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A Guide to Understanding UHF Passive RFID Antennas

When it comes to radio frequency identification (RFID) technology, 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 global RFID market, valued at US$ 16.83 billion in 2022, will reach an estimated US$ 39.30 billion by 2030. This substantial growth is expected to be propelled by a projected Compound Annual Growth Rate (CAGR) of 11.2% during the forecast period. 

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 UHF passive RFID 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 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.”

Passive RFID: What Is It?

Passive RFID operates without an internal power source, relying on energy from RFID readers and their antennas. When scanned, the RFID antenna emits an electrical signal converted into electromagnetic RF energy, activating the RFID tags in the scanning area. These tags respond with programmed information, requiring minimal energy to power their internal RFID chips.

The cost-effectiveness of Passive RFID tags, especially UHF RFID tags priced at a few cents, makes them a practical choice, a feat unattainable for battery-equipped tags. In contrast, Active RFID depends on batteries to power each tag, limiting adoption due to higher costs and a shorter lifespan.

Many businesses opt for RFID Inventory Management solutions and RFID Software to enhance overall efficiency and accuracy in inventory management. These tools leverage Passive RFID technology, simplifying tracking and management processes.

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 a passive 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.

  • Start with the Right RFID Chip: The chip’s capacity should align with your data needs, ensuring it can handle the required data in the proper format.
  • Opt for the Suitable RFID Inlay: Inlays feature antennas meticulously designed and tuned based on the specific materials they are intended for. The choice of metal, glass, cardboard, or materials with high liquid content influences the antenna design.
  • Consider Antenna Types: Near-field antennas are suitable for short-read ranges, while full-field, long-read range antennas are ideal for applications requiring extended reach. 
  • Anticipate Future Needs: Select RFID tags that meet your current requirements and anticipate future needs. Consider scalability and potential changes in your business that may affect data requirements.
  • Test and Validate: Before widespread implementation, conduct thorough testing and validation to ensure the selected RFID tag performs reliably in your specific environment and use case.
  • Consult with RFID Professionals: Given the complexities involved, it is highly recommended to consult with RFID professionals. Their expertise will ensure that the chosen passive RFID tag aligns perfectly with your application, offering optimal performance.

Exploring Passive RFID Frequencies: Comprehending the Spectrum

The passive RFID range extends across various frequencies, enabling versatile applications and uses in different industries. Passive RFID systems operate within three primary frequency ranges: Low Frequency (LF), High Frequency (HF), and Ultra-high Frequency (UHF).

Low Frequency (LF): LF RFID emits signals within the 30 – 300 kHz range, with common LF tags operating mainly on 125- or 134 kHz bands. Due to the limited transmission distance of radio waves in this frequency range, LF systems typically use one or two bands to avoid interference between systems.

High Frequency (HF): HF RFID operates within the 3 – 30 MHz range, with predominant use on the 13.56 MHz band. Similar to LF, HF is a short-range RFID technology capable of transmitting only a few inches up to about a foot. Near-field communication (NFC), a popular type of HF RFID, is widely utilized for data sharing and contactless payments.

Ultra-high Frequency (UHF): UHF RFID emits between 300 and 3 GHz, with most UHF RFID tags transmitting in the primary range of 860 – 960 MHz and a less frequently used band of 433 MHz. The global band of 860 – 960 MHz is subdivided into smaller region-specific bands, such as the US operating range limited to 902 – 928 MHz. It’s crucial to note that UHF RFID readers can only communicate on a specific frequency range, making it necessary to use different RFID readers and tags for HF/NFC and UHF applications.


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.

Exploring Passive RFID Applications: From Popular Uses to Optimal Tag Placement

Passive RFID applications dominate the landscape due to their widespread use compared to Active RFID. Once the appropriate tag is chosen, the challenge shifts to determining the optimal location to affix the tag to the target item. Regardless of the item’s composition or nature, the right tag placement hinges on how the item progresses through the business process and where, in the process, the tag needs to be read. 

Below is a list of popular Passive RFID applications and the frequency range utilized for each, organized by popularity.

  • Efficient Asset Management

Real-time tracking of assets within facilities using UHF RFID.

  • Securing Access

Regulate access to buildings, parking lots, and neighborhoods with HF/NFC RFID.

  • Optimizing Retail Inventory

Streamline the process of taking and managing retail inventory levels using UHF RFID.

  • Seamless Logistics Tracking

Document and monitor items at every stage of the transportation process with UHF RFID.

  • Efficient Work-in-Process (WIP) Management

Monitor and manage specific items throughout manufacturing using UHF RFID.


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