Reduction In Resonant Frequency Research Articles

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.

Resonant Frequency Reduction of Vertical Vibration Energy Harvester by Using Negative-Stiffness Magnetic Spring

This work studies the resonant frequency reduction of vibration energy harvesters so as to adapt low-frequency ambient vibrations. In a typical electromagnetic vibration energy harvester, it is common sense that the resonant frequency decreases with the spring stiffness. However, the mass gravity will result in a large initial deformation of the spring with small stiffness when the energy harvester is vertically installed. To solve the problem, this work proposes a method of resonant frequency reduction by adding a negative-stiffness magnetic spring which is arranged symmetrically at the two sides of the equilibrium point. The theoretical expression of resonant frequency is derived based on magnetic field calculation. Comparisons between the energy harvesters with and without negative-stiffness magnetic spring are implemented through simulations and experiments. The results show that the resonant frequency of the vertical energy harvester can be reduced as expected without an increase of initial spring deformation by using the negative-stiffness magnetic spring. This work can provide an effective approach to designing energy harvesters for applications with low-frequency vibrations.

Electromechanical Characteristics of Core Free Folded Dielectric Electro-active Polymer Soft Actuator

This paper investigates the active dynamic and electromechanical characteristics of a new thin folded dielectric electro-active polymer actuator developed by Danfoss PolyPower. The high voltage is supplied to the actuator during dynamic testing to identified the effect of the electrical field on dynamic characteristics. The electromechanical characteristics are investigated by varying the amplitude and frequency of the voltage supplied. The experimental results, such as natural frequency, amplitude response, and loss factor are presented to show the influence of such an electrical field on the characteristic of the actuator. There is a reduction of resonance frequency from 14 Hz to 12 Hz as voltage supply up to 2000 V. The actuating response of the actuator was subjected more to frequency rather than the amplitude of the voltage supplied. Hence, the results may guide the exploration of a new folded thin actuator as an active vibration controller.

Compressor Surge Frequencies Modeled by the Concept of Emptying and Filling Actions

Surge frequencies in compressors can vary much in dependence of many factors, such as compressor conditions, such as sizes, speeds, number of stages, and flowpath geometries, relative compressor locations, etc. The present investigation shows the basic behaviors of surge frequencies in multi-stage axial flow compressors, governed by a small number of essential parameters, which are obtained by physical insight to the phenomena and examinations in a trial-and-error manner on a n umber of numerical-experimental data. One of the essential parameters is a flowpath-average reduced resonance frequency, implying the number of excitations by the resonance frequency on the fluid particle in passing through the flowpath. Another one is also a reduced frequency formulated by modelling the emptying and filling actions in surge. A generalized basic framework of surge frequencies against resonance frequencies has been constructed by applying the numerical experimental data on a wide range of conditions of the compressors and the flowpaths in terms of both parameters. The framework thus prepared can be useful for practical purposes, such as for estimation of surge frequencies and surge degeneration (stall stagnation) boundaries, and also for understanding the effects of various related factors. It can provide a rule of thumb for estimation of surge frequency in the condition of sufficiently large values of the reduced resonance frequency parameter. It could serve also as a clue to further study on the details.

Auxetic clamped-clamped resonators for high-efficiency vibration energy harvesting at low-frequency excitation

Here, we utilize the auxetic concept to improve output electrical power and reduce resonance frequency for the piezoelectric vibration energy harvesting. An energy harvester consists of a proof mass and two supporter beams with piezoelectric patches, is proposed. Presented energy harvester prototype is appropriate for applications with limited allowable displacement. Three different auxetic structures are proposed and their performances are compared to the conventional plain system. Finite element (FE) modelling is provided to evaluate these structures and optimize their geometrical parameters and electrical resistance to achieve the best energy harvesting performance. The FE model is validated through experimental tests in which the energy harvesters with optimized parameters are excited by an electrodynamic shaker in different frequencies. It is shown that the proposed designs are able to remarkably enhance the harvested electrical power with respect to the plain structure. The experimental tests show that the Auxetic-I, II and III could enhance the output electrical power with a magnification factor of 10, 6.7 and 6.1 respectively, compared to the conventional structure. The resonant working frequency reduced up to 30.45%, 19.55% and 27.53% for different designs.

Dynamic acceleration response of a rock slope with a horizontal weak interlayer in shaking table tests.

The weak interlayer in a rock slope often plays a significant role in seismic rockslides; however, the effect of weak interlayer on the seismic slope response and damage process is still not fully understood. This study presents a series of shaking test tests on two model slopes containing a horizontal weak interlayer with different thicknesses. A recorded Wenchuan earthquake ground motion was scaled to excite the slopes. Measurements from accelerometers embedded at different elevations of slope surface and slope interior were analyzed and compared. The effect of the weak interlayer thickness on the seismic response was highlighted by a comparative analysis of the two slopes in terms of topographic amplification, peak accelerations, and deformation characteristics as the input amplitude increased. It was found that the structure deterioration and nonlinear response of the slopes were manifested as a time lag of the horizontal accelerations in the upper slope relative to the lower slope and a reduction of resonant frequency and Fourier spectral ratio. Test results show that under horizontal acceleration, both slopes exhibited significant topographic amplification in the upper half, and the difference in amplification between slope face and slope interior was more pronounced in Slope B (with a thin weak interlayer) than in Slope A (with a thick weak interlayer). A four-phased dynamic response process of both slopes was observed. Similar deformation characteristics including development of strong response zone and macro-cracks, vertical settlement, horizontal extrusion and collapse in the upper half were observed in both slopes as the input amplitude increased; however, the deformations were more severe in Slope B than in Slope A, suggesting an energy isolation effect of the thick interlayer in Slope A.

A tri‐band and miniaturized planar antenna based on countersink and defected ground structure techniques

In this article, a compact planar heart-shaped antenna based on countersink and partial ground plane techniques is proposed to operate as a multiband device for modern wireless systems. With a surface area of 28.5 mm2, the countersink technique (CT) has been developed to achieve high electromagnetic antenna performance. The CT consists of a particular multilayer configuration that uses two distinct materials where one of them with a radiating element on its top is placed inside another. In this article, a 508-μm thick Rogers RO4350B with a radiating patch designed on its top is thermally embedded into a 1.524 mm thick FR4 HTG-175. The slits are used to get multiband behavior, and their combination with the defected ground structure results in about 79.58% reduction in resonant frequency compared to the conventional antenna. A mathematical model is developed to predict the resonant frequency of the proposed antenna configuration. After modeling the heart-shaped antenna with an electromagnetic simulator, its prototype was manufactured and validated through experimental measurements. The CT considerably improved the antenna's performance compared to the use of a single layer technology for the same antenna configuration. The return loss read from −10 dB shows that the proposed antenna covers multiple modern wireless applications, including LTE bands, 5G, WLAN, WiMAX, and Unlicensed National Information Infrastructure (UNII) radio bands. Furthermore, the antenna operates as narrowband and wideband simultaneously on its lower/middle and upper operating frequency bands. A close agreement is found between simulated and measured results across all the frequency bands.

Optical and antibacterial properties of 1-butyl-3-methylimidazolium ionic liquids with trifluoromethanesulfonate or tetrafluoroborate anion

Two room temperature ionic liquids (RTILs) having the same cation (1-butyl-3-methylimidazolium [BMIM]+) and different anions (tetrafluoroborate [BF4]−or trifluoromethanesulfonate [TfO]−) have been investigated by ATR-FTIR, NMR, TGA/DTA, UV–vis spectroscopy, agar-disk diffusion, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assay. Structural investigations by ATR-FTIR and NMR spectroscopy demonstrated that the [BMIM]+ cation exhibits hydrogen bonding with the [BF4]−and [TfO]− anions via the C (2)-H and C (4, 5)-H of the imidazolium cation ring in addition to the protons of the alkyl and methyl groups. UV–vis spectroscopy revealed an energy gaps of 3.79 ± 0.13 and 3.37 ± 0.04 eV for [BMIM][BF4] and [BMIM][TfO], respectively. Single term Sellmeier oscillator model and the Drude-Lorentz model were employed for the first time to investigate the optical and dielectric properties of ionic liquids. Applying the former model, enables us to extract the average inter-band oscillator wavelength (λ0), the average oscillator strength (S0), single oscillator energy (E0), dispersion energy (Ed) while the latter gives the plasmon frequency (ωp), reduced resonance frequency (ω0) and the electron lifetime at femtosecond level. Antibacterial assay by MIC and MBC demonstrated that both ionic liquids have antibacterial activity against gram-positive and gram-negative bacterial strains.

Counterweight-pendulum energy harvester with reduced resonance frequency for unmanned surface vehicles

In this paper, a novel electromagnetic pendulum energy harvester with a counterweight is designed to harvest low frequency vibration from ocean waves for unmanned surface vehicles. This design is the first of its kind, allowing the natural resonant frequency of the pendulum to be reduced without increasing its length, thereby maintaining a high power output from the energy harvester at lower frequencies than previously possible with pendulums of the same size. Implementing a novel mechanical rotation rectifier (MRR) system for a high energy conversion efficiency, this counterweight pendulum energy harvester can provide multi-watt-level power at frequencies lower than 1 Hz, with a primary pendulum arm length of just 195mm. When actuated at 0.1 g rms, the pendulum energy harvester with a counterweight produced electrical power of 0.997 W at 0.75 Hz, compared to 0.168 W without the counterweight. The average normalised power output of the system at this frequency is 95.8 W/g2, corresponding to a power density of 6.11 W/g2/kg. Testing of a range of configurations of the pendulum mass and counterweight shows a clear linear relationship between the ratio of lengths of the pendulum arms and the reduction of the natural frequency of the system. This demonstrates empirically that this device is capable of operating under conditions in which existing energy harvesters are unable to provide adequate power, and therefore provides a significant development in energy harvesting in an ultra-low frequency marine environment.

Influence of rubber sheet on dynamic response of machine foundations

In this study, the efficiency of employing rubber sheets to modify the dynamic response of a concrete machine foundation model of size 400 × 400 mm is explored by conducting a series of steady-state vertical vibration tests. Rubber is a low-cost energy dissipater material having high resistance to erosion which can be used in a form of sheets and simply placed beneath foundations. With a lower shear modulus than soil, it is expected to reduce the resonant frequency of a vibrating system but to increase the resonant amplitude. The former is beneficial if moving the resonant frequency far away from the machine’s operating frequency, but the latter is not desirable. To protect the rubber from UV radiation degradation, it may be helpful to embed it in soil. In this study the effects of rubber sheet thickness, vibrating system weight (dead weight), angular dynamic force and embedment depth of rubber sheet were investigated via a series of near-full-scale laboratory tests. It was found that using rubber sheets with thickness of 12 mm can increase the equivalent damping ratio of bed (up to 28%), reduce resonance frequency (by up to 13.6%), decrease transmissibility and contrary to expectations, reduce resonant amplitude (by up to 22%). Nevertheless, the efficiency of employing a rubber sheet to dynamically retrofit machine foundation depends on the angular dynamic force amplitude and dead weight of the vibrating system.

Wideband absorbance pattern in adults with otosclerosis and ossicular chain discontinuity

ObjectivesEvidence from previous literature had shown that the use of a single frequency probe tone is not sensitive enough to detect middle ear pathologies, especially related to the ossicles, which hinders accurate diagnosis. The goal of the present study was to compare the outcome of wideband absorbance (WBA) tympanometry and to determine the difference in WBA pattern in adults with otosclerosis and ossicular chain discontinuity. Materials and methodsEstimated adult cases of otosclerosis (10 ears) and ossicular chain discontinuity (06 ears) along with healthy individuals (10 ears) in the age range of 24 to 48 years (mean age: 38.6 years) were considered for the study. WBA was measured at peak and ambient pressure along with resonance frequency and compared with the data obtained from the healthy individuals to determine the WBA pattern. ResultsData analysis revealed a distinct WBA pattern showing high absorbance at 750 Hz for ossicular chain discontinuity compared to healthy individuals, whereas the otosclerosis group showed reduced absorbance (p < 0.05) at low frequencies (250 Hz to 1500 Hz). WBA measured at the peak and ambient pressure did not elicit any significant difference across the frequencies. Also, the average WBA tympanogram measured between 375 Hz and 2000 Hz showed a significant difference in ambient pressure only in the otosclerosis group. In comparison to healthy individuals (901 Hz), ossicular chain discontinuity showed a significant reduction in resonance frequency (674 Hz), whereas in cases with otosclerosis had higher resonance frequency (1445 Hz). Conclusions and significanceThe present study showed different WBA patterns between the groups and the absorbance values were significantly different at the low frequencies. This suggests that WBA has the potential to differentiate ossicles related pathologies from normal and also between the ear with otosclerosis and ossicular chain discontinuity.

Spectral Analysis of Digital Filter Tuned for Mechanical Resonant Frequency Reduction in Multi-Mass Mechanical Systems in Electrical Direct Drive

Spectral Analysis of Digital Filter Tuned for Mechanical Resonant Frequency Reduction in Multi-Mass Mechanical Systems in Electrical Direct Drive

Enhanced the capability of magnetostrictive ambient vibration harvester through structural configuration, pre-magnetization condition and elastic magnifier

Vibration energy harvesting, which converts the mechanical vibrations that are commonly available in the surrounding environment to electrical energy, can realize self-power sensing, control and actuation, with the advantages of convenience, energy saving, eco friendliness and sustainability. However, it has some weakness, such as low output power, low efficiency, poor environmental adaptability and low reliability, which restrict its practical applications. It is necessary to optimize the harvester's structure, bias conditions and so on to adapt to the characteristics of ambient vibration, and then enhance the mechanical energy harvesting capability. This paper focuses on improving capability of the cantilever magnetostrictive harvester which is a new technology and still in the stage of proof-of working mechanism and concept prototype design. It systematically clarified the qualitative laws of the major factors affecting harvesting performance, including geometry, bias conditions, etc. Moreover, considering the low frequency characteristics of ambient vibration, it proposed an elastic magnifier with additional mass which can simultaneously enhance vibration harvesting, reduce resonance frequency and broaden effective frequency range. It was experimentally verified that the optimized magnetostrictive harvester can convert the mechanical vibration of 1 g acceleration into the voltage of 1210 mV. It was able to output 11 mW power to a load and the normalized power density reached to 18.3 mW/cm3/g. The magnetostrictive harvesting prototype successfully powered for multiple light emitting diode lamps, multiple digital display tubes and a low power electronic meter.

Frequency and damping effect of suspended silicon nitride membranes in water near the megahertz range

Understanding the behavior of water-immersed membranes in the megahertz range is critical to develop novel acoustic metamaterials compatible with biomedical ultrasound applications. Herein, we study the influence of water on the resonance frequency and quality factor near the megahertz range of silicon nitride membranes fully immersed in water using laser Doppler vibrometry. The resonance frequency of silicon nitride membranes significantly decreases in water compared to air. For a 40 µm wide membrane, the resonance frequency is reduced from 11.2 MHz in air to 1.24 MHz after immersion in water, which is confirmed by finite element method simulations. Our results indicate that the water mass loading plays a major role in the resonance frequency reduction, with a ratio of water mass to membrane mass of 102 and NAVMI factors of Γ∼1.3. We attribute the main losses to acoustic radiation with small contributions from viscous damping. We estimate that silicon nitride membranes with widths below 50 µm are required to build negative metamaterials operating above 1 MHz. The large NAVMI factors suggest strong coupling between membrane motion and acoustic waves in water, which is important to develop metamaterials able to manipulate acoustic fields.

First example of engineered β-cyclodextrinylated MEMS devices for volatile pheromone sensing of olive fruit pests

Olive oil is more preferred than other vegetable oils because of the increasing health concern among people throughout the world. The major hindrance in large-scale production of olive oil is olive fruit pests which cause serious economic damage to the olive orchards. This requires careful monitoring and timely application of suitable remedies before pest infestation. Herein we demonstrate efficacious utilization of covalently functionalized β-cyclodextrinylated MEMS devices for selective and sensitive detection of female sex pheromone of olive fruit pest, Bactocera oleae. Two of the MEMS devices, silicon dioxide surface-micromachined cantilever arrays and zinc oxide surface-microfabricated interdigitated circuits, have been used to selectively capture the major pheromone component, 1,7-dioxaspiro[5,5]undecane. The non-covalent capture of olive pheromones inside the β-cyclodextrin cavity leads to the reduction of resonant frequency of the cantilevers, whereas an increase in resistance has been found in case of zinc oxide derived MEMS devices. Sensitivity of the MEMS devices towards the olive pheromone was found to be directly correlated with the increasing availability of β-cyclodextrin moieties over the surface of the devices and thus the detection limit of the devices has been achieved to a value as low as 0.297 ppq of the olive pheromone when the devices were functionalized with one of the standardized protocols. Overall, the reversible usability and potential capability of the suitably functionalized MEMS devices to selectively detect the presence of female sex pheromone of olive fruit fly before the onset of pest infestation in an orchard makes the technology quite attractive for viable commercial application.

Limits to Thermal-Piezoresistive Cooling in Silicon Micromechanical Resonators

We study thermal-piezoresistive cooling in silicon micromechanical resonators at large currents and high temperatures. Crossing a thermal transition region corresponds to a steep reduction in resonance frequency, an abrupt plateauing in the effective quality factor, and a large increase in thermomechanical fluctuations. Comparing measurements with simulations suggests that the second-order temperature coefficients of elasticity of doped silicon are not sufficient to capture the drop in resonance frequency at large currents. Overall, our results show that there are clear thermal limits to cooling a resonant mode using current-controlled thermal-piezoresistive feedback in silicon.

The "Loopole" Antenna: A Hybrid Coil Combining Loop and Electric Dipole Properties for Ultra-High-Field MRI.

Purpose.To revisit the “loopole,” an unusual coil topology whose unbalanced current distribution captures both loop and electric dipole properties, which can be advantageous in ultra-high-field MRI.Methods.Loopole coils were built by deliberately breaking the capacitor symmetry of traditional loop coils. The corresponding current distribution, transmit efficiency, and signal-to-noise ratio (SNR) were evaluated in simulation and experiments in comparison to those of loops and electric dipoles at 7 T (297 MHz).Results.The loopole coil exhibited a hybrid current pattern, comprising features of both loops and electric dipole current patterns. Depending on the orientation relative to B0, the loopole demonstrated significant performance boost in either the transmit efficiency or SNR at the center of a dielectric sample when compared to a traditional loop. Modest improvements were observed when compared to an electric dipole.Conclusion.The loopole can achieve high performance by supporting both divergence-free and curl-free current patterns, which are both significant contributors to the ultimate intrinsic performance at ultra-high field. While electric dipoles exhibit similar hybrid properties, loopoles maintain the engineering advantages of loops, such as geometric decoupling and reduced resonance frequency dependence on sample loading.

Design of a Miniaturized 2.5-D Frequency Selective Surface With Angular Incidence and Polarization Stability

In this article, a miniaturized 2.5-D frequency selective surface with the band-stop response at 900 MHz is presented. The proposed FSS unit cell comprises rectangular spiral elements printed on both sides of the dielectric substrate. These spirals are connected with plated through-hole vias to form a “2.5-D closed loop”. The large perimeter of the closed loop increases the effective inductance and causes a reduction in resonant frequency and size of the unit cell. The structure is designed to operate at 900 MHz for shielding the interference from other GSM sources. The size of the proposed unit cell is 0.021λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.021λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> which is very compact with a figure-of-merit λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> /p = 47.6, where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the free-space wavelength of resonant frequency andp is the periodicity of unit cell. Further, the effect of substrate parameters on resonance performance has been studied. The proposed structure is polarization-independent and angularly stable for both TE and TM polarizations. A prototype of the FSS is fabricated and measured, where the measured responses show good agreement with the simulated responses.