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. 2016 Oct 19;16(10):1737.
doi: 10.3390/s16101737.

Mode Conversion Behavior of Guided Wave in a Pipe Inspection System Based on a Long Waveguide

Feiran Sun  1 , Zhenguo Sun  2   3 , Qiang Chen  4   5 , Riichi Murayama  6 , Hideo Nishino  7
Affiliations

Mode Conversion Behavior of Guided Wave in a Pipe Inspection System Based on a Long Waveguide

Feiran Sun et al. Sensors (Basel). .

Abstract

To make clear the mode conversion behavior of S0-mode lamb wave and SH0-plate wave converting to the longitudinal mode guided wave and torsional mode guided wave in a pipe, respectively, the experiments were performed based on a previous built pipe inspection system. The pipe was wound with an L-shaped plate or a T-shaped plate as the waveguide, and the S0-wave and SH0-wave were excited separately in the waveguide. To carry out the objective, a meander-line coil electromagnetic acoustic transducer (EMAT) for S0-wave and a periodic permanent magnet (PPM) EMAT for SH0-wave were developed and optimized. Then, several comparison experiments were conducted to compare the efficiency of mode conversion. Experimental results showed that the T(0,1) mode, L(0,1) mode, and L(0,2) mode guided waves can be successfully detected when converted from the S0-wave or SH0-wave with different shaped waveguides. It can also be inferred that the S0-wave has a better ability to convert to the T(0,1) mode, while the SH0-wave is easier to convert to the L(0,1) mode and L(0,2) mode, and the L-shaped waveguide has a better efficiency than T-shaped waveguide.

Keywords: EMAT; guided wave; mode conversion; pipe inspection; waveguide.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Pipe inspection system using a long waveguide [16].
Figure 2
Figure 2
Pipe inspection system with different shaped waveguides based on S0-mode lamb wave (a) longitudinal mode with T-shaped waveguide; (b) torsional mode with L-shaped waveguide [16].
Figure 3
Figure 3
Oscillation patterns of the (a) L(0,2) and (b) T(0,1) mode guided waves in pipes [16].
Figure 4
Figure 4
The dispersion curves of group velocity in the pipe: (a) longitudinal mode and (b) torsional mode.
Figure 5
Figure 5
The dispersion curves of group velocity in the waveguide: (a) lamb wave and (b) shear horizontaL(SH) wave.
Figure 6
Figure 6
The mode conversion experiments to prove the assumption.
Figure 7
Figure 7
Block diagram of experimental system.
Figure 8
Figure 8
The photo of the pipe inspection system.
Figure 9
Figure 9
The structure of meander-line coil EMAT for S0-mode guided wave.
Figure 10
Figure 10
Three configurations of permanent magnets (PMs) of EMAT: (a) two magnets; (b) four magnets; and (c) eight magnets.
Figure 11
Figure 11
The amplitude and signal to noise rate (SNR) value of S0 wave with different configurations of PMs shown in Figure 10.
Figure 12
Figure 12
The amplitude and SNR of S0 wave with a different number of turns of meander-line coil.
Figure 13
Figure 13
(a) The layout of PPM EMAT; (b) The outlook of PPM EMAT for SH0 wave.
Figure 14
Figure 14
The amplitude and SNR of SH0 wave with different number of PM rows.
Figure 15
Figure 15
The received signal in the free waveguide: (a) S0-wave; (b) SH0-wave.
Figure 16
Figure 16
The received signal converted from S0 wave when the distance between the waveguides is 0.5 m: (a) Longitudinal wave using T-shaped waveguide; (b) Torsional wave using L-shaped waveguide.
Figure 17
Figure 17
The received signal converted from SH0 wave when the distance between the waveguides is 0.5 m: (a) Longitudinal wave using L-shaped waveguide; (b) Torsional wave using T-shaped waveguide.
Figure 18
Figure 18
The efficiency of mode conversion to different mode guided waves in the pipe (a) converted from S0 and (b) converted from SH0.
Figure 19
Figure 19
The efficiency comparison between S0 wave and SH0 wave when they convert to the same mode guided wave in the pipe: (a) T(0,1) mode; (b) L(0,1) mode; (c) L(0,2) mode.
Figure 20
Figure 20
The efficiency comparison between two waveguides.
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