Design a Digital Notch Filter Based on Matlab Program for Photoacoustic Gas Sensing Systems

An efficient digital notch filter for 50Hz noise eliminated from low frequency photoacoustic gas sensing signal is presented in this paper by a Matlab program. The digital notch filter is consisted of the fast Fourier transform, a second order infinite impulse response notch filter, inverse fast Fourier transform, real and imaginary parts separating, phase shift for imaginary part, and pure noise eliminating from real and imaginary parts. A smooth waveform of low frequency photoacoustic signal can be achieved through the 50Hz digital notch filter and can be used as the analysis data to calculate the target gas concentration. The detectable sensitivity of the photoacoustic gas sensing system with the 50Hz digital notch filter can be obtained as 100 parts-per-billion acetylene when about 0.2 percent water vapor exists and interferes for the low concentration acetylene at 1530.37nm.