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There are three different types of passive RFID technologies: low-frequency (125 to 134 kHz), high-frequency (13.56 MHz) and ultrahigh-frequency (860 to 960 MHz). UHF has the longest read range (30 feet or more), while UHF readers emit beams of energy and the tags reflect back a signal using something called backscatter. The length of the beam can be scaled back by reducing the power output of the reader and attenuating the reader antenna’s signal, but the read field is not easily defined. Radio waves bounce off things and might open the door when the pet was 10 feet away.
LF and HF each have a read range of about 3 feet, and it’s much easier to control the read range of such technologies. The reader creates a bubble of energy that can be increased or decreased in size by changing the power output and the size of the reader antenna. If an animal walked into this read field, the tag under its skin or in its collar would trigger the door to open. You would need to experiment a little to get the size of the read field right.
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