Vertical propagation of low-frequency waves in finely layered media

Geophysics ◽  
2006 ◽  
Vol 71 (3) ◽  
pp. T87-T94 ◽  
Author(s):  
Alexey Stovas ◽  
Børge Arntsen
Keyword(s):  
Reflection Coefficient ◽  
Low Frequency ◽  
Effective Medium ◽  
Frequency Limit ◽  
Data Matching ◽  
Anisotropy Effect ◽  
Vertical Propagation ◽  
The Matrix ◽  
Backus Averaging ◽  
Time Average

Multiple scattering in finely layered sediments is important for interpreting stratigraphic data, matching well-log data with seismic data, and seismic modeling. Two methods have been used to treat this problem in seismic applications: the O’Doherty-Anstey approximation and Backus averaging. The O’Doherty-Anstey approximation describes the stratigraphic-filtering effects, while Backus averaging defines the elastic properties for an effective medium from the stack of the layers. It is very important to know when the layered medium can be considered as an effective medium. In this paper, we only investigate vertical propagation. Therefore, no anisotropy effect is taken into consideration. Using the matrix-propagator method, we derive equations for transmission and reflection responses from the stack of horizontal layers. From the transmission response, we compute the phase velocity and compare the zero-frequency limit with the effective-medium velocity from Backus averaging. We also investigate how the transition from time-average medium to effective medium depends on contrast; i.e., strength of the reflection-coefficient series. Using numerical examples, we show that a transition zone exists between the effective medium (low-frequency limit) and the time-average medium (high-frequency limit), and that the width of this zone depends on the strength of the reflection-coefficient series.

Comparison of seismic anisotropy of sedimentary strata at low- and high-frequency limits

Geophysics ◽  
2019 ◽  
Vol 85 (1) ◽  
pp. MR1-MR10 ◽  
Author(s):  
Fuyong Yan ◽  
De-Hua Han ◽  
Tongcheng Han ◽  
Xue-Lian Chen
Keyword(s):  
High Frequency ◽  
Seismic Anisotropy ◽  
Sedimentary Rocks ◽  
Low Frequency ◽  
Layered Media ◽  
Ray Theory ◽  
Frequency Limit ◽  
Anisotropic Properties ◽  
Velocity Anisotropy ◽  
Backus Averaging

The layer-induced seismic anisotropy of sedimentary strata is frequency-dependent. At the low-frequency limit, the effective anisotropic properties of the layered media can be estimated by the Backus averaging model. At the high-frequency limit, the apparent anisotropic properties of the layered media can be estimated by ray theory. First, we build a database of laboratory ultrasonic measurement on sedimentary rocks from the literature. The database includes ultrasonic velocity measurements on sandstones and carbonate rocks, and velocity-anisotropy measurements on shales. Then, we simulate the sedimentary strata by randomly selecting a certain number of rock samples and using their laboratory measurement results to parameterize each layer. For each realization of the sedimentary strata, we estimate the effective and apparent seismic anisotropy parameters using the Backus average and ray theory, respectively. We find that, relative to Backus averaging, ray theory usually underestimates the Thomsen parameters [Formula: see text] and [Formula: see text], and overestimates [Formula: see text]. For an effective layered medium consisting of isotropic sedimentary rocks, the differences are significant. These differences decrease when shales with intrinsic seismic anisotropy are included. For the same sedimentary strata, the seismic wave should perceive stronger seismic anisotropy than the ultrasonic wave.

Evaluation of Special Hearing Aids for Deaf Children

1971 ◽  
Vol 36 (4) ◽  
pp. 527-537 ◽  
Author(s):  
Norman P. Erber
Keyword(s):  
Hearing Aids ◽  
High Frequency ◽  
Hearing Aid ◽  
Low Frequency ◽  
Acoustic Stimulation ◽  
Deaf Children ◽  
Frequency Range ◽  
Frequency Limit ◽  
Unpublished Studies ◽  
Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

scholarly journals Tunable characteristics of low-frequency bandgaps in two-dimensional multivibrator phononic crystal plates under prestrain

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hai-Fei Zhu ◽  
Xiao-Wei Sun ◽  
Ting Song ◽  
Xiao-Dong Wen ◽  
Xi-Xuan Liu ◽  
...  
Keyword(s):  
Phononic Crystal ◽  
Real Life ◽  
Low Frequency ◽  
Acoustic Vibration ◽  
Crystal Plate ◽  
Frequency Noise ◽  
Two Dimensional ◽  
The Matrix ◽  
Noise Frequency ◽  
Realtime Control

AbstractIn view of the influence of variability of low-frequency noise frequency on noise prevention in real life, we present a novel two-dimensional tunable phononic crystal plate which is consisted of lead columns deposited in a silicone rubber plate with periodic holes and calculate its bandgap characteristics by finite element method. The low-frequency bandgap mechanism of the designed model is discussed simultaneously. Accordingly, the influence of geometric parameters of the phononic crystal plate on the bandgap characteristics is analyzed and the bandgap adjustability under prestretch strain is further studied. Results show that the new designed phononic crystal plate has lower bandgap starting frequency and wider bandwidth than the traditional single-sided structure, which is due to the coupling between the resonance mode of the scatterer and the long traveling wave in the matrix with the introduction of periodic holes. Applying prestretch strain to the matrix can realize active realtime control of low-frequency bandgap under slight deformation and broaden the low-frequency bandgap, which can be explained as the multiple bands tend to be flattened due to the localization degree of unit cell vibration increases with the rise of prestrain. The presented structure improves the realtime adjustability of sound isolation and vibration reduction frequency for phononic crystal in complex acoustic vibration environments.

scholarly journals Low-Frequency Expansion Approach for Seismic Data Based on Compressed Sensing in Low SNR

2021 ◽  
Vol 11 (11) ◽  
pp. 5028
Author(s):  
Miaomiao Sun ◽  
Zhenchun Li ◽  
Yanli Liu ◽  
Jiao Wang ◽  
Yufei Su
Keyword(s):  
Reflection Coefficient ◽  
Compressed Sensing ◽  
Objective Function ◽  
Low Frequency ◽  
Original Data ◽  
Seismic Exploration ◽  
High Signal ◽  
Inversion Process ◽  
Frequency Information ◽  
Low Snr

Low-frequency information can reflect the basic trend of a formation, enhance the accuracy of velocity analysis and improve the imaging accuracy of deep structures in seismic exploration. However, the low-frequency information obtained by the conventional seismic acquisition method is seriously polluted by noise, which will be further lost in processing. Compressed sensing (CS) theory is used to exploit the sparsity of the reflection coefficient in the frequency domain to expand the low-frequency components reasonably, thus improving the data quality. However, the conventional CS method is greatly affected by noise, and the effective expansion of low-frequency information can only be realized in the case of a high signal-to-noise ratio (SNR). In this paper, well information is introduced into the objective function to constrain the inversion process of the estimated reflection coefficient, and then, the low-frequency component of the original data is expanded by extracting the low-frequency information of the reflection coefficient. It has been proved by model tests and actual data processing results that the objective function of estimating the reflection coefficient constrained by well logging data based on CS theory can improve the anti-noise interference ability of the inversion process and expand the low-frequency information well in the case of a low SNR.

Onset of size effects in lattice thermal conductivity and lifetime of low-frequency thermal phonons

2012 ◽  
Vol 1404 ◽  
Author(s):  
A.A. Maznev
Keyword(s):  
Thin Film ◽  
Thermal Conductivity ◽  
Size Effects ◽  
Lattice Thermal Conductivity ◽  
Low Frequency ◽  
Square Root ◽  
Relaxation Rates ◽  
Frequency Limit ◽  
Conductivity Of Thin Films ◽  
Closed Form Formula

ABSTRACTThe onset of size effects in phonon-mediated thermal transport along a thin film at temperatures comparable or greater than the Debye temperature is analyzed theoretically. Assuming a quadratic frequency dependence of phonon relaxation rates in the low-frequency limit, a simple closed-form formula for the reduction of the in-plane thermal conductivity of thin films is derived. The effect scales as the square root of the film thickness, which leads to the prediction of measurable size-effects even at “macroscopic” distances ~100 μm. However, this prediction needs to be corrected to account for the deviation from the ω−2 dependence of phonon lifetimes at sub-THz frequencies due to the transition from Landau-Rumer to Akhiezer mechanism of phonon dissipation.

scholarly journals Nonlinear interaction between acoustic gravity waves

1996 ◽  
Vol 14 (3) ◽  
pp. 304-308 ◽  
Author(s):  
P. Axelsson ◽  
J. Larsson ◽  
L. Stenflo
Keyword(s):  
Gravity Waves ◽  
Nonlinear Interaction ◽  
Low Frequency ◽  
Resonant Interaction ◽  
Coupling Coefficients ◽  
Symmetric Form ◽  
Frequency Limit ◽  
Acoustic Gravity Waves

Abstract. The resonant interaction between three acoustic gravity waves is considered. We improve on the results of previous authors and write the new coupling coefficients in a symmetric form. Particular attention is paid to the low-frequency limit.

scholarly journals PORT RESONANCE MITIGATION MODELED INTRODUCING ARJ-R STRUCTURES

2020 ◽  
pp. 38
Author(s):  
Jose A. GONZALEZ-ESCRIVA ◽  
Josep R. MEDINA ◽  
Joaquin M. GARRIDO
Keyword(s):  
Reflection Coefficient ◽  
Physical Model ◽  
Large Scale ◽  
Low Frequency ◽  
Model Tests ◽  
Wave Interference ◽  
Low Frequency Oscillations ◽  
Physical Model Tests ◽  
Similar Cost ◽  
Interference Mechanism

ARJ-R caissons are based on the "long-circuit" concept (Medina et al, 2016) that allows the extension of the destructive wave interference mechanism to mitigate low frequency oscillations without enlarging the width of the caisson. The performance of the ARJ-R caissons is referred to its reflection coefficient (Cr) which was obtained through large-scale physical model tests (Gonzalez-Escriva et al, 2018). In this paper, the effectiveness of Anti-Reflective Jarlan-type structures for Port Resonance mitigation (ARJ-R) has been assessed numerically for the port of Denia (Spain). ARJ-R structures are constructible, with similar dimensions as conventional vertical quay caissons and with a similar cost (15percent more than conventional vertical caisson).Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/LomQEVpvjik

scholarly journals Терагерцовая спектроскопия магнитоэлектрика HoAl-=SUB=-3-=/SUB=-(BO-=SUB=-3-=/SUB=-)-=SUB=-4-=/SUB=-

2022 ◽  
Vol 130 (1) ◽  
pp. 59
Author(s):  
А.М. Кузьменко ◽  
В.Ю. Иванов ◽  
А.Ю. Тихановский ◽  
А.Г. Пименов ◽  
А.М. Шуваев ◽  
...  
Keyword(s):  
Crystal Field ◽  
Excited States ◽  
Ground State ◽  
Theoretical Study ◽  
Low Frequency ◽  
Local Symmetry ◽  
Matrix Elements ◽  
The Matrix ◽  
Excitation Conditions ◽  
Ground Multiplet

Experimental and theoretical study of submillimeter (terahertz) spectroscopic and magnetic properties of the rare-earth aluminum borate HoAl3(BO3)4 were performed at temperatures 3–300 K. In the transmittance spectra a number of resonance lines were detected at frequencies 2–35 cm–1 for different radiation polarizations. These modes were identified as transitions between the lower levels of the ground multiplet of the Ho3+ ion split by the crystal field, including both transitions from the ground state to the excited ones and transitions between the excited states. The established excitation conditions of the observed modes and the simulation of the spectra made it possible to separate the magnetic and electric dipole transitions and to determine the energies of the corresponding states, their symmetry, and the matrix elements of the transitions. Low-frequency lines that do not fit into the established picture of the electron states of Ho3+ were also found; these lines, apparently, correspond to the ions with the distorted by defects local symmetry of the crystal field.

SYNTHESIS OF ALLOY METAL NANOCLUSTERS IN SILICA GLASS BY SEQUENTIAL ION IMPLANTATION

2007 ◽  
Vol 06 (06) ◽  
pp. 423-430 ◽  
Author(s):  
B. JOSEPH ◽  
H. P. LENKA ◽  
P. K. KUIRI ◽  
D. P. MAHAPATRA ◽  
R. KESAVAMOORTHY
Keyword(s):  
Ion Implantation ◽  
Silica Glass ◽  
Metallic Nanoparticles ◽  
Rutherford Backscattering Spectrometry ◽  
Low Frequency ◽  
Peak Position ◽  
Negative Ion ◽  
Metal Nanoclusters ◽  
Cross Sectional ◽  
The Matrix

High fluence low energy negative ion implantation has been used to synthesize embedded metal nanoclusters of Au , Ag and Sb in silica glass. The Au - and Ag -implanted samples showed peaks, corresponding to surface plasmon resonance (SPR) in the optical absorption (OA) spectra, confirming the formation of metallic nanoparticles in the matrix. No SPR peak was observed in case of Sb -implanted samples which is attributed to the absence of pure metallic precipitates which could be detected in the OA spectrum. Low frequency Raman scattering (LFRS) measurements also confirm this. Cross-sectional transmission electron microscopy has been used to infer about the size distribution of the nanoparticles. Sequential implantations of Au and Ag or Au and Sb have been found to result in SPR peaks at locations in between those for nanoparticles of the constituent atoms, indicating the formation of alloy nanoparticles in the system. In case of the Au + Ag system, Rutherford backscattering spectrometry has been used to infer about the composition of the nanoparticles in terms of the concentrations of the metallic constituents. A direct, one-to-one correspondence between the SPR peak position and composition has been observed.

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