposed analysis is validated by comparing the resonances with the electromagnetic simulation results and real-time measured results from the fabricated prototype of the antenna. The prototype of the two-strip inductive-loaded stepped-impedance printed monopole antenna fabricated on the low-cost FR4 substrate, resonated for the ultra-wide frequency range from 2.58 to 10 GHz. [ABSTRACT FROM AUTHOR]

In this work, two fully-textile wearable devices, to be used as chipless identification tags in identification and tracking applications are presented. For the fabrication of the fully-textile tags, a layer of fleece was used as a substrate, while an adhesive non-woven conductive fabric was employed for the conductive parts. To allow radio-frequency identification of these chipless tags, two alternative techniques were used. One relies on associating a binary code with the resonance frequency of resonant devices: the presence/absence of the resonance peaks in the transmission scattering parameter, |S21|, of a set of resonators is used to encode a string of bits. The second technique for accomplishing radio-frequency identification of the chipless tags resorts to a frequency-shift coding technique, which is implemented by modifying the configuration of a hairpin resonator. The obtained numerical and experimental results confirm the suitability of the proposed strategies for obtaining entirely-textile, wearable chipless tags for identification and tracking purposes, which can be particularly useful, especially in the industrial sector. In this field, in fact, the proposed solutions would guarantee a seamless integration with clothes and would facilitate the user’s interaction with the IoT infrastructure. In this regard, one of the envisaged application scenarios related to the tracking of hides in the leather industry is also presented. [ABSTRACT FROM AUTHOR]

This Letter presents a novel continuously tunable microwave resonator based on liquid crystal (LC) material. The reconfigurable device is implemented in Decoupled Empty Substrate Integrated Waveguide (DESIW) technology. DESIW technology allows both magnetic and electric DC (or low frequency) biasing of the LC. The resonator is continuously tunable in a range of 600 MHz, resulting in a measured tunability range of 8.5% around a centre frequency of 7 GHz. Moreover, the measured insertion loss of the reconfigurable device is between 4.3 and 6.8 dB, thus obtaining a Q‐factor of 190‐172. [ABSTRACT FROM AUTHOR]

In this work, the authors exploited the whispering gallery mode (WGM) resonator properties as a thermometer. The sensor is made of a cylindrical sapphire microwave resonator in the center of a gold-plated copper cavity. Two coaxial cables act as antennas and excite the WGM standing waves in the cylindrical sapphire at selected resonance frequencies in the microwave range. The system affords a high quality factor that enables temperature measurements with a resolution better than 15 µK and a measurement standard uncertainty of 1.2 mK, a value approximately three times better than that achieved in previous works. The developed sensor could be a promising alternative to platinum resistance thermometers, both as a transfer standard in industrial applications and as an interpolating instrument for the dissemination of the kelvin.

This Letter presents a new design of balanced-to-unbalanced (B2U) filtering magic-T based on circular patch resonator. Without additional circuit, the prescribed in-phase and out-of-phase specifications of the magic-T are achieved by elaborately studying and exploring the electric field distributions of the degenerate resonant modes in the circular patch resonators. Meanwhile, the desired filtering responses are attained by virtue of the coupling extent between the two designed patch resonators in the back-to-back form. In the proposed design, a pair of TM11 modes at first make up passband. Meanwhile, nice common-mode suppression can be achieved at the balanced ports, and high isolation is achieved at the single-end ports, respectively. For demonstration, a prototype B2U filtering magic-T working at 4.3 GHz with 3 dB fractional bandwidth of 16.3% is implemented. Measured results coincide well with simulated ones, verifying the proposed design concept. [ABSTRACT FROM AUTHOR]