Measuring longer tubular objects using acoustic pulse reflectometry

Abstract

Acoustic pulse reflectometry is a noninvasive technique for measuring the internal dimensions of tubular objects. A sound pulse is produced using a loudspeaker and injected into the object under investigation via a source tube. The resultant object reflections are recorded by a microphone embedded in the wall of the source tube. Analysis of the reflections yields information about the bore profile of the object. At present, there is a restriction on the length of object that can be measured using the standard reflectometer. This restriction arises because after the object reflections pass the microphone they undergo further reflection at the loudspeaker. These source reflections return to the microphone as unwanted signal. Hence, there is only a finite time over which the object reflections can be accurately recorded which, in turn, limits the length of object that can be measured. In this paper, a method for removing the length restriction is described and preliminary results are presented. The method involves the cancellation of the incoming object reflections at the loudspeaker, thus preventing the formation of source reflections. [Work supported by EPSRC.]

Reconstructing blockages in a symmetric duct via quasi-isospectral horn operators

“…Other research works concern the use of classical acoustic methods based on impedance testing for the identification of cross-sectional area changes in vocal tracts or ear canals [2,3], although more efficient approaches have been recently developed for the analysis of these inherently dissipative systems, see, for example, [4,5]. Among advanced applications in the field, the research developed by Campbell and co-workers on the use of Acoustic Pulse Reflectometry for determining the internal dimensions of musical wind instruments [6] and for leak detection in tubular objects [7] should be also mentioned.…”

Detecting pipe changes via acoustic matched field processing

“…Modeling is usually involved which requires constraints on the nature of the pipe or its defects. The approach of pulse reflectometry plus modeling may detect pipe leaks and cross-sectional changes after analysis of the reflections plus impedance modelling of the pipe with and without a defect [1]. This approach can also be used to determine eigenvalue shifts [2]- [3] to detect finite duct blockages for one or two sets of termination conditions.…”

“…The results for pulse reflectometry plus modelling are usually validated by comparison with test data and usually involve the assumption of idealized acoustic conditions. Additionally, such an approach typically utilises only one microphone and thus, requires vital system calibration or some way to remove offsets in the data [1].…”

“…Acoustic methods for the inspection of pipes to locate blockages and damage have been used extensively [1]- [4] with primary applications related to the quality control of pipes used in chemical engineering, the oil and gas industries, the water industry, and in the manufacturing of musical instruments. Unlike many other inspection methods, acoustic methods can be fast and non-invasive.…”

Time domain wave separation using multiple microphones

“…[4][5][6] The major disadvantage of long source tubes is that acoustic losses become prohibitive at high frequencies, meaning that the bandwidth is limited; the major disadvantage of any two microphone method is that there are singularities when the intermicrophone distance matches integer multiples of half a wavelength. These singularities can be worked around by using more than two microphones.…”