Metal is a very tricky material to tag with RFID. Most RFID tags need about a half inch of separation between the tag and the metal to get any type of read range at all. There is no way for RFID to penetrate metal so placing tags inside metal and expecting to get a read is out of the question; however, reading a tag placed directly on metal is becoming easier.
Tag Recommendations
The NOX-TM4 is the recommended tag for Metal-Mount RFID tagging. It is small, durable, and has an average read range of 15'. The NOX-TM4 can withstand temperatures up to 400 degrees F and is encased in a durable material designed to withstand impact and intense heat.
Absorption
Metal reflects RF so none can pass through a metal sheet. Most RFID tags, when placed directly on metal, will have a highly diminished read range. This read range can be improved by using a spacer to put about a half inch of space between the metal and the RFID tag. Some tags are designed to be placed specifically on metal. Metal-mount tags use their metallic backing to amplify their own signal.
Placement
Placement of an RFID tag on metal should be avoided whenever possible; however, when a tag must be placed on metal, a metal-mount tag should be used. Standard RFID tags may be used in combination with a foam spacer specifically designed for use with the tags. Spacers are often large and fragile. Spacers can be used when shipping palletized loads, but are not recommended for most applications.
Pro-Tips
Expected RFID Read Ranges
Standard RFID tags will have a read range of inches up to a maximum of 1'. This range can be extended up to 10' to 15' by using a spacer.
Metal-Mount Gen2 hardened tags will read a minimum of 10' up to 15' when optimized.
Expected Costs of RFID Tag
Non-programmed Metal-Mount RFID tags can cost as much as $3.74 each on quantity 1 and as little as $1.67 each on quantities over 1000.
Pre-programmed Metal-Mount RFID tags cost approximately $2 each on quantities over 1000.
Spacers for standard RFID tags will add $0.30 to the cost of each label.
What RFID tag sizes are there?
Metal-Mount RFID tags are now as small as 38mm x10mm x2.8mm.
Metal-Mount RFID tags are designed to be as durable as the items they are applied to. Many can withstand temperatures up to 400 degrees F.
Other recommendations:
NOX-TM15
NOX-MTS + NOX-1 RFID Tag (Foam spacers combined with the NOX-1 RFID tag.)
MTS + TX-2 or TC-1 RFID Tag (Foam spacers combined with either the TX-2 or TC-1 RFID tag.)