A procedure for the numerical calculation of photoacoustic signals is introduced. It is based on the finite element method and uses an expansion of the signal into acoustic eigenmodes of the measuring cell. Loss is included by the incorporation of quality factors. Surface and volume loss effects attributable to viscosity and thermal conductivity are considered. The method is verified for cylindrical cells with excellent accordance. The application to photoacoustic cells of unconventional shape yields good agreement with experimental data.

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For energy efficiency and material cost reduction it is preferred to drive highintensity discharge lamps at frequencies of approximately 300 kHz. However, operating lamps at these high frequencies bears the risk of stimulating acoustic resonances inside the arc tube, which can result in low frequency light flicker and even lamp destruction. The acoustic streaming effect has been identified as the link between high frequency resonances and low frequency flicker. A highly coupled 3D multiphysics model has been set up to calculate the acoustic streaming velocity field inside the arc tube of high-intensity discharge lamps. It has been found that the velocity field suffers a phase transition to an asymmetrical state at a critical acoustic streaming force. In certain respects the system behaves similar to a ferromagnet near the Curie point. It is discussed how the model allows to investigate the light flicker phenomenon. Concerning computer resources the procedure is considerably less demanding than a direct approach with a transient model.

Articles you may be interested inSensitivity analysis of single-layer graphene resonators using atomic finite element method Photoacoustic sensor system for the quantification of soot aerosols (abstract) Rev. Sci. Instrum. 74, 509 (2003);In the field of photoacoustic sensors, research has mainly been concentrating on the investigation of cylinder shaped cells. For cylinder cells, important acoustical properties can be obtained by analytical methods. In recent years, cells with other shapes have come into focus. In these cases, the sound spectrum and other quantities of interest cannot be obtained by analytical means. Finite element tools, however, are well suited to deal with unconventional geometries. In this article we present results concerning the eigenmodes of T-shaped photoacoustic cells.

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