## 4 Conclusions and Discussions  
This study presents a novel self-powered multifunctional rotational speed sensor for bottomhole power drilling tools based on the triboelectric nanogenator. The sensor enables the measurement of rotational speed and angle under self-powered operation. Experimental results demonstrate a rotational speed measurement range of 0 to1000 rpm, an angular resolution of 30 degrees, and a measurement error less than 3.2%, demonstrating that it can meet the accuracy requirements for actual underground rotational speed and  
Figure 7: Condition adaptability experimental results. (**a**) Output voltage of the sensor at different temperatures; (**b**) output voltage of the sensor at different relative humidity levels; (**c**) output voltage waveforms of the sensor under different cycle numbers; and (**d**) fitted curves of the output voltage of the sensor under different cycle numbers.  
angle measurements. The maximum power generation is 6.4 uW under a 10 M\(\Omega\) load, demonstrating that it can meet the self-powering requirements of the sensor while also providing a potential power source for other instruments. The sensor operates reliably within a temperature range of 0 to 160 degrees Celsius and a relative humidity range of 0 to 90%, exhibiting excellent performance.  
Compared with conventional downhole rotational speed sensors, the developed multifunctional sensor offers several advantages. Firstly, its dual functionality, encompassing both rotational speed and angular displacement measurement, provides more precise data for dynamic control of surface drilling operations. Secondly, the generator has a self-powering capability. If the power output continues to increase in the future, it holds promise for solving the power supply challenges in underground environments. At the same time, it also provides a reference for rotational speed measurement in other fields.  
The current power output of the sensor remains relatively low, sufficient only for its own operation and insufficient to power other downhole drilling-while-drilling (DWD) measurement instruments and sensors. Therefore, future research will focus on three key approaches to increase the sensor's power generation. First, the sensor's structural design will be optimized to increase its effective triboelectric contact area. Second, novel triboelectric nanogenator materials will be selected to ensure optimal energy harvesting efficiency. Third, novel nanowire structures will be synthesized to modify the nanomaterial surface morphology, thereby enhancing power generation.  
Conceptualization, J.Y., J.L. and H.Z.; methodology, J.Y.; software, L.C.; validation, J.L., L.C. and H.Z.; formal analysis, J.L.; investigation, H.Z.; resources, L.C.; data curation, J.Y.; writing--original draft preparation, J.Y.; writing--review and editing, H.Z.; visualization, L.C.; supervision, J.L.; project administration, J.Y.; and funding acquisition, H.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Major Science and Technology Special Project: research and development on high efficiency downhole power drilling tool for high temperature resistant, grant number 2024 ZD1000903.  
Not applicable.  
The raw data supporting the conclusions of this article will be made available by the authors on request.  
The authors declare no conflicts of interest.