Electronic Cargo Seals: Context, Technologies, and Marketplace

2. The Characteristics of Electronic Seals

There are four clusters of electronic seals, representing four methods of communicating between the seal and its "reader:" radio frequency identification (RFID), infrared, direct contact, and very long range cellular or satellite. All but the simplest solutions are capable of reporting sensor information and data that goes beyond seal status and ID.

RFID Seals

RFID technologies are most common among electronic seals. Fundamentally, they marry RFID transponders or their components with manual seal components. There are two main types of RFID tags and seals, passive and active.

Passive seals do not initiate transmissions—they respond when activated by the energy in the signal from a reader. Interrogated by a reader, a passive seal can identify itself by reporting its "license plate" number, analogous to a standard bar code. The tag can also perform processes, such as testing the integrity of a seal. The beauty of a battery-free passive seal is that it can be a simple, inexpensive, and disposable device. Although not a formal term, it is useful to think of such devices as "pure passive"—a term that describes what most practitioners have in mind when they discuss passive RFID electronic seals.

Passive RFID seals can carry batteries for either or both of two purposes. The first is to aid communication by boosting the strength of the reflective signal back to the reader. This capability need not add much cost. The second purpose is to provide power so functions can be performed out of the range of readers. One example of the latter is to power a clock, continuously test the integrity of the seal, and record the time of tampering. Adding substantial capability could raise the cost of a passive seal sufficiently that it would be practical only as a reusable product.

Practitioners use three different terms to describe passive tags with batteries. They are semi-active, semi-passive, and battery-assisted passive. Since the terms seem to be interchangeable, this is a source of confusion in RFID tag discussions. Alien Technologies began using the term semi-passive and is now transitioning to the term battery-assisted passive since they find it reduces customer confusion. Since Alien is the only firm uncovered in this project that is developing a passive electronic seal with a battery, their choice of terms seems best: battery-assisted passive.

Other than Alien, all known passive electronic seals are "pure passive," with no battery whatsoever. Pure passive functionality is limited to testing the integrity of the seal when interrogated by a reader and reporting that status, its ID, and other on-board information to the reader (4). One manual seal manufacturer opposes batteries on passive tags, telling the author that "if I'm forced to use a battery on a seal, then it will be an active seal."

Passive seals tend to be short range and directional to maximize antenna exposure to reader signal strength. Maximum read range for electronic seals without battery-assisted communications tends to be two-three meters, with some debate in the industry about efficacy beyond two meters. Adding a battery can boost the range—Alien's design target is >30 meters—but concerns about safety, regulations, and the operating environment impose practical limits on power and range.

Active seals can initiate transmissions as well as respond to interrogation. All active tags and seals require on-board power, which generally means a battery.

A major attraction of active tags and seals is the potential for longer-range and omnidirectional communications—up to 100 meters. Expressed user needs for greater range and the ability of signals to wrap around obstructions in terminal operating environments prompted the international standards group working on electronic seal and read/write container RFID standards to add active RFID protocol(s).

At the lowest functionality, active seals must cost more than pure passive seals because of the battery and the ability to initiate communications, but the difference would be relatively small. Actual price differences between passive and active RFID seals in the marketplace tend to be much larger, reflecting design choices to host greater functionality on active tags—taking advantage of the battery, the potential to initiate communications, and the greater, more flexible range.

All active RFID electronic seals on or approaching the market monitor seal integrity on a near-continuous basis, and most capture the time of tampering and write it to an on-board log. Some can accept GPS and sensor inputs, and some can provide live "mayday" tampering reports as the events happen, mostly within specially equipped terminals.

Passive vs. active RFID seals. One may look at the trade-offs between these technologies from theoretical and practical perspectives.

Theoretically, the only difference between passive and active tags and seals is the ability to initiate communications from the tag—a distinction that means passive RFID tags could not initiate mayday calls. However, a designer could add on-board power to a passive tag, match other functionality and, setting aside regulatory, safety, and cost issues, increase read range and directional flexibility by increasing power and adding antennas. This perspective seems most appropriate to laboratory R&D discussions.

Practically, there is an unmistakable clustering in the market: Exhibit 2 summarizes choices made by firms in pursuit of customers and profit. All but one of the five passive RFID-based seal designs is battery-free. If the exhibit were more complex, including degrees of functionality, the clustering would be reinforced: the four "pure passive" solutions are simple, relatively short range, and low cost. All six of the active RFID-based designs have significantly more read range, greater functionality, and five of them are able to log and report the time of a tampering event. There is one crossover point, where Alien's battery-assisted passive RFID design seems close to the capability—and price points—of several active RFID designs.

Since there is no official or regulatory statement of security performance requirements for electronic cargo seals, one cannot be definitive about the relationship between passive and active RFID technologies and security requirements. However, given industry's design choices made so far, some suggest—fairly in the view of this author—that (pure) passive seals were generally the preferred solution for "pre-September 11" security requirements aimed against theft. On the other hand, the greater functionality associated with active seals seems to enhance their appeal for "post-September 11" security against terrorist tampering.

Exhibit 2: Technology Distribution of RFID Electronic Seals Found in This Market Survey

	On Board Power & Use
Seal Can Initiate Communications	None	Only to Boost Comm.	Only for Apps.	Both Comm & Apps
Yes, Active				6
No, Passive	4			1

Standards and Frequencies

Adoption of RFID in supply chain and security applications is hampered by a lack of standards and by what some call "the frequency wars." The two issues are interrelated.

Standards for electronic seals address technical protocols, interfaces, and frequencies. There are three related items to keep in mind, all under the purview of ISO Technical Committee (TC) 104, Freight Containers, Subcommittee 4, Working Group 2:

• ISO 10374 is the existing voluntary standard for RFID automatic identification of freight containers. It is a dual frequency passive read-only standard that includes 850-950 and 2400-2500 MHz. Globally, only two carriers use these tags, one primarily on chassis and the other on chassis, ocean containers, and many dray trucks.
• ISO 18185 is a Draft International Standard for electronic container seals. It includes passive and active protocols, enabling both simple low cost and more robust seals. The active protocols have been the focal point for "the frequency wars" in terms of freight containers.
• ISO 23359 is a New Work Item for read/write RFID for freight containers. Work started on this project in June 2002, and it seems likely to build closely on the draft seal standard.

Frequency choice begins with technical performance but includes political and regulatory issues. In crowded freight-oriented environments such as warehouses and terminals, the most effective frequencies appear to be between 100 and 1000 MHz. Frequencies below 100 MHz lose range rapidly because of inductive coupling or noise from electrical coupling. Frequencies above 1000 MHz, with shorter wavelengths, cannot wrap or diffract around objects such as vehicles and freight containers—they become more line-of-sight and subject to blind spots.

There are two kinds of political issues. The first is international and national spectrum regulation, which includes spectrum allocation and power and duty cycle regulation; this is an issue in part because there is no global frequency set aside for RFID logistics applications. The second political issue is about commercial interests, as different companies aim for market advantage.

In practical terms, five frequency bands are discussed today among firms and users most concerned with standards for electronic seals and related logistics applications. Exhibit 3 summarizes the five bands. The first four bands appear in the Draft International Standard for electronic cargo seals: 315, 433, and 915 MHz as active protocols and 862-928 MHz as the passive protocol. 2450 MHz, although endorsed by Japan and being part of the existing container read-only standard, was voted out of consideration for the electronic seal standard. The majority believes the frequency has inherent performance problems in freight terminals. Alien Technologies is the only firm that seems ready to challenge this view with a new electronic seal. 5800-5900 MHz, favored by the ITS community for Dedicated Short Range Communications (DSRC) applications, is not included in Exhibit 3 because of the widely held view that it is inappropriate for freight terminal and warehouse applications.

Exhibit 3: RFID Seal and Transponder Frequency Summary

Frequency (MHz)	ISO Standards Status	Theater Acceptance	"Sponsors"
315	Proposed for use under tri-frequency active protocol, ISO 18185	Much of Asia	Offered as options by e-Logicity and Hi-G-Tek
433	Proposed as stand-alone active protocol and as part of tri-frequency active protocol, ISO 18185	Europe and North America; parts of Asia (a)	Favored by e-Logicity, Encrypta, and Savi. Used in Europe by Hi-G-Tek and SecuReSeal
915	Proposed as stand-alone active protocol & as part of tri-frequency active protocol; also covered in passive protocol, ISO 18185. Covered in existing container read-only standard, ISO 10374	North and South America	Used in US by Hi-G-Tek and SecuReSeal. Passive use by TransCore
862-928	Agreed to for the passive protocol under ISO 18185	Pursuing global approval for passive RFID logistics applications	Uniform Code Council and EAN International (shipper-oriented standards and education organizations)
2450	Part of the existing container read-only standard, ISO 10374. Voted out of draft seal standard (passive and active) ISO 18185 because of performance concerns	Japan	Japanese firms and Alien

Most of the RFID-based seals discussed in this paper fall in the first three bands of the exhibit, with both passive and active applications of 915 MHz. Several vendors use much lower frequencies, such as 13.56 MHz and 125-134 kHz, where international frequency allocations are not an issue. Some active RFID designs use the lower frequencies as short-range supplements, for example for wake-up notifications; other designs are strictly short-range passive applications.

Infrared Seals

Infrared (IR) is a less common media choice than RFID. The Crown Agents/Universeal partnership uses IR and Encrypta offers IR as an option.

There do not appear to be any standards issues about IR, but there are unresolved disagreements about its technical merits. The Crown Agents contact reported they chose IR because of superior data bandwidth and speed, and their materials assert there are no sunlight interference issues. Concerns expressed by others included short range, slow data rates, effects of fog and rain, and susceptibility of some designs to generate false positive tampering signals. In addition, infrared systems are directional, offering line-of-sight performance without an ability to wrap around corners. Based on reports about Crown Agents' pilot with Mexican Customs, IR appeared to work well, although in a short-range application.

Contact Seals

Contact and near-contact technologies include contact memory buttons, PDA and electronic key plug-ins, low frequency RFID, and short range IR. Proponents of contact and near-contact solutions argue that it is important to have a human being visually observe the seal, and their solutions provide that added benefit. Proponents of longer-range solutions criticize the missed opportunity for labor and process timesaving.

• Contact memory buttons are proven devices in harsh environments. There are strong supporters in DoD and the Navy reportedly uses 500,000 of them. CGM offers a solution that combines memory buttons on the container and the locking bar.
• PDAs and electronic keys can provide battery power to passive seals and locks. Loran and Porter use them to eliminate on-board batteries and solve the power problem on ocean containers. Supra uses the approach to control an electronic padlock and have it function as a seal.
• Mega Fortris is using very short range—and unregulated—RFID for an inexpensive passive global seal.

Remote Reporting Seals

Remote reporting uses satellite or cellular communications. The great advantage is the ability to maintain visibility en route and to obtain near real-time event reports. It is a high-end capability, usually at high-cost. The only device found to be in use costs $4000, but much less expensive alternatives are in development. As costs drop, it will become increasingly attractive for security and management applications, especially for high-value and hazardous cargoes.

Exhibit 4 compares RFID, infrared, contact, and remote reporting seals.

Exhibit 4: Comparison of Technologies

Type of Seal	Positives	Concerns
RFID	Broad array of capabilities Passive can be very low cost Active can be high capability and moderate cost Can take person out of the inspection loop Movement on standards	Lack of standards, but this is being addressed Lack of global frequencies, especially in regard to active RFID
Infrared	Clearly effective at short ranges	Lack of clarity on strengths and shortcomings—contradictory information
Contact and Near Contact	Some are highly reliable in harsh environments Demands human involvement in seal inspection	Contact "keys" subject to loss and misuse Demands human involvement in seal inspection
Remote	Potential for immediate identification of problems Potential global coverage	High cost Usually requires significant outbound power
All	Potential to improve efficiency along with security	Risks of increasing complexity, opening new avenues of attack, and generating false confidence Need for independent assessment of vendor claims Need to assess operational impacts as well as technical performance Requirement to manage and sift increased data flow, identify false positives, and act on true positives

4. In some cases, such as CGM's Breakaway RFID Adhesive Seal, the seal is designed so a tampering event will disable the RFID element so it does not respond to interrogation.

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