Peak Resonance Frequency Research Articles

Estimativa de Velocidade de Onda de Cisalhamento pela Inversão Conjunta de Curvas HVSR e f-k sob a Hipótese do Campo Difuso: um Estudo de Caso do Deslizamento de Sobradinho

Brazilian landslides are characterized as shallow, clay rich and are commonly triggered by the summer rainfalls. Therefore, the landslide geological information, such as shear surface location, has a paramount importance in their mechanism comprehension. The most adapted methods for the estimation of shear wave velocity profile are borehole stratigraphic logs or Standard Penetration Test (SPT) and Cone Penetration Test (CPT). However, the present study applied shear wave velocity estimation of Sobradinho landslide (SLS) by a joint inversion of horizontal to vertical spectral ratio (HVSR) curve and dispersion curve (DC) extracted from frequency-wavenumber (f-k) analysis of ambient noise records. HVSR curves at all the stations in the area exhibit the ubiquitous resonance frequency peak at 2 Hz indicates that at these stations the substratum is common. The f-k results for E-W component let us obtain an acceptable DC between 5 and 7 Hz range. Finally, joint inversion was interpreted based on the diffuse field assumption. The initial model was proposed to be a three-layered over a half-space. Results of joint inversion indicate that the substratum is at 24 m depth, with Vs values close to 1500 m/s. DC defines two layers overlaying the substratum: superficial layer with velocities near to 200 m/s (7m thick), and the second layer with Vs value of 1000 m/s. We think that abrupt rheology (stiffness) change between the first and the second layer could provide an evidence of the landslide re-activation during moderate to strong rainfall events. The proposed methodology will prove a reconnaissance survey for the detailed geotechnical investigations that will confirm the obtained results.

Aggregation of Type-4 Large Wind Farms Based on Admittance Model Order Reduction

This paper presents an aggregation technique based on the resolution of a multi-objective optimization problem applied to the admittance model of a wind power plant (WPP). The purpose of the presented aggregation technique is to reduce the order of the wind power plant model in order to accelerate WPP simulation while keeping a very similar control performance for both the simplified and the detailed models. The proposed aggregation technique, based on the admittance model order reduction, ensures the same DC gain, the same gain at the operating band frequency, and the same resonant peak frequency as the detailed admittance model. The proposed aggregation method is validated considering three 400-MW grid-forming Type-4 WPPs connected to a diode rectifier HVDC link. The proposed aggregation technique is compared to two existing aggregation techniques, both in terms of frequency and time response. The detailed and aggregated models have been tested using PSCAD-EMTsimulations, with the proposed aggregated model leading to a 350-fold reduction of the simulation time with respect to the detailed model. Moreover, for the considered scenario, the proposed aggregation technique offers simulation errors that are, at least, three-times smaller than previously-published aggregation techniques.

Enhancing primary implant stability by undersizing implant site preparation: A human cadaver study

IntroductionThe aims of this human cadaver study were to analyze the primary stability of dental implants inserted by using different methods of preparation and to explore correlations among the bone density, peak insertion torque and resonance frequency analysis values. Materials and methodsForty-eight implants were placed into six human cadaver mandibles. The bone density of each implant recipient site was preoperatively measured by using computerized tomography (CT) in Hounsfield Units (HU). Three test groups were created according to the final drill size. The diameters of the final twist drills were 3 mm, 3.4 mm, and 3.8 mm in group T1, group T2, and group T3, respectively. The peak insertion torque and resonance frequency analysis values were recorded. ResultsThe mean bone density, insertion torque, and RFA values were 285 ± 90 HU, 42.8 ± 5 Ncm, and 74 ± 6 ISQ for all 48 implants, respectively. Statistically significant correlations were noted between bone density and insertion torque values (P < 0.05), bone density and RFA values (P < 0.01), and insertion torque and RFA values (P < 0.001). When considering the three test groups, the mean insertion torque, and RFA values were 47.1 ± 3 Ncm, and 83.1 ± 6 ISQ in Group T1, and 43.4 ± 5 Ncm and 73.4 ± 6 ISQ in Group T2, and 37.9 ± 6 Ncm, and 65.3 ± 5 ISQ in Group T3. ConclusionThe results of this study suggest that undersized implant site preparations may be helpful in enhancing primary implant stability and that there are significant correlations among bone density, maximum insertion torque, and RFA values.

Resolution of ambiguity between the depolarization and ferroelectric–relaxor transition temperature through dielectric studies in lead-free perovskite K0.5Bi0.5TiO3

Lead-free relaxor K0.5Bi0.5TiO3 (KBT) has been selected to measure its depolarization temperature (Td) and to establish the difference between the Td and the normal ferroelectric to relaxor transition temperature (TF-R), which is still in a debatable stage for the relaxor ferroelectric system. These parameters are determined separately from the electrically poled specimen through the simple dielectric measurement instead of the pyroelectric measurement or other sophisticated techniques. Albeit, the electric field induces the normal ferroelectric behavior in the nonergodic relaxor state, the relaxor nature appears again through the heating above the freezing temperature. The difference between the frequencies of resonance and anti-resonance peaks in the real part of permittivity remains constant up tõ240 °C, and it reduces to almost zero at ∼285 °C, which has been considered as the Td of KBT. At the temperature higher than Td, an anomaly is noticed in the temperature dependent permittivity as well as in the dielectric loss graph of KBT; this temperature indicates the emergence of the relaxor nature from the normal ferroelectric (TF-R). The Td of the KBT is even higher than some of the lead-free ferroelectrics, which signifies its better suitability for the piezoelectric application. This easy method can be adopted undoubtedly to confirm the Td of the ferroelectric specimen, even for the material of higher Td (above 300 °C).

Evaluation of various emulsifying salts addition on selected properties of processed cheese sauce with the use of mechanical vibration damping and rheological methods

The scope of the study was the employment of an innovative method beneficial to evaluate the impact of various emulsifying salts (ES) addition on selected properties of processed cheese sauces (PCS). The ES applied were disodium hydrogenphosphate (DSP), tetrasodium disphosphate (TSPP), pentasodium triphosphate (PSTP), sodium salt of polyphosphate n ˜ 20 (POLY) and trisodium citrate (TSC). Moreover, the examined effect was observed in two groups of samples, (i) PCS with non-adjusted pH and in (ii) PCS with adjusted pH. The hardness of the samples was influenced by the type of the applied ES, pH, and storage period. The PCS produced with DSP:TSPP (1:1; without pH adjustment) exhibited the higher hardness which was also confirmed by the increasing samples viscosity and storage modulus. The results obtained by the mechanical vibrations damping analysis were analogous to rheological analysis. Generally, it was found that more viscous PCS exhibited “better” vibration damping properties, which was reflected by a shift of the first resonance frequency peak position to lower frequencies. In case of all investigated samples it was verified that the increasing storage period caused increasing stiffness and led to a shift of the first resonance frequency peak position to higher frequencies.

Low-loss ultrasound transmission through glass assisted by resonance

We have investigated transmission of ultrasound signals from a speaker in air through a 400 µm thick borosilicate glass plate, similar to those found in consumer electronics products such as mobile phones and tablets. In order to enhance transmission, we took advantage of resonances in the glass plate and a cavity, which is placed between the glass and the microphone. The results show that it is possible to achieve transmission of a signal with bandwidth of approximately 5 kHz with less than −10 dB attenuation, and only −2 dB attenuation at the resonance peak frequency. With more optimized assembly the attenuation can be further reduced. Finite element simulations and analytical considerations show that there are two main resonance peaks, attributed to the glass resonance and cavity resonance, respectively. The geometry can be tuned to exploit the synergy of these two resonances in order to tailor the peak frequency, the bandwidth and to optimize transmission.

Design, Modeling and Experimental Validation of a Variable Resonant Electro-Hydraulic Fatigue Testing System

High frequency excitation in the electro-hydraulic mode, especially kilohertz regime, has already been realized owing to the merits of specially designed two-dimensional rotary valve (2D rotary valve). However, some sacrifice in the excitation amplitude is inevitable as pursuing the higher excitation frequency. A scheme for an electro-hydraulic excitation system working at resonant is proposed, which could accomplish high excitation frequency and large vibration amplitude simultaneously. More specifically, the resonant frequency of this system can be regulated as loads of the excitation system, which would greatly facilitate fatigue testing of different elastomeric materials. This paper investigates more details of the excitation characteristics in whole frequency domain, including non-resonance and variable resonance. The excitation waveforms, variable resonant frequency and resonant peak are derived and validated by experimental data. This work provides clear analytical expressions of the mathematical model, offers important guidance for the design of the system, and paves the way for the potential engineering application of the variable resonant excitation technology.

Plasmon Induced Transparency in Graphene-based Side Coupled two Rectangular Nano-cavities-like structures

Abstract We investigate numerically the plasmon analogue of electromagnetic induced transparency (EIT) in a compact graphene-based waveguide coupled to two rectangular nano-cavities-like structures made out of graphene nanoribbons. The cavities are placed symmetrically on each side of the bus waveguide, giving rise to a V-like state in analogy with three level atomic systems. In this configuration, the cavities are directly coupled to the waveguide, and consequently both play the role of the bright mode. By slightly detuning the Fermi energy level of the cavities, we show the possibility of generating a narrow transparency window, that’s, the plasmon induced transparency (PIT). The resonance peak occurs as a consequence of destructive interference between the cavities acting like coupled radiative oscillators. We also demonstrate that by appropriately shifting (symmetrically) the Fermi energy levels of the cavities, one could dynamically tune the resonance peak frequency. The proposed structure may help the design of highly integrated optical devices.

Application of Passive Seismic in Determining Overburden Thickness: North West Zambia

There are several ways to estimate overburden cover thickness. One of the non-invasive and inexpensive ways to rapidly estimate the cover thickness is the Horizontal-to-Vertical Spectral Ratio (HVSR) of the ambient seismic noise method. This approach utilises a broadband three-component sensitive seismometer to record ambient noise (or microtremor) induced by the wind, ocean waves and several anthropogenic activities. These microtremors are mainly composed of Rayleigh Waves which propagate in the surface layer. The Tromino® seismometer, which works on the HVSR principle, is a very light and portable instrument that records seismic noise in the frequency range of 0.1 to 1024 Hz, and is capable of estimating overburden cover up to 100’s of metres depth, depending on the ambient noise strength and geological setting of the survey area. The ratio of the horizontal-to-vertical (H/V) component of the shear wave (Vs) spectrum is used to calculate the peak resonance frequency at a particular survey station, which is used to estimate the overburden thickness by using one or more existing drill holes in the area, 1D modelling, or local geological knowledge about the overburden to get velocity information for calculating depth. This paper discusses different methods used to calculate the overburden thickness, which includes calculations using a hybrid approach and a regression equation. This paper shows the results of a Tromino® HVSR survey in North West Zambia and comparison of estimated overburden thickness using different methods. The results were further compared with those determined from Audio-MagnetoTellurics (AMT) and drilling data. Tromino® successfully estimated the overburden thickness and mapped the bedrock topography with reasonable accuracy.

Measurement of Unit Weight of Dry Sand Using Piezoelectric Sensor

Recently, an electro-mechanical impedance (EMI) technique has found wide application in the monitoring of concrete structures. This EMI technique was employed for measuring the unit weights of various grain sizes of sand and the relevant process is reported herein. A piezoelectric sensor (PZT, i.e., lead zirconate titanate sensor) was imbedded into small, medium, and large-sized grains of the Nakdong river sand and a surcharge was applied. The effect of an increase in unit weight owing to the surcharge was investigated in terms of the resonant frequency (peak frequency) and corresponding conductance at resonant frequency (peak conductance). A ceramic-coated PZT sensor was used to prevent the occurrence of a short circuit. The measured peak frequency and conductance from the PZT sensor were correlated with the unit weight of sand. With an increase in the unit weight of sand, the peak PZT frequency was found to have increased, however, the peak conductance was seen to have decreased. The peak PZT frequency and conductance were seen to be strongly correlated with the unit weight of Nakdong river sand except for the peak conductance of large grain sized sand.

Experimental and simulated verification of a frequency and amplitude tunable metamaterial absorber

In this paper, a dual band absorption characteristic of metamaterial absorber with three dielectric layers (SU-8 layer, VO2 layer, Al2O3 layer) is proposed and experimental confirmed in terahertz region. These absorption peaks are originated from cavity resonance and electrical resonance, respectively. Impedance matching phenomenon between the proposed metamaterial absorber and free space is achieved at resonance frequencies of absorption peaks. In order to reveal the effect of geometrical parameters on absorption peaks, two groups of experiments are carried out. It is found that the cavity and electrical resonance absorption peaks show a shifted to higher frequency with the radius of holes array increasing. However, for the increase in the VO2 layer thickness, the cavity and electrical resonance absorption peaks show a shifted to lower frequency. Absorption property is improved through optimizing structural parameters at room temperature condition. Moreover, measured results demonstrate that the cavity and electrical resonance absorption peaks show a shifted to higher frequency with the temperature increasing. Absorption intensities are tuned from 81% (25 °C) to 51% (97 °C) and 83% (25 °C) to 52% (97 °C), respectively. A new low-frequency absorption peak is achieved because that a new electrical resonance mode is effectively excited between the VO2 layer and bottom metal layer. The proposed metamaterial absorber with tunable property shows the applications possibility in sensing and detecting based on external stimulus (such as heat, or light) leading to the absorption spectrum change.

Numerical simulation of electron energy loss spectroscopy accounting for nonlocal effect in plasmonic nanoparticles

Interaction between an electron in straight uniform motion and a nearby plasmonic nanoparticle deposited in homogeneous medium is examined numerically in norecoil approximation. To account for the nonlocal effect occurring in the plasmonic medium Generalized Nonlocal Optical Response scattering problem statement is considered. Discrete Source Method is employed to construct the solution. Electron energy loss probability is computed as a function of incident field frequency and obtained surface plasmon resonance energy is compared to local response simulations. It is shown that surface plasmon resonance peak frequency blueshift can be resolved within the proposed approach.

Plasmon Excitation in BC3 Nanostructures from First Principles

The plasmonic of BC3 nanostructure was investigated employing time-dependent density functional theory (TDDFT). What is striking is that BC3 nanostructure possesses preferable absorbance in the visible region. By changing the size of the nanostructure, the resonance peak position of the absorption spectrum can be effectively regulated. Moreover, when excitation direction along the armchair-edge direction, the absorption spectra are clearly stronger in the low-energy zone respect to the impulse excitation polarizes in the zigzag-edge direction. In addition, with the change of layer spacing and number of layers, the resonance frequency and resonance absorption peak intensity of plasmonic can be effectively controlled. The remarkable optical properties of BC3 nanostructure suggest potential application of the system in solar cells and photolysis water devices.

Differentiating among conductive hearing loss conditions with wideband tympanometry

ObjectiveThis study was aimed to investigate whether wideband tympanometry (WBT) can distinguish among various kinds of conductive hearing loss and provide additional information. MethodsWe recruited normal subjects and patients with conductive hearing loss due to the following reasons: tympanic membrane perforation only, ossicular chain problem only, and one or other of those conditions combined with mastoid problems. Wideband absorbance at ambient pressure, peak pressure, resonance frequency, and averaged tympanogram data were measured by WBT and compared between the normal, tympanic membrane perforation only, ossicular chain problem only, and combined with mastoid problems groups. ResultsThe normal subjects showed an average peak pressure of −19.51daPa and an average resonance frequency of 965.94Hz. Tympanic membrane perforation only patients showed a very low peak pressure (−124.93daPa) and resonance frequency (73.12Hz). When patients have ossicular chain problems, they showed slightly low peak pressures (43.08daPa) without changes in the resonance frequency (1024.8Hz). Mastoid problem subjects showed slightly decreased resonance frequencies (787.71Hz). Tympanic membrane perforation subjects showed decreased absorbance at low frequencies and ossicular chain problem subjects showed decreases at high frequencies. When comparing the perforation only and ossicular chain subjects by absorbance at 707Hz, the area under the ROC curve was 0.719 (P<0.022). Mastoid problems subjects showed decreased absorbance at all frequencies. ConclusionWBT can help to distinguish tympanic membrane perforation only and ossicular chain problem patients. WBT may provide additional information on “combined with mastoid problems” patients.

Simultaneous Measurement of Thickness and Permittivity by Means of the Resonant Frequency Fitting of a Microstrip Line Ring Resonator

A simultaneous measurement method of the thickness and permittivity of a thin and uniform material which is attached onto the top of a sensor structure is presented. The sensor utilizes the fundamental and harmonic frequencies of a microstrip line ring resonator structure. The thickness and permittivity of a material under test are calculated from two simultaneous equations at the fundamental and second-harmonic frequencies. Fitting equations to calculate the peak resonant frequencies with respect to the thickness and permittivity are also derived. The structure is implemented with a microstrip line on the front side of a TLY-5A substrate and coplanar waveguide access lines on the backside. The permittivity and thickness of the test material are successfully measured simultaneously.

Shape Anisotropy and Resonance Mode Guided Reliable Interconnect Design for In-plane Magnetic Logic**Supported by the National Natural Science Foundation of China under Grant No 61302022.

Dipole coupled nanomagnets controlled by the static Zeeman field can form various magnetic logic interconnects. However, the corner wire interconnect is often unreliable and error-prone at room temperature. In this study, we address this problem by making it into a reliable type with trapezoid-shaped nanomagnets, the shape anisotropy of which helps to offer the robustness. The building method of the proposed corner wire interconnect is discussed, and both its static and dynamic magnetization properties are investigated. Static micromagnetic simulation demonstrates that it can work correctly and reliably. Dynamic response results are reached by imposing an ac microwave field on the proposed corner wire. It is found that strong ferromagnetic resonance absorption appears at a low frequency. With the help of a very small ac field with the peak resonance frequency, the required static Zeeman field to switch the corner wire is significantly decreased by ∼21 mT. This novel interconnect would pave the way for the realization of reliable and low power nanomagnetic logic circuits.

Modifications of Middle Atmosphere Conductivity During Sudden Ionospheric Disturbances Deduced From Changes of Schumann Resonance Peak Frequencies

AbstractThis paper presents a novel technique to reveal modifications of the Schumann resonance peak frequencies during sudden ionospheric disturbances (SIDs) caused by the solar X‐ray flares. An SID is associated with the abrupt reduction in ionospheric height over the day hemisphere during solar flares. Reduction of the daytime ionosphere lowers the average height of the Earth‐ionosphere cavity and leads to an increase in its resonant frequencies. An improved profile is used describing the middle atmosphere conductivity and its modification. The resonance frequencies of the Earth‐ionosphere cavity and the characteristic heights of the conductivity profile are computed by the full wave technique for various intensities of ionosphere modifications. Power spectra of the vertical electric field component are calculated using the 2‐dimensional telegraph equations for the uniform spatial distribution of global thunderstorms in the cavity with the day‐night nonuniformity for several observer positions relative to the solar terminator. Changes in the peak frequencies are obtained as a function of magnitude of ionosphere modifications. The weighted average frequency of Schumann resonance is calculated over the first three modes, and the linear fitting is performed for the dependence of this weighted average frequency on the SID intensity and/or on changes in the magnetic characteristic height of the conductivity profile. The data obtained might be used in further interpretations of observational data and in estimating the lower ionosphere modification by using Schumann resonance records.

Side Effects of Damping Element Insertion in LCL Filter for DC/AC Inverter

The negative impacts or side effects of a damper circuit insertion in an LCL passive filter utilized to filter DC/AC inverters output voltage is presented in this paper. For comparative study, this paper discusses two damping configurations, namely series and parallel damping, as well as the LCL filter without damping element. Four criteria are used to explore the impacts of the damper circuits, i.e. their total harmonic distortions (THDs), the output voltage amplitude, the output power and the power efficiency. Theoretically and emphirically shown by previous studies, the damper can indeed reduce the peak resonance frequency of the filter in its frequency response curve. However, in any circumstance, it can potentially reduce the inverters power and efficiency, voltage output amplitude, and cannot improve its THD reduction. The analysis results have shown that the side effects depends also on the load conditions, which are different for each damping circuit configuration.

Aerodynamic noise radiating from the inter-coach windshield region of a high-speed train

The aerodynamic noise has been the dominant factor of noise issues in high-speed train as the traveling speed increases. The inter-coach windshield region is considered as one of the main aerodynamic noise sources; however, the corresponding characteristics have not been well investigated. In this paper, a hybrid method is adopted to study the aerodynamic noise around the windshield region. The effectiveness of simulation methods is validated by a simple case of cavity noise. After that, the Reynolds-averaged Navier–Stokes simulation is used to obtain the characteristics of flow field around the windshield region, which determine the aerodynamic noise. Then the nonlinear acoustic solver approach is employed to acquire the near-field noise, while the Ffowcs-Williams/Hawking equation is solved for far-field acoustic propagation. The results indicate that the windshield region is approximately an open cavity filled with severe disturbance flow. According to the analysis of sound pressure distribution in the near-acoustic field, both sides of the windshield region appear symmetrical two-lobe shape with different directivities. The results of frequency spectrum analysis indicate that the aerodynamic noise inside inter-coach space is a typical broadband one from 100 Hz to 5k Hz, and most acoustic power is restricted in the low-medium frequency range (below 500 Hz). In addition, the acoustic power in the low frequency range (below 100 Hz) is closely related to the cavity resonance with the resonance peak frequency of 42 Hz. The overall sound pressure level at different speeds shows that the acoustic power grows approximately 5th power of the train speed. Two forms of outside-windshields are designed to reduce the noise around the windshield region, and the results show the full-windshield form is better in noise reduction, which apparently eliminates interior cavity noise of inter-coach space and lessens the overall sound pressure level on the sides of near-field by about 13 dB.

Vibration modes and sound characteristic analysis for different sizes of singing bowls

The singing bowl is used not only for the instrument of Buddhism but also for musical therapy. This work aims to investigate the correlation of vibration modes and percussion sound for singing bowls. A typical singing bowl is first selected to perform finite element analysis (FEA) for theoretical modal analysis (TMA) as well as experimental modal analysis (EMA). Modal parameters of singing bowl, including natural frequencies and mode shapes, can be obtained from analysis and experiment, respectively. Singing bowl FE model can then be updated and verified by adjusting material properties and used to predict structural vibration modes. The percussion sound of singing bowl is also measured to obtain its sound spectrum. The peak frequency response of singing bowl sound can be interpreted and contributed from circular vibration modes of the bowl. With the knowledge of sound generation mechanism for the singing bowl, this work also studies the percussion sound characteristics of seven different sizes of singing bowls. Results show the fundamental frequency and overtone frequencies of singing bowl percussion sound are higher for the smaller size. Interestingly, that the peak resonant frequencies have near the integer ratio relationship makes the singing bowl revealing harmony sound effects. The radiated sound spectrum can be well calibrated and predicted for different sizes of singing bowls. This work shows the analytical and experimental approaches in studying the singing bowl percussion sound that strongly correlated to structural vibration modes and can be adopted for future development of singing bowls.