Design Of Magnetostrictive Guided Wave Detection System

Magnetostrictive ultrasonic guided wave testing technology combines the advantages of electromagnetic ultrasonic and guided wave detection, it has the characteristics of non-contact, no need of coupling agent, small loss of propagation, comprehensive detection, etc. It can be effectively used for the detection of round steel of long distance and symmetric structure, such as pipes, cables, anchor, etc. Especially for detecting objects of external cladding layer, the use of magnetostrictive properties of ferromagnetic material itself, without removing the cladding can be defect identification and health assessment. Currently, magnetostrictive guided wave detection technology has become the forefront and hot spots of research of testing technology, most of the research mainly focus on the establishment of the theory model and the optimization design of the transducer. This paper on the basis of understanding the principle of detection, analyzes the conversion efficiency of magnetic acoustic, designs the testing system and carries out relevant experiments. The main research contents are as follows:First, we discuss the theory of magnetostrictive and guided wave, focus on guided wave of in the bar, propose magnetostrictive guided wave detection principle and based on magnetostrictive effect of guided wave excitation and reception in bars.Secondly, this paper based on magnetostrictive longitudinal guided-wave testing technology, focus on low energy efficiency of the electromagnetic ultrasonic transducer, for improve the conversion efficiency, respectively from the transducer consisting of three parts(magnetostrictive material, bias magnetic field and the induction coil) are analyzed, achieving the transducer design.Thirdly, the detection system is designed for magnetostrictive transducer, including the hardware circuit and the software system. Excitation end can provide a frequency, number of cycles, trigger interval adjustable Hanning window modulation single frequency narrow pulse signal, output power of up to nearly 40 W. Reception end for good noise rejection using differential preamp design, circuit overall gain is 120 dB to microvolt echo signals are sufficiently amplification, the realization of data acquisition.Finally, we using the transducer and detection system to detecting magnetostrictive materials, magnetostrictive transducer operating frequency is 300 kHz ~ 1MHz, realized sweep testing. For improve the accuracy of the test results, through signal processing techniques to the echo signal analysis and processing, and compare with the theoretical values,analyze error range verification the feasibility and practicality of system.