Acoustic signal treatment

Puchenkov and Malkin [107] and Chen and Diebold [108] presented theoretical treatments on the temporal profile of the acoustic wave induced by volume expansion. Both theories showed that the temporal profile of the thermally induced acoustic wave and the volume induced wave are different. The thermodynamic treatment told us that the TG signal by photoinduced structural change appears as the fast rise, which is determined only by the pulse width (if the chemical reaction proceeds very fast). This finding is consistent with the observations by Miller and co-workers [12,25,106]. If the volume expansion takes place after excitation, and is subsequently followed by contraction by the deactivation, the pressure wave induced by the volume change should be different from that expected by the thermal expansion [108]. Indeed, this expected different pressure wave was observed in the TG signal after the photoexcitation of emulsions [109a] and carbon particles [109b]. The pressure wave was explained by the thermal expansion... 

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