Papers by Keyword: Acoustic Signal

Abstract: In the paper, the optical fiber F-P acoustic emission sensing probe has been proposed to monitor online space-time progress of femtosecond laser plasma shock wave for the first time, the structure of sensing probe is microstructure with full optical fiber probes without glue, it can measure weak acoustic emission high frequency signal on femtosecond laser plasma shock wave. In the process of femtosecond laser ablating copper, iron and aluminum, we research and analyze the plasma shock wave acoustic emission signal change regulation under different laser pulse energy and different distance between the laser and the optical fiber sensing probe, and we analyze the feature of the acoustic emission signal spectrum. Experiment establishes a kind of new optical fiber sensing measurement method for femtosecond laser plasma shock wave acoustic emission signal.

Abstract: In real life transportation, we sense the environment not only using our eyes, but also using our ears. The acoustic environment contributes a big part of human’s sensing and shall be integrated into the existing internet of vehicles (IOV). The vehicles can communicate with each other via the propagation of the sound they make. The recorded sound signals, with some signal processing applied, can be used to obtain the location of the nearby vehicles and also be sent to the driver to increase his/her awareness of the situation even if the physical sound has been blocked by the door or window of the vehicle. In this paper, we propose such an acoustic IOV using an integrated system of microphone arrays and digital signal processors (DSPs).

Abstract: This paper introduces the related theory of sound waves , we collect the data through the acoustic wave sensors of the pipeline fault diagnosis system platform, decompose the signals to five layers by Mallat algorithm and wavelet function db4, compare the normal waves and leakage acoustic signal spectrum, and then get the power spectrum estimation for the decomposed signal at each level, we can see the signals energy feature in different frequency band. Feature extraction method based on wavelet transform can make the category of signal characteristics fully displayed in the different resolution band, it has a good application prospect in the field of acoustic signal processing.

Abstract: The phenomenon of Doppler Shift leads to the difficulty for fault diagnosis of train bearings with a high moving speed. So the elimination of the Doppler shift should be implemented firstly. A Doppler Shift elimination method for the wayside acoustic signal is proposed. The instantaneous frequency estimation based on STFT was applied to attain the IF vector. According to the acoustic theory of Morse, the data fitting was then carried out to achieve the fitting IFs, with which the re-sampling sequence could be established to eliminate Doppler Shift. To demonstrate the validity of this method, an experiment with the synthetic signal containing several frequency components had been carried out. The results show that the re-sampled signal was revised without Doppler Shift.

Abstract: The noises with high level from the different positions of the train lead to the difficulty for extraction of the acoustic signal from the train bearings. Thus the de-noising should be carried out to eliminate the influence of the noises. A new de-noising method has been proposed based on the Doppler Shift. With the crazy climber detection algorithm, all the instantaneous frequencies could be extracted. According to the acoustic theory of Morse, the information of the position of these acoustic sources is revealed. Finally, the variable digital filtering was employed to remove the noises from the other positions of the train. A simulation on the signal containing with ten frequency components demonstrated the validity of this method proposed and the useful components of the signal were enhanced.

Abstract: Helium is widely used as mixing with argon for a shielding gas in GMAW process of Aluminum in order to improve weld quality and increase heat transfer to the weld pool. It has been known that helium could affect metal transfer behavior; however, its behavior has not been well understood. In this study, an analysis of the metal transfer behavior in the GMAW of aluminum was studied. The main objective is to study the effect of Helium on metal transfer in two main regions, short circuit (low welding current region) and spray transfer (high current region). The composition of 5 types of shielding gases were pure argon, 75%Ar + 25%He, 50%Ar + 50%He, 25%Ar + 75%He and pure helium. The welding parameters were fixed at 90A/17.0V, 100A/18.2V, 140A/24.6V and 180A/27.6V. Aluminum plates were welded bead-on-plate in a flat position. The metal transfer behavior was analyzed by using acoustic signals and arc voltage signals. For the result, at low welding current of 90A and 100A with pure argon, short-circuit transfer mode was observed. Adding helium in gas mixture gave no effect in metal transfer mode in low welding current regions but the metal transfer rate was slightly increased. At high welding currents of 140A and 180A with pure argon, spray transfer mode was observed and when increasing helium in gas mixture resulted in changing from spray transfer to combined mode of spray-globular. In these high welding currents, adding helium in gas mixture resulted in decreasing the metal transfer rate since helium gas tended to promote globular metal transfer. Acoustic signal and arc voltage signal can be used effectively in determining modes of metal transfer.

Abstract: Based on the mobile rail flash butt welding machine UN5-150ZB, the synchronous data acquisition hardware system was designed to collect welding current, welding voltage and flash acoustic signal in welding process, and the software platform with the functions of signal collecting, waveform display and data operation was developed by higher-level programming language LabVIEW. After the welding current, welding voltage and flash acoustic signal in welding process had been collected, the mean, variance and mean square value of flash acoustic signal in time-domain were analyzed. Through comparison, the relationship between these characteristics and the stability of flash was analyzed. The result shows that the changes of mean and variance of flash acoustic signal are not obvious, and do not correlate with stability of flash, but the mean square value in time domain is closely associated with the stability of flash, and the stability of flash can be indicated by the mean square value.

Abstract: The application based on Backpropagation (BP) Algorithm network is conducted on identifying the categories and numbers of mechanical equipments by acoustic signal in battlefield targets. Collected signal was pre-processed and extracted the power spectrum feature of acoustic signal as input vectors of neural networks, then classified by neural networks and pattern recognition theorem. We employ the acoustic signals of six kinds of normal equipments as training samples to train the network. The experiment shows that the ratio of recognition of the acoustic signal processing system based on neural networks proposed is better than the conventional methods.

Abstract: The underwater opto-acoustic communication system for directional acoustic communication between an in-air platform and a submerged platform operating is important. The paper presents a new method to solve this problem with opto-acoustic technology, which combines high-energy laser, the opto-acoustic transmitter that optical energy is converted to acoustic energy at the water surface. The laser-based transmitter provides a versatile method for generating underwater sound. The acoustic pressure is linearly proportional to the laser power. The paper designed an experimental measurement system for the opto-acoustic communication. It made experiments for study on the waveform and spectrum characteristics of opto-acoustic signals. The paper also discuss the acoustic wave after optical breakdown in water with Nd:YAG laser pulses. The opto-acoustic signals can controll by adjusting the laser's parameters. The conclusion is that the opto-acoustic communication has some technical advantages. This system presents a change in the way communicational from the air.

Abstract: In order to rescue the problems of controlling laser bionic strengthening local stripe of mould surface quality, it is put forward thoughts about the laser bionic local melting stripe of mould surface quality detection based on acoustic signal. Analyzed with the relationship between defocusing distance and acoustic signal characteristic, laser bionic strengthening local stripe quality, the results show that acoustic signal is weakened with the increased absolute value of defocusing distance. As the defocusing distance is 0mm, the role of the laser is primarily ablation and the stripe quality is the worst; the function of laser on the surface materials is too weak to strengthen when the defocusing distance is -4mm; laser on target surface plays its role of strengthening, mainly owing to melting, with defocusing distance of +4mm. Overall tests show that, based on the quantitative detection of acoustic signal characteristic, it could inspect and control the quality of strengthening stripe, and it will realize the overall control of laser bionic strengthening mould surface quality with guiding significance.