Criteria for Selecting the Right RFID Tag

In order to select the right tag for your application, you must consider several factors that will affect the tag performance. As the market is flooded with hundreds of types of tags, there is no simple way to sort them all and pick the perfect one. However, we have gathered criteria that will help you with your selection.

• Tag Type – passive, active, semi-passive
• Tag Frequency – low, high, ultra-high, microwave
• Tag Orientation, Location and Placement
• Environmental Factors – metal, liquids, harsh environments
• Standards and Regulations Compliance – FCC, ETSI, ISO, Gen2
• Mandates Compliance – Walmart, DoD, etc.

Tag Type

The factors affecting tag type selection are read range requirements, sensor requirement, cost, size, weight, and the type of application. The most distinguishing factors between passive and active tags are read distance, size and cost.

• Active tags have much longer read ranges - over 100 meters (300 ft), while passive tags usually only about 10 meters (30 ft). The read ranges vary by product and manufacturer.
• Active tags due to their construction and battery are usually much larger than passive tags, which are most often in form of a smart label.
• Passive tags are cheaper than semi-passive or active tags. Tag cost should be considered relative to the cost of the items being tagged. For example, a $100 active tag attached to a container is economical, while a 25 cent tag attached to a box of cereals may not be.

Some applications dictate the type of tags used. For example, to monitor temperature within a refrigerated truck, you would need semi-passive or active tags with temperature sensors.

To monitor security and integrity of a shipping container, an active tag with an intrusion sensor may be used. A reusable tote or plastic container used in a manufacturing or food-processing plant may be fitted with a semi-passive tag. Since these totes and containers re-circulate inside the plant, the cost of the tag is not a major concern. For more information on tag types, read How to Select Correct Tag – Passive vs. Active.

Tip: When selecting tag, consider the cost of applying the tag to the object to ensure your ROI.

Tag Frequency

Selection of tag frequency depends on factors such as read range requirements, material to be tagged, and data rate.

Read Range

• LF and HF tags with shorter read ranges (few inches) are ideally suited for such applications such as access control and payment systems, which require a very small read range due to security.
• In tagging pallets used in a supply chain, a read range of 5 to 10 feet is required. UHF tags are well suited for this application.

Materials Tagged

Items with aqueous content require separation between the item and UHF or microwave tag. At the item level, few choices for tag placement are available and less opportunity exists to create an air gap between the tag and the object. In this type of situation, an HF tag with 2 to 3 feet of read range is an ideal choice. HF and LF tags are well suited for tracking humans and animals because living bodies have a high water content. The FDA has approved LF tags for human and animal implantation.

Objects with metals pose a special problem to tagging. Tags directly attached to metal objects are detuned and cannot work well regardless of the tag frequency. If UHF and microwave tags are attached to metal with a small air gap between the tag and the object, they can be easily read (LF and HF tags are more sensitive to metal and require a larger air gap). Or you can apply metal-mount tags that are specifically designed to work on metal surfaces. For more information about frequency selection, check out How to Select a Correct Tag – Frequency.

Tag Orientation and Location

Tag performance is affected by the orientation of the tag relative to the interrogator antenna. The best tag orientation occurs when the tag plane and the antenna plane are parallel to each other. At this orientation, the tags receive the maximum power. As the tag is rotated, it presents a smaller effective area to the incoming radio waves and thus collects less power. The tag read range decreases as the collected power decreases.

Even if the tag antenna is parallel to the reader antenna, it may have problem being read, especially if the reader antenna is linearly polarized and the tag antenna is a single dipole and the orientation of waves and tag antenna does not match. Due to this issue, circularly polarized antennas are used in 99% of applications, but this is something to be aware of in case, linear antennas are implemented. For more explanation, review RFID Reader Interrogation zones.

Environmental Factors

The environmental conditions that the tag may encounter during its lifetime are major considerations in tag selection. A tag embedded within the product may encounter high temperatures and pressures during product manufacturing, and it must be able to survive those conditions. Evaluate environmental conditions not only within your own facility but also in any environment the tag will travel through during its entire lifetime. These environmental conditions may affect the tag’s read range or read rate:

• The substrate may absorb moisture or may become brittle and crack.
• The adhesive may not hold the tag due to moisture or chemicals and the tag may fall off the item.
• The interconnection between the antenna and the IC may break due to vibration or due to repeated flexing of the tag.
• The antenna may be weakened due to corrosive effects of the chemicals in the environment.

You may need to use encapsulated tags that are protected from abrasion or chemicals in the environment.

RFID Standards Compliance

Tags may be selected for compliance with certain standards. The standards may be open, such as ISO, or they may be proprietary. It is a good practice to follow the open and popular standards, because more companies manufacturing products use these standards than proprietary ones, providing a wider choice of products. In addition, these products may be cheaper due to higher volume, and support for them may be available for a longer period. With the wide acceptance of EPC Gen 2 standards (now also ISO 18000-6c), it is best to use Gen 2–compliant products if you are going to use UHF. For more information on Standards, check out How to Select Correct Tag – Standards & Mandates.

Compliance Requirements

Many large organizations and government agencies have mandated that their suppliers provide goods with RFID tags. These published mandates may specify tag type, frequency, amount of memory, read range, read rate and speed, and protocol. In addition, the mandates may specify how the goods should be tagged. If you are supplying goods to one of the mandating companies, you have little choice in tag selection. The frequency and tag types are specified in the mandates. You may select tag manufacturer and tag model depending on the materials being tagged and the location of the tag on the goods. For more information on Standards, check out How to Select Correct Tag – Standards & Mandates.