free space wave

例句：

1. 1.The scientists were trying to detect the free-space wave.
   科学家们试图探测自由空间波。
2. 2.Free-space waves are important for communication systems.
   自由空间波对于通信系统非常重要。
3. 3. The researchers used a special device to measure the free-space wave.
   研究人员使用一种特殊的设备来测量自由空间波。