2017 Volume 14 Issue 5 Pages 20161275
Time-frequency domain reflectometry (TFDR) based on electromagnetic theory is first introduced to measure air gap in cables. By using the relationship between propagation velocity and permittivity in electromagnetic theory, the new relationship between the air gap and the propagation velocity in cables can be obtained. The proposed method adopts a chirp signal as an incident signal and uses a normalized cross-correlation function for deriving propagation velocity. To reduce signal distortion caused by cable attenuation characteristics, a modified overcomplete wavelet transform is applied. The air gap volume, which can be measured by the proposed method, can be used as an indicator of poor contact between the cable and connector. The performance of the proposed method is verified through experiments.