High-sensitivity fiber optic hydrogen sensor in air by optimizing a self-referenced demodulating method.

Self-referenced demodulating methods of fiber optic hydrogen sensors based on WO3-Pd2Pt-Pt composite film are studied in this paper. By employing the proper baseline intensity as sensing parameters, fluctuations of the sensing signal of the hydrogen sensor can be obviously depressed, and sensitivity can be greatly improved. Experimental results show that the resolution of the hydrogen sensor can reach 3 parts per million (ppm) when the hydrogen concentration is lower than 1000 ppm. Additionally, the hydrogen sensor shows better sensitivity toward lower concentrations of hydrogen, enabling a hydrogen threshold down to 10 ppm in air at room temperature. To the best of our knowledge, this is the lowest threshold reported for an optical hydrogen sensor operated at room temperature in air. Moreover, the sensor has good repeatability during hydrogen response. This work proposes a simple and novel method to improve the performance of fiber optic hydrogen sensors, which can greatly promote their potential application in various fields.

Research on Sparse Denoising of Strong Earthquakes Early Warning Based on MEMS Accelerometers.

In view of the fact that the noise in the same frequency band as the useful signal in the MEMS acceleration sensor observation data cannot be effectively removed by traditional filtering methods, a denoising method for strong earthquake signals based on the theory of sparse representation and compressive sensing is proposed in this paper. This skillfully realized the separation of strong earthquake signals from noise by adopting a fixed dictionary and utilizing sparse characteristics. Furthermore, considering the weakness of the sparse denoising method based on the fixed dictionary in the high signal-to-noise ratio, a spare denoising method based on learning an over-complete dictionary is proposed. Through the initial given seismic data, the ideal over-complete dictionary is trained to achieve seismic data denoising. In addition, for the interference waves of non-seismic events, this paper proposes an idea based on sparse representation classification to remove such non-seismic interference directly. Combining the ideas of noise reduction and non-seismic event elimination, we can obtain a standard sparse anti-interference denoising model for earthquake early warning. It's innovative that this model implements the sparse theory into the field of earthquake early warning. According to the experimental results, in the case of heavy noise, the denoising model based on sparse representation can reach average SNR of 8.73 and an average MSE of 29.53, and the denoising model based on compression perception can reach average SNR of 7.29 and an average MSE 41.34, and the denoising model based on learning dictionary can reach average SNR 11.07 and average MSE 17.32. The performance of these models is better than the traditional FIR filtering method (average SNR -0.73 and average MSE 260.37) or IIR filtering method (average SNR 4.73 and average MSE 73.95). On the other hand, the anti-interference method of the sparse classification proposed in this paper can accurately distinguish non-seismic interference events from natural earthquakes. The classification accuracy of the method based on the noise category of the selected test data set reaches 100% and achieves good results.