Numerical simulation study on effectiveness of shielding structure on ultrasonic transmission tomography

Ultrasonic tomography (UT) is a non-invasive multiphase flow detection technique. In ultrasonic transmission tomography, reconstruction images are derived from a direct wave signal transmitted through the materials in the sensing area. The maximum values of the received direct wave from the reference pattern and the measured pattern are normally used to reconstruct the images. The speed of sound in the pipe wall and the materials in the sensing area affect the received signal. This in turn affects image quality—especially when the arrival time of the direct wave propagated through the sensing area is close to the arrival time of the direct wave propagated through the pipe wall. Here, we describe a novel shielding structure for ultrasonic transmission tomography. The relative variation ratio (RVR) is defined and used to evaluate the validity of the shielding structure. Larger RVR values imply better signal resolution and better signal suppression. A simplified mode is discussed including the influence of the shielding structure’s design parameters on the received direct wave. The optimized shielding structure size was determined. A comparison of the results between the normal pipe and the shielding pipe indicated that the RVR increased from 57.25 to 91.27%. This proves that the shielding structure can suppress the effect of the signal from the pipe wall on received direct wave signals.