For Nondestructive Testing Of Electromagnetic Ultrasonic Transducer Device Design And Optimization Of The Magnet

Electromagnetic acoustic transducer (EMAT) is a new type of launching ultrasonic receiver, it is through the electromagnetic coupling method to generate and receive ultrasound. EMAT is non-contact and without coupling agent. it does not require pre-treatment of the work piece and has many other advantages. It has been used in non-destructive testing and evaluation of the broad masses, and effectively extends the technology of ultrasonic nondestructive testing applications. Based on the nature of the workpiece material to the mechanism of EMAT, there are three kinds of main forms: Lorentz force, magnetostriction and magnetization force. In the non-ferromagnetic material, the Lorentz force plays a major role; in ferromagnetic materials, it is the combined effect of three kinds of mechanism, and the most significant effect is magnetostrictive force. The EMAT has three main components: (1) magnet (magnetic field is used to provide a permanent magnet or electromagnet), (2) high-frequency coil (used to produce high-frequency magnetic field excitation), (3) Workpiece (Detection Object, It is an indispensable part of EMAT) - referred to as the three elements of EMAT. Electromagnetic ultrasonic transducer is built around the basic principles of the "three elements" carried out.As a result of electromagnetic ultrasonic transducer to participate in the energy conversion process of the workpiece while working, the working electric, magnetic, acoustic performance will directly affect the electromagnetic ultrasonic transducer characteristics. Due to the complexity of the work mechanism and the diversity of test characteristics of the workpiece, the design is usually based on the experience. Therefore, electromagnetic ultrasonic transducer has a lot of the problem about principle or application which is not resolved. The efficiency of transducer is not satisfied and has many other severely limits which stop the further promotion of the technology. In order to fundamentally improve or resolve these issues as soon as possible and put the electromagnetic ultrasonic transducer into a wider range of production practice, scholars optimize device performance objectives of the electromagnetic ultrasonic transducer carried out extensive and in-depth research, optimal design of a variety of methods. In this paper, the optimization of the object (including a conversion efficiency, the purity of sound, the sound field point, the probe lift-off size, as well as changes in the sensitivity of the distance, etc.) and design method (modeling and experimental method) discussed.In order to improve shortcoming that the electromagnetic ultrasonic transducer is inefficient, the author optimizes the design of the electromagnetic ultrasonic transducer and simulate it with software ansoft, specifical content as follows: 1. In the base of sound wave equation and Maxwell's equations, we discuss the establishment of the electromagnetic ultrasonic transducer of the mathematical model and aquire the mechanical - electromagnetic coupling equation.2. For a conversion efficiency of the decision factors, the rate relation of transducing energy and magnetostatic field. we improve the shape of the magnet and design a new type of permanent magnet group.3. The performance of permanent magnet group designed is simulated by ansoft software, the flux distribution,flux density nephogram,air gap flux density curve diagram are obtained.4. By comparing images of the bar magnet and the permanent magnet group, we conclude the permanent magnet group has many advantages, such as smaller size, closer structure, the bigger magnetic flux density, magnetic field energy concentration, better direction, and more flexible and convenient, economical, etc.At present, foreign technology in EMAT has entered the stage of industrial applications, while EMAT in our country has a late start. However, EMAT transducer is non-contact between the medium surface and the transducer and needn't add any sound coupling agent and has good reproducibility, high-speed testing for dynamic, high-temperature testing, economy, environmental protection and many other advantages, thus increasing the acoustic and all aspects of NDT personnel concerns. With the development of new analytical methods (such as finite element, boundary element method), signal processing methods (such as wavelet analysis) and the application of new technologies (for example, phased array technology, focusing techniques, resonance technology, imaging technology), The design systems of EMAT will be more perfect, more powerful and efficient . EMAT will also be greatly improved. It is foreseeable that in the near future electromagnetic ultrasonic non-destructive testing technology will be mainstream technology in the field and plays an irreplaceable role.