Tags can come in various forms, and each form is particular to a specific application. Of course, generic types of tags can be used for many applications; however, there may be situations in which you are not getting satisfactory results with all-purpose tags and you need a custom solution. Many manufacturers offer tags intended for specific applications, or they can customize the tag according to your needs and requirements.
Tags for specific applications differ by tuning (they are tuned to work better with certain materials such as metal, glass, liquids, and so forth) or they can have varied packaging designed to support their performance or withstand various environmental and handling conditions. Understanding the physics and material composition of an item to be tagged helps people leverage science to create a tag specific to that application. For instance, good RF engineers can measure the frequency response off of a sheet of metal and determine how that will affect the resonant frequency of a tag; then they can change the resonant frequency to account for that change, essentially using the metal object as a backplane of the tag component. Once again, physics makes it all happen.
You've learned about all the components that are necessary for the tag to function, except for one critical part: the tag packaging. Although the types of tag packaging conceivably can be limitless, I've put together a list that shows you the types of tag packaging, the applications they are used for, and their advantages and disadvantages:
Label (Also Called a Smart Label) An RFID inlay is integrated into a thin flexible paper or plastic sheet with an adhesive side. Labels usually come in the form of rolls or fan-folds, and are used in RFID printers and label applicators. Labels are manufactured in various sizes, most commonly 2"x 4", 4"x 4 ", and 4"x 6" , but you can also encounter labels of other dimensions. Labels are used mostly for tagging cases and pallets in the retail supply chain, but also are used for product (item) tagging, library books, and movie rentals. Labels are easily accessible, are relatively low cost, and offer fast and precise application methods, but they are not very sturdy.
Card (Also Called a Smart Card) An RFID inlay is integrated into a plastic card, and usually looks like a standard credit card. These types of tags are often used for access control to buildings, secure areas, and parking garages. Cards are more durable than labels but are a bit more expensive to produce.
Button An RFID inlay can be encased in sturdy plastic packaging in the form of a button, usually around 1 inch in diameter. The button can have an adhesive side or one or more holes for attachment. Buttons are usually attached to garments or sewn into them and are used for applications in laundry, dry cleaning, or clothing rental. There are machines available on the market that can automatically apply tags in the form of buttons.
Wristband A thin plastic strip carrying an RFID tag is usually placed on a wrist or other body part. The strip often uses adhesive or notches to connect the ends. Wristbands are used, for instance, in hospitals for patient identification or theft prevention (see the following "Proud Daddy" sidebar).
Real World Scenario-Proud Daddy
When my daughter was born, my thoughts turned away from RFID for a change, and I was focused on being the proud daddy. I was thinking only about cuddling her and giving her mom a much-deserved rest as I walked (on air) around the hospital corridors. Out of nowhere, alarms started ringing and the pudgy security staff with Taser guns were lumbering toward us, clearly upset by an interruption of their Dunkin' Donuts moment. (Well, they didn't really have the Tasers, but I was still feeling woefully outgunned holding a one-day-old.) After a couple of disoriented moments, I realized we had wandered near the exit door with RFID readers and antennas, and that "innocent" band my daughter had on her ankle was there to make sure that she did not leave the infant ward! So, although I couldn't steal my baby without facing down a chocolate-frosting-lipped constable, I did feel better knowing that no one else could either.
Glass Bead An RFID tag can be placed into a small cylindrical vial. The glass bead is used for animal tracking (mainly for pets) because it can be easily injected under the skin. Glass beads are also used for human tracking, such as for members of military special forces.
Key Fob A tag is integrated into a key fob used for vehicle access and immobilizer activation and deactivation.
Casing An RFID tag is inserted into a rugged plastic (or other RF-neutral material) container. This container can be of various sizes, depending on the tag and other components such as sensors, battery, and so on. Usually you will see active and semi-passive tags in casing. Tags in casing usually have to be attached manually. Encased tags are used in high-stress environments, where the tag has to be protected, as well as in applications common to semi-passive and active tags (container tracking, RTLS, etc.).
There are many ways to attach an encased tag. Sometimes the casing has openings; therefore, you will be able to use screws or zip-ties. If the casing has no holes, you can utilize adhesive Velcro, double-sided tape, or brackets to hold the tag in place.
Embedded Passive tags can be embedded into certain RF-neutral materials that provide protection for the tag's parts and/or spacing from a product surface, enabling them to function when they are placed on various materials. These tags include tags for use on metal that can have a ferrite layer or tags embedded in epoxy to protect them from damage. We've had calls to embed tags in everything from ceramic for a metal smelting business to salmon for tracking their spawning habits-but there was something fishy about that last company (sorry, I couldn't resist).
Integrated into Product Packaging RFID inlays can be integrated into a product or its packaging. For example, the inlay can be embedded into a carton, box, plastic container, bottle cap, or product label. The advantage of this method is fast tagging and usually better protection of tags against damage. However, if the tag fails, it may be difficult to repackage the product.
As you design the incorporation of the tag into the overall system and business process, you will have to choose how the tag is packaged. As you evaluate types of tag packaging, base your choice not only on size, application, and attachment method, but also on the tag's sturdiness. You may be interested in the cheapest tag possible that is easily applicable but does not last forever (in this case you are most probably going to choose smart labels) or you may be looking for a tag that will survive extreme conditions. When examining the tag for its rigidity, you must find out what environmental and handling conditions it will withstand, such as pressure, humidity, temperature, multiple attachments, and other factors. Sometimes this information is available from the manufacturer, but sometimes you will have to test it. There are some interesting attachment methods, such as OMRON's global tag that does not use adhesive (which is more susceptible to expansion and contraction in temperature changes), but rather an electronic weld to make the attachment very rugged.
Just as with humans, the environment can dictate how well tags work. Some items may require deep freezing or heat sterilization, so you will need tags that will not only survive these processes, but also function during and after. Not all tags will. Typically, the tags that are present in standard smart labels are intended for use in temperatures from -25°C (-13°F) to 70°C (158°F) and can be stored in temperatures from -40°C (-40°F) to 85°C (185°F). Some manufacturers produce tags that can withstand temperatures up to 250°C (482°F), which can be used, for instance, on medical items that are subjected to heat sterilization or in industries where extreme temperatures are common, such as the metallurgical industry. The operating and storage temperatures can differ by manufacturer, tag type, or tag packaging.
Real World Scenario-Labels and Extreme Temperatures
You might be thinking that if the tag was built to tolerate extreme temperatures, the packaging should be too. Several years ago I took this for granted as well, until I witnessed the manual application of labels in a near-desert warehouse without temperature control. You can imagine the dramatic change in temperatures not only season to season, but also day to day. During the hottest days, the labels would come off their backing almost without the adhesive, which "melted" and remained on the backing. In the coldest days, the labels would not stick properly on certain products because the adhesive was less tacky in low temperatures. The label converter had to be informed about this issue and had to change the properties of the label adhesive to avoid these problems in the future, and the client was left with a stock of tags that could be used only in good weather.
You're already at Chapter 4, so you know that some materials (such as liquids or metals) pose a problem for UHF RFID tags. Not only are some of these materials hard or impossible to penetrate by RF waves (liquids absorb the RF waves, metals reflect them), but they can also impair a tag that is placed on a surface of such material. The presence of this material could detune the tag, which would result in a drastically shorter read range. Detuning shifts the tag's operating or resonant frequency. If the tag's frequency were moved entirely out of the band of the reader's operation, the reader would not be able to read this tag at all.
To put it another way, a typical UHF tag has a resonant frequency of 915 MHz in the United States. The tags are designed with antennas that can pick up a signal starting at 900 MHz (15 MHz below the resonant frequency) and expanding up to 930 MHz (15 MHz above the resonant frequency), covering all the area in between where a tag may be frequency hopping (see Chapter 2, "Interrogation Zone Basics"). If a tag is put on a metal surface, the resonant frequency may change to 800 MHz and the range it can receive a signal on would then be 785 MHz (-15MHz) to 815 MHz (+15 MHz).
To increase performance in tough situations, manufacturers have developed tags that are intended for use with specific materials. These tags are specially tuned to be used with these materials and are enclosed in special packaging to support their function. For instance, there are special tags for use on metal, glass, containers with liquids, and minerals.
In very simple terms, if an engineer knows that a tag is being affixed to metal that will drop the tag's resonant frequency from 915 MHz to 800 MHz, a change of -115 MHz, she can design a tag that in free air would have a resonant frequency of 1030 MHz (+115 MHz). Then, when the tag is affixed to the metal object, the tag would return to the EPC standard resonant frequency of 915 MHz and be read from 902–928 MHz. If all of this makes sense to you, have no fear, you'll pass this exam with flying colors!
As a general rule of thumb, you should not use tags intended for one material on a product made of another material unless it has the same or similar chemical properties. Otherwise, the tag will not work well or may not work at all.
Although liquids generally absorb RF waves, you should know that the surfaces of liquids can be great reflectors (you can see yourself in the surface of water, after all). Metals are generally reflectors; however, they can also absorb some of the RF energy and dissipate it across the metal surface.