Measurement And Characteristics Of EMAT Radiation Sound Field Based On Tomography

As an integral part of the car's core,automotive engine testing of defects and performance is the key to car use and safety.Therefore,the detection of defects in the main components of the launch has become a key issue.With the development of non-destructive testing technology,it provides solid technical support for engine testing.Among them,the rise of electromagnetic ultrasonic testing technology has been widely applied and recognized by people.Electromagnetic ultrasonic transducer(EMAT,Electromagnetic Acoustic Transducer)is an important part of electromagnetic ultrasonic testing.It has the advantages of non-contact,no coupling agent,low requirements on the surface of the test piece,and high temperature environment.In order to ensure the rationality of the detection process and the accuracy and reliability of the detection results,it is necessary to accurately measure the distribution of the radiation sound field generated by the electromagnetic ultrasonic transducer in the test specimen.At present,the commonly used radiation sound field measurement methods include water immersion method and photoelastic method,but the EMAT-excited transverse wave cannot propagate in water,and EMAT cannot excite ultrasonic waves in transparent solid plastic,and water immersion method and photoelastic method cannot.The sound field is measured.In this paper,the method of tomographic measurement is proposed to measure the radiated sound field excited by the electromagnetic ultrasonic transducer in the test piece,and the characteristics and influence factors of the radiated sound field are analyzed.The main contents are as follows:(1)Firstly,the principle of electromagnetic ultrasonic transducer excitation ultrasonic wave in the test piece is analyzed,and the propagation process of ultrasonic wave in the test piece is studied.According to the excitation mechanism,the method of tomographic measurement is proposed to the electromagnetic ultrasonic transducer.The excited radiation field is measured,and the principle of tomography,ultrasonic excitation system and signal detection system are analyzed.(2)Based on the principle of tomographic measurement,an experimental system for measuring the radiated sound field based on electromagnetic ultrasonic transducer tomography was built.The receiving transducer in the tomography experiment system was first designed.Then,the mechanical control system and the electromagnetic ultrasonic excitation and receiving system in the tomography experiment system were designed and constructed.The stability of the tomography experimental system was analyzed by experiments.(3)Using the tomography measurement experimental system,the radiated sound field excited by the loop coil EMAT and the racetrack coil EMAT in the Al block is measured,and the influence of the receiving transducer on the excitation signal in the Al block is analyzed,and the reception is calculated.The compensation coefficient of the signal.It was verified that the tomography experiment system can measure the radiated sound field excited by EMAT.(4)In order to measure the excited radiated sound field in the cylinder head,cylinder and crankshaft of the automobile engine,the influence of different detecting components and different excitation frequencies on the radiated sound field is analyzed.Based on the tomography experimental system,the components of the engine components,namely Al and 20# steel,were used as the measurement objects to analyze the differences in the radiated sound field characteristics excited by the EMAT in different detection components.Secondly,the distribution of the radiated sound field of the runway coil EMAT in 20# steel with excitation frequency of 1MHz,1.5MHz and 2MHz and the influence of excitation frequency on the sound beam and sound pressure are compared.