And how can I prevent the reading of tags that I don't want interrogated?
Those are often two different issues.
There are several ways in which to contain RFID signals. Some companies build Faraday cages, which are typically metal mesh enclosures that block radio waves. These enclosures—named after British scientist Michael Faraday, who invented them—can be built around a conveyor belt so that passing items can be read without causing interference with nearby equipment. Enclosures can be built using any material that reflects radio waves, including Mylar.
Preventing extraneous reads on a mobile or handheld reader is a different issue. Passive ultrahigh-frequency (UHF) radio waves are emitted from a reader's antenna, much like light from a flashlight. The energy can be focused to some degree, but the waves can bounce off metal objects, causing tags to be read that you don't want interrogated. Some companies have developed software algorithms that measure signal strength and filter out weak signals, since those would likely be extraneous tags that you wouldn't want read.
—Mark Roberti, Founder and Editor, RFID Journal
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