Acoustical performance of layered beams in the lower frequency range

2017 ◽  
Author(s):  
Bohdan Diveyev ◽  
Solomiya Konyk ◽  
Mykhaylo Melnyk ◽  
Christina Vysocka
Keyword(s):  
Frequency Range ◽  
Layered Beams ◽  
Lower Frequency Range

Bandgap Properties of Two-Layered Locally Resonant Phononic Crystals

2020 ◽  
Vol 12 (07) ◽  
pp. 2050075
Author(s):  
Hongyun Wang ◽  
Heow Pueh Lee ◽  
Wei Xu
Keyword(s):  
Coating Thickness ◽  
Low Frequency ◽  
Phononic Crystals ◽  
Formation Mechanisms ◽  
Frequency Range ◽  
The Third ◽  
Resonance Frequencies ◽  
Rubber Coating ◽  
Lower Frequency Range ◽  
Mass Spring

Multi-layered locally resonant phononic crystals (LRPCs) with wider and multiple bandgaps (BGs) in low frequency range and small size of the unit cell have promising applications in noise and vibration controls. In this paper, a 2D two-layered ternary LRPC consisting of a periodical array of cylindrical inclusions embedded in an epoxy matrix is investigated by the finite element method (FEM), where the inclusion is comprised of two coaxial cylindrical steel cores with rubber coating. It is found that the size of the inclusion of the 2D two-layered ternary LRPC has significant effects on the BG properties. With the increase of the core radius and coating thickness, the first BG would shift to lower frequency range with its width decreasing, and the second BG width would become wider until the third BG appears. Especially, with the increase of the coating thickness, more bands and BGs would appear in the lower frequency range. Based on the formation mechanisms of the BGs, several mass-spring models to predict the frequencies of the first two BG edges are developed. The results calculated by these mass-spring models are in good agreement with those by the FEM except for the upper edge frequency of the second BG when the rubber coating thickness exceeds a certain value and the third BG is opened up. These proposed mass-spring models would allow for quick pre-estimation of the resonance frequencies, and facilitate the selection of possible parameters for the wider and lower frequency BGs to obtain the desired attenuation bands. The studies would also benefit the design of multiple BGs for some device applications.

Mechanical Power Flow Between Stiffened Plates and Viscoelastic Discrete Systems

1986 ◽  
Vol 108 (2) ◽  
pp. 155-164 ◽  
Author(s):  
E. Goldfracht ◽  
G. Rosenhouse
Keyword(s):  
Power Flow ◽  
Energy Analysis ◽  
Power Transmission ◽  
Discrete Systems ◽  
Vibration Energy ◽  
Stiffened Plates ◽  
Statistical Energy Analysis ◽  
Frequency Range ◽  
Lower Frequency Range ◽  
Fundamental Theorems

In this paper we primarily discuss a theory of power transmission and vibration energy distribution of dynamically loaded structures. The loads are random and the system comprises linked elements, which consist of machine-supported stiffened plates. Fundamentally, the theory is deterministic, but in addition it uses some features of the SEA. In fact, the analysis is intended to verify fundamental theorems of the Statistical Energy Analysis in the lower frequency range.

Utilizing Hollow-Structured Bamboo as Natural Sound Absorber

2015 ◽  
Vol 40 (4) ◽  
pp. 601-608 ◽  
Author(s):  
Azma Putra ◽  
Fazlin Abd Khair ◽  
Mohd Jailani Mohd Nor
Keyword(s):  
Absorption Coefficient ◽  
Hollow Structure ◽  
Front Surface ◽  
Normal Incidence ◽  
Frequency Range ◽  
Peak Absorption ◽  
Natural Sound ◽  
Average Absorption Coefficient ◽  
Lower Frequency Range ◽  
Bamboo Structure

AbstractStudies to find alternative low environmental-impact materials for acoustic absorbers are still progressing, particularly those originated from natural materials. However, most of the established works are mainly focused on the fibrous-type absorbers. Discussion on the non-fibrous-type absorbers is still lacking and this therefore becomes the objective of this paper. Use of bamboo by utilizing its hollow structure to absorb sound energy is discussed here. The normal incidence absorption coefficient was measured based on the length and diameter of the bamboo, as well as different arrangement of the bamboo structure subjected to the incidence sound, namely, axial, transverse, and crossed-transverse arrangements. The trend of absorption coefficient appears in peaks and dips at equally spacing frequencies. For all arrangements the peak of absorption can reach above 0.8. Introducing an air gap behind the bamboo shifts the peak absorption to lower frequency. Covering the front surface of the absorber improves the sound absorption coefficient for axial arrangement by widening the frequency range of absorption also towards lower frequency range. The transverse arrangement is found to have average absorption coefficient peaks of 0.7 above 1.5 kHz. By arranging the bamboo structure with crossed-transverse arrangement, the suppressed absorption peaks in normal transverse arrangement can be recovered.

Origin of Degradation in Perovskite Solar Cells by Intensity Modulated Photovoltage Spectroscopy Measurement (IMVS)

2021 ◽  
Vol 1028 ◽  
pp. 133-137
Author(s):  
Adhita Asma Nurunnizar ◽  
Alvin Fariz ◽  
Herman ◽  
Rahmat Hidayat
Keyword(s):  
Solar Cells ◽  
Charge Carrier ◽  
Conversion Efficiency ◽  
Cell Structure ◽  
Perovskite Solar Cells ◽  
Nyquist Plot ◽  
Frequency Range ◽  
Intensity Modulated ◽  
Transient Photovoltage ◽  
Lower Frequency Range

Perovskite solar cells (PSCs) based on lead halide perovskite have attracted much attention owing to the fast development of their power conversion efficiency (PCE) from 3.8% to 25%. Various factors play important roles in affecting the conversion efficiency of PSCs, such as charge carrier generation, transport, recombination, and collection. In addition, the presence of interfacial defects has also a crucial effect in charge carrier transfer and recombination processes. However, the origin and mechanism of interfacial charge recombinations in PSCs are still not comprehensively investigated. For that purpose, we have performed intensity-modulated photovoltage spectroscopy (IMVS) and transient photovoltage (TPV) measurements of PSCs, which were fabricated with FTO/c-TiO2/mp-TiO2/Perovskite/PTAA/Au cell structure. The solar cell (J-V) characteristics of the PSCs on the day-1, day-2, day-3, and day-6 after the cell fabrication, indicating a significant degradation of the cell with time. The Nyquist plots of IMVS measurement on the same day as the J-V measurement seem to be composed of two semicircles at a lower frequency range and a higher frequency range. The semicircle at the lower frequency range enlarged on the day-6 measurement, but the semicircle at higher frequency decreased. The change of this Nyquist plot is in agreement with a significant decrease in the J-V curves. The semicircle at lower frequency may be assigned to the ion diffusion or migration. Therefore, cell degradation may be caused by the liberation of ions (including iodide) from the surface of the perovskite crystal structure. It then increases recombination loss due to back charge transfer from TiO2 to perovskite as indicated by the changing of the semicircle at high frequency into a smaller semicircle. Therefore, the present results reemphasize that the improvement of PSC stability needs the prevention of ions liberations from the surface by introducing passivation substances. In addition, the results also show the practical usefulness of IMVS for inspecting PSC degradation due to such an ion liberation process.

Otoacoustic emissions in patients with hypotension

2003 ◽  
Vol 117 (4) ◽  
pp. 265-269 ◽  
Author(s):  
Dimitrios G. Balatsouras ◽  
Stavros Korres ◽  
Nikola Simaskos ◽  
Dimitrios Kandiloros ◽  
Eleftherios Ferekidis ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Hearing Loss ◽  
Systolic Blood Pressure ◽  
Otoacoustic Emissions ◽  
Distortion Product Otoacoustic Emissions ◽  
Frequency Range ◽  
Distortion Product ◽  
Cochlear Damage ◽  
Lower Frequency Range ◽  
Age And Sex

The aim of this study was to investigate the relation between hypotension and slowly developing hearing impairment, using otoacoustic emissions. A group of 42 patients was examined, with diastolic blood pressure ≤60 mmHg and systolic blood pressure ≤105 mmHg. The subjects underwent biochemical, cardiological, ENT and audiological examinations. Distortion product otoacoustic emissions (DPOAE) were recorded in the format of DP-gram. The results were compared to the data of 30 normal persons of similar age and sex, examined at the same laboratory. Audiometric results showed that 18 patients had mild or moderate symmetrical hearing loss in one or more frequencies, mainly in the lower frequency range. DPOAE of the patients had reduced amplitude as compared to controls or were even absent, in one or more frequencies. It may be concluded that a hypotensive condition could be a possible factor in the origin of cochlear damage and DPOAE may be useful in monitoring hypotensive patients.

scholarly journals Квазистационарное приближение в задаче возбуждения низкочастотных электромагнитных полей в литосфере

2021 ◽  
Vol 91 (1) ◽  
pp. 82
Author(s):  
Е.Д. Терещенко ◽  
П.Е. Терещенко
Keyword(s):  
Electromagnetic Field ◽  
Plane Wave ◽  
Low Frequency ◽  
Wave Impedance ◽  
Frequency Range ◽  
Actual Surface ◽  
The Earth ◽  
Analytical Formulas ◽  
Lower Frequency Range ◽  
Stationary Approximation

The paper considers the excitation of a horizontal grounded antenna of the ELF-ELF electromagnetic field and a lower frequency range in a two-layer environment. Approximate analytical formulas are obtained that describe quite completely behavior of fields in the low-frequency range. The accuracy of using the quasi-stationary approximation is analyzed. The possibility of replacing the actual surface impedance with a plane wave impedance, normally falling on the interface. For a number of experiments carried out on the Kola Peninsula in the framework of the international cooperation (FENICS-2014, FENICS-2019), the frequency boundaries of the applicability of the approximate approach in assessing conductivity of the Earth.

scholarly journals Spatiotemporal Distribution Characterization for Terahertz Waves Generated From Plasma Induced by Two-Color Pulses

2021 ◽  
Vol 9 ◽  
Author(s):  
Erli Wang ◽  
Yulong Wang ◽  
Wenfeng Sun ◽  
Xinke Wang ◽  
Shengfei Feng ◽  
...  
Keyword(s):  
Time Domain ◽  
Focal Plane ◽  
Spatiotemporal Distribution ◽  
Matching Theory ◽  
Thz Radiation ◽  
Phase Matching ◽  
Frequency Range ◽  
Terahertz Waves ◽  
Lower Frequency Range ◽  
The Time Domain

The spatiotemporal distribution of terahertz (THz) radiation from plasma has been demonstrated with the technology of THz focal-plane imaging. It has been found that the spatiotemporal distribution will vary with the frequency, as well as the length of plasma. A doughnut-shaped distribution appears in the lower frequency range, while the bell-shaped distribution corresponds to the higher frequency range. For plasmas with different lengths, their generated THz images in the time domain are similar, the THz images in the frequency domain as well. The spatiotemporal distributions are simulated with the off-axis-phase matching theory. All the findings will renew the understanding of the THz generation from plasma induced by two-color pulses.

scholarly journals Advanced non-dimensional dynamic influence function method considering the singularity of the system matrix for accurate eigenvalue analysis of membranes

2022 ◽  
Vol 14 (1) ◽  
pp. 168781402110729
Author(s):  
Sangwook Kang
Keyword(s):  
Influence Function ◽  
Vibration Analysis ◽  
Function Method ◽  
Accurate Result ◽  
Low Frequency ◽  
Free Vibration Analysis ◽  
System Matrix ◽  
Frequency Range ◽  
Influence Function Method ◽  
Lower Frequency Range

An advanced non-dimensional dynamic influence function method (NDIF method) for highly accurate free vibration analysis of membranes with arbitrary shapes is proposed in this paper. The existing NDIF method has the weakness of not offering eigenvalues and eigenmodes in the low frequency range when the number of boundary nodes of an analyzed membrane is increased to obtain more accurate result. This paper reveals that the system matrix of the membrane becomes singular in the lower frequency range when the number of the nodes increases excessively. Based on this fact, it provides an efficient way to successfully overcome the weaknesses of the existing NDIF method and still maintain its accuracy. Finally, verification examples show the validity and accuracy of the advanced NDIF method proposed.

ANALYSIS OF THE RECOVERED SIGNAL IN SYNCHRONIZED CHUA’S COMMUNICATION SYSTEM

1996 ◽  
Vol 06 (08) ◽  
pp. 1595-1600 ◽  
Author(s):  
YANQING CHEN ◽  
LIUQING PEI
Keyword(s):  
Numerical Simulations ◽  
Frequency Response ◽  
Input Signal ◽  
Output Signal ◽  
Secure Communications ◽  
Frequency Range ◽  
Lower Range ◽  
Lower Frequency Range ◽  
Driving Signal ◽  
Message Signal

The recovered message signal in the synchronized Chua’s system, which is proposed for secure communications, is analyzed by means of both numerical simulations and analytical methods. The results show that the characteristic of “frequency response” of the system is independent of the amplitude of the input message signal, and the amplitude of the recovered signal is suppressed by the system in the lower frequency range and amplified in the higher frequency range. Specifically, we find that, as the frequency of the input signal increases continuously, there is a band of frequency over which a resonance type of phenomenon occurs in the system whereby the input message’s amplitude is amplified, but the location of this band lies beyond the range of the main spectrum of the chaotic driving signal. The phase difference between input signal and output signal is also obtained. Furthermore based on numerical simulations, the characteristic frequency response of a synchronized Lorenz’s system is given, which also shows a band of resonance in the lower range of frequencies.

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