RFID tags are not like bar codes. Just because you see a tag doesn’t mean your RFID equipment will see it. Conversely, if you can’t see a tag, that doesn’t mean your RFID equipment won’t read it. To make sense of this contradiction, it’s important to understand the basic concepts about RFID tags, tag placement, and how tagged assets are going to be identified and tracked through the supply chain.
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If you’re implementing in retail, logistics, or transportation operations, that means understanding the complex journey of a product from manufacturer to store, and the different ways a tag’s readability may be affected. You must choose your real estate wisely and place RFID tags with consistency. It is time and money well spent because if your tagged product doesn’t read, either your customer will catch it and charge you a handling fee, or they won’t catch it and you’ll lose the cost of the product because your customer’s inventory will be wrong. You might even have to send a replacement product. Remember: Exception handling is far more costly than the price of an RFID tag.
1. Environmental considerations for RFID tag placement
Your customer’s or trading partner’s environment is different than yours. Yes, this is obvious, but until now, you probably didn’t care. Now, you need to care. Retailers have an extremely different design approach to their RFID solutions than their suppliers because they are dealing with thousands of companies shipping a wide range of products. Therefore, they will optimize their equipment configuration for the average product, not your specific product the way you will.
Although the physical layout of a distribution center and a retail store might be similar, there are several complicating factors that can negatively impact tags’ readability. First, it’s at this point in the supply chain that your product might come in contact with other products—either on a conveyor or as part of a mixed pallet. This means that your case could be next to one that includes metal or water, elements that can affect readability.
Second, some retailers’ distribution centers move cases on high-speed conveyors that operate at 600 feet per minute, and the retailers expect tags to be read at that rate. However, few manufacturers have tested their tags on conveyors that run above 300 feet per minute.
However, the biggest infrastructure challenge is the retail store itself. Stores receive loose cases of products piled into a truck (as in the image below). Once unloaded from the trailer, products might be placed on push carts, hand carried, or conveyed. The problem lies in the lack of conformity of movement. Retailers are most interested in what direction products are moving. They want to know as products come in through the dock doors, move from the backroom to the sales floor, leave through exterior doors, and, finally, when the case is recycled. Many manufacturers are concerned only that cases are moving in one direction: out.
This means your choice of tag and tag placement must be suited for the most challenging environment, which is most likely outside your facility and scope of control. Because your retail customers have little control over what RFID tag is used and where it is placed, they are relying on you to tag products correctly.
Most likely, your current bar code label is going to be replaced by a label with an RFID tag in it, also known as a “smart-label,” like the one pictured below. The characteristics of the tag in your label are very important.
2. RFID tag standards
The global standards for RFID tags used with pallets, cases, and items in the supply chain are ISO/IEC 18000–6:2010 and EPCglobal Class 1 Gen 2. These two standards are extremely close to one another and have similar requirements. You can narrow down your shopping list by only considering tags that are certified by EPCglobal. The complete list can be found here. The certified tags come in a variety of shapes, sizes, and prices.
At this point, you need to select a few different tags for testing with your products. You may decide to use different tags for single items, cases or cartons, or pallets. The RFID Network team has published a comprehensive set of benchmark reports on durable asset tags.
3. In what geographic areas will the RFID tag(s) operate?
Different regions of the world have different standards regulating the use of radio frequency (RF) emitting products. Standards are developed and issued by international, regional, national, and industry-specific entities. For example, in the United States, there's the Federal Communication Commission (FCC); in Europe it’s the EU Council. The Association of American Railroads (AAR) and International Air Transport Association (IATA) have their own standards. The more global the standard, the more entities are involved in the development. If you are tagging in the United States and shipping to a U.S. destination, then a tag suited for the FCC is fine. However, if you are tagging in Asia and shipping products to both Europe and the United States, then you should consider a tag suited for international operations.
Keep in mind that the differences between reader operation in the various regions go beyond what frequency range is used. There are differences in emitted power, how the reader hops between frequencies, and more. To simplify things a little, the table below can give you an idea of what kind of performance you can expect, based on tag reader combination being used.
For example, a tag tuned for 902–928 (US FCC) will work best with an RFID reader operating within the specifications of 902–928 (US FCC). The tag will still work in Europe, Japan, and other regions, but its performance will not be as good as a tag suited to the region. A tag tuned for global operation should perform well across all regions.
Tag tuning / Reader |
902-928 (US FCC) |
865-869 (EU) |
952-955 (JPN) |
Other regions |
902–928 (US FCC) |
Best |
Fair |
Fair |
Fair |
865–869 (EU) |
Fair |
Best |
Fair |
Fair |
952–955 (JPN) |
Fair |
Fair |
Best |
Fair |
Global operation |
Good |
Good |
Good |
Good |
4. RFID tag size
Size does matter. A larger tag antenna normally provides greater read range and better overall performance. However, a 4 in. × 4 in. tag will not fit on a small bottle of medication. Consider the available space for tag placement.
5. RFID tag orientation
Few implementations have the ability to control tag orientation 100 percent of the time. In the supply chain, your product may be flipped in any direction once it leaves your facility. The tag may even end up facing down on a conveyor. Some RFID tag antennas and RFID chips are better designed for operation in environments where orientation is not controlled, such as airline baggage handling.
6. The temperature, humidity, and climate in which RFID tags operate
Be sure to note the temperature and humidity extremes that your products are exposed to, and make sure the tags you select are rated to operate within those extremes. A special coating on the label face may also be needed to resist water. More important, double-check the type of adhesive used to affix the tag on the product. If your tag is going to get frozen or wet, you don’t want it to come off because it no longer sticks.
7. RFID tag memory
Some tags have additional memory capacity that may be used to store information such as date of manufacture or expiration. Additional tag memory may be necessary in applications where needed information must be stored in the tag because it cannot be retrieved using a database search with the tag ID.
8. RFID tag reading, writing, or both?
Consider that there will most likely be the need for the RFID tag to be encoded, or written to, during one or more processes. Some companies affix tags to items at the point of manufacture, but don’t encode the tagged items at a later point in time, often after they have been packaged.
Bulk encoding can provide additional return on investment (ROI) by allowing manufacturers to delay customer-specific encoding criteria until the end of the packaging process, when it can be done on demand. The process of bulk-encoding UHF RFID tagged items has both hardware and software components. When bulk-encoding a packaged set of tagged items, the first, and usually most challenging, step is to identify all the desired tags to be encoded.
Once uniquely identified, the process of encoding the tags is relatively simple. ThingMagic has written an application note you may download titled, “Designing Bulk Encoding Applications Using UHF RFID Technology.”
9. Method of RFID tag attachment
You may affix a tag mechanically or with an adhesive, depending on the situation. In environments that require durability, mechanical fixtures (using cable ties, screws, bolts, pop rivets, or brackets) are the preferred methods of attachment. They are more reliable and less prone to failure, especially in cases of high mechanical stress or variable/extreme temperatures. Our team has not seen an instance where the addition of metal screws or rivets has adversely impacted performance by any measurable amount.
Adhesive fixture must used when the RFID tag cannot be mechanically attached. It is extremely important not to underestimate the importance of the adhesive used to affix the RFID tag to the tagged item. If the wrong adhesive is used, the tag will become detached. This topic is so important, we have a detailed article about it here.
Certain adhesives have a known lifetime until failure. Our team recommends discussing the adhesive used with your tag provider to ensure it will meet your specific environmental (e.g., temperature ratings, impact resistance, chemical resistance) and lifetime requirements. A quality tag provider will be able to tell you the specifics. Here are a few things to know before contacting your tag provider:
• What will the composite materials be affixed to?
• What are the temperature and humidity ranges the tag will be exposed to, and for how long?
• Will the tag be subjected to washing, and if so, what detergents will be used?
10. RFID tag placement: Where do you stick it?
You cannot simply place a tag wherever is convenient, and expect it to read 100 percent of the time. Some factors that affect tag performance are the composite materials of both product and packaging because some materials, like water, absorb RF; the position of products inside the packaging; and how cases and cartons build a pallet. Tag placement must be carefully considered not only to ensure performance but to prevent damage. The best results require trying different tag placements and testing the results.
Consider the following:
The composite materials of both product and packaging. RF waves can easily pass through certain types of materials, while other materials can reflect or absorb the RF. You can’t see this with your eyes because light waves (and therefore bar codes) reflect differently. The image below illustrates how your RFID reader “sees” a box with a flashlight in it. The red color means the RF waves are not passing through the product, while the green areas indicate a strong signal. The tag will read better in the green areas than the red areas.
The position of the products inside the packaging. The image below shows an open box with a DVD player in it. The metal components of the DVD player will reflect the RF waves of the tags used in supply-chain operations. If you look closely, you can see there is cardboard packing between the side of the box and the actual player. Because cardboard is a RF-friendly material (i.e., something that lets RF waves pass through it easily), it provides a better location for the tag than the area near the metal.
How products sit in the case or carton. For supply-chain RFID tags, products that contain water can be challenging. Water will absorb some of the RF signal, making it difficult for tags to be read. A tag is less affected when there is an air gap between it and the water. For example, take the case of water pictured below. The air gaps between items can be used to improve tag performance. By placing the carton tag at the top on the outside of the box, read performance will be good.
Some tags work with both far-field and near-field antennas. By using a near-field antenna and tag combination, it is much easier to overcome the water problem.
How the cases or cartons build a pallet. When cases and cartons are stacked on top of each other, it can be challenging to read all the tags, especially with pallets of mixed goods. The image below illustrates how your RFID reader “sees” through the boxes on this pallet. The darker the green, the better the readability. Some cases are missing entirely, which means they cannot be read at all, while other cases are white, showing they are read very little. As you can see, there are areas that RF waves cannot pass through. That’s why it’s important to consider RFID when building pallets. When receiving pallets, the retailers focus on reading the single pallet tag that describes the contents. But if all of the case or carton tags can be read as well, the retailer can verify that all the products are there. One simple way to help is to have as many tags facing out as possible.
Test, record, reposition, test, record…
Now that you know the main factors that affect tag performance, it’s time to start testing your tags in different positions. This can be a very monotonous process. The tags that you selected earlier now get affixed to your products and then (hopefully) read by your RFID equipment. When you consider all the different tags, tag placements, orientations, and hardware configurations, there can be literally hundreds of different test scenarios, each with different results. (That’s why we recommend that you select only a few tags.) Ultimately, what you want to know is what tag to use and where it should go on the item, case, and pallet.
With the case of deodorant pictured below, you’ll note that when the tag is placed on the bottom right, it gets only a 20-percent read, yet the same tag placed in the top left gets 100-percent read. The water in the product is concentrated at the bottom and absorbs the RF signal. At the top, there is an air gap that lets the RF waves travel through.
A couple of rules to remember:
• Place the tag on the exterior of packaging. That makes it easier to replace failed or poorly performing tags.
• Avoid crush or fold points of the box. If a RFID tag is “slapped” on the box just as it goes out the door, and if the tag is on the crush point, the tag readability may be compromised because the antenna can become separated from the integrated circuit.
• Consider the packaging graphics. You don’t want to put a tag over instructions or other valuable consumer information.
• Club stores sell cases or cartons of products as items, so the previous rule applies in these instances, too.
• A tag will not read if it’s placed on packaging that uses metallic ink.
• Don’t be afraid to redesign the packaging to be more RFID-friendly. If you don’t change it, your marketing department will, eventually.
Understand your options for determining RFID tag placement
Now that you know about proper RFID tag placement, how do you go about doing it? There are several options:
• Bring in outside consultants. The right RFID consultant can help you narrow down the search for the right RFID tags quickly, especially if you’re facing a deadline.
• Use an RFID lab. The labs have environments similar to retail customers: very fast conveyors and dock door portals. Working with a lab can help you know what kind of performance can be expected once the tagged products leave your control.
• Tag it yourself. Do you think you can do it?
• Consider how many SKU’s you have: 10, 20, 100? Determining the best tag and placement can take a lot of time.
Tag selection and placement: step-by step recommendation
1. Start by examining your highest-volume and most physically challenging SKUs (e.g., those that contain metal and water).
2. Bring in outside expertise on tag placement to help with those products. This article should give you enough information to intelligently interview applicants.
3. Work side-by-side with the experts so you can learn the techniques and eventually take on the responsibility of tag placement. This will get you up to speed quickly.
4. Even if you’re working with an expert, if you’re not 100-percent confident about an SKU, send it to an RFID lab.
5. Educate operations personnel because they are the people who have to apply the tags. The importance of proper tag placement must be clearly communicated. Your customers may not thank you for doing this, but at least they won't charge you—and you’ll gain some appreciation of that investment.
11. RFID tag warranty
Every RFID tag supplier we’ve spoken to claims to warranty their tags. However, it is important to read the fine print. Some suppliers guarantee the tag will read, but at what distance? We’ve seen variances in RFID tag performance of up to a meter. Inconsistent performance between tags causes big problems in production. For instance, one of our engineers tested 250 RFID tags of the exact same model to ensure a minimum 12-foot read range. Even though all the RFID tags read, 27 of them had to be discarded because of poor performance. That’s more than 10 percent. Consider that when looking at RFID tag cost.
12. RFID tag cost
A better-performing tag may cost a little more, but it could result in huge savings later on. For example, if you’re debating between the 10-cent tag vs. the 12-cent tag, consider this: a 2-cent difference adds up when you consider thousands, if not millions, of products, but look at what you’re paying per year for replacing lost orders. One supplier was losing $3 million per year from lost product before implementing RFID using a 12-cent tag. Using the higher-priced tag, the company lost less than $500,000 per year—a savings of $2.5 million. That paid for 20,833,333 tags.
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