## 3 Results  
### Changes in Wave Velocity of Specimens After Microwave Treatment  
The propagation of ultrasonic waves within rock is significantly affected by its fracture structure. When ultrasonic waves encounter fissures, they are partially reflected or refracted, which alters both their path and speed. Therefore, by analyzing the propagation characteristics of ultrasonic waves in rock, internal fissures can be inferred, offering a macroscopic evaluation of the rock's structural integrity and properties. The experiment utilized the HS-YS4A rock acoustic parameter tester, which supports a frequency range of 100 kHz to 20 MHz. This device was manufactured by the Xiangtan Electronic Research Institute, China. This instrument is equipped with a cylindrical ultrasonic transducer, enhancing its capability to accurately measure acoustic parameters in various rock samples. Ultrasonic measurements were conducted on different groups of basalt using a sampling frequency of 10 MHz to determine the wave velocity. Data showing substantial velocity variances were excluded, and the wave velocities of the remaining specimens were averaged, as presented in Table 2.  
Figure 4: Principle of NMR signal release. Figure 3: Experimental instruments with microwave radiation after the sample. (**a**) Experimental equipment. (**b**) Basalt sample after microwave irradiation. After absorbing 3 kW and 6 kW of microwave energy, the basalt specimens displayed a pattern where the rate of wave speed reduction initially intensified before diminishing, as shown in Figure 5. This pattern occurs because, at the beginning of microwave exposure, the rock absorbs microwave energy, leading to increased water evaporation and accelerated mineral decomposition. The associated temperature rise induces thermal stress within the rock, causing the formation and expansion of microcracks, which in turn accelerates the decline in wave speed. However, once the intensity and duration of microwave radiation surpass certain thresholds, the internal damage to the rock reaches a critical state, causing the rate of wave velocity reduction to peak before rapidly decreasing. This decline is due to the extensive damage, which reduces the rock's efficiency in absorbing further microwave energy. In this study, longitudinal wave velocity is used to quantitatively characterize the damage in microwave-treated rock specimens [38]. The damage coefficient is defined as follows:  
\[F_{D}=1-(\frac{V_{P}^{post}}{V_{P}^{pre}})^{2} \tag{1}\]  
In this context, \(V_{P}^{pre}\) represents the longitudinal wave velocity of the rock specimen before microwave treatment, and \(V_{P}^{post}\) represents the longitudinal wave velocity of the rock specimen after microwave treatment. The damage coefficient is calculated to quantify the extent of damage induced by microwave radiation. The closer the damage coefficient is to 1, the greater the damage inflicted on the rock specimen by the microwave treatment. The results, as shown in Table 2, illustrate the relationship between microwave exposure and rock deterioration based on this damage coefficient. Under 3 kW of microwave radiation, the damage coefficient of the specimen after 30 s of irradiation is only 29.89% of that after 60 s, whereas the damage coefficient after 90 s reaches 85.25% of that after 120 s. Similarly, under 6 kW of microwave radiation, the damage coefficient after 30 s is 36.93% of that after 60 s, while the damage coefficient after 90 s reaches 94.51% of that after 120 s. These results demonstrate the progressive nature of damage as irradiation time increases, with higher power levels significantly accelerating the accumulation of damage. Furthermore, the extent of damage to basalt follows a pattern where the rate of damage initially intensifies and then diminishes as the irradiation duration is extended. This section may be divided by subheadings. It should provide a concise and precise description of the experimental results, their interpretation, as well as the experimental conclusions that can be drawn.