Introduction
Radio Frequency Identification (RFID) is not a new technology, with the initial application being IFF (Identification Friend or Foe) used by aircraft during World War 2.
Since that time it has found a variety of uses including key fobs, contactless payment, proximity cards for building security, and toll collection. These days, thanks to increases in RFID performance and standards like EPC Class 1 Generation (Gen) 2, RFID readers and tags are finding new life in applications like defense logistics, healthcare and the enterprise as well. According to one estimate alone, the RFID market is poised to surge from millions to tens of billions of tags over the next five years. While this growth bodes well for RFID reader and tag manufacturers alike, it also creates a number of interesting challenges, not the least of which is how to ensure tag operation on metal. This problem is especially troublesome in the aerospace asset tracking arena, such as with airplane parts featuring metal casings and components (see Figure 1). A new patent-pending, high dielectric material with high magnetic permeability can offer manufacturers an ideal solution for ensuring RFID tags will operate as expected on metal products.
Figure 1. One airplane can contain thousands of parts which can be tracked using RFID
An Emerging Challenge
RFID systems consist of a tag, or transponder, and a reader, also known as an interrogator. The RFID tag is comprised of a small silicon microchip attached to an antenna and is capable of transmitting unique information at a distance of up to several meters in response to a query from a reading device (see Figure 2).
Figure 2. Various components of the tag are shown here. Normally, the antenna is external to the tag chip and large in size.
During operation, the reader sends out electromagnetic waves. The tag antenna, which is attached to an object, is tuned to receive these waves. The tag – for the purpose of this discussion, a passive tag - will identify itself when it detects a signal from a reader that emits a radio frequency transmission. Each RFID tag carries information on it such as a serial number, model number, color, place of assembly, or some other type of data. When these tags pass through a field generated by a compatible reader, they transmit this information back to the reader, thereby identifying the object.
Essentially what is happening is that the RFID reader continuously emits RF carrier signals, and keeps observing the received RF signals for data. The presence of a tag modulates the RF field, and the same is detected by the reader. The tag then absorbs a small portion of the energy emitted by the reader, and starts sending modulated information when sufficient energy is acquired from the RF field generated by the reader. In this case, the data modulation can be accomplished by either direct modulation or FSK or Phase modulation. The reader demodulates the signals received from the tag antenna, and decodes the same for further processing.
While RFID systems have become quite common in everyday life, metal poses a unique challenge to their effective operation. RFID tags are designed to efficiently receive energy transmitted from the reader. Since a passive RFID tag has no power source, it must derive all its power from the incoming wave. If this energy is not transferred to the chip efficiently, the chip will not power up and the tag won’t be read. A well designed RFID tag antenna is said to be ‘tuned’ to the reader frequency and presents a good ‘match’ to the incoming energy. In proximity to metal, the tag antenna becomes detuned - creating a mismatch. As a result, the tag can no longer efficiently transfer power to the chip at the reader frequency. Greater transmit power therefore is necessary to read the tag, deteriorating the read range. Put simply, the metal interferes with the signals sent between the RFID tag and the reader, causing signal reflection, detuning and grounding which may reduce, or even negate RFID’s effectiveness.
Using an RFID tag on a metal object is especially problematic with ultra high frequency (UHF) RFID (tags) systems. While these systems offer a greater read/write range, they are less able to penetrate obstacles such as metal. Higher frequency radio waves tend to bounce off of metal objects.
Real time tracking of aerospace parts can provide a boon in efficiency and safety in locating parts, determining maintenance schedules and ensuring that only approved parts are used. The conventional way of dealing with the read on metal problem today is to employ a dielectric material like foam to offset the tag from the computer. This foam is typically 1⁄4 to 3⁄4 of an inch thick. Here, the further the tag is away from the metal the better its range. But what happens if a situation arises in which there is a restriction on the thickness of the foam? Consider, for example, that a tagged laptop computer must fit into a docking station and therefore the foam isolator used must be extremely thin – much more so than the nominal 1⁄2 to 3⁄4 of an inch. And what about situations where the esthetics of the overall product is crucial? In these cases, the foam offset tag simply falls short.
Granted a foam offset tag does have the benefit of being inexpensive, but at the same time, its performance is not always guaranteed. In aerospace applications and others that require high-value asset tracking, a higher performance, ultra-thin, more esthetically pleasing alternative is often required.
Emerson & Cuming Microwave Products Value Proposition
As a company strongly committed to addressing the problem of RFID read on metal, Emerson & Cuming Microwave Products now offers a patented, thin elastomer which when placed between an RFID tag and metal will allow the tag to be read. Known as ECCOPAD®, this isolator material is substantially thinner than the usual foam spacers, enabling the RFID tag to be read on metal while maintaining a low profile (see Figure 3). It can be used to separate RFID tags from metal by a mere 1/10 th of an inch.
Figure 3 Emerson & Cuming Microwave Products ECCOPAD® isolators enable the use of RFID tags on or near metallic surfaces. Isolators are available for use at HF (13.56 MHz) and UHF (915 MHz).
While standard RFID tags can not be read when placed on metal or near metal because it detunes the antenna, ECCOPAD® is engineered with specific electromagnetic properties which serve to retune the tag antenna to the correct frequency, thereby enabling communication with the reader. Featuring a unique two layer design, ECCOPAD® is comprised of a back layer which is placed next to the metal and a front layer which sits next to the tag (see Figure 4). The back layer is made of a material with high magnetic permeability. This is essential for retuning the antenna in a reasonably thin layer. In contrast, the front layer consists of a pure dielectric material that fine tunes the performance of the tag antenna.
An ECCOPAD® material optimized for a particular tag may not work with another tag. This stems from the fact that ECCOPAD® layers may differ in both electromagnetic parameters and thickness. Consequently, there is no universal ECCOPAD® material that will work with all RFID tags. ECMP has developed the ECCOPAD MetalTag which is a small form factor (2.5”x0.625”) EPC Gen 2 compatible tag with outstanding performance in read on metal applications.
Figure 4. The ECCOPAD® MetalTag is designed with a small form factor and outstanding read range when used directly on metal
Table: ECCOPAD® isolators are designed for a variety of popular Gen 2 RFID tags. To reduce confusion, the company has unified several similar designs. The unified design, called ECCOPAD® UHF-G2, maximizes read on metal performance for the tags listed above.
Complementing the leading features and functionality of the ECCOPAD® material, is the company’s unique value proposition. Emerson & Cuming Microwave Products:
• Has a long history of excellence and expertise in making components for the military. It was founded in 1948 with this goal in mind.
• Offers the benefits associated with the infrastructure of a large company (e.g. R&D facilities etc...), but with the personal customer service and responsiveness of a small company.
• Was the first to become ISO certified (ISO 9001:2000) and to use automation in manufacturing. This automation increases yields up to 95-100%, ensures electrical consistency and enables the company to run upwards of 20,000 square feet per day.
• Offers global manufacturing via facilities in Randolph, Massachusetts and Westerlo, Belgium.
• Has excellent global R&D facilities (e.g. an engineer can show up with a new application and the company can turn around a new material for it in literally just a few days).
Conclusion
High-value asset tracking applications, such as with aerospace supplies featuring metal casings and components, are especially prone to the problem of RFID read on metal. A line of patented, high dielectric materials with high magnetic permeability from Emerson & Cuming Microwave Products can offer today’s engineers a substantially thinner solution than the usual spacers. These materials not only enable the RFID tag to be read on metal, but maintain a low profile as well.
For more information on this topic, visit Emerson & Cuming Microwave Products at www.eccosorb.com. For sales or technical inquires, contact the Technical Manager Paul Dixon via email at pdixon@eccosorb.com or by phone at (781) 961-9600.