Signal Analysis Of Infrasound

Infrasonic wave is a kind of sound whose frequency is less than20Hz, and it is known as subaudio wave. Subsonic wave has a low frequency, a long wavelength, and diffraction occurs easily, so infrasonic wave is not prone to decay and uneasy to be absorbed by water and air, etc. It can also bypass some of the major obstacles in the process of transmission, study has proved that some subsonic wave can circumnavigate the globe2to3times. Although human ear can’t hear infrasonic wave, the sound is widespread. In nature, some phenomena like volcanic eruptions, tsunami, thunder and lightning, storms at sea, sea slap, water swirling, air turbulence, tornadoes, magnetic storm, aurora are likely to be accompanied by infrasonic waves. In human activities, nuclear explosion, missile flight, ship navigation, cars flashed past, large buildings shook, all of these phenomena can produce subsonic wave, even during phonation of air blower, mixer, loudspeakers, subsonic wave can be also produced. Some vibrational frequencies of human body’s organs also resemble certain frequencies of infrasonic waves, so when subsonic waves are resonated with human organs, it will produce great harm to human body, even kills people. The research of making effective analysis of infrasound signal can find its implications in the military, meteorology, nature disaster forewarn, health detection of large structural, and medical science.Fourier transform and wavelet analysis are commonly used method is in the signal analysis methods. Fourier transform is based on frequency characteristic analysis of signal, it is the most classic and basic analysis method, but it have great limitation in processing nonlinear signal. Wavelet analysis is developed on the basis of Fourier, it has inherited the characteristics of Fourier transform, it has the feature of multi-resolution ability which has a wide application. After the comparison, this paper choose wavelet analysis method to analyze the signal of subsonic wave.Hilbert Huang transform is a new method proposed and improved gradually by Chinese American N. E. Huang in1998, which is used to process non-linear and non-stationary signal, this new method is well applied in many fields. This paper is based on wavelet analysis and the Hilbert Huang transform method to conduct research of analyzing subsonic wave signal. The specific work of this paper as follows:(1)The research and comparison of the infrasonic wave signal analysis algorithm. First of all, theoretically introduce and research Hilbert-huang algorithm and wavelet analysis algorithm which chosen and applied by this article, including concept of the algorithm, formula and calculation method, etc. On this basis, compare the application characteristics and shortcomings of two kinds of algorithms in the field of signal analysis. Wavelet algorithm is the representative of the time domain analysis and it make the analysis meaningful only to the choice wavelet base, so it is limited by a wavelet base on the application. Hilbert-huang has developed as a new adaptive algorithm, and has a good effect on the nonlinear and non-stationary signal analysis.(2) The realization of the HHT algorithm on MATLAB. Simulation signal as an example, realize its empirical mode decomposition and obtain desired number of IMF components and a residual amount, then make Hilbert transform of signal on the basis of the EMD decomposition, get the Hilbert spectrum and marginal spectrum of the signal which is the time-frequency spectrum. To verify the effectiveness of HHT in signal analysis, analysis bearing data from U.S. Case Western Reserve University electrical engineering laboratory Rolling fault simulation experiment station by HHT, then get the bearing fault location.(3) Research of signal de-noising method. Using wavelet de-noising, the EMD de-noising and joint de-noising complete infrasonic signal de-noising, and contrast select the better method. Joint de-noising method is designed in this paper as a new de-noising method.(4) Analysis infrasonic wave. To complete the infrasonic wave signal extraction in the sound signal and obtain relevant parameters.Finally, make outlook for the follow-up questions and future work base on the summary of the work in this paper.