Generalized Time Response Formulation for Array Fields

1971 ◽  
Vol 49 (14) ◽  
pp. 1929-1939
Author(s):  
J. F. A. Ormsby ◽  
M. R. Weiss
Keyword(s):  
Transient Response ◽  
Pulse Shape ◽  
Linear Array ◽  
Input Pulse ◽  
Leading Edge ◽  
Far Field ◽  
Viewing Angle ◽  
Antenna Feed ◽  
Generalized Time ◽  
Field Integral

An analysis is provided for the far-field transient response of a linear array antenna. The analytic formulation uses a particularly concise vector field integral equation and is generalized in two ways. First, in contrast to earlier work, the effects of fill time and delay time are simultaneously treated and second, the solutions are derived in terms of the far-field impulse response providing closed form expressions for a large variety of input signals.Results are a function of input pulse shape, viewing angle, frequency, and antenna feed mechanism. Specific analytic computations are given for a variety of pulse shapes, antenna illumination functions, and pulse feeds. To illustrate the formulas, particular numerical results and curves are displayed comparing the leading edge transient response of a center-fed system using both rectangular and cosine shaped pulses at two viewing angles.

Comparison between DOA Estimation Subspace methods for incoherent and coherent signals

2015 ◽  
Vol 1 ◽  
pp. 18
Author(s):  
Ahmed Abdalla ◽  
Suhad Mohammed ◽  
Tang Bin ◽  
Jumma Mary Atieno ◽  
Abdelazeim Abdalla
Keyword(s):  
Linear Array ◽  
Doa Estimation ◽  
Far Field ◽  
Matlab Simulation ◽  
Subspace Methods ◽  
Coherent Signals ◽  
Uniform Linear Array ◽  
Pros And Cons ◽  
Basic Concepts ◽  
And Performance

This paper considers the problem of estimating the direction of arrival (DOA) for the both incoherent and coherent signals from narrowband sources, located in the far field in the case of uniform linear array sensors. Three different methods are analyzed. Specifically, these methods are Music, Root-Music and ESPRIT. The pros and cons of these methods are identified and compared in light of different viewpoints. The performance of the three methods is evaluated, analytically, when possible, and by Matlab simulation. This paper can be a roadmap for beginners in understanding the basic concepts of DOA estimation issues, properties and performance.

Localisation of mixed near‐field and far‐field sources using the largest aperture sparse linear array

2018 ◽  
Vol 12 (2) ◽  
pp. 155-162 ◽  
Author(s):  
Ali Akbar Ebrahimi ◽  
Hamid Reza Abutalebi ◽  
Mahmood Karimi
Keyword(s):  
Linear Array ◽  
Near Field ◽  
Far Field ◽  
Sparse Linear Array

scholarly journals An analytical and experimental investigation of aerofoil–turbulence interaction noise for plates with spanwise-varying leading edges

2019 ◽  
Vol 865 ◽  
pp. 137-168 ◽  
Author(s):  
Lorna J. Ayton ◽  
Paruchuri Chaitanya
Keyword(s):  
Noise Reduction ◽  
Analytic Solution ◽  
Piecewise Linear ◽  
Separation Of Variables ◽  
Leading Edge ◽  
Test Case ◽  
Far Field ◽  
Mean Flow ◽  
Flat Plates ◽  
Leading Edges

This paper presents an analytic solution for gust–aerofoil interaction noise for flat plates with spanwise-varying periodic leading edges in uniform mean flow. The solution is obtained by solving the linear inviscid equations via separation of variables and the Wiener–Hopf technique, and is suitable for calculating the far-field noise generated by any leading edge with a single-valued piecewise linear periodic spanwise geometry. Acoustic results for homogeneous isotropic turbulent flow are calculated by integrating the single-gust solution over a wavenumber spectrum. The far-sound pressure level is calculated for five test-case geometries; sawtooth serration, slitted $v$-root, slitted $u$-root, chopped peak and square wave, and compared to experimental measurements. Good agreement is seen over a range of frequencies and tip-to-root ratios (varying the sharpness of the serration). The analytic solution is then used to calculate the propagating pressure along the leading edge of the serration for fixed spanwise wavenumbers, i.e. only the contribution to the surface pressure which propagates to the far field. Using these results, two primary mechanisms for noise reduction are discussed; tip and root interference, and a redistribution of energy from cuton modes to cutoff modes. A secondary noise-reduction mechanism due to nonlinear features is also discussed and seen to be particularly important for leading edges with very narrow slits.

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.

scholarly journals Time and Frequency Localized Pulse Shape for Resolution Enhancement in STFT-BOTDR

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Linqing Luo ◽  
Bo Li ◽  
Yifei Yu ◽  
Xiaomin Xu ◽  
Kenichi Soga ◽  
...  
Keyword(s):  
Pulse Shape ◽  
Signal To Noise Ratio ◽  
Resolution Enhancement ◽  
Input Pulse ◽  
Rectangular Pulse ◽  
Time Domain Reflectometry ◽  
Frequency Resolution ◽  
Gaussian Shape ◽  
Time Frequency ◽  
New Research

Short-Time Fourier Transform-Brillouin Optical Time-Domain Reflectometry (STFT-BOTDR) implements STFT over the full frequency spectrum to measure the distributed temperature and strain along the optic fiber, providing new research advances in dynamic distributed sensing. The spatial and frequency resolution of the dynamic sensing are limited by the Signal to Noise Ratio (SNR) and the Time-Frequency (T-F) localization of the input pulse shape.T-Flocalization is fundamentally important for the communication system, which suppresses interchannel interference (ICI) and intersymbol interference (ISI) to improve the transmission quality in multicarrier modulation (MCM). This paper demonstrates that theT-Flocalized input pulse shape can enhance the SNR and the spatial and frequency resolution in STFT-BOTDR. Simulation and experiments ofT-Flocalized different pulses shapes are conducted to compare the limitation of the system resolution. The result indicates that rectangular pulse should be selected to optimize the spatial resolution and Lorentzian pulse could be chosen to optimize the frequency resolution, while Gaussian shape pulse can be used in general applications for its balanced performance in both spatial and frequency resolution. Meanwhile,T-Flocalization is proved to be useful in the pulse shape selection for system resolution optimization.

Transient Response Control of Two-Mass System via Polynomial Approach

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Yue Qiao ◽  
Junyi Cao ◽  
Chengbin Ma
Keyword(s):  
Time Constant ◽  
Transient Response ◽  
Controller Design ◽  
Polynomial Method ◽  
Transient Responses ◽  
Mass System ◽  
Response Control ◽  
Characteristic Ratio ◽  
Starting Point ◽  
Generalized Time

This paper discusses the application of polynomial method in the transient response control of a benchmark two-mass system. It is shown that transient responses can be directly addressed by specifying the so-called characteristic ratios and the generalized time constant. The nominal characteristic ratio assignment (CRA) is a good starting point for controller design. And the characteristic ratios with lower indices have a more dominant influence. Two practical low-order control configurations, the integral-proportional (IP) and modified-integral-proportional-derivative (m-IPD) controllers are designed. The primary design strategy of the controllers is to guarantee the lower-index characteristic ratios to be equal to their nominal values, while the higher-index characteristic ratios are determined by the interaction with the generalized time constant and the limits imposed by zeros, a specific control configuration, etc. The demonstrated relationship between the transient responses and the assignments of characteristic ratios and generalized time constant in simulation and experiments explains the effectiveness of the polynomial-method-based controller design.

Transient Response Study on Rolling Effectiveness of Multiple Control Surfaces

2002 ◽  
Author(s):  
Deman Tang ◽  
Aiqin Li ◽  
Earl H. Dowell
Keyword(s):  
Transient Response ◽  
Three Dimensional ◽  
Wind Tunnel Test ◽  
Leading Edge ◽  
Control Surface ◽  
Multiple Control ◽  
Wing Model ◽  
Aerodynamic Model ◽  
Control Surfaces ◽  
Dry Friction Damping

In the present paper, a transient response study of the effectiveness of trailing and leading edge control surfaces has been made for a rolling wing-fuselage model. An experimental model and wind tunnel test are used to assess the theoretical results. The theoretical model includes the inherently nonlinear dry friction damping moment that is present between the spindle support and the experimental aeroelastic wing model. The roll trim equation of motion and the appropriate aeroelastic equations are solved for different combinations of leading and trailing edge control surface rotations using a reduced order aerodynamic model based upon the fluid eigenmodes of three dimensional vortex lattice aerodynamic theory. The present paper provides new insights into the transient dynamic behavior and design of an adaptive aeroelastic wing using trailing and leading edge control surfaces.

Near- and far-field beam forming using a linear array in deep and shallow water

2014 ◽  
Vol 135 (4) ◽  
pp. 2393-2393
Author(s):  
Richard L. Culver ◽  
Brian E. Fowler ◽  
D. Chris Barber
Keyword(s):  
Shallow Water ◽  
Linear Array ◽  
Beam Forming ◽  
Far Field

scholarly journals Far-Field Analysis on Reflecting Colors of Dielectric Nanosphere Metasurface

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Seokhyeon Hong ◽  
Young Jin Lee ◽  
Kihwan Moon ◽  
Youngsoo Kim ◽  
Eunso Shin ◽  
...  
Keyword(s):  
Silicon Nanoparticles ◽  
Visible Spectrum ◽  
Large Degree ◽  
Field Analysis ◽  
Far Field ◽  
Emission Rates ◽  
Viewing Angle ◽  
Metallic Nanoparticle ◽  
Strong Light ◽  
Color Filters

Photonic resonances in nanostructures have been exploited in reflective or transmission color filters, which can provide vivid colors. Metallic nanostructures have been widely studied to demonstrate a variety of color filters based on strong light interaction due to plasmonic resonances. However, because of the severe absorption loss of metal in visible light, dielectric nanoparticles having Mie resonances are a popular study focus in recent years to achieve vivid colors. In contrast to the behaviors of point-like electric dipole in metallic nanoparticle, the interplay of the electric and magnetic Mie resonances in dielectric nanoparticle enables a large degree of freedom in manipulating the directivity of light scattering, reflecting/transmitting color, and spontaneous emission rates. Here, we propose a color reflector based on an array of silicon nanoparticles that shows reflectance greater than 70% and vivid colors over the entire visible spectrum range, which covers sRGB color area. Viewing angle dependencies of the color and brightness are also investigated by calculating color-resolved far-field patterns, while exhibiting maintenance of the color and high reflectance over a broad viewing angle.

Sign in / Sign up

Export Citation Format

Share Document