Frequency domain analysis-based electromagnetic ultrasonic thickness measurement method

Abstract

The invention belongs to the field of electromagnetic ultrasonic non-destructive detection and discloses a frequency domain analysis-based electromagnetic ultrasonic thickness measurement method. Themethod includes the following steps that: (a) a test piece with known thickness and a test piece to be subjected to thickness measurement are selected; and (b) the thickness of the test piece to be subjected to thickness measurement is calculated through using a formula. The step (a) further includes the following steps that: (a1) an electromagnetic ultrasonic sensor excitation coil sends signals,and the induced electrical signals of a receiving coil are collected as calibration signals; and (a2) a section of echo signals is intercepted from the calibration signals, and are subjected to re-sampling, full-cycle extension, low-pass filtering, positive half-cycle signal extraction and fast Fourier transformation sequentially, so that a spectrogram is obtained, and a spectrum corresponding topartial frequency bands are selected from the spectrogram, and a frequency corresponding to the peak of the spectrum is obtained. According to the method of the present invention, thickness information is converted from a period which is difficult to read in the time domain to a peak value which is easy to read in the frequency domain, and therefore, with an original circuit not modified, a use lift-off effect can be enhanced, and detection accuracy can be improved.

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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