A device that measures the moisture content of materials using radio frequency radiation absorption by water vapor is called a Radio Frequency Moisture Sensor.
The sensor emits radio frequency waves into the material being tested. Water vapor in the material absorbs a portion of this radiation, resulting in a decrease in the signal strength received by the sensor.
Moisture sensors can be used to detect water damage in buildings, roofs, and other structures. By measuring the moisture content of the material, the sensor can identify areas with excessive moisture, indicating potential leaks or water damage.