Analysis of some basic properties of multicavity photoacoustic Helmholtz cells

The paper presents results of comparative analysis of some basic properties of multicavity photoacoustic Helmholtz cells. The analysed cells were three-cavity Helmholtz resonators formed from a standard dual-cavity photoacoustic Helmholtz cell with an additional cavity connected by means of a capillary with the sample cavity of the cell at the other end. Influence of change of the volume of the additional cavity as well as diameter and length of the connecting duct on the microphone signal vs. frequency was studied. Analysis was based on computer simulations in which a modified transmission line model was used. The model was improved by introducing of additional damping factors which values were extracted from measurements of number of practically implemented dual-cavity photoacoustic Helmholtz cells. The analysis showed that additional cavity makes it possible to improve shape of the frequency response of the cell. In particular it is possible to extend range of frequencies in which resonance properties of the cell can be used for the purpose of photoacoustic signal amplification. It should be noticed that choice of the cell dimensions must be careful, as some combinations decrease resonance properties of the cell.