When tags are attached to metal objects, the main factor that reduces tags radiation efficiency is that incident electromagnetic waves totally reflect from the metallic surface with a 180° phase reversal.
The reflected wave will cancel the incident wave and reduce the energy available to activate the RFID tags chips
Studies have proven that spacing between the tag and the metal object significantly increases read rates.
Moreover, when a radio wave hits an obstacle smaller than its wavelength (λ(915 MHz) = 0.327 m), scattering occurs and wave patterns are redirected with random phase and amplitude.
RF waves are being reflected and scattered randomly on the cans since they are smaller than 0.327 m in diameter and length.
Tagging metallic objects requires special tags or tag spacing, but tagging cardboard cases with metallic objects inside offers much more flexibility.
In our test, the cases of cans were tagged, which are rectangular and made of cardboard.
The content was cylindrical metal cans.
This configuration offers spacing of 4 to 15 mm of space between the tags and the metallic cans.
Attention was not put towards precise tag positioning; therefore, some tags may have been closer to metal than others.