| Popis: |
Summary The attenuation of the rock sample measured by ultrasonic transducer is disturbed by a number of factors, and the diffraction effect is one of the main influencing factors to the spectral ratio method. The aluminium is selected as the reference sample in conventional spectral ratio method. However, it will be affected by strong diffraction effects when the sample with low velocity, especially the low-frequency transducers are used. Although diffraction can be corrected by using theoretical correction method, the accuracy of the correction decreases as the diffraction effect increases. It can only be corrected from the experimental method. So, an improved method is presented for diffraction correction in this paper. The aluminium is replaced by the sample with similar acoustic properties to the test sample. Meanwhile the Q value of the reference sample should be known. Then the lucite is the best chose for reference sample in improved method whose velocity is lower than aluminium and physical and chemical properties are stable. The numerical simulation and physical models are used to study the feasibility and accuracy of the improved method. |
