Ultralow Frequency Region Research Articles

Development of a new base isolation system using the concept of metamaterials

Metamaterials are making a breakthrough in seismic wave manipulation with their ability to yield wave filtration properties that cannot be realized inherently through conventional construction materials. The popularly used seismic vibrational control techniques, such as base isolation, fall short at low-frequency regions of the spectrum and fail to encompass both flexible and rigid structures. Using the concept of metamaterials, the phenomena of local resonance and Bragg scattering can create a stop band region of frequencies that undergo vibrational wave filtration. This study proposes a two-dimensional periodic foundation system with steel-silicone embedded assemblies to serve as local resonators. The proposed foundation can cover a wide and ultra-low frequency region in its band gap, enveloping the principal frequencies of seismic waves (i.e., 0.2 Hz to 10 Hz). This two-dimensional periodic foundation can also exhibit a Bragg region without local resonators but is made more efficient with the help of steel-silicone resonators (SSR). Upon experimental testing, the scaled-down prototype of the proposed foundation with three locally resonant panels embedded with SSR showed an average of 50 % attenuation of displacement within the frequency band gap (i.e., 2.54 Hz to 8.08 Hz). Moreover, the experimentation showed a 73 % attenuation at the resonant frequency of SSR. Experimental testing affirmed the frequency band gap obtained through mathematical formulation. Furthermore, the theoretical results demonstrate that the full-scale proposed periodic foundation would be able to achieve a band gap that covers frequencies from as low as 0.3 Hz to 7.35 Hz. This study is the first attempt to set the baseline for periodic foundations capable of fully mitigating the entire spectrum of seismic vibrational effects on structures.

Exploring nonlinear degradation benefit of bio-inspired oscillator for engineering applications

Nonlinear structure design is an indispensable link in the development of vibration isolation, energy harvesting and fault diagnosis technologies. It is also one of the most effective technical means to improve the performance of structures in engineering applications. In this study, a bio-inspired nonlinear oscillator is proposed and the benefits of nonlinear degradation in engineering applications are explored. First, the degradation bistable oscillator and high-order quasi-zero stiffness oscillator can be obtained after the degradation of the bio-inspired nonlinear oscillator. Through the amplitude-frequency analysis, it is found that the nonlinear degradation can reduce the unstable solution in the ultra-low frequency region and reduce the resonant frequency of the bio-inspired nonlinear oscillator. Therefore, the degeneration nonlinear oscillator can realize the large-amplitude inter-well motion at ultra-low frequency or low random excitation intensity. Secondly, the theory and method of vibration isolation and energy harvesting based on the nonlinear degradation mechanism are proposed, and the vibration isolation and energy harvesting performance of the oscillator under harmonic and stochastic excitations are analyzed. Finally, the use of the stochastic resonance of the degeneration bistable oscillator can greatly improve the signal-to-noise ratio, enhance the weak fault signal, and realize early fault diagnosis. The related results help to deepen the understanding of nonlinear degenerate systems and provide new technical approaches for engineering applications.

A dual quasi-zero-stiffness sliding-mode triboelectric nanogenerator for harvesting ultralow-low frequency vibration energy

A major purpose of energy harvesting from ambient vibration is to power sensors for structural health monitoring and environment monitoring. However, most types of ambient vibration are in the low-frequency region, which would make conventional energy harvesters inefficient. In this paper, the first attempt to combine a quasi-zero-stiffness (QZS) mechanism and a triboelectric nanogenerator is made, and a QZS triboelectric nanogenerator (QZS-TENG) is devised. In this QZS system, a negative stiffness mechanism (NSM) is constructed by using QZS springs to achieve ultra-low stiffness in a much larger displacement region than that of a traditional QZS device. Based on the geometrical relationship, the exact expression of the restoring force of the QZS-TENG is derived firstly, and then is fitted as a polynomial to obtain its approximate analytical dynamic responses. The electrical properties of the QZS-TENG, including its open circuit voltage, short circuit current, output voltage, output current and output power, are presented in both analytical and numerical results. The numerical results show excellent agreement with the analytical ones, and most importantly, the QZS-TENG exhibits an excellent energy harvesting performance in the ultralow frequency region. This work provides a new application of a QZS mechanism to harvest the ultralow-frequency vibration energy by combining a TENG.

In-Situ Ultra-Low Frequency SERS Observation at Electrified Interfaces

Surface-selective spectroscopy is a powerful tool to study various interfacial phenomena such as electrochemical reactions at electrode/electrolyte interfaces. However, structural information on the solid and liquid phases next to the interface have been separately observed using different spectroscopic methods: e.g., X-ray spectroscopy for solid phases and vibrational spectroscopy for liquid phases. Recently, we have extended the detectable frequency range of surface enhanced Raman scattering (SERS) into the ultra-low frequency region down to 10 cm-1, which corresponds to THz region [1]. This enables us to observe not only molecular vibrations but also extramolecular vibrations and surface phonons of the metal lattice [2]. These information should provide deeper insight into catalytic and electrocatalytic reaction mechanisms. In this talk, we will demonstrate in-situ and simultaneous detection of vibrational information on both solid-electrode and liquid-electrolyte phases at the interface. [1] M. Inagaki, K. Motobayashi, K. Ikeda, “Electrochemical THz-SERS Observation of Thiol Monolayers on Au(111) and (100) Using Nanoparticle-assisted Gap-Mode Plasmon Excitation” J. Phys. Chem. Lett., 8, 2017, pp. 4236-4240. [2] M. Inagaki, K. Motobayashi, K. Ikeda, submitted.

Physical origin of Davydov splitting and resonant Raman spectroscopy of Davydov components in multilayerMoTe2

We systematically study the high-resolution and polarized Raman spectra of multilayer (ML) MoTe2. The layer-breathing (LB) and shear (C) modes are observed in the ultralow-frequency region, which are used to quantitatively evaluate the interlayer coupling in ML MoTe2 based on the linear chain model, in which only the nearest interlayer coupling is considered. The Raman spectra on three different substrates verify the negligible substrate effect on the phonon frequencies of ML MoTe2. Ten excitation energies are used to measure the high-frequency modes of N-layer MoTe2 (NL MoTe2; N is an integer). Under the resonant excitation condition, we observe N-dependent Davydov components in ML MoTe2 , originating from the Raman-active A'1(A21g) modes at ~172 cm-1. More than two Davydov components are observed in NL MoTe2 for N larger than 4 by Raman spectroscopy. The N-dependent Davydov components are further investigated based on the symmetry analysis. A van der Waals model only considering the nearest interlayer coupling has been proposed to well understand the Davydov splitting of high-frequency A'1(A21g) modes. The different resonant profiles for the two Davydov components in 3L MoTe2 indicate that proper excitation energy of ~1.8-2.2 eV must be chosen to observe the Davydov splitting in ML MoTe2 . Our work presents a simple way to identify layer number of ultrathin MoTe2 flakes by the corresponding number and peak position of Davydov components. Our work also provides a direct evidence from Raman spectroscopy of how the nearest van der Waals interactions significantly affect the frequency of the high-frequency intralayer phonon modes in multilayer MoTe2 and expands the understanding on the lattice vibrations and interlayer coupling of transition metal dichalcogenides and other two-dimensional materials.

Time domain dielectric relaxation study on charging and discharging current of barium stannate titanate ferroelectric ceramics

Time domain measurement is an indispensable experimental method for ultralow frequency region (even lower than 1 Hz) and nonlinearity study of ferroelectric materials. The charging and discharging currents of BaTi1-xSnxO3 (BTS) ceramics have been collected in both paraelectric and ferroelectric phases. Kohlrausch-Williams- Watts (KWW) relation with two parameters (β and τ) was employed in discharging current analysis. Our results show that the higher β values in paraelectric phase indicate near Debye relaxation behavior, and lower βvalues in ferroelectric phase tie with possible diffusion controlled universal relaxation law (URL).

1H nuclear magnetic resonance study of hydrated water dynamics in perfluorosulfonic acid ionomer Nafion

We have studied the dynamics of hydrated water molecules in the proton exchange membrane of Nafion by means of high-resolution 1H nuclear magnetic resonance (NMR) measurements. “Bound” and “free” states of hydrated water clusters as well as the exchange protons were identified from the NMR chemical shift measurements, and their activation energies were obtained from the temperature-dependent laboratory- and rotating-frame spin-lattice relaxation measurements. Besides, a peculiar motional transition in the ultralow frequency region was observed at 373 K for the “free” hydrated water from the rotating-frame NMR spin-lattice relaxation time measurements.

OS1004 水素環境での極低周波数域におけるS10Cの疲労き裂進展挙動

OS1004 水素環境での極低周波数域におけるS10Cの疲労き裂進展挙動

超低周波数領域における多孔板構造吸音特性予測技術の研究(Part2,ワークショップ「低周波音に関する最新技術」,振動・騒音改善技術)

Sound absorbing characteristics for perforated panel at ultra low frequency were studied. Principle of sound absorption of perforated panel has two mechanisms. One is friction loss in a flow of cylindrical tube, which is proportional to particle velocity in a hole. The other is pressure loss as orifice, which is proportional to square of particle velocity in a hole. Therefore sound absorbing characteristics are depend on sound particle velocity and sound pressure level. We applied calculation method to predict the sound absorbing characteristics of perforated panel in ultra low frequency region by using transfer matrix method and measured those at ultra low frequency using two-microphone method. Calculated values are in good agreement with measured values.

Dynamic heat capacity at the gel to liquid-crystalline phase transition in large unilamellar vesicles of dimyristoylphosphatidylcholine in the ultralow frequency region.

Dynamic heat capacity at the gel to liquid-crystalline phase transition in large unilamellar vesicles of dimyristoylphosphatidylcholine in the ultralow frequency region.

Effect of filler concentration on electrical conductivity and ultralow-frequency dielectric properties

The effect of filler concentration on the dielectric properties in the ultralow-frequency region and on the electrical conductivity was studied for ethylene propylene rubber. First, we investigated the relation between the electrical conductivity and filler concentration: as the volume fraction of fillers q/sub a/ increased, the conductivity decreased in the low filler concentration region but increased abruptly in the high filler concentration region. The decrease and increase in conductivity can be explained with the action of carrier traps at the interface between EPR and fillers and with the formation of highly conductive paths of filler across the sample, respectively. Secondly, we studied the dielectric properties in the ultralow-frequency region which was obtained from the discharge current. As q/sub a/ increased, the relaxation time decreased in the low filler concentration region and then rose in the high filler concentration region. The polarization in the high filler concentration region can be explained by two-layer interfacial polarization between filler and rubber. >

Dielectric permittivity measurements in the ultralow frequency region

A new dc transient method is described for fast measurements of dielectric permittivity in the μHz frequency region. A square-wave voltage pulse is applied to the dielectric instead of the usual step voltage pulse. The whole transient current is measured two times faster than in the conventional method using the step voltage.

Dielectric relaxation measurements in the ultralow frequency region

Refinements in the dc transient current method are described for precision measurements of dielectric permittivity from 50 mHz down to 1 μHz. Relaxation increment, relaxation time, and distribution of the relaxation times for a test sample of poly(vinyl acetate) have been measured with satisfactory accuracy as judged by comparison with results from steady-state measurements. Convenient procedures for numerical Fourier transformation of the observed current are described to easily obtain the complex permittivity.

A new method of measuring the viscoelastic properties of polymer systems in fluid and highly elastic states using forced vibrations in the ultralow-frequency region

A method is considered for measuring the dynamic mechanical characteristics of polyer systems using forced vibrations in the ultralow-frequency region down to 10−6 Hz. The essence of this method lies in the fact that during the measurement process the motion of the polymer sample is controlled with a set amplitude and frequency, and the dynamic characteristics of the polymer are determined from the controlling mechanical stress. The method is illustrated using the results of measurements of the components of the complex modulus for polybutadiene over a wide range of temperatures and frequencies without making use of superimposition.