RFID Line-of-Sight ...

RFID Terms

... "Line-of-Sight: In order for any communication to occur, a signal transmitted from interrogator or the RFID tag must reach the other device. Unless the device is in a completely shielded metal enclosure, some radiation will usually reach the device. This radiation may arrive in a direct line of sight path or it may arrive via scattered reflections from man-made or natural terrain features. However, the amount of radiation (and its phase) which reaches the device is very important. If a passive device is being used, sufficient radiation must reach a tag so that the tag can not only can interpret the information content of the signal, but must also be sufficient to power the signal transmission of the tag back to the interrogator. Therefore, passive devices usually have a significant degradation in their range when they are not in the direct line of sight to the interrogator, because otherwise they will not receive enough RF radiation to allow for a successful re-transmission of RF radiation. Active tags are much more non-line-of-sight tolerant, because they only need to receive enough radiation to allow for the incoming signal to be successfully interpreted. They then re-transmit using their own on-board power supply. " ...