This paper presents an all-optical high-sensitivity resonant photoacoustic (PA) sensor to realize remote, long-distance and space-limited trace gas detection. The sensor is an integration of a T-type resonant PA cell and a particular cantilever-based fiber-optic acoustic sensor. The finite element simulations about the cantilever vibration mode and the PA field distributions are carried out based on COMSOL. The all-optical high-sensitivity resonant PA sensor, together with a high-speed spectrometer and a DFB laser source, makes up of a photoacoustic spectroscopy (PAS) system which is employed for CH4 detection. The measured sensitivity is 0.6 pm/ppm in the case of 1000 s average time, and the minimum detection limit (MDL) reaches 15.9 parts per billion (ppb). The detective light source and the excitation light source are all transmitted by optical fibers, therefore remote and long-distance measurement of trace gas can be realized. Furthermore, the excitation light source and the acoustic sensor are designed at the same side of the PA cell, the sensor may be used for space-limited trace gas detection.

This paper presents a narrowband active noise equMizer (ANE) that can either amplify or attenuate acoustic narrowband noise. The output of the ANE system contains residual narrowband noise components, the amplitudes of which can be linearly and arbitrarily controlled by adjusting the gain parameter of the ANE, thus providing the desired noise shaping capability. Each ANE consists of a sinusoidal reference input, a gain parameter and two adaptive weights. A novel pseudo error minimum method is developed to effectively use the least mean square algorithm. Simulations were conducted to verify effectiveness of the algorithm and validity of the analysis. Real-time ANE experiments implemented on a DSP56001 system board have also been presented.

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