RFID Intro

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With RFID tags that don't have a power source (referred to as passive tags), RFID works by having a reader transmit radio waves which are picked up by these tags and used as a power source. When powered up, the tags are able to respond to commands from the reader as well as to communicate back.

 

The UHF Gen 2 standard (also referred to as EPCglobal Class 1 Gen 2, and ISO/IEC 18000-6C) is a global standard for RFID in the UHF radio frequency band.

 

 

RFID-tags

 

RFID tags may come pre-coded with a unique Electronic Product Code (EPC) on each tag. (These codes are typically 96- or 64-bits in length).

 

Other classes of RFID tags allow the EPC to be programmed with the RFID equivalent of a UPC code and serial number to allow the EPCs to be known by multiple parties (such as the various partners in a supply chain). Wikipedia has a list of these standard identity types at http://en.wikipedia.org/wiki/Electronic_Product_Code.

 

Tags may also come with writeable regions (banks) of non-volatile memory to allow data to be stored in the tag.

 

For asset tracking within a location, pre-coded tags may be sufficient. These will come with unique EPCs, but it is fine to use any of these tag types with StockCheck.

 

 

RFID Antennas

 

The RFID antenna in the MC3090Z reader is circularly polarized which provides great flexibility.

 

In contrast, antennas may be linearly polarized, either vertically or horizontally. (It may be helpful to think of linear polarization as being analogous to a barcode scanner's scan line).

 

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Fig. Drawing showing energy transmission for vertically- and horizontally-polarized antennas.

 

Why this matters is that there is an antenna in an RFID tag as well that receives the transmitted energy from the reader. The orientation of this tag antenna relative to the reader's antenna affects the amount of power that a tag receives, and hence the read range is affected as well.

 

A tag antenna may be laid out as a strip to conform to size and shape constraints, such as this one from Confidex:

 

Confidex

 

For maximum power transfer for such a tag, the antenna polarization should match the orientation of the tag.

In this case, if an actual label was laid out flat on the screen as you see it, it will be best read with a horizontally-polarized antenna face-on.

 

With circularly polarized antennas, the energy field rotates about an axis, distributing the energy entirely across all planes. While there is some compromise (any orientation only receives half the transmitted power), it makes the reader insensitive to the orientation of the tag's antenna. Tags are best read then by having the plane of the tag's antenna parallel to the plane of the antenna.

 

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Fig. Drawing showing energy transmission for a circularly-polarized antenna.

 

 

Tag Management

 

The tag Electronic Product Codes (EPCs) are electronic and therefore invisible. A decision will have to be made as to whether to associate visible, human-readable IDs with the tags. (For StockCheck visible IDs are optional and it does not depend on them for operation).

 

These visible IDs can take the form of barcode labels or they can be as simple as handwritten codes. Some tag manufacturers such as Omni-ID provide an option to supply tags marked with visible codes on them as well. You can also consider RFID printers, which are able to program the tag EPCs, as well as print a human-readable label which can include barcodes.

 

RFID-Printer

 

Fig. An RFID printer can program EPCs on inlaid RFID tags as well as print human-readable information and barcodes on a "smart label".

Zebra RP4T

Fig. Zebra RP4T mobile RFID printer.