Resonance Frequency Shift Research Articles

Numerical research on supercavity sensing driven by guided resonance in a terahertz all-metal metamaterial absorber

Terahertz metamaterial sensing features high sensitivity and rich fingerprint spectrum, which shows an application potential of the great significance. However, limited by low-quality resonances and insufficient sensitivity, the sensing performance of terahertz metamaterials remains at a moderate level. In this paper, we numerical investigate a high-performance terahertz sensor based on plasmonic supercavity sensing. The proposed metamaterial sensor features an adjustable high quality absorption resonance ascribed to guided resonance excited by band-folding effect. Also, the terahertz plasmonic sensor inherently characterizes a high sensitivity owing to the all-metal design, which can limit the resonant field within the structured metal surface to fully couple with analyte. Based on these advantages, the proposed all-metal sensor demonstrates the maximum resonance frequency shift, sensitivity and sensing figure of merit are about 66%, 1.6 THz/RIU and 218, respectively, substantiating the sensing superiority. The proposed metamaterial absorber shows potential in spectroscopy, in addition to being a multifunctional absorber and sensor.

Electromagnetic response of disordered superconducting cavities

We present the results for the resonant frequency shift and quality factor of disordered niobium (Nb) superconducting radio-frequency cavities driven out of equilibrium by the resonant microwave field. The theory is based on the non-equilibrium theory of superconductivity for the current response to the electromagnetic field at the vacuum–metal interface. We are able to accurately predict the observed frequency shifts with a precision of order fractions of kHz over the full temperature range 0 < T ≤ Tc, including the negative frequency shift anomalies that are observed very near Tc. The origin of these anomalies is shown to be the competition between the normal metal skin depth and the London penetration depth, which diverges as T→Tc−. An analytical approximation to the full current response, valid for |T − Tc|≪ Tc, accounts for the negative frequency shift near Tc. The non-monotonic dependence of the quality factor on the quasiparticle scattering rate is related to the pair-breaking effect of disorder on the superfluid fraction and, thus, the London penetration depth.

Electro-mechanical impedance technique for concrete strength monitoring: Three-dimensional model development and experimental verification

During the application of the electro-mechanical impedance (EMI) technique for detecting the strength development of concrete, in some cases, the piezoelectric sensor is embedded in the concrete. Normally, there are two methods to embed the piezoelectric sensor: PS-EMI and CPS-EMI. For both methods, the observed resonance frequency of the piezoelectric sensor increases with the increase of the concrete strength. However, there is a contradiction in the trend of conductance amplitude at the resonance frequency, which has to an extent puzzled the researchers in this area. In this paper, we developed a three-dimensional EMI model for the embedded piezoelectric sensor. We discussed the underlying mechanism, which induces the conductance spectrum difference for the PS-EMI and CPS-EMI, and experimental verification was carried out. By plotting the evolution of the concrete strength as a function of the resonance frequency shift, it was found that both embedding methods can be used in practical applications.

Textile Antenna Sensor in SIW Technology for Liquid Characterization.

This study showcases the creation of an innovative textile antenna sensor that utilizes a resonant cavity for the purpose of liquid characterization. The cavity is based on circular substrate integrated waveguide (SIW) technology. A hole is created in the middle of the structure where a pipe is used to inject the liquid under test. The pipe is covered by a metal sheath to enhance the electromagnetic field's penetration of the tube, thus increasing the device's sensitivity. The resonance frequency of the proposed system is altered when the liquid under test is inserted into the sensitive area of the structure. The sensing of the liquid is achieved by the measurement of its dielectric properties via the perturbation of the electric fields in the SIW configuration. The S11 measurement enables the extraction of the electromagnetic properties of the liquid injected into the pipe. Specifically, the dielectric constant of the liquid is determined by observing the resonance frequency shift relative to that of an air-filled pipe. The loss tangent of the liquid is extracted by comparing the variation in the quality factor with that of an air-filled pipe after eliminating the inherent losses of the structure. The proposed SIW antenna sensor demonstrates a high sensitivity of 0.7 GHz/Δεr corresponding to a dielectric constant range from 4 to 72. To the best of our knowledge, this article presents for the first time the ability of a fully textile SIW cavity antenna-based sensor to characterize the dielectric properties of a liquid under test and emphasizes its differentiating features compared to PCB-based designs. The unique attributes of the textile-based antenna stem from its flexibility, conformability, and compatibility with various liquids.

Stiffness of Contacts between Adsorbed Particles and the Surface of a QCM‐D Inferred from the Adsorption Kinetics and a Frequency‐Domain Lattice Boltzmann Simulation

AbstractA simulation based on the frequency‐domain lattice Boltzmann method (FreqD‐LBM) is employed to predict the shifts of resonance frequency, Δf, and half bandwidth, ΔΓ, of a quartz crystal microbalance with dissipation monitoring (QCM‐D) induced by the adsorption of rigid spheres to the resonator surface. The comparison with the experimental values of Δf and ΔΓ allows to estimate the stiffness of the contacts between the spheres and the resonator surface. The contact stiffness is of interest in contact mechanics, but also in sensing because it depends on the properties of thin films situated between the resonator surface and the sphere. The simulation differs from previous implementations of FreqD‐LBM insofar, as the material inside the particles is not included in the FreqD‐LBM algorithm. Rather, the particle surface is configured to be an oscillating boundary. The amplitude of the particles' motions (displacement and rotation) is governed by the force balance at the surface of the particle. Because the contact stiffness enters this balance, it can be derived from experimental values of Δf and ΔΓ. The simulation reproduces experiments by the Krakow group. For sufficiently small spheres, a contact stiffness can be derived from the comparison of the simulation with the experiment.

A microstrip patch antenna for 5G mobile communications

The advantages of microstrip patch antennas include small size, adaptable surface, ease of fabrication, and compatibility with integrated circuit technology. Numerous experiments have been done over the past few decades to enhance the performance of this antenna, and both military and commercial sectors have found many uses for it. This paper introduces a microstrip patch antenna with an operating frequency of 28GHz for 5G mobile communication. This research designed and simulated a rectangular microstrip patch antenna with 3.494 mm * 5.3 mm * 0.003 mm. The proposed antenna resonates at 28 GHz with a reflection coefficient of -24 dB, a bandwidth of 280 MHz, and a gain of 2.2 dBi. The inset feed technique matches the 50 Ω transmission line impedance. In the design, Rogers RT5880 substrate and copper ground are used. The antenna’s geometry was calculated, and simulated results were analyzed using Computer Simulation Technology Microwave Studio. In conclusion, the proposed antenna has a reflection coefficient of -24 dB, VSWR of 1.24, an input impedance of 51.6Ω, and a gain of 2.2 dBi at operating frequency with a compact geometry can be used in 5G mobile communications. The future shift in resonance frequencies and beams can be considered to make the antenna operate as a smart antenna.

Acoustic frequency analysis of the vibrational resonant frequencies of Special Nuclear Material containment

The increase of the resonant frequencies of a Magnox containment package that have been detected by an electromagnetic acoustic transducer and a microphone, are the result of an increase in internal pressure of the package. Therefore, it is possible to infer an internal pressure measurement of the Magnox package by measuring the shift of different resonant frequencies. A model of the Magnox package has been constructed to predict the acoustic vibrational resonant frequencies of the package wall and the corresponding mode shapes. Laser Doppler vibrometer measurements of the Magnox package wall have confirmed the presence of the predicted mode shapes and the resonant frequencies at which they occur have been reasonably estimated by the model.

Modeling, design, and optimization of a dielectric elastomer acoustic liner

The modeling, design, and optimization of an embedded dielectric elastomer (DE) membrane acoustic liner is considered. The acoustic impedance of the liner is modified when the DE is subjected to voltage, resulting in a reduction of the in-plane stress. A lumped element model of an embedded dielectric elastomer acoustic liner is derived and validated in a normal incidence impedance tube and is subsequently used to optimize its performance. The optimization cost functions include (1) maximization of the average absorption coefficient over a targeted frequency range, 400 – 1600 Hz and (2) maximization of the change in the liner fundamental resonance frequency when the membrane is activated. Good agreement between measured and predicted absorption is observed. Tuning of the resonant frequency requires a numerical solution for resonance using the imaginary part of the impedance, since a simple analytical expression for resonance cannot be derived due to the complex coupling between the acoustics of the liner and the electro-mechanics of the DE membrane. Nonetheless, resonant frequency shifts predicted with the lumped element model compare favorably to those measured with the activated liner sample, with a shift of 213 Hz.

Thermal measurements of a muscle-mimicking phantom during ultra-high field magnetic resonance imaging

Abstract At ultra-high field MRI (Bo>7T) it is crucial to predict and control the patient safety. Commonly patient safety is controlled by the power deposited in the tissue (specific absorption rate - SAR). However, temperature distributions do not always correlate directly with SAR distributions, which makes temperature control also a crucial parameter to guarantee patient safety. In this work, temperature changes were accessed by MR thermometry, specifically by the proton resonance frequency shift technique (PRF). A phantom mimicking muscle tissue was used to evaluate the temperature rise caused by the radiofrequency (RF) absorption during 7T MRI, applied through a commercial birdcage head coil. A pulse-sequence protocol was implemented for both, the generation of temperature increase and the MR thermometry. To control the temperature, a digital thermometer was used, and oil tubes were utilized to dismiss the drift effects for PRF. Measurements of the phantom’s dielectric characteristics, i.e. conductivity and permittivity, were in good agreement with the literature values for muscle. Spatio-temporal evaluations showed a temperature increase in time via RF exposure and the feasibility of measuring temperature maps using the PRF shift method. The accuracy of the PRF shift method increased when the drift effects were quantified and dismissed, indicating a PRF reading accuracy differing less than 0.5 °C from the thermometer. Results also validate our heating and temperature imaging protocol. This study is a valuable contribution to the evaluation of heating effects caused by RF absorption and demonstrates potential impact on future thermal investigations, which may use different heating sources, as well validate thermal simulations.

Maltodextrin-overlaid polyvinyl acetate nanofibers for highly sensitive and selective room-temperature ammonia sensors

Various ammonia sensors based on different materials have continuously been developed and employed to enable real-time monitoring of ammonia gas in the environment. Efforts are put not only to improve their sensitivity and selectivity towards the target gas but also to operate them at room temperature. Here, we investigated the effect of overlaying maltodextrin with different concentrations on the surface of polyvinyl acetate (PVAc) nanofibers on ammonia sensing performances, in which quartz crystal microbalance (QCM) was utilized as a transducer to measure the resonance frequency shift affected by the adsorbed gas molecules. Higher concentrations of the overlaying maltodextrin led to larger nanofiber diameter and more functional active groups on the active nanofibrous layers. PVAc nanofibers with 0.05% maltodextrin overlay demonstrated the highest sensitivity of 0.525 Hz·ppm−1 at room temperature, which was 6.4 times higher than their bare counterpart (nanofiber without maltodextrin overlay). That sensor also possessed fast response and recovery times of 32 s and 17 s with a low detection limit (1.92 ppm). Besides its high reproducibility, reversibility, and repeatability, the sensor exhibited outstanding selectivity to other gas analytes and good long-term stability for 32 days of testing. This research shows that maltodextrin overlay can be used as a low-cost alternative route to increase the performance of organic material-based ammonia sensors, especially polymer nanofibers.

Magnetic resonance fingerprinting based thermometry (MRFT): application toex vivoimaging near DBS leads.

The purpose of this study is to demonstrate the first work ofT1-based magnetic resonance thermometry using magnetic resonance fingerprinting (dubbed MRFT). We compared temperature estimation of MRFT with proton resonance frequency shift (PRFS) thermometry onex vivobovine muscle. We demonstrated MRFT's feasibility in predicting temperature onex vivobovine muscles with deep brain stimulation (DBS) lead.B0maps generated from MRFT were compared with gold standardB0maps near the DBS lead. MRFT and PRFS estimated temperatures were compared in the presence of motion. All experiments were performed on a 3 Tesla whole-body GE Premier system with a 21-channel receive head coil (GE Healthcare, Milwaukee, WI). Four fluoroptic probes were used to measure the temperature at the center of a cold muscle (probe 1), the room temperature water bottle (probe 2), and the center and periphery of the heated muscle (probes 3 and 4). We selected regions of interest (ROIs) around the location of the probes and used simple linear regression to generate the temperature sensitivity calibration equations that convertT1maps and Δsmaps to temperature maps. We then repeated the same setup and compared MRFT and PRFS thermometry temperature estimation with gold standard probe measurements. For the MRFT experiment on DBS lead, we taped the probe to the tip of the DBS lead and used a turbo spin echo sequence to induce heating near the lead. We selected ROIs around the tip of the lead to compare MRFT temperature estimation with probe measurements and compared with PRFS temperature estimation. Vendor-suppliedB0mapping sequence was acquired to compare with MRFT-generatedB0maps. We found strong linear relationships (R2> 0.958) betweenT1and temperature and Δsand temperatures in our temperature sensitivity calibration experiment. MRFT and PRFS thermometry both accurately predict temperature (RMSE < 1.55 °C) compared to probe measurements. MRFT estimated temperature near DBS lead has a similar trend as the probe temperature. BothB0maps show inhomogeneities around the lead. MRFT estimated temperature is less sensitive to motion.

Non-contact assessment of porosity in metal 3D printed parts by vibration spectra

Volumetric porosity as a common defect in metal 3D printing (3DP) that can significantly impede the mechanical properties of products. Traditional methods of porosity control (microscopy) and non-destructive testing (computed tomography) usually are not applicable at the production site. In this study, sensitivity of three examined testing modalities based on acoustic methods and vibration analysis to changes in the volumetric porosity of 3DP parts was examined. Test objects were cylindrical specimens made of AlMg powder by 3DP with a gradually dosed porosity from 0.5 to 4.0%. Ultrasonic testing by through transmission showed the best accuracy using ultrasound velocity and pulse intensity parameters. Shifts of resonant frequency and spectral density and appearance of side harmonics were the manifestations of increased porosity using vibration approaches. The method comprising a loudspeaker as a vibration exciter and an optoelectronic device for remote sensing of vibration is the most attractive from the point of view of application to objects of complex geometry.

A Microwave Voyage into Swelling Phenomenon: Investigation of Polydimethylsiloxane and VOCs Interaction.

When exposed to specific gases, polymers undergo swelling, leading to physiochemical changes that can significantly affect their performance. Monitoring this swelling phenomenon requires innovative approaches. This study focuses on investigating the real-time resonant microwave behavior of two polydimethylsiloxane (PDMS) structures (solid and porous) in interaction with tetrahydrofuran (THF) and acetone, which are primary swelling agents. A microwave measurement method is proposed using an 8.63 GHz planar split ring resonator (SRR). The device's resonant frequency downshifts to 7.75 and 8.42 GHz when solid and porous PDMS blocks are placed on the split ring gap. Interaction of the solid PDMS and porous PDMS with target gases caused a change in PDMS structure resulting in alterations in the dielectric properties of the PDMS/gas system, as evidenced by the resonator's transmission amplitude and resonant frequency shifts. The magnitude of these shifts depends on the type and concentration of the solvent gas. The PDMS-integrated SRR exhibits a sensitivity of 25.3 MHz/1 ppt THF and 7 MHz/1 ppt acetone. Additionally, the solid block demonstrates response times of 6800 and 4200 s for swelling and deswelling, respectively, when in exposure to 25 ppt concentrations of THF and acetone. Overall, this study underscores the substantial potential of microwave resonators as versatile tools for investigating the physical changes in polymers during their interaction with gases, contributing to the understanding of polymer-gas interactions and opening avenues for further research and diverse applications.

Towards Monitoring and Identification of Red Palm Weevil Gender Using Microwave CSRR-Loaded TL Sensors.

This paper presents for the first time the design of a microwave sensing setup for the potential monitoring and identification of red palm weevil (RPW) gender type. The microwave sensor consists of a planar two-port transmission line (TL) with a single complementary split-ring resonant (CSRR) inclusion etched from the bottom metallic layer. The CSRR sensor is placed on top of a customized non-conductive container. The microwave sensing setup was designed, numerically demonstrated, fabricated and tested experimentally. Simulated results correlate quite well with the experimental data. Moreover, the sensitivity of the CSRR sensor when in close proximity to different RPW genders was evaluated both numerically and experimentally. Based on the measured results from 15 RPW samples with different body sizes, different RPW gender types showed unique microwave signatures. A notable shift in the sensor's resonance frequency was achieved, where on average a resonant frequency shift of 10% for adult RPWs was achieved, while a 2.4% frequency change was obtained for larvae (young) RPWs. Hence, the proposed microwave sensing setup can be adopted in field trials to examine and differentiate between various RPW genders at various developmental stages.

A Highly Sensitive and High-Resolution Resonant MEMS Electrostatic Field Microsensor Based on Electrostatic Stiffness Perturbation.

This paper proposes a highly sensitive and high-resolution resonant MEMS electrostatic field sensor based on electrostatic stiffness perturbation, which uses resonant frequency as an output signal to eliminate the feedthrough interference from the driving voltage. The sensor is composed of a resonator, driving electrode, detection electrode, transition electrode, and electrostatic field sensing plate. The working principle is that when there is an electrostatic field, an induction charge will appear at the surface of the electrostatic field sensing plate and induce electrostatic stiffness on the resonator, which will cause a resonant frequency shift. The resonant frequency is used as the output signal of the microsensor. The characteristics of the electrostatic field sensor are analyzed with a theoretical model and verified by finite element simulation. A device prototype is fabricated based on the Silicon on Insulator (SOI) process and tested under vacuum conditions. The results indicate that the sensitivity of the sensor is 0.1384Hz/(kV/m) and the resolution is better than 10 V/m.

High-sensitivity non-cooled near-infrared detector based on lithium niobate surface acoustic wave resonators combined with MXene Ti3C2Tx quantum dot thin films.

In this study, we propose the design of a surface acoustic wave (SAW) near-infrared sensor combined with an MXene quantum dot thin film to improve the infrared absorption efficiency at near-infrared wavelengths. A YZ-cut lithium niobate (LiNbO3) SAW resonator is fabricated as an infrared sensing unit with a resonant frequency shift reflecting the change in infrared radiation. It was observed that the responsivity of the near-infrared sensor (with a base frequency of 460 MHz) increased by approximately 88.89%. Thus, the proposed device exhibits high-performance infrared detection. Owing to the passive wireless capability of the device, it has wide applications.

Sensitivity Enhancement of THz Metamaterial by Decoupling its Resonance from the Substrate's Fabry–Pérot Oscillations

AbstractLC‐circuit‐based resonant metamaterials (MM) operating in the terahertz (THz) are proven to detect the presence of nanoparticles within the capacitive gap of nanoantennas, manifesting a red‐shift in the resonance frequency. Sensitivity reduction (reduced red‐shift) due to the interaction/coupling of the substrate's Fabry–Pérot (FP) oscillations with the MM resonance is discussed. This new discovery of coupling is more probable and intense in thicker semiconductor substrates used in standard complementary metal‐oxide semiconductor processes, due to the high density of the FP oscillations and thus the probability for coupling with the single MM resonance increases. This also results in reducing the quality factor (Q‐Factor) of MM resonance, as well as the dielectric response to nanoparticles spread on the MM surface, by reducing the resonance frequency shift (ΔF) and thus the sensitivity of resonant MM. A sensitivity restoration of the MM resonance's red‐shift by decoupling it from the FP oscillations after thinning down the substrate by standard backside polishing is shown. The research is based on a combination of rigorous CST system‐level simulations along with THz impedance spectroscopy laboratory experiments: up to a fivefold enhancement of sensitivity of the thinned substrate compared with the conventional thick substrates is shown. This work has potential applications in the high‐sensitivity detection of nanomaterials and bio‐sensing at ultra‐low concentrations.

Room temperature nonlinear optical mass sensing based on a hybrid nanoresonator system

We present a strong coupled quantum dot-nanomechanical resonator system and investigate its nonlinear optical properties using optical pump-probe technology. The process of evolution of the nonlinear Kerr spectrum is studied for different resonator frequencies under low temperature and room temperature, respectively, and the results indicate that even at room temperature the nonlinear Kerr spectrum can still be resolved. In addition, we further theoretically propose a room temperature nonlinear optical mass sensing scheme based on the hybrid nanoresonator system. When the masses of external nanoparticles (such as biomolecules including baculovirus, coronavirus, DNA, etc.) are attached to the nanomechanical resonator, the resonance frequency shift caused by nanoparticles can be measured by nonlinear Kerr spectrum, and then the mass of nanoparticles can be determined. The hybrid coupled nanoresonator system will have potential applications in ultra-sensitive and high-resolution mass sensors.

Simultaneous crack and temperature sensing with passive patch antenna

This article presents a novel passive patch antenna sensor for simultaneous crack and temperature sensing, and the antenna sensor has the ability of temperature self-compensation. The passive patch antenna sensor consists of an underlying patch and an overlapping sub-patch. The off-center feeding activates resonant modes in both transverse and longitudinal directions. The resonant frequency shift in transverse direction is used for environmental temperature sensing, while the structural crack width can be sensed by the longitudinal resonant frequency shift after temperature compensation. Furthermore, the unstressed design of the antenna can also eliminate the issue of incomplete strain transfer ratios. In this article, the relationships between the antenna resonant frequencies, the environmental temperature, and the structural crack width were studied. Simulations were conducted to determine the optimal off-center fed distance of the patch antenna sensor. Furthermore, a series of experimental tests were also conducted, where the passive patch antenna was fabricated and installed on the concrete components as well as an actual building. Continuous monitoring was performed for several days to test the temperature sensing ability of the passive patch antenna, and the sensed crack width after temperature compensation was compared with the actual results. The results of these experiments demonstrate the feasibility of using the passive patch antenna for simultaneous temperature and crack sensing.

Synthesis, structure and electromagnetic properties of FeCoCu/C nanocomposites

FeCoCu ternary nanoparticles distributed and stabilized in the carbon matrix of FeCoCu/C metal-carbon nanocomposites have been synthesized using controlled IR pyrolysis of precursors consisting of the “polymer / iron acetylacetate / cobalt and copper acetates” type system obtained by joint dissolution of components followed by solvent removal. The effect of the synthesis temperature on the structure, composition and electromagnetic properties of the nanocomposites has been studied. By XRD was shown that the formation of the FeCoCu ternary nanoparticles occurs due to the interaction of Fe3С with the nanoparticles of the CoCu solid solution. An increase in the synthesis temperature leads to an increase in the size of the metal nanoparticles due to their agglomeration and coalescence as a result of matrix reconstruction. Furthermore, ternary alloy nanoparticles having a variable composition may form depending on the synthesis temperature and the content ratio of the metals. Raman spectroscopy has shown that the crystallinity of the carbon matrix of the nanocomposites increases with the synthesis temperature. The frequency responses of the relative permittivity and permeability of the nanocomposites have been studied at 3–13 GHz. It has been shown that a change in the content ratio of the metals noticeably increases both the dielectric and the magnetic losses. The former loss is caused by the formation of a complex nanostructure of the nanocomposite carbon matrix while the latter one originates from an increase in the size of the nanoparticles and a shift of the natural ferromagnetic resonance frequency to the low-frequency region. The reflection loss has been calculated using a standard method from the experimental data on the frequency responses of the relative permittivity and permeability. It has been shown that the frequency range and the absorption of electromagnetic waves (from –20 to –52 dB) can be controlled by varying the content ratio of the metals in the precursor. The nanocomposites obtained as a result of the experiment deliver better results in comparison with FeCo/C nanocomposites synthesized under similar conditions.