Tension Force Identification of Hollow Stranded Steel Wire Cables Using Millimeter-Wave Radar

To address the challenge of accurately capturing the internal vibration of hollow stranded steel wire cables encased in HDPE sheaths, this study proposes a non-contact cable tension identification method based on millimeter-wave radar. Exploiting the superior penetration capability of millimeter waves through non-metallic materials, the method enables direct measurement of millimeter-scale vibration displacement of the steel strands inside the sheath and establishes a tension inversion model based on multiple vibration frequencies. Validation through laboratory-scale cable model experiments and field tests demonstrates that the millimeter-wave radar reliably penetrates the high-density polyethylene (HDPE) sheath to acquire true internal vibration signals with sub-millimeter displacement accuracy. Under long cable conditions (>100 m), strong coupling between sheath and strands results in high consistency between radar-identified and accelerometer-measured frequencies, with maximum relative errors below 1%. In contrast, for short cables (<80 m), reduced coupling causes discrepancies in vibration characteristics, leading to relative errors up to approximately 3.45%, necessitating correction considering the coupling effect. Frequency identification results across different measurement points exhibit high stability, with standard deviations below 1%. The findings indicate that the proposed method is well-suited for high-precision tension identification in long cables or well-coupled conditions, offering significant potential for practical engineering applications.