User's Manual

MPR series User’s Manual: Draft version 0.95 11/4/04 page 20
there is no radiated power, there is usually very little issue with regulatory compliance in using LF tags and
readers.
High-frequency (HF) tags and readers operate at 13.56 MHz. This frequency is available for industrial use
in most jurisdictions worldwide. The wavelength is about 20 meters (60 feet), still larger than most reader
or tag antennas, so inductive coupling is used as in LF tags and readers. However, the higher frequency
provides a larger induced voltage, so the reader usually uses a single-turn coil, and transponders typically
incorporate 3-5 turns of wire. HF transponders can be readily constructed on a flat plastic substrate the
size of a credit card, forming Smart Cards widely used as identification badges and credit cards with
enhanced functionality. Typical read range varies from a few cm to a meter or so (a few inches to 3 feet),
again dependent on reader antenna size.
When long read range is required, ultra-high-frequency (UHF) tags and readers are appropriate. The
MPR-series cards are UHF RFID readers. UHF systems typically operate at frequencies between 860 and
960 MHz, depending on the regulatory jurisdiction. In the United States, unlicensed operation is allowed in
the Industrial, Scientific, and Medical (ISM) band at 902-928 MHz. The wavelength at these frequencies is
about 33 cm (13 inches), so the reader and tags are roughly comparable in size to the wavelength. The
reader antenna creates a radiated electromagnetic wave, which can propagate long distances. UHF tags and
readers can thus exploit radiative coupling to achieve read ranges not available for LF or HF devices.
Read range for passive UHF tags can be as much as 10 meters (30 feet) with an appropriate directional
antenna; longer ranges are achievable using semi-passive tags.