With the continuous development of optical communication technology, fiber grating sensing technology obtained the unprecedented development of fiber Bragg grating sensor with strong ability of resisting electromagnetic interference resistance to corrosion, high sensitivity, small body Low cost advantages, has the incomparable advantages of traditional sensors, in the national defense military aerospace and other fields has been widely used in [1-3] in the practical application of fiber Bragg grating sensor and sensing signal is very susceptible to noise interference, the measurement precision of the fiber Bragg grating sensor is affected, so to remove the noise of the fiber Bragg grating sensor research has the vital significance.
At home and abroad in recent years, some studies mechanism of fiber Bragg grating sensor signal denoising studies [7, 8], but the study also not enough in-depth the earliest using Fourier transform to deal with the noise of the fiber Bragg grating sensor signal, in order to improve the quality of the fiber Bragg grating sensor signals, but as a result of the Fourier transform of signal decomposition scale is coarser, cannot effectively eliminate the noise of the fiber Bragg grating sensor signal [9-11] In order to solve the limitations of Fourier transform, some scholars wavelet transform denoising method was adopted to realize FBG sensing signal quality of ascension, the decomposition scale is more detailed, more thoroughly remove noise, but the algorithm of wavelet threshold denoising process, the threshold selection is critical, whether hard or soft threshold threshold was adopted to realize, the current disagreed on threshold selection criteria, and the implementation process is very complicated, not easy to operation.
Outline of the wavelet transform is a method of multi-scale decomposition can effective denoising signal in noise, in order to solve the problem of the current fiber Bragg grating sensor signal noise, design a fiber Bragg grating sensor based on contour wavelet transform signal denoising method, the experimental results, improve the outline of the wavelet transform can eliminate noise in the fiber Bragg grating sensor signals, won the high quality of the grating sensor signal.
Fiber Bragg grating sensor is a kind of wavelength modulated sensor. As the wavelength is a constant, it is not affected by the optical fiber loss and energy of the light source, so its performance is better than other types of fiber sensor. Its working principle is shown in figure 1.
Appens, reflection wavelength will have corresponding change, so that we can according to the detection wavelength to be the measured value of the fiber grating, such as temperature and pressure center wavelength drift (Δ
The relationship between the center wavelength drift (Δ
The relationship between the center wavelength drift (Δ
Let E be the elastic modulus of the fiber Bragg grating, and the formula for calculating the refractive index change of the fiber Bragg grating is
In the process of fiber Bragg grating sensing, the refractive index is related to many factors, especially the interference of noise is the biggest, which brings adverse effects to the measurement results such as temperature and pressure. For this reason, contour transformation is introduced in this paper to carry out denoising processing on the fiber Bragg grating sensing signal, so as to improve the measurement accuracy such as temperature and pressure.
Aiming at the limitation of the wavelet transform, some scholars raised the outline of the wavelet transform, this method can from two aspects of measure frequency, by the signal processing has a certain direction, make the effective signal to concentrate for a signal containing noise, outline of the wavelet transform of the original signal by base structure approaching, outline of the wavelet transform at the same time also has a certain anisotropic characteristics through the Laplacian pyramid to multi-scale decomposition of noise signal, find some of the specific signal and noise, through the direction of the filter to filter noise operation, after denoising signal Firstly, the fiber Bragg grating sensor signal is sampled and the low frequency information of the fiber Bragg grating sensor signal is obtained. Then, the fiber Bragg grating sensor signal is sampled, and the high frequency information of the fiber Bragg grating sensor signal is obtained. In figure 2, X represents the fiber Bragg grating sensor signal, and H G is a low-pass filter.
The process of three-level directional subband division of direction filter is shown in figure 3. The sub-bands of the upper level are sampled by resampling operator and the sampling results are output.
As the useful FBG sensor signal and noise show different characteristics in contour wave transformation, the FBG sensor signal is transformed in different levels, and the noise in the FBG sensor signal is removed according to the appropriate threshold value.
Set the original fiber Bragg grating sensor signal {
There are many threshold selection methods for contour wave transformation. Due to the universal and easy implementation of the Universe threshold method, this paper selects the Universe threshold method to determine the threshold of the optical fiber grating sensor signal denoising, and the high-frequency sub-band threshold of the Universe threshold method is determined as follows
Where,
Step1: contour wave transform is performed on signal f(x) of fiber Bragg grating sensor with noise. The coefficients of contour transform domain are as follows:
Step2: according to the denoising rules, the contour transformation coefficient
Step3: perform contour wave reconstruction and transformation on the estimated value
In order to analyze the denoising effect of the fiber Bragg grating sensing signal of contour wave transform, Matlab 2014 was used as the test platform to conduct the denoisingexperiment. The signal of fiber grating sensor with noise is shown in figure 4.
COMPARES THE PERFORMANCE OF THE CLASSICAL RASTER SENSING SIGNAL DE-NOISING METHOD
Denoising method | PSNR | MSE |
---|---|---|
The wavelet transform | 20.33 | 8.00 |
The literature[17] | 22.19 | 7.72 |
Contour wave transform | 24.73 | 7.24 |
Serious impact on the quality of the fiber Bragg grating signal noise, its application scope and bring certain actual application value of interference, in order to eliminate the adverse effect, was proposed based on wavelet transform outline of fiber grating sensing signal denoising method, according to outline the multi-scale wavelet transform and directional advantages, the fiber Bragg grating sensor signal decomposition, found in the decomposition of the signal noise data, and through the corresponding filter to remove noise, and through the inverse operation outline of the wavelet transform denoising signal after refactoring, improves the signal-to-noise ratio of the fiber Bragg grating sensor signals, and compared with other denoising method has carried on the experiment. The contrast method can remove some useful signals while removing noise, while the method in this paper may keep the useful signal as much as possible, and at the same time improve the real-time performance of the fiber Bragg grating sensing signal.