RFID (Radio Frequency IDentification)
RFID (Radio Frequency IDentification) Is a technology that dates to the second World War where radio waves were used to identify aircraft as a friend or foe. In the 21st century RFID technology has advanced to where it can be used to identify cereal boxes in your local supermarket. Broadly speaking RFID is a technology enabling the transfer of information to and from a memory source (microchip) without contact using energy in the RF spectrum.
Emerson & Cuming Microwave Products has developed unique solutions to enable RFID tags to be read when placed on metal. ECCOPAD® MetalTag is a small form factor, thin Gen 2 compliant, inexpensive read on metal tag.
An RFID system consists of a reader or interogator that emits a signal in the HF or RF spectrum and an RFID tag. The tag consists at minimum of the microchip containing information and an antenna to receive the energy from the reader. In an 'active' RFID system the tag would actually transmit information back to the reader. These systems can have several hundred feet of read range. In a 'passive' RFID system the tag has no power source and must rely on the power transmitted from the reader to operate. Passive RFID systems have considerably less read range than active sytems (in general, no more than 30' of read range) but the tags are considerably less expensive.
HF, UHF
Two popular frequencies used in passive RFID are 13.56 MHz (HF) and 860-960 MHz (UHF). HF readers use magnetic field coupling to read the tag. The tag is designed to resonate at 13.56 MHz so when in the presence of a magnetic field at 13.56 a voltage is established across the microchip which allows it to turn on and interact with the reader. The chip will modulate the properties of the tag in a manner which can be detected by the reader. Read range with HF systems are less than 1 meter.
An emerging frequency range for RFID is the UHF band from 860-960 MHz. This range actually encompasses three separate bands which are used in the EU (865-868 MHz), the US (902-928 MHz) and Japan (952-956 MHz). In a perfect world there would only be one frequency but various issues in the separate regions prevent this. UHF readers transmit a free space electromagnetic wave. The tag microchip must receive sufficient power from this wave to 'turn on'. The tag will then modulate the backscatter (reflection) of the tag in a manner that can be read by the reader. Read ranges of UHF systems can approach 30' or more.
RFID on metal
Both passive RFID types share the characteristic that the tags can not be read when they are placed on metal. In general, the tags will not read within a half inch or so of metal so spacer made of a foam material is sometimes used. This is thick and bulky and has a tendency to be damaged when it extends so far from the object. ECMP has developed the ECCOPAD® line of RFID isolators which serve to enable RFID tags to read on metal objects with considerably less thickness than the traditional approach.
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