The effect of diffraction on the ultrasonic velocity measured by the pulse interference method has been investigated in VHF range theoretically and experimentally. Two silicate glasses are taken as the specimens, thei...The effect of diffraction on the ultrasonic velocity measured by the pulse interference method has been investigated in VHF range theoretically and experimentally. Two silicate glasses are taken as the specimens, their frequency dependences of longitudinal velocities are measured in the frequency range of 50-350 MHz, and the phase advances of ultrasonic signals caused by diffraction effect are calculated using A. O. Williams' theoretical expression. For the velocity error due to diffraction effect, the experimental results are in good agreement with the theoretical prediction. It has been shown that the velocity error due to diffraction effect is directly proportional to dθ21 (f)/df, whereθ21 (f) is the phase advances difference between the two partial reflection signals used in velocity measurement and f is the ultrasonic frequency.展开更多
In this paper, a novel pulse interference filter for fiber Bragg grating （FBG） interrogation based on the tunable Fabry-Perot （F-P） filtering principle is proposed and experimentally demonstrated. The self-develop...In this paper, a novel pulse interference filter for fiber Bragg grating （FBG） interrogation based on the tunable Fabry-Perot （F-P） filtering principle is proposed and experimentally demonstrated. The self-developed FBG interrogation system is devised for the aircraft health management of key structures. Nevertheless, the pulse interference is detected in the reflection spectrum of FBG causing interrogation system unstable. To address the problem, the first-order lag pulse broadening filter is proposed in this paper. The first-order lag filter is applied to preprocess and smooth the original signal, meanwhile enhancing the signal-to-noise ratio （SNR）. Afterwards, peaks of reflection spectrum are distinguished with pulse interference by pulse broadening. Experimental results indicate that 634 peaks are detected before adopting the first-order lag pulse broadening filter. Comparatively, the number of peaks decreases to 203 after filtering the interference pulse, and the correct rate of peak detection is higher than 98.5%. Through the comparison with the finite impulse response （FIR） filter, the advantage of first-order lag filter is proved. The vibration monitoring experiment demonstrates that this system has high dynamic precision with a dynamic interrogation range of 0Hz-400Hz, and the maximum repetition rate of 800Hz.展开更多
Spikes detection and sorting play an important role in study of neural information coding.Spikes were generally obtained by threshold detection after filtered in traditional detection,which failed to suppress the rand...Spikes detection and sorting play an important role in study of neural information coding.Spikes were generally obtained by threshold detection after filtered in traditional detection,which failed to suppress the random pulse interference(RPI),In this paper,a novel algorithm was provided to suppress RPI using integrated feature.The raw neural signals from the primary visual cortex in rats were detected with microelectrode array.After the feature differences between spikes and RPls were compared,the features which include waveform and non-waveform features were extracted respectively,and then the integrated feature was established based on Fisher's discrimi nant ratio to separate between spikes and RPls.The test results of simulation and experiment show that the separability capability of the integrated feature is nearly two times greater than the individual feature,the average correct recognition rate of spikes and RPls is over 93%,and the detection rate of spike is effectively improved.展开更多
文摘The effect of diffraction on the ultrasonic velocity measured by the pulse interference method has been investigated in VHF range theoretically and experimentally. Two silicate glasses are taken as the specimens, their frequency dependences of longitudinal velocities are measured in the frequency range of 50-350 MHz, and the phase advances of ultrasonic signals caused by diffraction effect are calculated using A. O. Williams' theoretical expression. For the velocity error due to diffraction effect, the experimental results are in good agreement with the theoretical prediction. It has been shown that the velocity error due to diffraction effect is directly proportional to dθ21 (f)/df, whereθ21 (f) is the phase advances difference between the two partial reflection signals used in velocity measurement and f is the ultrasonic frequency.
文摘In this paper, a novel pulse interference filter for fiber Bragg grating （FBG） interrogation based on the tunable Fabry-Perot （F-P） filtering principle is proposed and experimentally demonstrated. The self-developed FBG interrogation system is devised for the aircraft health management of key structures. Nevertheless, the pulse interference is detected in the reflection spectrum of FBG causing interrogation system unstable. To address the problem, the first-order lag pulse broadening filter is proposed in this paper. The first-order lag filter is applied to preprocess and smooth the original signal, meanwhile enhancing the signal-to-noise ratio （SNR）. Afterwards, peaks of reflection spectrum are distinguished with pulse interference by pulse broadening. Experimental results indicate that 634 peaks are detected before adopting the first-order lag pulse broadening filter. Comparatively, the number of peaks decreases to 203 after filtering the interference pulse, and the correct rate of peak detection is higher than 98.5%. Through the comparison with the finite impulse response （FIR） filter, the advantage of first-order lag filter is proved. The vibration monitoring experiment demonstrates that this system has high dynamic precision with a dynamic interrogation range of 0Hz-400Hz, and the maximum repetition rate of 800Hz.
基金National Natural Science Foundation of China,grant number:60841004,60971110
文摘Spikes detection and sorting play an important role in study of neural information coding.Spikes were generally obtained by threshold detection after filtered in traditional detection,which failed to suppress the random pulse interference(RPI),In this paper,a novel algorithm was provided to suppress RPI using integrated feature.The raw neural signals from the primary visual cortex in rats were detected with microelectrode array.After the feature differences between spikes and RPls were compared,the features which include waveform and non-waveform features were extracted respectively,and then the integrated feature was established based on Fisher's discrimi nant ratio to separate between spikes and RPls.The test results of simulation and experiment show that the separability capability of the integrated feature is nearly two times greater than the individual feature,the average correct recognition rate of spikes and RPls is over 93%,and the detection rate of spike is effectively improved.
