Decrease In Resonant Frequency Research Articles

Eigenmodes and resonance vibrations of graphene nanomembranes

Natural and resonant oscillations of suspended circular graphene and hexagonal boron nitride (h-BN) membranes (single-layer sheets lying on a flat substrate having a circular hole of radius $R$) have been simulated using full-atomic models. Substrates formed by flat surfaces of graphite and h-BN crystal, hexagonal ice, silicon carbide 6H-SiC and nickel surface (111) have been used. The presence of the substrate leads to the forming of a gap at the bottom of the frequency spectrum of transversal vibrations of the sheet. The frequencies of natural oscillations of the membrane (oscillations localized on the suspended section of the sheet) always lie in this gap, and the frequencies of oscillations decrease by increasing radius of the membrane as $(R+R_i)^{-2}$ with nonezero effective increase of radius $R_i>0$. The modeling of the sheet dynamics has shown that small periodic transversal displacements of the substrate lead to resonant vibrations of the membranes at frequencies close to eigenfrequencies of nodeless vibrations of membranes with a circular symmetry. The energy distribution of resonant vibrations of the membrane has a circular symmetry and several nodal circles, whose number $i$ coincides with the number of the resonant frequency. The frequencies of the resonances decrease by increasing the radius of the membrane as $(R+R_i)^{\alpha_i}$ with exponent $\alpha_i<2$. The lower rate of resonance frequency decrease is caused by the anharmonicity of membrane vibrations.

Electromagnetic performance of three-dimensional woven spacer microstrip antenna with various conductive fibers in extreme temperatures

Due to its excellent light-weight, mechanical, and electromagnetic performance, the three-dimensional woven spacer microstrip antenna (3DWS-MA) has become a promising communication device to be applied in aerospace or high-speed vehicles. To explore the electromagnetic performance of 3DWS-MA in extreme environments, microstrip antennas based on three-dimensional woven glass fiber/epoxy spacer composites (3DWSC) with different conductive yarn (copper wire, nickel-coated carbon yarn and carbon nanotube yarn) were manufactured and tested at various temperatures (from –196°C to 150°C). The results showed that the 3DWSC exhibited superb dielectric properties ([Formula: see text]) with a low volume density of 0.5 g[Formula: see text]cm−3, rendering good electromagnetic performance of the prepared antenna (S11 value of –23 dB and gain of 7 dB). When the temperature increased from –196°C to 150°C, the dielectric constant of 3DWSC increased from 1.57 to 1.67, resulting in the decrease of resonance frequency of 3DWS-MAs (maximum offset is 60 MHz). In addition, the resistance changing ratios of the conductive fibers also reached 105% with the temperature increase, resulting in degradations of S11 values (maximum 17 dB). Furthermore, among the three types of 3DWS-MAs, the 3DWS-MA (carbon nanotube yarn) exhibited the most stable S11 value at low temperatures (from –196°C to 0°C), while the 3DWS-MA (copper) showed low return loss and stable resonance frequency at high temperatures (from 20°C to 150°C).

High-sensitivity liquid-metal-based contact lens sensor for continuous intraocular pressure monitoring

Intraocular pressure (IOP) is a crucial physiological indicator for the diagnosis and treatment of glaucoma. The current infrequent IOP measurement during an office visit is insufficient to characterize the symptoms. Here, an LC resonator strain sensor in a contact lens, composed of a stretchable inductance coil using liquid metal and a chip capacitor, was developed for real-time IOP monitoring. The lens sensor was operated on the basis of ‘mechanical-electrical’ principle. The rising IOP will increase the curvature radius of the cornea and stretch the inductance coils through the cornea and tear film, leading to a decrease in resonant frequency. The theoretical model of the whole process has been established and explored. The sensor has been scientifically designed and fabricated to be ultra-soft, comfortable, safe without leakage and has a stable signal. The sensor was calibrated on two silicone rubber model eyeballs, respectively, showing linear and stable responses. An experiment on porcine eyes in vitro was conducted. The sensor can track IOP changes and shows much higher sensitivity than the current mainstream lens sensors, which is even an order of magnitude higher than the existing inductive sensor. The high-sensitivity and ultra-flexible liquid-metal-based lens sensor is a promising approach for 24 h continuous IOP monitoring in clinics.

Detecting Intralabyrinthine Pressure Increase by Postural Manipulation with Wideband Tympanometry and Distortion Product Otoacoustic Emissions.

Intracranial pressure increase is known to affect inner ear pressure through the cochlear and vestibular aqueducts. This finding forms a good model for inner ear pressure studies. Standard techniques used to detect this pressure increase are neither reliable nor easily repeatable or cheap. Studies with immitancemetry and otoacoustic emissions have been giving hopeful results. This study aims to confirm the results in the literature with wideband tympanometry and add a new parameter of otoacoustic emissions to inner ear pressure testing. Wideband tympanometry (WBT) and distortion product otoacoustic emissions (DPOAE) tests were applied to 40 healthy participants in sitting, supine, and Trendelenburg positions. DPOAE were measured under ambient or peak pressure. Resonance frequency, tympanic peak pressure, 1000, 1500, 2000, 3000, 4000, and 6000 Hz frequencies in DPOAE were measured. The increase in the tympanic peak pressure and the decrease in resonance frequency (RF) due to position change were found statistically significant (p<0.01). Signal noise ratio (SNR) decrease at 1 kHz frequency and SNR increase at 2, 3, 6 kHz in the normal protocol, SNR decrease at 1 kHz in the pressurized protocol were found statistically significant (p<0.01). RF in WBT and 1 kHz DPOAE SNR parameters were found useful in supporting the diagnosis in pathologies that increase intracranial pressure and inner ear pressure. Future research may ease their widespread use in clinical practice as they are non-invasive and rapidly applicable.

Size optimization of metamaterial structure for elastic layer of a piezoelectric vibration energy harvester

Vibration energy harvesters are attracting attention as sensor node power sources for the Internet of Things society because they are maintenance-free. Vibration energy harvesters, which generate power efficiently by utilizing structural resonance, have difficulty in reducing the size of the device and matching low-frequency bands. In this study, a piezoelectric vibrational energy harvester (PVEH) is proposed with mechanical metamaterials for the elastic layer, which has a low resonance frequency and high-power output. We designed the dimensions of the metamaterial structure for the elastic layer of the PVEH, and the bending stiffness was varied by changing the size of the periodic structure of the metamaterial structure to adjust the device’s performance. Finite element analysis was performed for four metamaterial PVEHs with different periodic structure sizes. The metamaterial PVEH with the smallest structure had a 16 % decrease in resonance frequency and 100 % increase in power generation compared to the metamaterial PVEH with the largest structure. The proposed PVEHs were fabricated by photolithography, and their performance was evaluated by vibration tests. In a sinusoidal excitation with an acceleration of 0.2G, assuming that the vibration is caused by human body motion, the metamaterial PVEH with the smallest structure shows a resonance frequency of 32 Hz and a maximum output power of 1.3 μW. Compared to the conventional flat plate-type PVEH, the resonance frequency is reduced by 48 % and the power output is 3.2 times higher in the proposed PVEH. An increase in flexibility due to metamaterial structures has an advantage that there is no need to change materials or processing processes as compared with the case of using the low stiffness substrate.

Analysis on enhancing the sensing behavior of ionic polymer metal composite based sensors

In this paper, an in-depth analysis of IPMC (ionic polymer metal composite) as sensors is performed, motivated by application to flapping wing micro air vehicles. The effect of water uptake for different IPMC samples reveals a correlation between IPMC metal content and water uptake. The effect of introducing a mass to the end of High-frequency IPMC (HFI ∼ 20.9 Hz) sensor shows an improvement in the IPMC sensing behavior, whereas, for the Low-frequency IPMC (LFI ∼ 8.9 Hz) sensor, there is a reverse trend. Gold (Au) coating on an HFI sensor results in a decrease in resonant frequency. Different mass loaded on the Au coated HFI beams reveals that the pre-bending by adding end mass to HFI sensor is beneficial up to a specific mass level, after which the sensing voltage decreases. The optimized mass loading for the Au coated HFI is determined.

The Effect of Draft Ratio of Side-By-Side Barges on Fluid Oscillation in Narrow Gap

In the present study, the effects of the draft ratio of the floating body on the fluid oscillation in the gap are investigated by using the viscous fluid model. Numerical simulations are implemented by coupling wave2Foam and OpenFOAM. The Volume of Fluid (VOF) model is used to capture the free surface waves. It is verified that the numerical results agree well with the experimental and other results. It is firstly found that, within the water depth range investigated in the present study, the depth of the wave tank has a significant effect on the numerical results. As the depth of the wave tank increases, the oscillation amplitude of the narrow-gap fluid largely decreases and the resonant frequency of the fluid oscillation in the narrow gap increases. The results also reveal that the draft ratio of floating bodies has a significant nonlinear influence on the resonant frequency and on the oscillation amplitude of the fluid in the narrow gap. With an increase in the draft of either the floating body on the wave side or the one on the back wave side, the resonant frequency decreases. The increase in the draft of the floating body on the wave side causes an increase in the reflection wave coefficient and leads to a drop in the fluid oscillation amplitude, and the increase in the draft of the floating body on the back wave side triggers a decrease in the reflection wave coefficient and results in an increase in the fluid oscillation amplitude. Meanwhile, the viscous dissipation induced by the fluid viscosity synchronously increases with the oscillation amplitude of the fluid in the increasing gap. Moreover, it is found that the draft ratio mainly affects the horizontal force of the floating body on the back wave side and that the highest calculated force increases with the draft ratio.

Directional seismic response to the complex topography: A case study of 2013 Lushan Ms 7.0 earthquake

Azimuthal variations in site response can provide a good insight into the site amplification and seismic conditions of geohazard occurrences. In this study, multiple directional site response methods, including D-Arias (Directional-Arias), D-SER (Directional- Shaking energy ratio), D-HVSR (Directional-Horizontal to vertical spectral ratio) and D-SSR (Directional — Standard spectral ratio), are adopted to analyse seismic data of the 2013 Lushan Ms 7.0 earthquake captured by the self-established Lengzhuguan (LZG) station which consists of the complex topography of isolated ridge, large mountain and some typical micro-reliefs. The results show that the isolated ridge could cause stronger site responses than the large mountain, and whose pronounced response direction is roughly perpendicular to its ridgeline. With the growth of elevation, the site resonant frequency decreases. The different microreliefs on the mountain cause different site responses, which present as protruding slope > linear slope. The site response mainly exists on the surficial layer of the mountain and shows that with the increase of the distance to mountain surface, the site response gets weaker, the site resonant frequency gets higher, and the pronounced response direction is perpendicular to its ridgeline.

Broadband Electron Spin Resonance Study in a Sr2FeMoO6 Double Perovskite.

We report broadband magnetic resonance in polycrystalline Sr2FeMoO6 measured over the wide temperature (T = 10–370 K) and frequency (f = 2–18 GHz) ranges. Sr2FeMoO6 was synthesized by the sol–gel method and found to be ferromagnetic below TC = 325 K. A coplanar waveguide-based broadband spectrometer was used to record the broadband electron spin resonance (ESR) both in frequency sweep and field sweep modes. From the frequency sweep mode at fixed dc magnetic fields, we obtain the spectroscopic splitting factor g ∼ 2.02 for T ≥ TC K, which confirms the 3+ ionic state of Fe in the material. The effective g value was found to decrease monotonically with decreasing temperature in the ferromagnetic regime. Resonance frequency decreases and the line width of the spectra increases as the temperature decreases below TC. At room temperature (RT) and above, the line width (ΔH) of the ESR signal increases linearly with frequency, giving Gilbert damping constant α ∼0.032 ± 0.005 at RT. However, at lower temperatures, a minimum emerges in the ΔH vs frequency curve, and the minimum shifts to a higher frequency with decreasing temperature, confining the linear frequency regime to a narrow-frequency regime. Additional inhomogeneous broadening and low-field-loss terms are needed to describe the line width in the entire frequency range.

Experimental and theoretical investigations about the nonlinear vibrations of rectangular atomic force microscope cantilevers immersed in different liquids

Nonlinear flexural vibrations of rectangular atomic force microscope cantilever have been investigated by both the theoretical model and experimental works. As for the theoretical model, the Timoshenko beam theory which takes the rotatory inertia and shear deformation effects into consideration has been adopted. To increase the accuracy of the theoretical model, all necessary details for cantilever and sample surface have been taken into account. Differential quadrature method as a simple and fast numerical method has been used for solving the differential equations. During the investigation, the softening behavior was observed for all cases. It was also seen that raising the amplitude of vibrations led to a decrease in the nonlinear resonant frequency to linear resonant frequency ratio. The effects of different parameters such as normal and lateral contact stiffness, cantilever thickness, the angle between cantilever and sample surface and tip height in the presence of air as environment on the softening behavior were also examined. It was also demonstrated that increasing the lateral and normal contact stiffness, but decreasing the Timoshenko beam parameter would lead to an increase in the amplitude of vibrations for the first and second modes. The vibrational behavior of cantilever immersed in different liquids including water, methanol, acetone and carbon tetrachloride has been studied. Results show that increasing the liquid density reduces the nonlinear frequency. Furthermore, experimental works were compared with theoretical model for water and air environments. Results show good agreement.

Effect of clamped beam pattern on resonant frequency shift of microresonator under near-infrared laser irradiation

In this study, we investigated the effect of the resonator beam shape on the thermal stress and the resonance frequency change when providing heat to the resonator beam by near-infrared laser irradiation. This investigation provides crucial data for optical and heat sensing application using microresonators. The microresonator beam with an optical absorber for near-infrared region was fabricated, varying the numbers of beams and corners. When irradiating the optical absorber with a laser, the resonant frequency decreased. It is because the photothermal effect provides compressive stress in the beam, resulting in resonant frequency decrease. The resonant frequency change rate increased with decreasing the number of beams. According to the analytical results, we confirmed that the analytical thermal stress determined the resonant frequency change rate in the same beam length. The corner remarkably decreased the resonant frequency change rate. The straight beams bend to the orthogonal direction by the thermal expansion of another straight part of the beam, resulting in deformation of the beam in the axial direction. Therefore, the reaction force and compressive stress in the axial direction reduces.

Ga-, Y-, and Sc-substituted M-type ferrites for self-biasing circulators in LTCC microwave modules

The partial substitution of Fe3+ by diamagnetic Me3+ in BaMexFe12-xO19 with Me = Ga and Y (0 ≤ x ≤ 2) was studied. Samples were synthesized by the mixed-oxide route and their properties were compared to BaScxFe12-xO19 ferrites. It was shown by XRD that the hexagonal lattice parameters with x for Me = Ga and Sc vary continuously. For Me = Y no single-phase ferrites were obtained indicating that the solubility limit for Y in Ba ferrite is very limited. For Me = Ga and Sc, the saturation magnetization at room temperature is reduced with x. The coercivity as well as the ferromagnetic resonance frequency remain almost unchanged for Ga-substituted ferrites, whereas for Sc-substituted ferrites the coercivity and ferromagnetic resonance frequency decrease with x. Thick films of Sc-ferrite (x = 0.5) were screen-printed onto LTCC tape substrates and post-fired at 900°C. Application of a magnetic field during drying allows fabrication of textured ferrite layers. Alternatively, ferrite tapes and LTCC tapes were successfully co-fired at 900°C.

The effects of nonlocal and surface/interface parameters on nonlinear vibrations of piezoelectric nanoresonator

In current work, Gurtin–Murdoch surface/interface and nonlocal theories are presented to investigate nonlinear vibration and stability analysis of piezoelectric nanoresonator simultaneously subjected to direct and alternating voltages. Complex averaging method combined with arc-length continuation is used to achieve the nonlinear frequency response and stability analysis of the piezoelectric nanoresonator. It is concluded that ignoring surface and small-scale effects lead to inaccurate results in vibration response of the piezoelectric nanoresonator. Also, with increasing dimensionless nonlocal parameter and decreasing nanoshell stiffness, dimensionless natural frequency, the resonance amplitude, the range of instability with saddle-node bifurcations and nonlinear hardening behavior, and also resonance frequency decrease. In addition, it is found that when the surface/interface effects corresponding to higher surface/interface density are considered, natural frequency is increased. Also, regardless the Lamé’s constants lead to decreasing of piezoelectric nanoresonator stiffness, and as a result, the dimensionless natural frequency is lower than all cases. The rest of the surface/interface parameters do not have much effect on the dimensionless natural frequency. Also, with increasing electrostatic and piezoelectric voltages, the oscillation amplitude and range of the piezoelectric nanoresonator system’s instability and all nonlinear behavior of piezoelectric nanoresonator are increased.

Atomistic modeling and dynamic analysis of boron nitride nanotube in the presence of hexagonal defect

The feasibility of defective Single-Walled Boron Nitride Nanotube (SW-BNNT) has been explored in the present paper employing finite element based three-dimensional atomistic modeling approach. The effect of missing of three conjugate BN pairs in SW-BNNT resulting in formation of hexagonal defect in SW-BNNT on resonance frequency has been analyzed in the present paper. Two different types of SW-BNNT i.e., armchair (5, 5) and Zigzag (5, 0) BNNT of 5 nm length have been analyzed for cantilever and bridged configuration.Further, present work explores the effect of position of defect on resonance frequency in SW-BNNT. The simulation results revels that resonance frequency decreases due to presence of defect and this reduction in frequency increases if the position of defect moves towards free end in the case of cantilever configuration. On the contrary for bridge configuration the resonance frequency decreases continuously if position of defect moves from fixed end to midpoint.Thus it can be concluded that due to presence of defect in nanotube, the resonance frequency decreases and suggests that stiffness is more dominating than mass of nanotube.

Sensitive Relative Humidity Monitoring Sensor Based on Microwave Active Resonator With PEDOT:PSS

In this paper, a relative humidity monitoring sensor based on an active resonator with PEDOT:PSS is studied in the microwave regime. The proposed active resonator is patterned on a printed circuit board and excited by electromagnetic field coupling. The active resonator consists of two parts: a passive core resonator and an active circuit. The passive core resonator senses the humidity via the PEDOT:PSS conducting polymer film, which is located in the area of the passive core resonator with the strongest electric field. The active circuit compensates for the loss of the passive core resonator to enhance the quality factor and thus improve the sensitivity of the relative humidity sensor. By combining the passive core resonator with the active circuit, the active resonator exhibits a high quality factor (2887), which is 90 times that of the passive core resonator alone. Moreover, the sensitivity of the proposed humidity sensor is improved when using the active resonator. To verify the performance of the proposed humidity sensor, a commercial sensor is placed alongside the proposed sensor in a well-controlled environment chamber. According to the experimental results, as the relative humidity increases, the transmission coefficient (S 21 ) increases, while the resonance frequency decreases. As a result, the sensor exhibits an increase in S 21 of 3.58 dB and a decrease in the resonance frequency of 8.85 MHz when the relative humidity changes from 30% to 85%.

Reaction-Based Amine and Alcohol Gases Detection with Triazine Ionic Liquid Materials.

We demonstrated in this work the use of affinity ionic liquids, AIL 1 and AIL 2, for chemoselective detection of amine and alcohol gases on a quartz crystal microbalance (QCM). These detections of gaseous amines and alcohols were achieved by nucleophilic aromatic substitution reactions with the electrophilic 1,3,5-triazine-based AIL 1 thin-coated on quartz chips. Starting with inexpensive reagents, bicyclic imidazolium ionic liquids AIL 1 and AIL 2 were readily synthesized in six and four synthetic steps with high isolated yields: 51% and 63%, respectively. The QCM platform developed in this work is readily applicable and highly sensitive to low molecular weight amine gases: for isobutylamine gas (a bacterial volatile) at 10 Hz decrease in resonance frequency (i.e., ΔF = −10 Hz), the detectability using AIL 1 was 6.3 ppb. Our preliminary investigation on detection of the much less nucleophilic alcohol gas by AIL 1 was also promising. To our knowledge, no example to date of reports based on nucleophilic aromatic substitution reactions demonstrating sensitive gas detection in these triazine ionic liquids on a QCM has been reported.

Inkjet Nozzle Failure by Heterogeneous Nucleation: Bubble Entrainment, Cavitation, and Diffusive Growth

Piezoacoustic drop-on-demand (DOD) inkjet printing is widely applied in high-end digital printing due to its unprecedented precision and reproducibility. Micron-sized droplets of a wide range of chemical compositions can be deposited; however, the stability of piezoacoustic DOD inkjet printing can sometimes be compromised through the stochastic entrainment of bubbles within the ink channel. Here, bubble nucleation, translation, and growth are studied in an experimental silicon-based printhead with a glass nozzle plate using high-speed imaging that is triggered by changes in the ink-channel acoustics. It is found that impurities in the ink can trigger bubble nucleation upon their interaction with the oscillating meniscus. Cavitation inception on a dirt particle during the rarefaction pressure wave is identified as a second mechanism for bubble formation. The acoustic driving pressure within the ink channel, and its change upon bubble nucleation, are obtained from a fit of a Rayleigh-Plesset-type bubble-dynamics equation to the measured time-resolved radial dynamics of the bubble. The measured decrease in channel resonance frequency after bubble entrainment results in a 24% increased ink-jet length. The nucleated bubbles translate toward the ink-channel walls due to acoustic radiation forces and ink streaming. The convective ink flow is characterized using high-speed particle-tracking velocimetry. The vortical flow near the oscillating meniscus is shown to trap the impurities, thereby increasing the particle-to-meniscus interaction probability and, correspondingly, the bubble-entrainment probability.

Enhanced magnetoelectric torque effect in Pb(Zr,Ti)O3/NdFeB bi-cantilever composites

A piezoelectric/ferromagnetic bicantilever composite, constructed with a Pb(Zr,Ti)O3 beam fixed at the middle point and NdFeB magnets attached at both free ends, has been designed and exhibited a giant magnetoelectric torque (MET) effect. The low-frequency and resonant MET effect in the bicantilever composite is more than twice as much as that in the single cantilever composite with the same components and geometry dimension. As the magnet mass increases, the MET effect first increases nearly linearly and then tends to saturate while the resonant frequency decreases. When the magnets are attached asymmetrically at the tip, the MET effect is stronger than that of the symmetric attachment. Our results will give more choices for preparing the magnetoelectric device used as an ac magnetic field sensor, energy harvester, etc.

Fatigue Properties of Maraging Steel after Laser Peening

Maraging steels are precipitation hardening steels used for highly loaded components in aeronautical and tooling industry. They are subjected to thermomechanical loads and wear, which significantly shorten their service life. Improvements of their surface mechanical properties to overcome such phenomena are of great interest. The purpose of our research was to investigate the influence of pulse density and spot size of a laser shock peening (LSP) process on the surface integrity with the fatigue resistance of X2NiCoMo18-9-5 maraging steel. Surface integrity was analyzed through roughness, residual stress, and microhardness measurements. The tests performed on resonant testing machine confirmed LSP is a promising process for increasing fatigue resistance of a component. Fatigue crack occurs, when the resonance frequency decreases. This moment, when the fatigue crack initiation phase ends and the fatigue crack propagation phase starts, was chosen as the moment of failure. We have proved LSP is a successful method in improving fatigue resistance of maraging steel by appropriate combination of laser spot size and pulse density tested in our research.

Output Power of Piezoelectric MEMS Vibration Energy Harvesters Under Random Oscillation

The output characteristics of MEMS piezoelectric vibration energy harvesters (PVEHs) under random oscillations are analysed. We fabricated cantilever-type MEMS-PVEHs using Pb(Zr,Ti)O3 films. The autocorrelation function of the transient displacement of the cantilever tip under random oscillations features a narrow-band random vibration. From the power spectral density (PSD) of the output voltage of the PVEHs, the resonance frequency decreases and the full-width at half-maximum increases with increasing vibration acceleration. By comparing output properties under various sinusoidal oscillations, nonlinear effects including the soft-spring effect and nonlinear damping effect clearly influence the output characteristics under random oscillations. The power generation is proportional to the square of the vibration acceleration even in the acceleration region where nonlinear effects become conspicuous.