Design And Research Of Electromagnetic Ultrasonic Testing System For Focusing Transducer

With the acceleration of China's industrialization process and the rapid development of industrial technology,the importance of non-destructive testing technology has gradually emerged.Non-destructive testing(NDT)is an important technique for detecting specimen defects and aging without damaging the specimen.At present,we are facing serious problems caused by structural aging,so it is of great significance to detect the structural defects caused by fatigue,stress,heat aging and corrosion of the test pieces.Among traditional non-destructive testing techniques,ultrasonic testing(UT)is the most common non-destructive testing technology applied to critical structures such as pipes and cured enclosures,which ensures the safety of critical components and avoids huge economic losses and serious Environmental pollution.Common ultrasonic testing methods include piezoelectric testing and electromagnetic ultrasonic testing.Piezoelectric detection technology has some obvious shortcomings.For example,the coupling agent must be used in the detection process,so there is a large acoustic impedance between the transducer and the air layer,the air layer and the test piece,and the energy for excitation cannot be used.Pass it completely.Compared with piezoelectric detection technology,the biggest advantage of electromagnetic ultrasonic transducer(EMAT)is that it does not require a coupling agent and can be detected non-contact.At the same time,electromagnetic ultrasonic testing technology has inherent shortcomings,namely low energy conversion efficiency,low echo signal amplitude,low signal-to-noise ratio,etc.These are places that cannot be ignored when designing electromagnetic ultrasonic testing system.In view of the shortage of existing electromagnetic ultrasonic testing system,the low amplitude of traditional transducer echo signals and the low resolution of defect space,an electromagnetic ultrasonic testing platform capable of using focusing transducers is designed.This paper first discusses the electromagnetic ultrasonic transduction mechanism and the working principle of two kinds of focusing transducers.The three-dimensional and two-dimensional software is used to construct the spatial and planar structure of the focusing transducer,and it is imported into COMSOL multiphysics simulation software.In the experiment,the multi-parameters of the focusing transducer,such as the permanent magnet size,are simulated and optimized,and the focused sound field model is constructed,which further improves its theoretical feasibility.In the hardware system design of the electromagnetic ultrasonic testing platform,firstly,according to the basic principle of the control PLL in the FPGA,the stable clock signal with adjustable frequency,duty cycle and cycle number is designed;to prevent the front-end high-voltage circuit from impacting the front-end FPGA control.The circuit is designed with an optocoupler circuit that can directly contact the front and rear ends.To improve the ability to drive the N-type MOS transistor,a dedicated driver chip for the MOS transistor is used,which greatly improves the ability to drive the MOS transistor;A MOS tube consists of a full-bridge inverter conversion circuit that converts a DC signal into an AC signal,and outputs a pulse excitation signal of high frequency,high voltage,and large current.In the signal conditioning circuit,a three-stage amplifying circuit capable of amplifying the echo signal is first designed.Then a bandpass filter with adjustable center frequency is selected for filtering the echo signal.A display interface that can be used to observe signal waveforms is designed using Labview software and can be used to observe defect waveforms in real time.Piezoelectric ultrasonic,conventional EMAT,and focused EMAT were tested on aluminum plates with artificial manufacturing defects.The results show that the amplitude of the focused EMAT echo is higher than that of the conventional EMAT,which has obvious focusing effect and is practical.The effect is outstanding.