Quantitative Detection of Rock Crack Width Using Microwave Resonance Vibration Eigenvalues

To accurately detect micro crack widths in rocks in real time, a new method based on a microwave resonance vibration model is proposed. Repeated experiments carried out by the developed microwave resonance vibration model-based sensor and the measuring apparatus determined that the center frequency of this model is 3.665 GHz. The experimental verification on various crack widths (below 1 mm) is performed after the calibration experiment of taking the plug gauge and dial gauge as standard. The relationship between the actual value and the amplitude of the output voltage of the microwave signal is analyzed; in addition, the influence of different environmental relative humidity and specimen water content on rock crack width measurement results is discussed. The experimental results show that, under the condition of a resonance vibration frequency of 3.575 GHz, the proposed method can accurately and directly determine the micro crack width in rocks. The detection system is developed with a relative error of less than ±5%, the minimum value of stability detection is
$50~\mu \text{m}$
, and the fastest response speed of 0.28 ns. In terms of the influence of different environmental relative humidity and specimen water content on the measurement results, the greater the relative humidity, the higher the specimen water content, and the greater the influence on the measurement results. It provides an important reference for rock crack width variation monitoring and serves well for the rock masses engineering stability evaluation.