Reduction In Resonant Frequency Research Articles

Shaking table tests on concrete blocks anchored at the bottom of hydrogen storage vessels considering field installation conditions

ABSTRACT In this study, a scale model was created based on field investigation and design standards to evaluate the structural safety of a vertical hydrogen storage vessel stored in gas and liquid form during an earthquake, and a shaking table test was performed. Through testing, it was recognized that fixed anchors were also vulnerable to earthquakes, and additional seismic performance tests were conducted. In Set 1, where gas was stored, no damaged areas were observed during the maximum input seismic motion (EQ 200 %). In Set 2, where liquid was stored, cracks began to appear between the concrete block and the foundation at EQ 100 %, corresponding to the seismic design standard, and progressed to complete destruction at EQ 150 %. Cracks between the concrete block and the foundation led to a decrease in resonant frequency, accompanied by an amplification in acceleration. A reduction in resonant frequency by more than 15 % is anticipated to result in severe damage to the substructure, indicating a potential for brittle failure due to concrete damage prior to anchor failure. The anchors exhibited residual loads of over 80 % of the design load on average, confirming the use of anchors meeting seismic performance requirements.

Nonlinear dynamics of diamagnetically levitating resonators

The ultimate isolation offered by levitation provides new opportunities for studying fundamental science and realizing ultra-sensitive floating sensors. Among different levitation schemes, diamagnetic levitation is attractive because it allows stable levitation at room temperature without a continuous power supply. While the dynamics of diamagnetically levitating objects in the linear regime are well studied, their nonlinear dynamics have received little attention. Here, we experimentally and theoretically study the nonlinear dynamic response of graphite resonators that levitate in permanent magnetic traps. By large amplitude actuation, we drive the resonators into nonlinear regime and measure their motion using laser Doppler interferometry. Unlike other magnetic levitation systems, here we observe a resonance frequency reduction with amplitude in a diamagnetic levitation system that we attribute to the softening effect of the magnetic force. We then analyze the asymmetric magnetic potential and construct a model that captures the experimental nonlinear dynamic behavior over a wide range of excitation forces. We also investigate the linearity of the damping forces on the levitating resonator, and show that although eddy current damping remains linear over a large range, gas damping opens a route for tuning nonlinear damping forces via the squeeze-film effect.

3D‐structure coupled monopole designs with lower frequency resonance

AbstractIn this study, we investigated three‐dimensional configurations involving a monopole‐coupled wired ring, a hollow metallic cylinder, and wired helix spring to achieve resonance lower than quarter‐wave resonance. The resonance frequency of a quarter‐wave monopole, originally 2.05 GHz, was significantly lowered by 54.53% through effective coupling with a wired ring, and a quarter‐wave monopole properly coupled with a hollow metallic cylinder experienced a large decrease of 64.34%. The primary incentive for connecting a wired ring to a hollow metallic cylinder is to significantly reduce resonance frequency. Efforts were also made to lower resonance frequency in a wired helix spring with a length close to that of the wired ring, resulting in a substantial 78.83% reduction in resonance frequency. The −10 dB bandwidth was 14.63% for the quarter‐wave monopole, 27.21% for the monopole‐coupled wired ring, 33.71% for the monopole‐coupled hollow metallic cylinder, and 4.69% for the monopole‐coupled helix spring. The ka values for the monopole‐coupled wired ring, hollow metallic cylinder, and helix spring were 0.35, 0.27, and 0.16, respectively. Hence, these antennas can be classified as electrically small antennas. The achieved resonant frequencies have applications in various wireless communication scenarios. The experimental results from the fabricated prototype agree well with the simulation results.

Design of Non-Planar Dipole Antenna for Enhanced Resonant Frequency Reduction

Design of Non-Planar Dipole Antenna for Enhanced Resonant Frequency Reduction

Calibration and limitations of a fixed-partly fixed resonant column apparatus

The small-strain shear modulus of soils and rocks is an important input parameter in geotechnical analyses. Its estimation using the resonant column apparatus relies on accurate knowledge of the rotational inertia of the apparatus’s active end. Due to the complex geometry of the active end, its inertia is typically found from a calibration exercise. In this study a range of aluminium calibration bars and steel masses were used to compare two different calibration exercises presented in the literature. The resulting values of active end inertia are shown to be highly method-dependent. The method of compensating for the drive connection stiffness by finding the apparatus resonant frequency is found to introduce errors at low stiffness. The combined use of calibration bars and masses reduces scatter but yields poor results for stiff bars. An alternative approach to mitigate both of these problems is suggested. Active end inertia is found to be constant using this alternative approach. While effects of base inertia and reaction mass inertia are found to be small for this apparatus, compliance of the drive system is shown to significantly reduce resonant frequencies at high stiffnesses which increases the apparent active end inertia. This reduction in resonant frequency is modelled and used to derive frequency correction factors, which reduce errors in shear modulus to within acceptable limits when using the constant value of active end inertia. This demonstrates the potential for increasing the limit of sample stiffness where sufficient calibration data are available.

Theoretical study on resonance frequencies of vibration modes of Janus-Helmholtz transducer

Janus-Helmholtz transducer has the characteristics of high-power and broadband transmission due to the coupling between the longitudinal resonance of the driver and the liquid cavity resonance of Helmholtz resonator. Traditional view holds that the low frequency resonance peak in the transmitting voltage response curve in water is fluid cavity mode of Helmholtz resonator while the high frequency resonance is the longitudinal mode of Janus transducer. However, in the past few decades, a large number of experimental studies have found that this conclusion is questionable. This work is to distinguish the two resonances in the response curve and the two vibration modes of Janus-Helmholtz transducer. Based on the Janus-Helmholtz transducer prototype reported in the literature, the resonance frequencies of the vibration modes of Janus-Helmholtz transducer are studied theoretically. The structure dimensions and material parameters of the prototype are listed in detail. The test results and simulation results of conductivity are also presented. The longitudinal resonance of the driver is determined by using the equivalent circuit method and finite element analysis. Radiation masses of both Janus transducer and typical longitudinal vibration transducer are also calculated to analyze the phenomenon of the sharp decrease of longitudinal resonance frequency in water. Acoustic modal analysis by using ANSYS software is performed to investigate the resonance frequency of complex Helmholtz resonator in Janus-Helmholtz transducer. Correction length on the vent introduced by external fluid sound radiation is used to obtain the accurate Helmholtz resonance frequency. The sound pressure distribution of Helmholtz resonator obtained through finite element method is investigated, and the correct equivalent formula for solving the Helmholtz resonance frequency is obtained. The results reveal that the first resonance in the response curve is driver resonance while the second one is Helmholtz resonance, which is contrary to the traditional view. The considerable reduction of driver resonance frequency in water is mainly due to the large radiation mass on the four large radiation surfaces of the Janus transducer, which also causes the sharp response of driver resonance. In Janus-Helmholtz transducer, there are two Helmholtz resonators with the same size, instead of only one resonator in the traditional view. The two resonance frequencies solved by the method proposed in this work are in good agreement with the test and simulation results. These conclusions play an important role in correctly understanding the structure and characteristics of Janus-Helmholtz transducer at source, as well as provide technical support for structural optimization and innovation, thus improving the acoustic emission properties of the transducer.

Numerical study on weakening vortex-induced vibration of semi-ring diversion type component

Conventional spoiler components are commonly employed to mitigate vortex-induced vibration (VIV), but their effectiveness varies significantly. Therefore, detailed comparative studies should be made between different components and a more comprehensive suppression method will be proposed. In this paper, numerical simulations are conducted to explore the weakening effect of hydrodynamic shapes on VIV of structures. Different spoiler components, including rectangular spoiler, fairing, and fin plate are investigated, and for further optimization, a novel concept of semi-ring diversion type component is proposed. The attenuation effects of different components on vibration are compared. In addition, sensitivity analyses of the diversion component, including slit width (XW), front angle (α), and nozzle size (BL), are conducted at various reduced velocities to determine the optimal sizes. Results indicate that traditional spoiler components have inherent shortcomings in terms of weakening efficiency, which can only reduce the maximum resonance value (Ay(max)) to 50%–77%, extend the dimensionless critical velocity (Ucr) by −0.5–1.5, and shorten the length of frequency lock-in interval to 2.5–3, compared to the bare cylinder. The diversion component effectively reduces the frequency of vortex shedding around the cylinder. The optimal vibration damping effect is achieved when XW = 0.03, α = 60°, and BL = 0.11. Compared to the bare cylinder, the structure shows a substantial reduction in resonant frequency by 69%, a threefold decrease in the length of the frequency lock-in interval, a 68.2% reduction in Ay(max) and a delay in Ucr of 2.65, demonstrating a potential mitigation device for VIV.

Reduced resonance frequency and enhanced coupling coefficient in fishtailing magnetoelectric resonator

Reducing the resonance frequency of the first-order longitudinal vibration mode for a bulk magnetoelectric (ME) resonator has been a challenge for very low frequency (VLF) magnetic sensing and transmitting application. In this work, we design and fabricate a fishtailing ME resonator that reduces the anti-resonance frequency from 18.8 to 12.2 kHz and the resonance frequency from 18.2 to 11.5 kHz compared with conventional 1–1 typed resonator. Meanwhile, a significant enhancement of the resonant ME coupling coefficient [from ∼8271 to ∼11 400 V/(cm Oe)] is also realized. Finite element simulation and lumped mass method are used to calculate and analyze the principles of the reduced resonance frequency and the reasons for enhanced coupling performance. The geometry tailoring method in this work is believed to inspire applications of the resonant ME effect at very low frequency.

Experimentally verified numerical model for asymmetric ferrite core wireless power transfer with on-chip interfacing circuits

This paper presents a novel numerical model for asymmetric ferrite core wireless power transfer, which has been experimentally verified. The research focuses on addressing the challenge of reducing the resonance frequency in wireless power transfer technology, particularly for cost reduction in power transfer systems. To achieve this, a toroidal ferrite core is utilized to decrease the self-resonant frequency, and the transmission parameter is measured using a vector network analyzer. Inductive wireless power transfer designs operating at MHz frequencies often suffer from low current efficiency due to the quality factor of the resonant coils. To overcome this limitation, finite element analysis is employed to optimize the cross-sectional area of the inductors, specifically for high-frequency wireless power transfer. The results demonstrate the effectiveness of the optimized coils, achieving an impressive transfer efficiency of nearly 98% at 5 cm, with an operating frequency of 21.6 MHz. Furthermore, the system is enhanced with a CMOS-based interfacing circuit, designed to enable system-on-chip power transfer for Internet of Things (IoT) applications. This integrated system design contributes to the advancement of wireless power transfer technology by not only addressing resonance frequency reduction but also proposing a cost-effective and efficient solution for power transfer in IoT applications.

Compact wideband microstrip antennas using C, H, and W‐shape ground plane for GSM band applications

AbstractProximity‐fed compact wideband rectangular and circular microstrip antennas by employing H‐shape, C‐shape, and W‐shape ground plane profiles are proposed. Optimum results are obtained in rectangular microstrip antenna using H‐shape ground plane. Against the conventional ground plane, it gives 16% bandwidth improvement, supported by 17.29% and 31% reduction in resonant mode frequency and patch area, respectively. The proposed design exhibits a broadside pattern with a gain of 6.1 dBi and can find applications in GSM 900 band.

Adaptive Notch Filter in a Two-Link Flexible Manipulator for the Compensation of Vibration and Gravity-Induced Distortion

This paper presents a 2-link, 2-DOF flexible manipulator control using an inverse feedforward controller and an adaptive notch filter with a direct strain feedback controller. In the flexible manipulator, transient and residue vibrations inhibit the full potential of the manipulator. Vibrations caused by abrupt changes in the direction of the links are referred to as transient vibrations, whereas residual vibrations occur when the arm takes too long to settle after engaging in the intended task. The feedforward adaptive notch filter will reduce transient vibration caused by the manipulator arm beginning and halting suddenly, while the strain feedback will assure the quick decay of leftover vibrations. Maple, Maplesim, and MATLAB tools were used to model the manipulator and create the inverse controller and adaptive notch filter. The experiments took place in the dSPACE control desk environment. The experimental results of the spectral power of strain resulting from the two strategies are compared. From the results, the adaptive notch filter control had over an 80% improvement in the reduction in resonant frequencies that contribute to vibration. The results confirmed the feasibility of the approach, characterized by very minimal transient vibrations and a quick settling of the end effector.

Analytical Approaches for Effects of Edge-Located EBG Structure With Defected Ground Structure on Cavity-Mode Resonances of Power/Ground Planes

The effects of an edge-located electromagnetic bandgap (EL-EBG) structure including a defected ground structure (DGS) on the cavity-mode resonances of power/ground planes are analyzed for the power integrity design of high-speed packages and printed circuit boards (PCBs). The EBG structure localized in the power/ground planes significantly affects the power integrity characteristics. However, previous studies did not consider this effect. An analytical equation and a numerical method based on the contour integral method (CIM) are developed to examine the EL-EBG effect on cavity-mode resonance. The proposed method reveals that the employment of the EL-EBG structure results in resonance frequency reduction, generation of hybrid-type mode, irregular relationship between mode resonance frequencies, and different distribution of mode intensity compared to conventional open-ended power/ground planes. The proposed CIM modeling and analysis for investigating the distinctive features of the EL-EBG effect are validated using full-wave simulations and measurements. The rigorous analysis of the EL-EBG effect enables the improvement of power integrity design for power/ground planes combined with EBG structures. Moreover, the proposed CIM modeling can obtain fast and accurate results for EL-EBG power/ground planes compared to full-wave simulations.

FSS bandwidth design using miniaturized elements for angular stability in transmission

Frequency-selective surfaces (FSSs) are commonly employed at microwave frequencies in electromagnetic filtering applications. This paper reports the use of cascaded dual miniaturized elements for radio secure environments where miniaturized elements have been used creating a reduced unit cell (<0.1 wavelengths), and exceptional angular stability. Thin, flexible and optically transparent FSS samples were fabricated by laser engraving elements into a conductive aluminium layer, with a supporting Mylar substrate (relative permittivity 2.7), and thickness of 65 μm. The linearly polarized transmission response was investigated numerically by exploring the scattering parameters and the surface currents at resonance. Miniaturized elements in both single and cascaded FSS structures, have been explored to create both broadband and multiband responses across the L and S frequency bands. The theoretical and experimental results were in good agreement for the fabricated dual element dual layer translated band-stop FSS, displaying a resonant frequency reduction of 70% compared to a square loop with the same dimensions, along with significantly broad operation bandwidths of 118% and 104% for simulated and measured, respectively. These improvements were due to the selection of the individual elements in the array, their geometric arrangement, and the introduction of additional layers with lateral offsets.

Deeply subwavelength giant monopole elastodynamic metacluster resonators.

The giant monopole resonance is a well-known phenomenon, employed to tune the dynamic response of composite materials comprising voids in an elastic matrix which has a bulk modulus much greater than its shear modulus, e.g. elastomers. This low frequency resonance (e.g. for standard elastomers, where and are the compressional wavelength and void radius, respectively) has motivated acoustic material design over many decades, exploiting the subwavelength regime. Despite this widespread use, the manner by which the resonance arising from voids in close proximity is affected by their interaction is not understood. Here, we illustrate that for planar elastodynamics (circular cylindrical voids), coupling due to near-field shear significantly modifies the monopole (compressional) resonant response. We show that by modifying the number and configuration of voids in a metacluster, the directionality, scattering amplitude and resonant frequency can be tailored and tuned. Perhaps most notably, metaclusters deliver a lower frequency resonance than a single void. For example, two touching voids deliver a reduction in resonant frequency of almost 16% compared with a single void of the same volume. Combined with other resonators, such metaclusters can be used as meta-atoms in the design of elastic materials with exotic dynamic material properties.

Abrupt Variations in Deep Surge Frequencies in High-Pressure-Ratio Multi-Stage Axial Flow Compressors

High-pressure-ratio multi-stage axial flow compressors tend to show complicated behaviors of frequencies in deep surges, including discontinuous changes. The phenomena for a nine-stage compressor were investigated by one-dimensional numerical simulations. The phenomena were found to occur somewhere in the range of roughly (90 – 100)% of the design speed, where incomplete surge recoveries, i.e., premature surge recoveries accompanied by immediate re-stallings, tend to occur, resulting in longer surge periods and lower surge frequencies. The incomplete surge recoveries are found to occur by premature unstalling owing to re-ingestions of the reversed hot air produced by the preceding surge, which is too hot for the compressor to work normally. The re-ingestion temperature, and the duration time of the hot re-ingestion relative to the normal suction appear to affect significantly the recovery process. It tends to occur essentially in the range of (90 -100)% of the design speed, where the compressor working conditions are changeable sensitively to small changes in the working conditions. The situations are found to be governed mainly by the following parameters; the representative tip Mach number, the reduced resonance frequency related with the suction flowpath, and the relative location of the compressor in the whole flowpath. Sufficiently below and above the sensitive speed range, the situations keep their respective stable and continuous surge behaviors. In the higher speed range, the deep surges having lowered frequencies at higher speeds become the normal state. The phenomena depend strongly on the design conditions, i.e., speed and pressure ratio and number of stages. The above conclusions suggest the natures of the discontinuous frequency behaviors in high-pressure-ratio multi-stage compressors, although they are qualitative in that they are strongly influenced by the present particular design conditions and the accuracies of the employed analysis.

Design of a Chipless RFID Tag to Monitor the Performance of Organic Coatings on Architectural Cladding.

Coating degradation is a critical issue when steel surfaces are subject to weathering. This paper presents a chipless, passive antenna tag, which can be applied onto organically coated steel. Simulations indicated that changes associated with organic coating degradation, such as the formation of defects and electrolyte uptake, produced changes in the backscattered radar cross section tag response. This may be used to determine the condition of the organic coating. Simulating multiple aging effects simultaneously produced a linear reduction in tag resonant frequency, suggesting coating monitoring and lifetime estimation may be possible via this method. For coatings thinner than calculations would suggest to be optimum, it was found that the simulated response could be improved by the use of a thin substrate between the coated sample and the antenna without vastly affecting results. Experimental results showed that changes to the dielectric properties of the coating through both the uptake of water and chemical degradation were detected through changes in the resonant frequency.

Long term stability of cantilever gas nanosensors to detect Euschistus heros (F.) pheromone release by rubber septa

This work presents the use of cantilever gas nanosensors coated with PANI/PSS and PANI.Ag to monitor the release of neotropical brown stink bug, Euschistus heros (F.) pheromone in rubber septa (insect pheromone dispenser). The rubber septa was impregnated with the 2,6,10-methyl trimethyltridecanoate compound, the main component of the sexual pheromone of E. heros stink bug. Studies were conducted to detect and determine the pheromone release ratio under laboratory conditions during two months. Both cantilever nanosensors showed a daily reduction in resonance frequency when exposed to the rubber septum containing the pheromone, which was not observed in the control cantilever. The relative humidity did not presented influence on the nanosensors resonance frequency. The stability of the cantilever nanosensors was evaluated for 365 days (twelve months). Was observed a slight reduction of 1.4% in the resonance frequency for the nanosensor of PANI/PSS after 300 days of storage, and of 0.32% for the nanosensor PANI.Ag after 360 days. In this way, the gas nanosensors can be stored for long time presenting a long-term stable response and used successfully to detect the release of pheromone molecules.

Significant Reduction of Resonant Frequency by Multi-Layered Dielectric Material-Loaded Coaxial Cavity for Microwave Heating

This paper presents a microwave heating method using a cavity whose size is much smaller than the free-space wavelength. The resonant frequency was reduced by inserting multi-layer dielectrics into the cavity, and an appropriate mode was generated in the cavity to heat a specific area inside it. High-permittivity dielectrics were used to make the cavity resonate in the frequency range of a few gigahertz. A formula for the resonant frequency of the multi-layer dielectric material-loaded cylindrical cavity was analytically derived. The frequency reduction by using a dielectric-loaded cylindrical cavity geometry was predicted from the derived formula, from 12.2 GHz to 4.6 GHz, whereas the experiment results showed a reduction from 10.8 GHz to 4.5 GHz. The analytical and the experiment results were compared and analyzed with simulations, which showed good agreement. The heating efficiency at the target in the multi-layered dielectric geometry was analyzed. The electric field inside the target material was measured to prove the temperature response of the microwave heating and was compared with the simulation result. This paper confirms a technical possibility of microwave heating of a smaller-sized cavity with an insertion of low-loss dielectric material in the vicinity of a heating target.

The Role of Wideband Tympanometry in the Diagnosis of Meniere's Disease.

Meniere's disease (MD) is a clinical syndrome characterized by spontaneous recurrent vertigo, usually accompanied by hearing loss, tinnitus, and aural fullness. The cause of MD remains unclear and is generally considered to be associated with endolymphatic hydrops. Studies showed that patients with MD could have eustachian tube dysfunction (ETD). ETD can disrupt the pressure balance between the middle and inner ear and impair the inner ear's function. In recent years, several studies have attempted to identify MD by using wideband tympanometry (WBT). However, there are limited studies in this area. There is no consensus on how to use WBT to diagnose Meniere's disease. Therefore, we endeavored to conduct a narrative review in this aspect based on the latest research findings. Reduction in resonance frequency and absorbance are characteristic of MD and can identify Meniere's disease. The use of an increase in the integrated area of absorbance as an indicator for identifying MD is controversial. WBT seems to be ineffective as a diagnostic tool during the acute episodes of Meniere's disease. Patients with MD may benefit from WBT. WBT has excellent potential for future use in Meniere's disease. However, further large sample sizes, multicenter studies are needed.

Slot Antenna Miniaturization Using Folded Slot for ISM Band Applications

A novel antenna miniaturization technique of microstrip-fed slot antenna, using a folded slot topology, is highlighted. Antennas are designed with slits on both sides of folded slot and metallic strips on the bottom of the substrate. An unfolded radiating slot of 30.00 mm length is folded to 15.44 mm, without compromising the radiation pattern or return loss characteristics. The proposed antenna exhibits 60.27% reduction in resonant frequency for slits and strips’ loaded folded slot topology in comparison with 48.01% reduction in resonant frequency of previous works. These antennas also offer improved impedance bandwidth. The gain performances of these antennas are improved by placing a dielectric slab on the bottom of the substrate without compromising the radiation pattern characteristics.