passive RFID tags

A Guide to Understanding UHF Passive RFID Tags

When it comes to radio frequency identification (RFID) solutions, ultra-high frequency (UHF) passive RFID tags are an extremely popular option because they are very cost-effective, yet still have one of the longest read ranges. They have no power of their own — which is why they are called “passive” tags — so they are powered by the radio frequency energy transmitted from RFID readers/antennas. A UHF passive RFID tag consists of four sub-components: and RFID chip, an antenna, an inlay, and a carrier.

The RFID chip is an integrated circuit that provides several key attributes related to operating frequency, memory type and capacity, data transmission/receipt, and power. In other words, the chip is the brains of the RFID tag. The antenna, which is attached to the chip, collects radio frequency waves used to power the chip. The antenna also transmits attribute data from the chip. Together, the chip and the antenna comprise the RFID inlay.

An inlay is typically a plastic substrate that the chip and antenna are placed on so they can be connected. Inlays come in two types: wet and dry. A wet inlay features an adhesive so it can be applied to a surface; a dry inlay has no adhesive. The choice of inlay depends on the purpose and placement of the tag on an object.

There are literally hundreds of different types of inlays, each designed with a specific application in mind. Different industries have different requirements for inlays, so there are inlays for pharmaceutical, automotive, retail, manufacturing, and healthcare applications. The inlays are designed for optimum performance when affixed to the material they are intended for. Inlay manufacturers ship their products to RFID tag producers, like Lowry Solutions, who then produce finished products that are ready to be applied.

The carrier is the material or package that the inlay is placed in. The simplest carrier is label stock (think barcode label), where the inlay is laminated into the label stock using specialized converting equipment. Examples of other carriers include plastic capsules or ID badges. Sometimes carriers are made of specialized materials that make it easy to mount the RFID tag on liquid containers or metal, or in high-heat or hazardous environments. These types of carriers are often referred to as “hard tags.”

How to choose the proper passive RFID tag

Selecting the proper RFID tag can be difficult because there are literally thousands on the market today. So how do you figure out what kind of tag you need?

The selection process starts with the RFID chip. Your business’s data requirements will determine the kind of chip you need because the chip’s capacity must provide the proper amount of data in the proper format.

Then you should select the RFID inlay. This process depends on the physical properties of the product to which you want to apply an RFID tag. The antennas on individual inlays are designed and tuned to specific materials. Antennas will have different designs if the inlay is being applied to metal or glass versus cardboard, and different yet again for materials with a high liquid content.

There are near-field antennas that provide short-read ranges versus full-field, long-read range antennas, depending on your requirements. It is highly advised that you consult an RFID professional to ensure that you select the right tag for your application.

Where do I place the tag?

Once you’ve chosen the right tag, the challenge becomes selecting the ideal location to place the tag on the targeted item. Regardless of what the item is or what it’s made of, proper tag placement depends on how the item traverses the business process and where in the process the tag needs to be read. With this knowledge, which is typically obtained in an RFID site survey, the tag can be optimally placed to ensure that it is read.

When you’re implementing your RFID project, don’t forget to consider how you’re going to apply your passive RFID tags to your target object. There is a cost associated with this, and in some applications, it can be significant.

For example, if you’re implementing an RFID asset tracking application, you need to install an RFID tag on each asset (typically a permanent tag). Depending on the number of assets and where they reside, implementation could be expensive. This cost needs to be figured into the overall project.

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