scholarly journals Beam diffraction effects in sound transmission of a fluid-embedded viscoelastic plate at normal incidence

2016 ◽  
Vol 140 (1) ◽  
pp. EL67-EL72 ◽  
Author(s):  
Magne Aanes ◽  
Kjetil Daae Lohne ◽  
Per Lunde ◽  
Magne Vestrheim
Keyword(s):  
Sound Transmission ◽  
Normal Incidence ◽  
Viscoelastic Plate ◽  
Diffraction Effects ◽  
Beam Diffraction

Crystal Polarity Determination by Electron Channeling

2001 ◽  
Vol 7 (S2) ◽  
pp. 334-335
Author(s):  
J. Tafto
Keyword(s):  
Experimental Conditions ◽  
Electron Channeling ◽  
Structure Factors ◽  
Small Crystals ◽  
Polarity Determination ◽  
Convergent Beam ◽  
Interface Structures ◽  
Diffraction Effects ◽  
Beam Diffraction

Multilayers, heterostructures, nanostructures and composites are of great interest to the materials scientists, and frequently we encounter crystals lacking centrosymmetry. Thus crystal polarity determination on a microscopic scale is becoming increasingly important in describing interface structures and the internal defects in small crystals. in many cases the polarity of a crystallite can be determined by convergent beam electron diffraction, CBED. Powerful alternatives are to monitor the electron induced x-ray emission, EDS, or electron energy losses, EELS, under channeling conditions. While the determination of the phase of the structure factors, and thus the determination of the crystal polarity, relies on many beam diffraction effects when the CBED technique is used, two-beam experiments provide information about the phase of the structure factor when localized EDS or EELS signals are detected under channeling conditions.The experimental conditions used to determine the polarity and absolute orientation from electron channeling are similar to those used in ALCHEMI experiments to locate small amounts of atoms by electron channeling.

An improved approach for normal-incidence sound transmission loss measurement using a four-microphone impedance tube

2020 ◽  
pp. 107754632092690
Author(s):  
Zechao Li ◽  
Sizhong Chen ◽  
Zhicheng Wu ◽  
Lin Yang
Keyword(s):  
Transfer Matrix ◽  
Sound Absorption ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Sound Insulation ◽  
Sound Transmission Loss ◽  
The Common ◽  
Wavefield Decomposition ◽  
Insulation Performance

The main aim of this study is to introduce an improved method for determining the sound properties of acoustic materials which is more precise than the common wavefield decomposition method and simpler than the common transfer matrix method. In the first part of the article, a group of formulae for calculating sound transmission loss is represented by combining the wavefield decomposition and transfer matrix methods. Subsequently, a formula for calculating sound absorption coefficients is derived from these formulae by definition. Furthermore, the present formulae are validated by comparing the experimental results achieved with the present formulae and those results obtained by other methods recorded in published articles. Eventually, it is demonstrated that the method can accurately measure the sound insulation performance of materials and the sound absorption properties of limp and lightweight materials.

On the determination of enanttomorphs from non-systematic many-beam effects in CBED patterns

1989 ◽  
Vol 47 ◽  
pp. 484-485
Author(s):  
K. Marthinsen ◽  
R. Høier
Keyword(s):  
Structure Factor ◽  
High Accuracy ◽  
Convergent Beam Electron Diffraction ◽  
Bragg Condition ◽  
Sign Problem ◽  
Three Phase ◽  
Convergent Beam ◽  
Diffraction Effects ◽  
Beam Diffraction

A convergent beam electron diffraction (CBED) method which makes it possible to determine structure factor magnitudes and phases with high accuracy has recently been suggested. It is based on detailed simulations of non-systematic many-beam diffraction effects in the disks. Basis for the phase determination is an asymmetry which may appear in a line h with respect to the Bragg condition of the coupled reflection g near a three-beam condition. Approximate analytical three-beam solutions show that the sign and size of this asymmetry depends on the structure factor phases Θh of the reflections h involved through a term cos(Φ) where Φ is the three phase structure invariant, Φ = Θh + Θg + Θh-g. The magnitude of the phase invariant is thus in principle available, but not the sign. The aim of the present work has been to discuss the origin of the sign problem and the possibilities of distinguishing +/−Φ.

Reflection and transmission of obliquely incident Rayleigh waves at a vertical discontinuity between two welded quarter-spaces

1979 ◽  
Vol 69 (5) ◽  
pp. 1409-1423
Author(s):  
Thomas C. Chen ◽  
Leonard E. Alsop
Keyword(s):  
Free Surface ◽  
Phase Velocity ◽  
Rayleigh Waves ◽  
Velocity Ratio ◽  
Normal Incidence ◽  
Angle Of Incidence ◽  
Reflection And Transmission ◽  
Obliquely Incident ◽  
Vertical Boundary ◽  
Diffraction Effects

abstract We use an approximate method to study the reflection and transmission of obliquely incident Rayleigh waves on a vertical boundary between two welded quarter-spaces. For two media with a phase velocity ratio of 1.16 our calculation shows that the transmitted energy follows a reciprocity relation and decreases from near 100 per cent at normal incidence to 50 per cent at about 40°. The reflected energy is less than 1 per cent for angles of reflection less than 40°. When the Rayleigh wave impinges upon the less rigid medium, the reflected energy decreases as the angle of incidence increases; whereas for incidence at the more rigid medium, the reflected energy decreases at first, and then it increases as the angle of incidence increases. Since boundary conditions on the free surface are not taken into account by our method, diffraction effects are ignored. The effect of neglecting the free surface requirement is difficult to quantify, but we believe that it is small since the calcualted and experimental results agree well at normal incidence.

A hybrid method of predicting the acoustical properties of multi-layered materials

2021 ◽  
pp. 107754632110381
Author(s):  
Zechao Li ◽  
Lin Yang ◽  
Hongbin Ren ◽  
Sizhong Chen ◽  
Zheng Liu ◽  
...  
Keyword(s):  
Noise Control ◽  
Transmission Loss ◽  
Hybrid Approach ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Layered Materials ◽  
Acoustical Properties ◽  
Transmission And Reflection Coefficients ◽  
Standing Wave Tube ◽  
Laminated Materials

Many numerical and measuring approaches are widely used in predicting and analysing the acoustic performances of laminated materials for noise control applications. However, numerical methods generally require a set of non-acoustic parameters, and the measuring methods are not available for exceedingly thick materials. The main aim of this article is to address a hybrid approach of evaluating the normal incidence sound transmission loss and absorption coefficients of multi-layered materials. This method is performed with some special parameters that contain the sound transmission and reflection coefficients of each sub-layer of a multi-layer specimen and can be measured by a standing wave tube system. The accuracy and feasibility of the present method are validated by the experimental and numerical comparisons between different methods and samples. Moreover, this present approach can be applied as a numerical tool of estimating the acoustical behaviours of multi-layered structures in noise control treatments, such as automotive, building and aerospace industries.

scholarly journals Normal Incidence of Sound Transmission Loss of a Double-Leaf Partition Inserted with a Microperforated Panel

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
A. Putra ◽  
A. Y. Ismail ◽  
R. Ramlan ◽  
Md. R. Ayob ◽  
M. S. Py
Keyword(s):  
Mathematical Model ◽  
Transmission Loss ◽  
Low Frequency ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Sound Transmission Loss ◽  
Engineering Structures ◽  
Air Mass ◽  
Noise Barrier ◽  
The Mathematical Model

A double-leaf partition in engineering structures has been widely applied for its advantages, that is, in terms of its mechanical strength as well as its lightweight property. In noise control, the double-leaf also serves as an effective noise barrier. Unfortunately at low frequency, the sound transmission loss reduces significantly due to the coupling between the panels and the air between them. This paper studies the effect of a microperforated panel (MPP) inserted inside a double-leaf partition on the sound transmission loss performance of the system. The MPP insertion is proposed to provide a hygienic double-leaf noise insulator replacing the classical abrasive porous materials between the panels. It is found that the transmission loss improves at the troublesome mass-air-mass resonant frequency if the MPP is located closer to the solid panel. The mathematical model is derived for normal incidence of acoustic loading.

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