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| Method | Key to Figure 1 | Transducer | Positives | Comments |
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| Through transmission | (a) | T + R | Simpler electronics compared to (c) | Continuous wave and pulse operation are possible |
| Pitch-catch | (b) | T + R | Single side access required only compared to (a) | Same as (a) |
| Pulse-echo | (c) | T/R | Single transducer required only compared to (a, b) | Pulse operation only |
| Backscatter | (d) | T/R | No reflector required compared to (c) | Same as (c); effective for highly scattered media |
| Acoustic emission | (e) | R | No need for transmitter and its driver | Signals are difficult to interpret; limited applicability |
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