Numerical simulations of an electromagnetic actuator in a low-frequency range for dipole acoustic wave logging

Abstract

In dipole acoustic logging, transducers are required to work in a low frequency range to measure shear wave velocities so as to analyze the characteristics of formations. An electromagnetic actuator in a low-frequency range for dipole acoustic logging is simulated by using the Finite Element Method. The 3-D harmonic response analyses of the transducer have been conducted to evaluate the radiation performance. In the frequency range of 0-5 kHz, the vibration modes at 400Hz and 674Hz are possible to be excited due to the way the force loads apply. The simulation results show that with the external radiation structures added, the sound pressure level generated by the transducer is increased largely especially in the low frequency range below 1 kHz and the frequency response curve becomes flat and wide in the entire frequency range. The performance of the whole transducer can be improved by adjusting the radiation structure sizes to change the 1st vibration mode and by optimizing the design of internal electromagnetic actuator to change the 2nd vibration mode effectively. Besides, the directivity patterns show the transducer performs as a perfect dipole source in the operating frequency range which is beneficial to the dipole acoustic logging in a borehole.