Variation Of Resonant Frequency Research Articles

A New Miniaturized Low-Profile and Stable Dual-Band FSS with 2.5D Structure for ISM Bands

Based on 2.5-Dimensional (2.5D) frequency selective surface (FSS) structures, a new miniaturized frequency selective surface structure is proposed in this work to operate as a bandreject filter in the 2.4 GHz (2400 to 2483.5 MHz) and 5 GHz (5150 to 5350 MHz and 5470 to 5725 MHz) ISM (Industrial, Scientific, and Medical) bands. The FSS has the metallization layer formed by a square loop with an internal cross loop, with each geometry being responsible for a rejection frequency range. The main characteristics of the structure are discussed, emphasizing the resonance frequency variation as a function of the increasing number of vias. Numerical results are obtained through simulations using the commercial software ANSYS HFSS. In addition, by analyzing numerical results for structures with different numbers of vias, it was possible to obtain expressions for calculating the first resonance frequency for each geometry. The cell size of the 2.5D FSS of the proposed cell is only 0.0883 λ0, where λ0 corresponds to the free-space wavelength of the lower resonance frequency. The FSS presents dual polarization, angular stability for angles up to 50° and its simulated response presented two resonant frequencies, the first at 2.65 GHz and the second at 5.34 GHz, with relative bandwidths of 38.11% and 35.96%, respectively. For comparison and validation purposes, the prototype is fabricated and measured. A very good agreement between the simulation and measurement results is observed.

Optothermal effect on frequency measurement of suspended graphene mechanical resonator

In this work, the influence of the optothermal effect on mechanical resonance properties of a graphene mechanical resonator is investigated based on an optical fiber-based Fabry–Perot cavity. When optical power rise, the resonance frequency blueshifts in an exponential relationship, whereas amplitude rises in a linear relationship. The tuning range of resonance frequency can reach up to 9.95 % with a total optical power variation of 2.00 mW. The resonance frequency variation tuned by the optothermal effect shows good stability and repeatability. The result is helpful for deviation analysis in graphene mechanical resonators measurement employing optical actuation and detection methods. It can be further used to design graphene mechanical resonator-based tunable devices.

Thin Dielectric Layers Evaluation Using Tunable Split-Ring Resonator Based Metasurface in THz Frequency Range

The paper presents the evaluation of thin dielectric layers using a tunable split-ring resonator-based metasurface in the THz frequency range. Tunable unit cells of a metasurface allow its resonant frequency variation using some external excitation. This can be done in various ways. In this work, the behavior of such a metasurface is investigated by monitoring the resonant frequency value when the unit cell geometry is changed. Such behavior is utilized for the quality evaluation of a thin dielectric layer placed in vicinity of a metasurface. A change in dielectric permittivity noticeably affects the resonant frequency of a metasurface. In order to examine the state of the material under test, finite element method simulations were made for a 15 µm thin layer. As a result, the approximation-based relations between resonant frequencies (obtained for various geometries of structural element—in tunability range) and dielectric parameters of the examined material were derived. These relations carry more information than in the case of just one resonant frequency (the case of a non-tunable metasurface) and can be utilized for permittivity evaluation.

Stable output performance generated from a magneto-mechano-electric generator having self-resonance tunability with a movable proof mass

A magneto-mechano-electric (MME) generator that converts an ambient magnetic field to useable electricity has the potential as an autonomous power source for sensor networks without or supporting driving batteries. However, the output of a typical MME generator decreases when temperature changes lead to resonant frequency drift of the generator. Herein, a broadband MME generator having self-resonance tunability with a movable proof mass was described for continuously generating stable output energy over a range of surrounding temperatures. The designed MME generator with a movable proof mass presented a wide bandwidth of 14.7 Hz, which was 865 % compared to that of a typical MME generator with a fixed proof mass (1.7 Hz). Owing to the self-resonance tunability, the broadband MME generator presented a lower output degradation (0.7 vs. 2.1 mW for a typical MME generator), even when the temperature changed from −30 °C to 60 °C. Under temperature variation, the broadband MME generator generated stable output energy that was sufficient to continuously operate the IoT sensors and maintain the brightness of 120 white LEDs with high intensity. Thus, the MME generator with self-resonance tunability is anticipated to provide a stable energy source, even under harsh environments that induce variable resonant frequency.

Reynolds Stress Tensor Measurements In A Shear-Thinning Fluid Using Magnetic Resonance Velocimetry: A Parameter Study With The FDA Benchmark Nozzle

Compared to refractive index matching in laser optical measurement techniques, magnetic resonance velocimetry (MRV) is assumed to be comparatively robust to changes in fluid composition when the principal components of the mixture provide a measurable MRI signal. In previous studies, MRV measurements were performed with different mixtures of water and glycerol, and no significant errors arose regardless of the mixing ratio. MRV is therefore proposed as a promising method for providing experimental data for a wide range of fluids that may also replicate different viscosity models. However, MRV can suffer from so-called chemical shift artifacts caused by slight variations in resonance frequency of differently bound hydrogen protons. These effects may arise when additional components are added to the flow medium. In this study, the ability of MRV to measure different flow mixtures is investigated. The long-term goal is to provide comprehensive experimental validation data for viscosity models in numerical simulations. Measurements were performed in stationary fluid samples as well as in flow measurements at the sudden expansion of the FDA benchmark nozzel. It is shown that MRV can provide reliable results for a Newtonian fluid and a shear-thinning fluid.

Terahertz meta-biosensor based on high-Q electrical resonance enhanced by the interference of toroidal dipole

Electrical dipole resonances typically have low Q factor and broad resonant linewidth caused by strong free-space coupling with high radiative loss. Here, we present a strategy for enhancing the Q factor of the electrical resonance via the interference of a toroidal dipole. To validate such a strategy, a metasurface consisting of two resonators is designed that responsible to the electric and toroidal dipoles. According to constructive and destructive hybridizations of the two dipole modes, enhanced and decreased Q factors are found respectively for the two hybrid modes, compared to the one for the conventional electric dipole resonance. As a practical application of such high Q resonance, we further experimentally investigate the sensing performance of the metasurface biosensor by detecting the cell concentration of lung cancer cells (type A549). Moreover, through monitoring both resonance frequency and amplitude variation of the metasurface biosensor, the dielectric permittivity of the lung cancer cells is delicately estimated by the conjoint analysis of both simulated and measured results. Our proposed metasurface paves a promising way for the study of multipole interference in the field of nanophotonics and validates its effectiveness in biomedical sensing.

Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale: observations, modelling and insights to improve monitoring systems

Summary Slope instabilities, including prone-to-fall rock columns, are known to exhibit clear vibrational modes. The resonance frequencies of these modes can be tracked by seismic instrumentation, allowing the rock column's mechanical and structural properties to be monitored, as well as providing precursors of imminent irreversible failures. In previous studies, superficial thermoelastic effects were assumed to drive daily fluctuations in resonance frequencies, but no qualitative or quantitative evidence was provided. The results presented here corroborate this hypothesis and quantify the physical processes involved. We interpreted daily variations of resonance frequencies in the Les Arches study site (Vercors, French Prealps) using a thermo-mechanical finite-element model. Modelled fluctuations of the resonance frequencies over a day closely matched experimental observations, reproducing the daytime frequency increase of around 2 per cent. In addition, our model provides explanation of the various behaviours observed across study sites: the frequency response strongly depends on solar exposure, as well as the timing and intensity of both radiative and convective heat fluxes. We highlight acousto-elastic constants as key parameters of our semi-quantitative model, although they remain poorly constrained here. For future instrumentation, we therefore recommend the deployment of pyranometers on rocky sites to accurately invert these parameters over time, thus allowing rock fracturing to be quantitatively tracked by acousto-elastic monitoring.

L2Ti0.85(Mg1/3Nb2/3)0.15O3/MgTiO3/L2Ti0.85 (Mg1/3Nb2/3)0.15O3 tri-layer co-fired microwave dielectric ceramics: A strategy to suppress non-linear variation of resonant frequency with temperature and achieve a high Q value

In many microwave dielectric ceramics systems, like MgTiO3–CaTiO3, MgTiO3–SrTiO3, and tri-layer MgTiO3/TiO2/MgTiO3, the resonant frequency shows a non-linear variation over a wide temperature range (−40 – 105 °C), indicating that the negative τf (−40 – 25 °C) value deviates from zero when the positive τf (25–105 °C) value is tuned to zero. To suppress the non-linear variation of resonant frequency in the range of −40 – 105 °C, a well-established and efficacious method has been proposed by introducing Li2Ti0.85(Mg1/3Nb2/3)0.15O3 ceramic to the MgTiO3 system. Furthermore, a tri-layer architecture ceramic was designed to improve the dielectric properties. Compared with randomly distributed samples, the Q × f value can be increased by up to 51%. Moreover, the electric field distribution was simulated by the finite element method with the aid of the eigenmode solver of high frequency structure simulator (HFSS) to clarify the dielectric mechanism and predict the microwave dielectric characteristics of the tri-layer structure ceramics. Finally, tri-layer Li2Ti0.85(Mg1/3Nb2/3)0.15O3/MgTiO3/Li2Ti0.85(Mg1/3Nb2/3)0.15O3 ceramic with wide temperature stability and high Q × f value was obtained [εr = 18.4, Q × f = 85 000 GHz, τf+ = −3.8 ppm/°C (25–105 °C), τf− = 4.0 ppm/°C (−40 – 25 °C)], which refines the theory of non-linear variation of resonant frequency and holds promise for application in the 5G communication system.

I-Shaped Metamaterial Using SRR for Multi-Band Wireless Communication

A novel I-shaped metamaterial (ISMeTM) using split-ring resonator (SRR) for multi-band wireless communication is presented in this paper. The proposed ISMeTM unit cell structure is designed using the three-square split-ring resonators (SSRRs) and I-shaped copper strip at the center. The size of the proposed ISMeTM is 10 × 10 × 1.6 mm3 while utilizing the FR-4 dielectric substrate material. The analysis of various array arrangements, variation in the ring gap, variation in strip length, and the variation in strip width is performed to achieve the optimum results for multi-band operation. The effective permittivity, permeability, and refractive index of the unit cell have been analyzed. The design and simulation of the ISMeTM unit cell and arrays are performed using the Computer Simulation Technology (CST) Studio Suite and MATLAB. The equivalent circuit of the ISMeTM is designed using the Advanced Design System (ADS) software. The split ring’s inner loop’s gap functions as a capacitor, while the metallic ring itself functions as an inductor. Electric resonance is created by the interaction between the split ring and the electric field. The interaction of magnetic fields with metallic loops during EM propagation in the structure causes the magnetic resonance. The variation in dimensions of the structure causes the variation in the inductance and capacitance, which causes the variation in resonant frequency. The proposed design is optimized after several parametric analyses. A comprehensive analysis of 1 × 2, 2 × 2, and 2 × 4 array is also investigated. The results confirm the multi-band operation of the proposed ISMeTM. The proposed ISMeTM is suitable for the multi-band C/X/Ku-band microwave applications.

Analysis and design considerations of coupler tuning based on improved equivalent circuit and 3D-EM simulations

Power coupler is critical for the successful development of high-intensity linacs. As a main task in its design, pulsed heating affects the beam brightness, even might damage the structures on high-repetition rates. Although shaping the incident RF-pulse can reduce such risk by speeding up the field filling time, a complicated RF sub-system is inevitable. While another mechanism of reducing the filling time, which is increasing the coupling factor, presents its advantages. In this context, based on the analysis of temperature rise for a coupled cavity, the resonant frequency variations have been qualitatively investigated by improving the equivalent circuit via adopting a mutual inductance, the results have been verified by electro-magnetic (EM) codes. Moreover, by taking a waveguide-coupler with an inserted-post for instance, further EM simulations have demonstrated that the tunable coupler can achieve a balance among a proper coupling range, a small frequency offset and an acceptable field-asymmetry. The proposed analysis methods can be extended to provide preliminary guides in designing adjustable RF couplers.

On the Behavior of Self-Triplexing SIW Cavity Backed Antenna With Non-Linear Replicated Hybrid Slot for C and X-Band Applications

In this paper, a substrate integrated waveguide (SIW) based self-triplexing antenna (STA) with non-linear replicated hybrid slot (NLR-HS) is presented. To the author’s best knowledge, the concept of NLR is the first of its kind in the literature used for obtaining self-triplexed operation. Initially, the SIW cavity is loaded by a hexagonal slot merged with two rectangular transverse slots that together produce two distinct resonances around 5.23 and 7.50 GHz. The variation in resonant frequencies of both lower and upper frequency bands can be modelled by applying NLR on the hexagonal slot. To achieve the self-triplexing operation, a coaxial probe-fed parasitic hexagonal patch is placed concentrically inside the hexagonal slot. The third resonance is centered around 10.82 GHz and can be modelled with the help of the gap between the hexagonal slot and parasitic patch.To validate the proposed idea, the design is fabricated and experimentally tested. Moreover, the antenna shows a front-to-back ratio (FTBR) better than 25 dB, average isolation of 43 dB and measured gain (efficiency) values of 7.33 (97.39%), 6.66 (95.82%), and 6.28 (97.83%) dBi at three resonances. Good agreement between the simulated and measured results makes the proposed STA a good candidate for practical applications.

Development of temperature analysis environment for Cyber-Physical Systems on IoT platform: a study of dynamical properties under temperature change in machine tool spindle unit using carbon fiber reinforced plastics

Industrial networks with a database for collecting and analyzing machine information and process data are key components in production systems in Industry 4.0. In proposed IoT system, more than 300 temperature sensors were externally mounted on a carbon fiber reinforced plastics structured machine tool, and their information was collected through an OPC UA server. Based on impact tests, the spindle nose temperature was found to be correlated to the variation in compliance and resonant frequency. The carbon fiber reinforced plastics structured spindle shaft conducted heat quickly and induced a temperature increase after stopping spindle rotation. The IoT system of a temperature-analysis environment can contribute to experimental analysis and model construction for intelligent technologies.

Miniaturized High-Frequency Humidity Sensor Based on Quartz Crystal Microbalance

In this paper, a high-frequency quartz crystal microbalance (QCM) detection unit is fabricated by dry thinning or wet etching, whose resonant frequency is about 61 MHz and the package size is only 5.0 mm long and 3.2 mm wide. After coated a mixed solution of sodium alginate (SA) and γ-polyglutamic acid (PGA) as the humidity sensitive film over the detection unit, we obtain the proposed QCM sensor. Then, we analyze the variations of resonance frequency and relative humidity, and the response/recovery time. By practical tests, the proposed sensor exhibits a very high sensitivity of 2727.41 Hz/%RH and a decent detection limit of 0.011 %RH. The proposed QCM sensor could be widely applied to measure various environmental parameters for its high performance and portability. Due to its excellent performance and small size, we further prepared a 2× 4 sensor array which will be more widely tested and applied in the future.

Active and selective manipulation of dual transparency windows in hybrid graphene-vanadium dioxide metamaterial

Active and selective manipulation of dual–spectral electromagnetically induced transparency (EIT) metamaterial constructed by three graphene strips and vanadium dioxide (VO2) layer is proposed and demonstrated numerically. Simulation results illustrate that the dual-spectral EIT-like effect are induced by adjacent graphene strips acted as bright and bright mode and excited opposite-phase electric field distributions. One or two of EIT-like windows can be modulated by selectively varying graphene strip’s Fermi energy. Meanwhile, the Fermi energies of three graphene strips are varying simultaneously, the position of dual transparency windows as a whole obviously exhibit blue shift. Moreover, the amplitude of dual–spectral EIT windows can be simultaneously manipulated while frequency remain rough constant during the phase transition process of VO2. The physical mechanism underneath the phenomenon of actively and selectively tunable EIT, which is revealed by theoretically calculated results based on the classical three-oscillator model, can be attributed to the variation of resonance frequency, coupling coefficient and losses of the resonators caused by varying Fermi energy of graphene strips and conductivity of VO2.

Development of a Microwave Sensor for Solid and Liquid Substances Based on Closed Loop Resonator.

In this work, a compact dielectric sensor for the detection of adulteration in solid and liquid samples using planar resonators is presented. Six types of filter prototypes operating at 2.4 GHz are presented, optimized, numerically assessed, fabricated and experimentally validated. The obtained experimental results provided an error less than 6% with respect to the simulated results. Moreover, a size reduction of about 69% was achieved for the band stop filter and a 75% reduction for band pass filter compared to standard sensors realized using open/short circuited stub microstrip lines. From the designed filters, the miniaturised filter with Q of 95 at 2.4 GHz and size of 35 mm × 35 mm is formulated as a sensor and is validated theoretically and experimentally. The designed sensor shows better sensitivity, and it depends upon the dielectric property of the sample to be tested. Simulation and experimental validation of the designed sensor is carried out by loading different samples onto the sensor. The adulteration detection of various food samples using the designed sensor is experimentally validated and shows excellent sensing on adding adulterants to the original sample. The sensitivity of the sensor is analyzed by studying the variations in resonant frequency, scattering parameters, phase and Q factor with variation in the dielectric property of the sample loaded onto the sensor.

Spallation-based numerical simulations of ice-induced vibration of structures

A full-scale 3D numerical simulation model of ice-induced vibration of structures has been developed (using LS-Dyna™) and applied to the Molikpaq facility for an ice-encroachment event similar to that which occurred on May 12, 1986 in the Beaufort Sea. The bulk ice sheet used for the simulations had elastic properties, and its dimensions were 6 km × 6 km × 2.5 m. Where ice crushing occurred at the structure-ice interface the ice model used was a crushable foam that incorporated regular spallation events. Typical characteristics of ice-crushing in the brittle regime were manifested by the model. That is, a narrow horizontal hard zone (relatively-intact high-interface-pressure ice) was present in the mid-height region of the ice-edge contact area. Soft-zone material (shattered spall debris from the hard zone) was also represented. Evolution of the hard-zone contact area involved rapid reductions in size during spallation events, immediately followed by fast growth during consequent elastic surging of the near-field ice sheet and structure towards each other, and then some slower growth (due to the bulk ice-sheet velocity) until the next spalling event. The specified ‘thickness’ of the spalls was 5.4 cm, as previously determined from Molikpaq records of the frequency of the spalling events as a function of ice-sheet speed. Spallation (and associated rapid drops in load) occurred at regular intervals whenever a critical amount of hard-zone stress was reached at the ice-structure interface. The amplitude of the Molikpaq repetitive movements in response to the sawtooth loading from the spalling events depended on whether the resonant frequency of the structure/ice system was higher (for a strong response) or lower (for a weak response) than the spalling frequency, where the spalling frequency is directly proportional to the ice-sheet speed. The continuously variable resonant frequency of the structure/ice system had a maximal limiting value (~ 2.1 Hz), designated as the At-Spallation-Resonant-Frequency (ASRF), that was essentially determined by the time duration of load drops at spallation events. The simulations inherently accounted for the variable effective mass and effective spring constant of the ice sheet.

Regression analysis‐based identification model of key impactful parameters on buried antennas

SummaryThe antenna's bandwidth is strongly dependent on its physical properties and the environment where it is located. Nevertheless, for transmitting devices embedded permanently in the soil, the propagation medium's properties are unstable due to dielectric permittivity's spatial and temporal changes. Relying on soil parameters values, we present three new multivariable regression models allowing a good fit to the dataset curves with antenna's resonant frequency variations prediction of about 98%. Precisely, such models have been obtained with the help of the multiple linear regression analysis method. Additionally, the results revealed that amongst four considered parameters (i.e., volumetric moisture, bulk density, specific density, and temperature), volumetric moisture is the most influencing factor on the antenna operating frequency band with a correlation coefficient of −0.989, whereas it equals 0.04, −0.035, and −0.002 for the temperature, bulk density, and specific density, respectively.

Performance prediction of graphene-based patch antenna using different ground plane dimensions

This paper focuses on the development of a rectangular patch antenna with varied ground plane sizes (i.e. short edge, double ground, triple ground) using a thin film graphene-coated patch on flame retardant-4 (FR-4) glass epoxy substrate which is designed to function at 2.45 GHz. Diffraction of radiation from the ground plane's edges occurs with finite ground planes, resulting in variations in radiation pattern, radiation conductance, and resonant frequency. The ripple in the primary pattern decreases as the size of the ground plane grows larger. Even though the ground patch is built of Perfect Electric Conductor (PEC), various parametric results demonstrate that graphene patch gives a lower reflection coefficient (S11) and VSWR, as well as superior gain and directivity, when compared to copper patch. As a result, graphene-coated patches could be an excellent substitute for copper conductive patches.

Wireless power transfer system based on frequency and impedance matching hybrid adjustment against system detuning

System detuning caused by a variation in the distance between the transmitting and receiving terminals can greatly reduce the transmission power and efficiency of a magnetic resonance-coupled wireless power transmission (WPT) system, which limits the WPT application scope. This paper proposes a magnetic resonance coupling wireless power transmission system, which is based on jointly and continuously adjustable frequency compensation (CAFC) and two-transistor-controlled variable capacitor circuits (TCVCs). Therefore, this system can reach the resonant state by using CAFC and two-TCVCs when the transmission distance is changed. The proposed system can adaptively adjust combinations of the operating frequency and equivalent compensation capacitor’s capacitance to achieve impedance matching avoiding the phase difference caused by the imaginary part of the impedance, thus maintaining stable transmission efficiency under the condition of transmission distance variation. Compared to the traditional magnetic coupled resonant circuit based on impedance matching or variable resonant frequency, the proposed system achieves higher efficiency and stability and dynamic distance adaptation.

Microwave detection with various sensitive materials for humidity sensing

Most of the humidity or gas sensing researches focus on the optimization of sensitive materials, while the studies of microwave detection focus on its sensitive-field control. It is necessary to implement the cooperative study on microwave detection with different types of sensitive materials for a better understanding of the operation mechanism as well as providing a way for performance enhancement. This study presents the double split-ring resonator as the sensitive electrode, where various sensitive materials, including polymer by pure Polyimide (PI), ceramic composite by PI-TiO2, metal composite by PI-Ag composite, are respectively tested as the sensing materials. The S-parameter is tested as the humidity indicators after coating on the sensitive regions with a strong electric-magnetic field. Owing to the improved dielectric properties by doping strong-polarity TiO2 nanoparticles into PI, the higher sensitivity with the maximum of 880.0 kHz/%RH and 0.322 dB/%RH is realized. The introduction of Ag nanoparticles facilitates the water vapor adsorption and desorption showing the sensitivity of 330.0 kHz/%RH and 0.149 dB/%RH, due to the high active-site density and surface roughness. By analyzing variations in resonant frequency and return loss, the microwave sensing mechanism of different sensitive materials is fully discussed from the perspective of polarization, dielectric property, and sensitive area.