Firstly, an object made of metal close to an antenna operates as a reflector and furthermore, metallic surface of object in the vicinity of an antenna changes its radiation pattern, input impedance, radiation efficiency and resonant frequency.
These changes depend on the size and shape of the metallic object and also on the distance of the antenna from the object
RFID tags require a minimum RF signal power, defined by the sensitivity of the receiver circuit, to be activated and to be able to return a signal to the reader.
Consequently, tagging metallic products or using an RFID system inside a metal environment (such as a sea container) can present serious difficulties.
Although previous research has been done on indoor propagation of radio waves, only few specialize on RF behavior inside a metal environment such as a sea container