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A two-dimensional Fourier transform method for the measurement of propagating multimode signals
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1991
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EngineeringMeasurementSurface WaveMechanical EngineeringSpectrum EstimationEducationWave MotionNonlinear AcousticBiomedical Signal AnalysisVibrationsIsometric ProjectionComputational ElectromagneticsTimefrequency AnalysisInstrumentationLamb WavesMultidimensional Signal ProcessingWave PropagationStructural Health MonitoringFourier AnalysisUltrasoundSignal ProcessingMultimode SignalsWaveform AnalysisFrequency Domain Analysis
The paper presents a technique for analyzing propagating multimode signals. The method uses a two‑dimensional Fourier transform of the time‑history recorded at equally spaced points along the propagation path. The 2‑D FFT accurately measured Lamb wave amplitudes and velocities in steel plates of various thicknesses, with results matching analytical predictions and demonstrating its effectiveness for identifying individual Lamb modes.
A technique for the analysis of propagating multimode signals is presented. The method involves a two-dimensional Fourier transformation of the time history of the waves received at a series of equally spaced positions along the propagation path. The technique has been used to measure the amplitudes and velocities of the Lamb waves propagating in a plate, the output of the transform being presented using an isometric projection which gives a three-dimensional view of the wave-number dispersion curves. The results of numerical and experimental studies to measure the dispersion curves of Lamb waves propagating in 0.5-, 2.0-, and 3.0-mm-thick steel plates are presented. The results are in good agreement with analytical predictions and show the effectiveness of using the two-dimensional Fourier transform (2-D FFT) method to identify and measure the amplitudes of individual Lamb modes.