A Dual Frequency Electromagnetic Ultrasonic Testing System

Abstract

The invention discloses a double-frequency electromagnetic ultrasonic detection system. The double-frequency electromagnetic ultrasonic detection system consists of a digital signal generator, a poweramplifier, a duplexer, a magnet, a coil, a metal specimen, a pre-amplifier, a high-pass filter, a low-pass filter and a signal processor, wherein the digital signal generator is used for alternatively generating two types of digital signals at different frequency, the digital signals are inputted into the power amplifier to complete power amplification, and the coil is driven via the duplexer; the coil is used for exciting ultrasonic waves and receiving ultrasonic echo, and the ultrasonic echo signal is inputted into the pre-amplifier via the duplexer; the signal is amplified by the pre-amplifier and is divided into two paths, and the two paths of signals are respectively inputted into the low-pass filter and the high-pass filter; the filtered signals are inputted into the signal processor, the stand-off distance is determined by the amplitude of the low-frequency signal, and the size of the defect is determined according to the stand-off distance and the amplitude of high-frequency defect echo signal, so as to still quantitatively represent the defect size even when the stand-off distance is changed.

Description

technical field [0001] The invention relates to an electromagnetic ultrasonic nondestructive testing technology, in particular to a dual-frequency electromagnetic ultrasonic testing system and a testing method. Background technique [0002] Electromagnetic ultrasonic transducer EMAT (electromagnetic acoustic transducer) is a transducer that uses electromagnetic coupling to excite and receive ultrasonic waves. It has the characteristics of high precision, no coupling agent, non-contact, suitable for high temperature detection, etc., and is often used For defect detection, dimension measurement, stress detection, etc. of metal rods, plates, pipes, etc. The mechanism of electromagnetic ultrasound is divided into two types: Lorentz force mechanism and magnetostrictive mechanism. The mechanism of Lorentz force is: the high-frequency pulse current is passed into the excitation coil, and the eddy current J is coupled in the metal sample due to electromagnetic induction, and the ex...

AI Technical Summary

Problems solved by technology

When implementing defect detection, the size of the defect is generally judged by the amplitude of the defect echo, but if the lift-off distance changes, even if the same defect is detected, the amplitude of the echo will be different, which gives Quantitative characterization of defect size poses difficulties

In practical applications, mechanical support is often used to fix the distance from the probe to the sample, but this method is not reliable when the surface of the sample is uneven

The invention solves the problem that the size of the defect cannot be effectively characterized under the condition that the lift-off distance changes

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