Macro Machined Photoacoustic Non-Resonant Cell

Abstract

Photoacoustic spectroscopy (PAS), which is widely used in gas sensing applications, is capable of a wide dynamic range, simplicity of use, high selectivity and sensitivity and also possesses novel detection characteristics when the cell are scaled into a micro system design. In a PAS system which is based on the photoacoustic effect, if the parameters of light power, chopper frequency, and absorption coefficient of the target analyte were decided, the level of the acoustic signal is inverse proportional to the radius square of the cell in which the sample is laid. So, miniaturizing the size of the cell can improve the system’s sensitivity. In our experiment, we initially designed a macro photoacoustic non-resonant cell (PNC) using stainless steel. As the macro cell is scaled to a dimension approaching the microelectromechanical systems (MEMS) level, the basic information gained from these initial tests is a special reference to fabricating a MEMS scale device. The non-resonance test conducted at 100 Hz demonstrated large signals (15.89mV) for CO2concentrations at 600 ppm and high signal-to-noise (S/N) values (~ 85:1). Then a structure of monolithic MEMS photoacoustic cavity was proposed which incorporate a three-wafer.