Excitation series design and pulse compression synthesis for high-resolution Lamb wave inspection

2018 ◽  
Vol 18 (5-6) ◽  
pp. 1464-1478
Author(s):  
Jiadong Hua ◽  
Liang Zeng ◽  
Jing Lin ◽  
Liping Huang
Keyword(s):  
Lamb Wave ◽  
Pulse Compression ◽  
Lamb Waves ◽  
Dispersion Compensation ◽  
Synthesis Method ◽  
Side Lobe ◽  
Main Lobe ◽  
Window Functions ◽  
Windowing Technique ◽  
Lobe Width

Lamb wave pulse compression is a promising technique for ultrasonic nondestructive evaluation and structural health monitoring, in which the excitation waveform is designed to exhibit attractive auto-correlation characteristics including short main-lobe width and small side-lobe amplitude. However, narrowing main-lobe will increase side-lobe amplitude, and vice versa. Conventional time windowing technique is a balance between main-lobe width and side-lobe amplitude. An improvement over time windowing is proposed using pulse compression synthesis method. In this method, a series of excitation waveforms are used to actuate Lamb waves, each response is processed by pulse compression, and all the compression signals are summed together. The excitation series are constructed as linear chirps weighted with different combinations of rectangular and Hanning window functions. The selection of the combination coefficients is optimized to ensure best signal summation. The effectiveness of the proposed method is demonstrated by an experiment, and the robustness to inaccuracy in dispersion compensation is also evaluated. Application of the proposed method for damage detection is demonstrated by a further experiment.

scholarly journals Optimization of two-stage NLFM signal using Heuristic approach

2020 ◽  
Vol 13 (44) ◽  
pp. 4465-4473
Author(s):  
Chandu Kavitha ◽  
Keyword(s):  
Optimization Algorithm ◽  
Frequency Modulation ◽  
Pulse Compression ◽  
Piecewise Linear ◽  
Side Lobe ◽  
Linear Frequency Modulation ◽  
Main Lobe ◽  
Design And Optimization ◽  
Linear Frequency ◽  
Scripting Language

Background/Objectives: The design of appropriate Non-Linear Frequency Modulation (NLFM) signals continues to be the focus of research in radar pulse compression theory for sidelobe reduction. This study focuses on a heuristic design and optimization algorithm to optimize the side lobe values of the NLFM signal designed using two-piece wise linear frequency modulation (LFM) functions. Methods: 1) Heuristic search identifies the optimum B1, T1, and B2, T2, which yield the lowest sidelobe value of the designed function.2) Compute all the side lobe values of the designed NLFM signal using an algorithm developed in Python scripting language. To plot a complete contour map for all the calculated side lobe values, which helps identify the associated variations in the range of side lobe values. Finally, optimize the side lobe values keeping the main lobe width and time-bandwidth (BT) product unchanged by designing a dynamic optimization algorithm. Findings: The algorithm developed considered all side lobe levels after the main lobe for optimization. The focus is mainly on the peak sidelobe ratio (PSLR) value without affecting the other parameters. The results demonstrate that the achieved side lobes exhibit their desired levels. Novelty: The method is useful in all types of hardware associated with weather radar applications to military solutions. The technique can be extended to other multistage signals consisting of piecewise linear Segments. Keywords: Contour; LFM; NLFM; optimization; PSLR

FIR Filter Design Using Modified Lanczos Window Function

2012 ◽  
Vol 566 ◽  
pp. 49-56
Author(s):  
Md. Abdus Samad ◽  
Jia Uddin ◽  
Md. Razu Ahmed
Keyword(s):  
Filter Design ◽  
Side Lobe ◽  
Fir Filter ◽  
Window Function ◽  
Main Lobe ◽  
M 10 ◽  
Low Pass ◽  
Significant Performance ◽  
Fir Filter Design ◽  
Lobe Width

Attenuated side lobe peak in the range of around ~-45dB is required in many applications of signal processing and measurements. However, the problem is usual window based FIR filter design lies in its side lobes amplitudes that are higher than the requirement of application. We propose a modified Lanczos window function by heuristic by examining the Lanczos window, which has better performance like equiripple, minimum side lobe compared to the several commonly used windows. The proposed window has slightly larger main lobe width of the commonly used Hamming window, while featuring 5.1~18.5 dB smaller side lobe peak. The proposed modified Lanczos window maintains its maximum side lobe peak about -55.2~-51.9 dB compared to -39~-36.7 dB of Hamming window for M=10~14, while offering roughly equal main lobe width. Our simulated results also show significant performance upgrading of the proposed modified Lanczos window compared to the Kaiser, Gaussian, and Lanczos windows. The proposed modified Lanczos window also shows better performance than Dolph-Chebyshev window. Finally, the example of designed low pass FIR filter confirms the efficiency of the proposed modified Lanczos window.

Improved Window Function in the Application of MFCC Feature Parameter Extraction

2014 ◽  
Vol 556-562 ◽  
pp. 3703-3706
Author(s):  
Le Qiang Bai ◽  
Xue Wei Zhang
Keyword(s):  
Recognition Rate ◽  
Parameter Extraction ◽  
Side Lobe ◽  
Window Function ◽  
Main Lobe ◽  
Impact Function ◽  
Extraction Algorithm ◽  
Feature Parameter ◽  
Lobe Width ◽  
Kaiser Window

In view of spectrum leakage and the contradictory problem of spectrum accuracy of main lobe and reducing spectrum leakage, MFCC algorithm based on improved window function is proposed. Improved window function is based on the mathematical analysis of Kaiser window, and under the condition of finite sampling points minuses weighted impact function where is at the frequencies that side lobe peaks of correspond to. The amplitude of improved window compared with Kaiser window is smaller, and main lobe width is the same, solving the conflicting problem of main lobe width and side lobe amplitude and reducing spectrum leakage. The experimental results show that speech recognition rate of MFCC feature parameter extraction algorithm based on improved window function is better than Kaiser window and Hamming window.

A signal domain transform method for spatial resolution improvement of Lamb wave signals with synthetically measured relative wavenumber curves

2018 ◽  
Vol 18 (5-6) ◽  
pp. 1633-1651 ◽  
Author(s):  
Jian Cai ◽  
Xiaopeng Wang ◽  
Zhiquan Zhou
Keyword(s):  
Spatial Resolution ◽  
Lamb Wave ◽  
Damage Identification ◽  
Lamb Waves ◽  
Dispersion Compensation ◽  
Resolution Enhancement ◽  
Transform Method ◽  
Glass Fiber Reinforced ◽  
Resolution Imaging ◽  
Time Distance

In practical structural health monitoring with Lamb waves, the signal spatial resolution is usually restricted by not only dispersion but also the space duration of excitation waveforms, that is, the initial spatial resolution for the signals before traveling. As a result, the final resolution and accuracy of damage identification could be badly impaired. To overcome this problem, a signal domain transform method is presented in this article. In signal domain transform, the original dispersive Lamb wave signals are transformed from the time to distance domains, with the time–distance scaling on the excitation waveforms particularly modified. Then, both dispersion compensation and initial spatial resolution enhancement can be actualized to efficiently improve the signal spatial resolution. Considering the practical situation that the structural property parameters could be unavailable to theoretically derive the requisite wavenumber relations, signal domain transform with synthetically measured relative wavenumber curves is further explored. After the frequency domain representation and spatial resolution of Lamb wave signals are basically analyzed, the principle and numerical realization of signal domain transform are investigated. Hereafter, the synthetic measurement of relative wavenumber curves for signal domain transform is discussed and preliminarily validated in an aluminum plate. Finally, signal domain transform is applied for high-resolution imaging of adjacent multiple damages. The efficiency of signal domain transform and signal domain transform–based imaging methods has been well demonstrated by the experimental study on a glass fiber–reinforced composite plate with unknown material parameters.

scholarly journals Convolutional Windows for Side Lobe Reduction

2019 ◽  
Vol 8 (10) ◽  
pp. 3526-3529
Keyword(s):  
Frequency Modulation ◽  
Pulse Compression ◽  
Side Lobe ◽  
Linear Frequency Modulation ◽  
Side Lobe Level ◽  
Chirp Signal ◽  
Sidelobe Level ◽  
Linear Frequency ◽  
Radar Systems ◽  
Window Functions

A lot of applications in radar systems necessitate low range side-lobe performance which is achieved by pulse compression processing. Linear Frequency Modulation (LFM) signal is mainly used chirp signal for this processing. The paramount drawback in LFM is the first side-lobe level of -13dB at the receiver side. In this paper, LFM signal is modified by using simple two-stage piece wise linear frequency modulation (PWLFM) functions. The autocorrelation function of this PWLFM signal exhibited low peak sidelobe level ratio (PSLR) value compared to its counterpart LFM signal. An attempt is made to further reduce the side lobe values by using novel Convolutional windows. The simulation results confirm a significant side lobe reduction by the LFM signal designed using PWLFM functions when a more flexible Power of Cosine window function is applied compared to all other window functions.

scholarly journals An Efficient Destructive Interference Based on Side Lobe Suppression Method in SONAR Beamforming

2021 ◽  
Vol 16 (1) ◽  
pp. 107-120
Author(s):  
S. Pillai ◽  
T. Santhanakrishnan ◽  
R. Rajesh
Keyword(s):  
Side Lobe ◽  
Beam Pattern ◽  
Primary Beam ◽  
Main Lobe ◽  
Destructive Interference ◽  
Rectangular Window ◽  
Window Functions ◽  
Suppression Method ◽  
Beamforming Technique ◽  
Side Lobe Suppression

A novel beamforming technique that resembles the principle of interference is proposed for sonar arrays to suppress the side lobes while the main lobe is kept intact. It uses two window functions. The first one is a rectangular function that produces a primary beam pattern. A secondary new window function is derived and its beam pattern is steered such that the null or trough of the main lobe of the new window coincides with the peak or crest of the first side lobe of the rectangular window and so on to other major side lobes. Pattern multiplication was used to get a final beam pattern. The approach is simulated and verified through a sonar array with 24 hydrophone sensors.

A novel time–frequency transform for broadband Lamb waves dispersion characteristics analysis

2021 ◽  
pp. 147592172097928
Author(s):  
Zhi Luo ◽  
Liang Zeng ◽  
Jing Lin
Keyword(s):  
High Resolution ◽  
Lamb Wave ◽  
Lamb Waves ◽  
Dispersion Compensation ◽  
Wave Mode ◽  
Linear Mapping ◽  
Mapping Technique ◽  
Dispersion Characteristics ◽  
Frequency Compensation ◽  
Time Frequency

Owing to carrying rich information about structure flaws, broadband Lamb waves are considered as a promising tool for non-destructive testing. However, since every Lamb wave mode has its own dispersion characteristics, the feature extraction among broadband multimodal Lamb wave is challenging. Time–frequency representation is significantly effective to analyze dispersive signals. In this article, taking advantages of the idea of dispersion compensation, two kinds of time–frequency domain dispersion analysis methods for broadband Lamb wave were proposed. The first one is based on the concept of the general parameterized time–frequency transform. A kernel function related to group delay was designed and the time–frequency compensation transform was proposed. The other one combines the segment linear mapping technique and the short-frequency Fourier transform, called the time–frequency de-dispersion transform. Both these two methods work well in representing multimodal Lamb wave signals with high resolution. However, time–frequency de-dispersion transform outperforms in representing multipath Lamb waves than time–frequency compensation transform. Moreover, a mode purification strategy was also proposed for distinguishing the interested mode from interferences. According to verification in synthetic and experimental data, not only the multimodal components but also multipath echoes are represented in time–frequency plane with high resolution. Finally, the proposed method shows a great robustness to inaccuracies in the dispersion data.

scholarly journals Mode Separation for Multimodal Ultrasonic Lamb Waves Using Dispersion Compensation and Independent Component Analysis of Forth-Order Cumulant

2019 ◽  
Vol 9 (3) ◽  
pp. 555 ◽  
Author(s):  
Xiao Chen ◽  
Dandan Ma
Keyword(s):  
Independent Component Analysis ◽  
Fourth Order ◽  
Lamb Wave ◽  
Lamb Waves ◽  
Dispersion Compensation ◽  
Single Mode ◽  
Component Analysis ◽  
Independent Component ◽  
Mode Separation ◽  
Fourth Order Cumulant

Ultrasonic Lamb wave testing has been successfully applied in nondestructive testing. However, because of Lamb wave multimodal and dispersion characteristics, the received signals are often multimodal and overlapping, which makes them very complicated. This paper proposes a mode separation method by combining dispersion compensation with the independent component analysis of fourth-order cumulant. Taking two-mode overlapped signals as an example, the single-mode dispersion compensation is performed according to the measured distance difference between the two sets of signals. The two sets of signals are returned to the same distance. The fourth-order cumulant independent component analysis method is further used to process the Lamb wave signals of different superposition situations at the same distance. The corresponding mode signal contained in the two sets of signals is separated through the joint diagonalization of the whitened fourth-order cumulant matrix. The different modes are compensated and separated successively, achieving the multimodal signal separation. Experimental results in steel plates show that the presented method can accurately achieve mode separation for the multimodal overlapping Lamb waves. This is helpful for the signal processing of multimodal Lamb waves.

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