Acoustic interferometer

About: Acoustic interferometer is a research topic. Over the lifetime, 1493 publications have been published within this topic receiving 19355 citations.

On the wavenumber spectra for sound within subsonic jets

Abstract: This paper explores the nature of sound spectra within subsonic jets. Three problems of increasing complexity are presented. First, a point source is placed in a two-dimensional plug flow and the sound field is obtained analytically. Second, a point source is embedded in a diverging axisymmetric jet and the sound field is obtained by solving the linearized Euler equations. Finally, an analysis of the acoustic waves propagating through a turbulent jet obtained by direct numerical simulation is presented. In each problem, the pressure or density field is analyzed in the frequency-wavenumber domain. It is found that acoustic waves can be classified into three main frequency-dependent groups. A physical justification is provided for this classification. The main conclusion is that, at low Strouhal numbers, acoustic waves satisfy the d'Alembertian dispersion relation.

Phase Changes in Reflected Sound Waves

Abstract: Phase changes in waves are just varied enough and just unfamiliar enough to students to be confusing. The phase changes upon reflection of waves on a string and of sound waves are usually the first to be encountered by students, and can give a bridge to other such changes found, for example, in electromagnetic waves. Before digital oscilloscopes, phase changes in sound waves had to be taken on faith or tested indirectly. Now they are quite easy to show. This note describes an experiment that demonstrates phase changes of a reflected sound pulse in a long air-filled tube. The demonstration also gives an easy and straightforward measurement of the speed of sound, and shows that air temperature matters while pressure does not, as theory predicts.1

5.2. Connected-Element Interferometry

Abstract: Publisher Summary This chapter deals with two applications of phase-measuring interferometers: the accurate measurement of position (astrometry), and the determination of source structure, in particular, mapping observations. In both cases, the determination of the difference in phase between incoming signals (the interferometer phase) is crucial. Essential features for the interpretation of measurements of interferometer phase are a known baseline and stable electrical lengths for the various local oscillator and signal paths. The effective baseline may be varied, either by tracking the source over a range of hour angles so that the orientation and projected length of the baseline change, or by using movable elements in the interferometer. Both methods may be employed in the same instrument. In a tracking interferometer, the difference in electrical paths from the source to the two antennas changes continuously. The variation in path difference across the field of view of the interferometer is illustrated in the chapter. The disturbing effects of tropospheric irregularities under calm and disturbed conditions are discussed and an overview of Green Bank three-element interferometer is also presented.