Abstract
In dipole acoustic logging, transducers are required to work in a low frequency range, such as 0.5–5 kHz, to measure shear wave velocities so as to accurately analyze the anisotropy parameters of formations. In this paper, an electromagnetic actuator is designed for more effective low-frequency excitations than conventional piezoelectric bender-bar transducers. A numerical model has been set up to simulate electromagnetic actuators to generate flexural waves. The Finite Element Method (FEM) has been applied to simulating the radiation modes and harmonic responses of the actuator in a fluid, such as air and water. In the frequency range of 0–5 kHz, the first ten vibration modes are simulated and analyzed. The simulation results of 3-D harmonic responses of the sound field, such as the deformation, acoustic sound pressure, and directivity pattern, have been conducted to evaluate the radiation performance. From the simulation results, it is concluded that the second asymmetric mode at 670 Hz could be excited more easily than the others. This oscillated-vibration mode is useful to be applied in a dipole source. The frequency response curve is broad and flat and the electromagnetic actuator is beneficial to generate the wideband signal in a required low frequency range, especially below 1 kHz.
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