The reduction of energy.
Attenuation in RFID applications: the weakening of RF energy from an RFID tag or from a reader. The energy emitted by the reader decreases with distance. The rate of decrease is proportional to the inverse square of the distance. Passive UHF RFID tags reflect back a signal at very low power levels. A tag's reflected signal decreases as the inverse fourth power of the distance between tag and reader. Attenuation be increased by external factors as well. For instance, water absorbs UHF energy, causing signal attenuation.