The matching layer design of borehole wall ultrasonic imaging logging transducer

In this paper, the finite element method is used to investigate the influence of matching layer on the center frequency and the frequency bandwidth when the borehole wall ultrasonic imaging logging transducer operates in the mud. Our numerical results show that the characteristic impedance and the thickness of the matching layer influence the resonance frequency and the harmonic peak. With the increase of the characteristic impedance, the first order thickness mode resonant frequency reduces while the second order increases, which makes the valley deeper and deeper on the curve of conductance. When the characteristic impedance reaches a certain value, the center frequency and -3dB relative bandwidth steeply change. With the increase of the thickness of the matching layer would lower the first and second order thickness mode resonant frequency, the -3dB relative bandwidth increases at first then decreases that leaves the maximum. The value range of the characteristic impedance and the thickness of the matching layer is obtained for a certain frequency bandwidth. This work can be used to lower the manufacture difficulty and increase the range of matching layer material choice.