Electronic Product Code (EPC)
The standard frequency range used for tracking pallets, cases, and items in global chain applications is the UHF (Ultra High Frequency) RFID/EPC. If you are looking for a standard for closed-loop applications such as work-in-progress (WIP) management and asset tracking, well, there isn't one so it is wise to use a technology that is best suited for your needs. It means using the UHF standard intended for supply chain, or using other RFID technology, or even using a totally different tracking system. Most companies have problems using with UHF RFID for it does not work with liquids and metals but what they don't know is that it is possible for UHF RFID to work on metals, just a few tweaks and it will work.
Magnet Coupling and Passive Backscatter
Keep in mind that even in its basic ways, UHF equipment works differently from HF equipment. HF equipment uses a near-field method termed magnet coupling while UHF equipment usually uses a far-field system that is known as passive backscatter. Granting these features that exist on both frequencies, readers that are available on the market normally support one or the other.
The design needed to be different in antenna geometry for both tags and readers. Far-field can provide you much longer read ranges - a classic fixed reader can read a passive UHF tag up to 25 feet away - depending upon the tag features, physical and environmental circumstances. Battery-powered tags can be read at greater distances. Whilst, near-field will offer you read ranges between a few inches and a few feet at most. It is clear that in supply chain applications, the longer the read range the better suited it is in identifying pallets and cases.
For comprehensive technical facts on UHF RFID tags and their process, read the expert's article entitled Passive UHF RFID Tags on The RFID Network.
Passive UHF Tags On Metal
You are not wrong. It is possible for passive UHF tags to work directly on metal items. The only thing you need to do if you are working on far-field enhancements is to have at least 1/8 inch distance between the tag and the metal; yes, that is the secret. If that is not followed then the metal will short out the tag and it will not read. There are now a lot of UHF tags available on the market precisely intended for this kind of applications.
The images that is found on The RFID Network depict how two UHF metal mount tags are installed unswervingly on steel vehicle transporters. There is one tag placed on each side of the carrier. A single antenna which is the read point is mounted in each work cell. Since the read points could not steadily be installed on the same side of the cell, and the UHF passive backscatter can't read through metal, two tags per transporter are mandatory. Cost will not be a problem as you'll soon see.
The requirements defined the smallest tag quality that was suitable is 200+ reads per second when the tag was placed in a horizontal alignment at a 6 foot distance from the antenna. These tags read up to 13 feet away. The $2.50 tags are used over and over, thousands of times, so the per-use cost is less than 1¢. It is still in production today and it has never missed a tag.
UHF Tags in Water
Water distorts Radio Frequency (RF) waves and diminishes their range when using UHF far-field spectrum and that is a fact. In order to make UHF tags work in water, work with air gaps in the packaging for bottled beverages where far-field range is required and build pallets with tags on packaging facing out as much as possible.
For short-range, near-field applications such as item level tracking, magnetic coupling may be the best solution. Other companies have designed UHF tags that use the near-field magnetic coupling component. Consequently, the UHF tags can be applied directly to liquid-filled containers or even immersed.
Other reasons why UHF is suitable for global supply chain: