Abstract
In the previously finite element and analytical model for the excitation process of electromagnetic acoustic transducer (EMAT), it is generally assumed that the EMAT coil is provided with a current of a limited amplitude. Meanwhile, pulse power amplifier, resistance of transmission line, impedance matching network and coil equivalent impedance are not taken into consideration. In this paper, an excitation equivalent circuit model for the EMAT is established, effects of the output voltage and output impedance of pulse power amplifier, impedance matching parameters and characteristics of the excitation coil on the EMAT conversion efficiency are considered. Based on experiments, influences of connecting mode (series or parallel) of multi-layer coil, coil conductor diameter and number of coil layers on the EMAT efficiency with various frequencies are studied. Results show that for the multi-layer spiral coil EMAT at 1MHz and 2MHz, it is better to use parallel connecting method. The EMAT efficiency is rapidly decreased with the increase of number of coil layer when spiral coils are connected in series. When the EMAT coil is perfectly matched, the output impedance of the pulse generator, resistance of transmission line and the EMAT dynamic coil impedance (number of layers, wire diameter, excitation frequency) also meet special conditions, the EMAT excitation efficiency can be maximized.
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