scholarly journals The far-field properties of ultrashort pulsed beams with constant waist width in free space

2005 ◽  
Vol 54 (12) ◽  
pp. 5642
Author(s):  
Zou Qi-Hui ◽  
Lü Bai-Da
Keyword(s):  
Free Space ◽  
Far Field

Sound from a propeller at angle of attack: a new theoretical viewpoint

1995 ◽  
Vol 449 (1936) ◽  
pp. 315-328 ◽  
Keyword(s):  
Wave Equation ◽  
Mach Number ◽  
Free Space ◽  
Angle Of Attack ◽  
Environmental Concerns ◽  
Far Field ◽  
Flight Direction ◽  
Propeller Noise ◽  
Efficiency Increase ◽  
Field Noise

Accurate prediction of propeller noise is required to satisfy airplane noise certification regulations and environmental concerns. Propellers typically operate with their shafts at some angle to the flight direction but this factor has been ignored in noise calculations until recently. In this paper, far field noise formulas are devel­oped by applying the free-space Green’s function for the convected wave equation to loading sources on a propeller whose shaft may be at an angle to the flight direction. The resulting inflow angularity influences noise in two distinct ways. First, loading is modulated causing generation of more efficient radiation modes. Second, the radiation modes themselves are modified, causing a further efficiency increase. The first effect is well known; the second effect has only recently been recognized and is the focus of this paper. The noise formulas exhibit the same spinning mode behaviour seen in previous analyses but with higher levels radiated into the crossflow. Since the modes are no longer purely spinning, the term ‘wobbling mode’ has been coined to describe their behaviour. This paper summarizes the earlier literature on this subject, explores the radiation formulas in detail, and presents some calculations that illustrate the magnitude of the angular inflow effect. It is shown that the inflow angle influences modal efficiency only through changing the Mach number of the source relative to the observer.

SCATTERING OF ELECTROMAGNETIC WAVES BY A MOVING CYLINDER IN FREE SPACE

1967 ◽  
Vol 45 (9) ◽  
pp. 2999-3007 ◽  
Author(s):  
S. W. Lee ◽  
R. Mittra
Keyword(s):  
Angular Dependence ◽  
Lorentz Transformation ◽  
Doppler Shift ◽  
Free Space ◽  
Electromagnetic Waves ◽  
Stationary Problem ◽  
Small Radius ◽  
Far Field ◽  
Field Patterns ◽  
Moving Cylinder

Scattering of electromagnetic waves by a moving cylinder in free space is studied by an application of Lorentz transformation. It is shown that the solution in the transformed coordinates can be derived readily from a knowledge of the solution of the corresponding stationary problem. Several important characteristics of the scattered far-fields are investigated in detail for a cylinder of small radius. These include the calculation of the far-field patterns and the angular dependence of the Doppler shift.

Classical capacity of free-space optical communication

2004 ◽  
Vol 4 (6&7) ◽  
pp. 489-499
Author(s):  
V. Giovannetti ◽  
S. Guha ◽  
S. Lloyd ◽  
L. Maccone ◽  
J.H. Shapiro ◽  
...  
Keyword(s):  
Optical Communication ◽  
Free Space ◽  
Information Capacity ◽  
Far Field ◽  
Free Space Optical Communication ◽  
Free Space Optical ◽  
Classical Information ◽  
Classical Capacity ◽  
Space Optical Communication

The classical-information capacity of lossy bosonic channels is studied, with emphasis on the far-field free space channel.

Free-space asymptotic far-field series

2009 ◽  
Vol 26 (11) ◽  
pp. 2410 ◽  
Author(s):  
Riccardo Borghi ◽  
Miguel A. Alonso
Keyword(s):  
Free Space ◽  
Far Field
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