Parametric dependencies for photoacoustic leak localization

Abstract

Unintended gas or liquid leaks from manufactured components or manufacturing systems may be detrimental to consumers, manufacturers, and the environment. Thus, leak testing is important for quality, safety, and environmental reasons. This paper describes parametric dependencies for photoacoustic leak localization. The technique is based on the interaction of 10.6-micrometer radiation from a carbon dioxide (CO2) laser and a photoactive tracer gas, sulfur hexafluoride (SF6). For the current investigations, acoustic signals are generated by scanning a laser beam at high speed through gas plumes formed above calibrated leaks. These signals are remotely measured with a four-microphone linear array and analyzed using Bartlett and minimum-variance-distortionless (MVD) matched-field processing (MFP) techniques to determine leak location. This paper extends prior work in photoacoustic leak testing through (i) use of more signal frequencies; (ii) parametric study of four different laser scan rates; and (iii) examination of mismatch between the actual acoustic environment and the propagation model used in the MFP; and (iv) presentation of leak localization results on a curved surface. For a 12-watt CO2 laser exciting the small SF6 gas plume produced by a one-cm3-per-day leak with microphones placed 0.41 m from the leak location, root-mean-square localization uncertainties as small as +/-0.5 mm on a line scan of 0.46 m can be achieved when the largest possible number of signal frequencies fall in a measurement bandwidth of approximately 70 kHz.

Non-line-of-sight sound source localization using matched-field processing

“…The superscript H denotes the conjugate transpose and boldface type denotes a vector or matrix. The MVD processor output takes a similar form as the Bartlett but the MVD weight vector (w MV ) is selected to optimize the match to a signal at the interrogation point and reject signals and correlated noise from other locations, 6,8,20 making it adaptive. The MVD processor output is given as…”

“…In applications of photoacoustic detection and localization of gas leaks, 7,8 MFP was utilized in an environment where sound arrived from both direct and reflected paths. In ongoing efforts on acoustic localization in urban environments, [9][10][11] MFP and time reversal focusing have been utilized along with finite-difference time-domain (FDTD) modeling of a complex urban environment to localize single acoustic pulse sources.…”

Stand-Off Chemical Detection Using Photoacoustic Sensing Techniques—From Single Element to Phase Array

“…For example, it is commonly seen in phased array antennas for detecting radar with high directivity radio frequency beams [20]. However, in the domain of PA sensing specifically, for example, Yonak and Dowling et al [21,22] report usage of multiple microphones followed by signal processing with the Matched Field Processing (MFP) technique [23]. Such techniques can suppress ambient noise levels, enhance the signal, improve the Signal-to-Noise Ratio (SNR), and also extend the outdoor chemical detection distance-range.…”

Air Leak Localization Method Based on Infrared Thermography Using Local Gray-Entropy Difference Algorithm

“…Most current study into leak localization is focused on petroleum and natural gas pipelines, while there is very little new work done on the leak of vessels [1]. Traditional approaches , such as air bubbling test, are fading out due to their inconvenience or low efficiency [2][3]. A new method is put forward here in an attempt to reach the advantages of higher efficiency and better anti-jamming ability .…”