Investigation of a radial-mode-excited piezoelectric tube for photoacoustic gas sensing

We report a piezoelectric (PZT) tube photoacoustic spectroscopy (PAS) gas sensing system, in which a PZT tube serves as both an acoustic resonator and a transducer. To suppress the external disturbance and fully use the internal surface of the PZT tube, we investigate the radial modes for PAS sensing. By exciting its 003-radial mode, the signal-to-noise ratio is more than one order of magnitude higher than that of its commonly used 100 longitudinal mode. We take water vapor as an example to demonstrate its sensing performance, achieving a minimum detection limit of 0.32 ppm, corresponding to a normalized noise equivalent absorption (NNEA) coefficient is 5 × 10^− 9 cm^− 1·W·Hz^− 1/2, and the R-square value of the concentration response fitting is 0.9998. A method to efficiently determine the resonant frequency is studied, which can effectively improve the stability of the sensor system when dealing with external disturbances. With a high acoustic coupling efficiency, simple structure and less disturbance by radial resonant mode, this proposed PZT-PAS technique would promote the PAS application for practical sensitive gas sensing.