| Electromagnetic ultrasonic technology has been developed rapidly and applied widely in recent decades, because it has a lot of advantages such as independent of couplant, non-contact etc. Due to the rapid development of national economic construction, the demand of aluminum alloy plate is increasing. Inevitably, there will be some defects in plates on account of limitations of aluminum alloy sheet production process. So the research which is electromagnetic acoustic transducer(EMAT) used on aluminum alloy plate not only have theoretical significances but also have application values. It increases the difficulty in practical application that low electromagnetic acoustic transducer conversion efficiency resulting in the received echo signal induced voltage is small.In this paper, electromagnetic acoustic transducer of body waves used on thick aluminum alloy plate will be optimized to enhance the echo amplitude of the induced voltage signals. Beforehand, the 3 kinds of electromagnetic acoustic transducer mechanism are analyzed briefly. Then the working process of Lorentz force mechanism is analyzed emphatically, established the mathematical model at the same time. Based on the mathematical model, a two-dimensional finite element model of electromagnetic acoustic transduce is established by the finite element software.Aiming at enhancing the electromagnetic acoustic transducer echo signals in the flaw detection, the butterfly coil is chose to establish a bulk wave electromagnetic acoustic transducer two-dimensional finite element model, and the orthogonal experiment method is used to optimize the model. Aiming at most of existing electromagnetic acoustic transducer finite element models are ideal models,the effects circuit parameters were ignored to simulation results. In this paper, taking the thickness measurement for example, a spiral coil electromagnetic acoustic transducer model including the circuit part is built to design. After calculating theequivalent impedance, a spiral coil electromagnetic acoustic transducer two-dimensional axisymmetric finite element model is established by choosing the double layers spiral coil, then orthogonal experiments are designed to optimize the model.Two sets of test results are analyzed through extreme difference analysis. In the flaw detection, comparing the defect echo signal of voltage value with different configurations strength level, optimizational configuration parameter values of magnet and coil are obtained. Also it is obtained the optimum width ratio of the magnet and the coil in the present structure. In the thickness measurement, the optimized spiral coil EMAT echo amplitude is higher than the original one. |
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