A physical interpretation of the far‐field directivity pattern of lithium niobate bar transducers

1996 ◽  
Vol 80 (9) ◽  
pp. 5489-5493 ◽  
Author(s):  
Jamal Assaad ◽  
Christian Bruneel
Keyword(s):  
Lithium Niobate ◽  
Physical Interpretation ◽  
Directivity Pattern ◽  
Far Field

An Extrapolation Method to Compute Far-Field Pressures From Near-Field Pressures Obtained by Finite Element Method

1995 ◽  
Author(s):  
Jamal Assaad ◽  
Christian Bruneel ◽  
Jean-Michel Rouvaen ◽  
Régis Bossut
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Near Field ◽  
Radiation Condition ◽  
Directivity Pattern ◽  
Extrapolation Method ◽  
External Boundary ◽  
Finite Width ◽  
Far Field ◽  
Element Method

Abstract The finite element method is widely used for the modeling of piezoelectric transducers. With respect to the radiation loading, the fluid is meshed and terminated by an external nonreflecting surface. This reflecting surface can be made up with dipolar damping elements that absorb approximately the outgoing acoustic wave. In fact, with dipolar dampers the fluid mesh can be quite limited. This method can provides a direct computation of the near-field pressure inside the selected external boundary. This paper describes an original extrapolation method to compute far-field pressures from near-field pressures in the two-dimensional (2-D) case. In fact, using the 2-D Helmholtz equation and its solution obeying the Sommerfeld radiation condition, the far-field directivity pattern can be expressed in terms of the near-field directivity pattern. These developments are valid for any radiation problem in 2D. One test example is described which consists of a finite width planar source mounted in a rigid or a soft baffle. Experimental results concerning the far-field directivity pattern of lithium niobate bars (Y-cut) are also presented.

Light Induced Ferroelectric Domain Nucleation in LiNbO3 Crystal

2009 ◽  
Vol 79-82 ◽  
pp. 1383-1386
Author(s):  
Yun Lin Chen ◽  
Hai Wei Li ◽  
Yuan An Li
Keyword(s):  
Light Intensity ◽  
Lithium Niobate ◽  
Visible Light ◽  
Lithium Niobate Crystal ◽  
Ferroelectric Domain ◽  
Light Diffraction ◽  
Far Field ◽  
Light Wavelength ◽  
Irradiation Intensity ◽  
Diffraction Patterns

Using the tightly focused visible light (wavelength λ=488nm) illuminating, the ferroelectric domain patterns of the undoped lithium niobate crystal have been demonstrated. The influence of the visible light intensity on the domain nucleation field was investigated. The reduction of nucleation field decreases exponentially with increasing incident irradiation intensity. Once a domain is nucleated it can be dictated by the far-field light diffraction patterns. An assumption is proposed that the reduction of nucleation field is directly related to the defects mobility and structure of the crystals.

scholarly journals On the noise prediction for serrated leading edges

2017 ◽  
Vol 826 ◽  
pp. 205-234 ◽  
Author(s):  
B. Lyu ◽  
M. Azarpeyvand
Keyword(s):  
Leading Edge ◽  
Directivity Pattern ◽  
Destructive Interference ◽  
Far Field ◽  
Low Frequencies ◽  
Power Spectral ◽  
Edge Scattering ◽  
Field Noise ◽  
Sound Reduction ◽  
Dipolar Pattern

An analytical model is developed for the prediction of noise radiated by an aerofoil with leading-edge serration in a subsonic turbulent stream. The model makes use of Fourier expansion and Schwarzschild techniques in order to solve a set of coupled differential equations iteratively and express the far-field sound power spectral density in terms of the statistics of incoming turbulent upwash velocity. The model has shown that the primary noise-reduction mechanism is due to the destructive interference of the scattered pressure induced by the leading-edge serrations. It has also shown that in order to achieve significant sound reduction, the serration must satisfy two geometrical criteria related to the serration sharpness and hydrodynamic properties of the turbulence. A parametric study has been carried out and it is shown that serrations can reduce the overall sound pressure level at most radiation angles, particularly at small aft angles. The sound directivity results have also shown that the use of leading-edge serration does not significantly change the dipolar pattern of the far-field noise at low frequencies, but it changes the cardioid directivity pattern associated with radiation from straight-edge scattering at high frequencies to a tilted dipolar pattern.

Far-field Directivity Patterns For (YZw)36° Lithium Niobate Bars.

1993 ◽  
pp. 415-418
Author(s):  
Jamal ASSAAD ◽  
Christian BRUNEEL ◽  
Jean-Noël DECARPIGNY ◽  
Bertrand DUBUS
Keyword(s):  
Lithium Niobate ◽  
Far Field ◽  
Directivity Patterns

Far-Field Performances Prediction of High Frequency Projectors Using Secondary Source Array Method

2016 ◽  
Vol 25 (02) ◽  
pp. 1750002 ◽  
Author(s):  
Shiquan Wang
Keyword(s):  
High Frequency ◽  
Near Field ◽  
Directivity Pattern ◽  
Field Method ◽  
Voltage Response ◽  
Secondary Source ◽  
Far Field ◽  
Comparison Of The Results ◽  
Source Array ◽  
Good Agreement

This paper investigates the prediction of the far-field performances of high frequency projectors using the second source array method (SSAM). The far-field parameters can be calculated accurately using the complex acoustic pressure data of two very close parallel planes which lie in the near-field region of the projector. The paper simulates the feasibility of predicting the far-field parameters such as transmitting voltage response and the far-field directivity pattern. The predicting results are compared with that calculated using boundary element method (BEM). It shows very good agreement between the two methods. A planar high frequency projector is measured using the near-field method. In order to verify the predicting results, the far-field measurement is performed for the same projector. The comparison of the results shows that the near-field method is capable to precisely predict the far-field parameters of the projector.

scholarly journals Lithium niobate photonic crystal waveguides: Far field and near field characterisation

2006 ◽  
Vol 265 (1) ◽  
pp. 180-186 ◽  
Author(s):  
M.-P. Bernal ◽  
N. Courjal ◽  
J. Amet ◽  
M. Roussey ◽  
C.H. Hou
Keyword(s):  
Photonic Crystal ◽  
Lithium Niobate ◽  
Near Field ◽  
Far Field ◽  
Photonic Crystal Waveguides

Study of Far—Field Directivity Pattern for Linear Arrays

2011 ◽  
Author(s):  
Chiselev Ana-Maria ◽  
Moraru Luminita ◽  
Onose Laura ◽  
Madalin Bunoiu ◽  
Iosif Malaescu
Keyword(s):  
Directivity Pattern ◽  
Far Field ◽  
Linear Arrays
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