On-Metal Tag

What Is an On-Metal Tag?

An on-metal tagon-metal tagSpecially designed NFC tagNFC tagPassive unpowered device storing data, powered by reader's RF fieldView full → functioning on metal surfacesView full → is a specially engineered NFC tag designed to operate when mounted directly on metal surfaces. Standard NFC tags fail completely on metal because metallic surfaces create eddy currents that absorb RF energy, detune the antenna, and prevent the tag from harvesting enough power from the reader's field. On-metal tags solve this problem by incorporating a ferrite absorber or spacer layer that shields the antenna from the metal substrate.

Why Standard Tags Fail on Metal

When a standard NFC tag is placed on a metal surface, two problems occur simultaneously:

1. Eddy current absorption. The reader's alternating magnetic field induces circular currents (eddy currents) in the metal surface. These currents generate an opposing magnetic field that cancels the reader's field at the tag's antenna, drastically reducing the energy available for inductive coupling.

2. Antenna detuning. The metal surface acts as a secondary conductor that changes the tag antenna's effective inductance, shifting the resonant frequency away from 13.56 MHz. Even if sufficient energy reaches the tag, the detuned antenna cannot efficiently harvest it or perform load modulation for the return signal.

Together, these effects typically reduce the read range of a standard tag on metal from several centimeters to zero.

How On-Metal Tags Work

On-metal tags use one or more countermeasures to restore NFC functionality on metal:

Ferrite absorber layer. A thin sheet of flexible ferrite material (typically 0.3-1.0 mm thick) is placed between the tag's antenna and the metal surface. Ferrite absorbs the magnetic field lines that would otherwise reach the metal, preventing eddy current formation. The antenna operates as if the metal were not present.

Spacer layer. A non-conductive spacer (foam, plastic, or air gap) separates the antenna from the metal surface. The increased distance reduces the intensity of eddy currents. A spacer of 1-3 mm can significantly improve performance, though it increases the tag's total thickness.

Modified antenna designantenna designEngineering NFC antennaNFC antennaCoil antenna creating electromagnetic field for NFC communicationView full → geometry for performance requirementsView full →. Some on-metal tags use antenna designs specifically optimized for metal-backed operation, with adjusted inductance and additional resonance compensation to maintain tuning at 13.56 MHz when mounted on metal.

On-Metal Tag Specifications

Applications

On-metal tags are essential in numerous industrial and commercial scenarios:

Asset tracking. Metal equipment, tools, machinery, and vehicles need NFC tags for identification and maintenance tracking. On-metal tags attached to metal assets enable tap-to-identify workflows.

Industrial automation. Manufacturing environments use on-metal tags on metal jigs, pallets, and containers for process tracking and quality control.

IT asset management. Servers, networking equipment, laptops, and other metal-bodied IT assets use on-metal tags for inventory management.

Automotive. NFC tags on vehicle bodies, engine components, and metal parts enable supply chain tracking and authentication of genuine parts.

Selection Criteria

When choosing an on-metal tag, consider ferrite thickness versus read range (thicker ferrite provides better shielding but increases profile), adhesive type (industrial-grade acrylics for metal bondingbondingElectrical connection process between IC die and antennaView full →), environmental rating for outdoor and industrial deployments, and chip selection (the same families used in standard tags work in on-metal configurations).