scholarly journals Suppression of sound radiation to far field of near-field acoustic communication system using evanescent sound field

2015 ◽  
Vol 55 (1) ◽  
pp. 017301 ◽  
Author(s):  
Ayaka Fujii ◽  
Naoto Wakatsuki ◽  
Koichi Mizutani
Keyword(s):  
Acoustic Communication ◽  
Communication System ◽  
Near Field ◽  
Sound Radiation ◽  
Sound Field ◽  
Far Field

Active Control of Low-Frequency Sound Radiation From Vibrating Panel Using Planar Sound Sources

2001 ◽  
Vol 124 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Kean Chen ◽  
Gary H. Koopmann
Keyword(s):  
Active Control ◽  
Near Field ◽  
Low Frequency ◽  
Sound Radiation ◽  
Sound Field ◽  
Sound Power ◽  
Frequency Range ◽  
Sound Sources ◽  
Frequency Sound ◽  
Secondary Sources

Active control of low frequency sound radiation using planar secondary sources is theoretically investigated in this paper. The primary sound field originates from a vibrating panel and the planar sources are modeled as simply supported rectangular panels in an infinite baffle. The sound power of the primary and secondary panels are calculated using a near field approach, and then a series of formulas are derived to obtain the optimum reduction in sound power based on minimization of the total radiate sound power. Finally, active reduction for a number of secondary panel arrangements is examined and it is concluded that when the modal distribution of the secondary panel does not coincide with that of the primary panel, one secondary panel is sufficient. Otherwise four secondary panels can guarantee considerable reduction in sound power over entire frequency range of interest.

Real time sound field visualization in the near field, far field and at absorbing surfaces

2008 ◽  
Vol 123 (5) ◽  
pp. 3439-3439
Author(s):  
Hans‐Elias De Bree ◽  
Emiel Tijs ◽  
Tom Basten
Keyword(s):  
Real Time ◽  
Near Field ◽  
Sound Field ◽  
Far Field

Acoustic communication

2018 ◽  
Author(s):  
Heiner Römer
Keyword(s):  
Acoustic Communication ◽  
Background Noise ◽  
Near Field ◽  
Background Information ◽  
Natural Environments ◽  
Far Field ◽  
Sensory Receptors ◽  
Substrate Vibration ◽  
Field Sound ◽  
Mechanical Disturbances

This chapter, takes a broad look at insect acoustic communication, by including near-field and far-field sound, as well as substrate vibration, as signals. These mechanical disturbances differ greatly in their physical properties—they propagate in their natural environments over distances that can span from a few millimetres up to several hundred metres. Therefore, background information is provided to understand how the insect sound-emitting systems for the different signals work and in which behavioral contexts they are used. Evidence is also provided to describe the substantial changes signals undergo on their way to receivers, the effects of background noise on communication and how unintended receivers may represent costs in this system. Finally, a short overview of the structure and evolution of the tremendous diversity of sensory receptors is presented.

Integrated “CFD - Acoustic” Computational Approach to the Simulation of Aircraft Fan Noise

2014 ◽  
Author(s):  
Piergiorgio Ferrante ◽  
Paolo di Francescantonio ◽  
Pierre-Alain Hoffer ◽  
Stéphane Vilmin ◽  
Charles Hirsch
Keyword(s):  
Unsteady Flow ◽  
Sound Propagation ◽  
Noise Source ◽  
Acoustic Radiation ◽  
Near Field ◽  
Sound Field ◽  
Computational Approach ◽  
Far Field ◽  
Fan Noise ◽  
Field Noise

An innovative computational approach, integrating mesh generation, CFD simultaneous analysis of noise source and propagation, with acoustic radiation, is presented and applied to the simulation of the Advanced Noise Control Fan (ANCF) developed by NASA Glenn Research Center. The tonal noise source and the sound propagation in the nacelle duct and in the nacelle near field are simultaneously predicted, starting from the engine geometry and parameters, with a single CFD analysis based on an efficient Nonlinear Harmonic (NLH) method. The sound radiation to the far field is computed with the Green’s function approach implemented in a BEM frequency domain solver of the convective Helmholtz equation. The present method provides to a gain of close to two orders of magnitude compared to standard approaches, based on full unsteady flow simulations, followed by a near-field FEM based approach and a BEM method for the far-field noise propagation. The final comparison between the numerical results and the measurements highlights the capability of the methodology to efficiently predict the unsteady flow field and the radiated sound field.

The structure of rotating sound fields

1993 ◽  
Vol 440 (1909) ◽  
pp. 257-271 ◽  
Keyword(s):  
Near Field ◽  
Azimuthal Angle ◽  
Sound Field ◽  
Evanescent Waves ◽  
Source Distribution ◽  
Dimensional Structure ◽  
Main Beam ◽  
Far Field ◽  
Contour Plots ◽  
Radiation Zone

An account is given of the three-dimensional structure of the sound field produced by a spinning sinusoidal distribution of thickness or loading sources. Particular attention is paid to the creeping evanescent waves in the near field and their physical interpretation as trapped edge waves; an exponentially small amount of energy leaks or tunnels through them to emerge as far-field acoustic radiation (as it does through the inhomogeneous waves carried by a waveguide in a cylindrically layered medium). The dependence of the structure on three parameters is investigated in detail: the Mach number M at the outermost radius of the source; the harmonic number n , defined so that the source strength is a function of nθ , where θ denotes azimuthal angle; and the type of source, i. e. thickness or loading. Parameter values considered include those for subsonic, sonic and supersonic motion, and for high and low harmonics. The field is calculated by reducing a special case of Rayleigh’s double integral to a single integral containing a function related to the Chebyshev polynomials, then integrating numerically to give contour plots of pressure as a function of position on various plane and cylindrical sections. These show that the evanescent waves occupy a spherical or ellipsoidal region, and consist of crescents of alternating high and low pressure, shaped and arranged like the segments of an orange; its ‘peel’ marks the transition to the propagating spiral waves of the far field, i. e. the radiation zone. Contour plots on meridional sections are similar to those for the oscillating hertzian electric dipole, suggesting that the field is approximately that produced by a suitably phased arrangement of its acoustic counterpart. When M > 1, the source distribution straddles both the evanescent and the radiation zone; at high supersonic M , the meridional contour plots display an intense beaming pattern, with side-lobes between the main beam and source plane. The results of the paper agree with previous work on propeller acoustics, especially the asymptotic theory.

Numerical Simulation and Experimental Research of Hydrophone Flow Noise

2020 ◽  
Author(s):  
Mingyuan Li ◽  
Jianzhang Liu ◽  
Yan Wei ◽  
Fengzhong Qu ◽  
Minhao Zhang ◽  
...  
Keyword(s):  
Flow Field ◽  
Acoustic Communication ◽  
Communication System ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Sound Field ◽  
Underwater Acoustic Communication ◽  
Acoustic Analogy ◽  
Underwater Acoustic ◽  
Flow Noise

Abstract Underwater acoustic communication is an important technology in deep-sea research. In underwater acoustic communication system, when hydrophone as acoustic receiver is exposed to sea environment and moves along with an underwater vehicle, its performance is prone to be affected by various ambient noises, among which its generated flow noise is the major source. This would especially influence the performance and shorten the communication distance of underwater acoustic communication system. In this paper, we try to unveil how the flow field is correlated with the flow noise of hydrophone. The Large Eddy Simulation (LES) method and acoustic analogy were used to simulate the flow field and the sound field around hydrophone, respectively. The flow noise of hydrophone at different moving velocities was obtained. Then experiments in an anechoic tank were carried out to verify the simulation results. The subsequent analysis of the experimental results shows that the flow noise has obvious influence on underwater communication, and as the hydrophone moves faster, its sound pressure level climbs up higher. This study also further verifies the reliability of simulating the flow noise of bare hydrophone by computational fluid dynamics, and provides the theoretical basis for improving the signal-to-noise ratio of low-frequency underwater acoustic communication system.

Reconstruction of Sound Field Based on Mono-Poles Array Modes

2012 ◽  
Vol 226-228 ◽  
pp. 316-319
Author(s):  
Yong Fa Nie ◽  
Hai Chao Zhu ◽  
Rong Fu Mao
Keyword(s):  
Acoustic Field ◽  
Near Field ◽  
Single Point ◽  
Sound Field ◽  
Far Field ◽  
Acoustic Source ◽  
Radiation Mode ◽  
Field Reconstruction ◽  
Radiation Noise ◽  
Phase Angles

To effectively reduce radiation noise of the structures, the information detailed of the acoustic field is required. An approach of acoustic field reconstruction based mono-poles array modes is developed. The acoustic source is expressed as the form of some mono-poles array superposition which is defined as mono-poles array radiation mode. The amplitudes of these mono-poles are equal and their phase angles are in phase or out of phase in each array form. The amplitudes of mono-poles array modes are obtained by means of the complex pressures measured in near field, and then the whole acoustic field can be reconstructed. Feasibility of this approach is verified through a numerical example of a single-point harmonic excited and simple supported plate and the error analysis shows that the near field reconstruction result is accurate and the far field reconstruction result is more accurate.

scholarly journals Microphone and Loudspeaker Array Signal Processing to Build a "Radiation Keyboard" for Authentic Samplers

2020 ◽  
Author(s):  
Tim Ziemer ◽  
Niko Plath
Keyword(s):  
Array Signal Processing ◽  
Near Field ◽  
Minimum Energy ◽  
Music Performance ◽  
Sound Radiation ◽  
Sound Field ◽  
Intersection Point ◽  
Radiation Characteristics ◽  
Time Frequency ◽  
Wave Field Synthesis

To date electric pianos and samplers tend to concentrate on authenticity in terms of temporal and spectral aspects of sound. They barely recreate the original sound radiation characteristics, contribute to the perception of width and depth, vividness and voice separation, especially for instrumentalists, who are located in the near field. This paper describes an operational procedure to measure, store, and synthesize the complete sound of a harpsichord, including its spatial sound radiation characteristics. First, actuators excite the instrument at the intersection point of each string with the bridge with an exponential sine-sweep. Then, the radiated sound field is recorded in the near and the far field with microphone arrays. The pressure distribution in the near field is propagated back to the soundboard of the instrument, using Minimum Energy Method. The vibration of each single string is captured with lightweight contact microphones. The soundboard is then replaced by an array of 128 loudspeakers. The loudspeaker signal is a convolution of the back-propagated sweep recording with the string recording to perform a wave field synthesis. Above the spatial Nyquist frequency, the Radiation Method is applied to perform a sound field synthesis which is valid for the listening region of the instrumentalist. The result is an electric harpsichord, that approximates the sound of a real harpsichord precisely in time, frequency, and space domain. Applications for such a radiation keyboard are music performance, instrument and synthesizer building and interactive psychoacoustic research.

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