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A growing demand to monitor gaseous components in the environmental air, in traffic zones, and in chemical processes develops in the modern society for optimisation, safety and protection purposes. Especially the automotive traffic is a major source of exhaust gases. Solid electrolyte sensors meet future requirements concerning the response behaviour; the long‐term stability and the price that are connected with the application in on board exhaust measurement.

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This paper deals with recent advances in acoustic experimental methods and especially acoustic imaging. The paper covers two areas of interest to acousticians. In the first part, it is explained how near-field acoustic holography (NAH) can be extended with beamforming in the near-field, focalization. The combination of the two methods is providing now a source localization solution with a good spatial resolution over the complete frequency range without the burden of measuring a large number of points as would be required if only NAH was used. In the second part of the paper, a method is described that goes one step beyond source localization. It is interesting to locate the noise sources, but from an engineering standpoint it is even more interesting to know the internal sources/forces causing these noise sources. In this part is explained how source localization techniques in conjunction with artificial excitation of the structure can provide information on the internal sources of the structure.

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