An Electromagnetic Ultrasonic Thickness Measurement Method Based on Frequency Domain Analysis

Abstract

The invention belongs to the field of electromagnetic ultrasonic nondestructive testing, and discloses an electromagnetic ultrasonic thickness measuring method based on frequency domain analysis. The method comprises the following steps: (a) selecting a test piece with a known thickness and a test piece with a thickness to be measured, and performing the following steps respectively: (a1) the excitation coil of the electromagnetic ultrasonic sensor sends out a signal, and the induction electric signal of the receiving coil is collected as a receiving signal; (a2) Intercept a segment of the echo signal on the received signal and perform resampling, full cycle extension, and low-pass filtering in sequence; (a3) ​​Take the positive half cycle signal of the processed signal, and perform fast Fourier transform to obtain the spectrogram , select the frequency spectrum corresponding to some frequency bands in the spectrum diagram, and calculate the frequency corresponding to the peak value of the frequency spectrum; (b) use the formula to calculate the thickness of the test piece to be tested. Through the present invention, the thickness information is transformed from a period that is difficult to read in the time domain to a peak value that is easy to read in the frequency domain, increases the use of lift-off on the basis of not changing the original circuit, and improves the detection accuracy.

Description

technical field [0001] The invention belongs to the field of electromagnetic ultrasonic nondestructive testing, and more specifically relates to an electromagnetic ultrasonic thickness measurement method based on frequency domain analysis. Background technique [0002] Electromagnetic ultrasound is a new technology in the field of non-destructive testing. It has the advantages of simple structure, no need for couplant, and can adapt to a certain lift-off. This technology uses electromagnetic coupling to excite and receive ultrasonic waves. Compared with the traditional ultrasonic testing technology, it has the advantages of high precision, no need for couplant, non-contact, suitable for high temperature testing, and easy to excite various ultrasonic waves. In industrial applications, electromagnetic ultrasound is getting more and more attention and attention. Electromagnetic ultrasound is a metal conductor in an alternating magnetic field, which will generate eddy currents ...

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Problems solved by technology

[0003] At present, the invention patent application with the application number 201610172021.0 discloses an electromagnetic ultrasonic thickness measurement method based on the digital acquisition circuit system; the invention patent application with the application number 201510582587.6 discloses an electromagnetic The method of measuring the thickness of metal materials, the above-mentioned technology is mainly carried out around the acquisition of the time domain cycle of the electromagnetic ultrasonic echo signal, focusing on how to extract the time interval of the echo signal through various methods, because the electromagnetic ultrasonic energy conversion efficiency is low, so it is subject to the The impact is large, and the circuit noise will affect the measurement of the echo period, resulting in the small lift-off that the existing electromagnetic ultrasonic instrument can achieve, and the signal processing circuit is complex

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