Radio-frequency identification (RFID) originated in the logistics industry, but repeated attempts have been made in recent years to use the technology in asset tracking. One advantage of RFID tags is that the information they contain can be changed with most chip variants. Devices can record metadata such as purchase dates, asset IDs, or the last battery change date.

A complex topic like RFID is easier to understand if you start by looking at the hardware. The modules or cards, referred to as tags, are attached to individual assets and come in two variants: passive and active. Passive tags are available in the form of stickers, key rings, or HellermannTyton cable ties (Figure 1), whereas passive tags are larger, require maintenance, and need an energy source.

Figure 1: This cable tie can be attached easily to school bags and other goods.

Tag Tech

The most important argument for passive tags is that they are generally maintenance free. Glued to the inside of a plastic housing, they become trackable "for life," because the energy comes from the reader.

Active tags differ from their passive counterparts first in that they are not maintenance free: They draw their energy from a (usually long-life) primary cell built into the tag, which inevitably leads to a larger design but is not necessarily a disadvantage. For example, mounted on metal, an active tag is superior to its passive counterpart in terms of range, with its greater radio power and physical size.

Passive tags operate in three frequency bands: low frequency, high frequency, and ultra high frequency. Low-frequency tags are the earliest version of RFID based on the Wiegand standard, and they operate in the lowest band at a frequency range of 125-134kHz. Their disadvantage is the maximum amount of data that can be stored: just a few bytes. On the other hand, the cards are very cheap. The achievable range depends strongly on the reader.

All low-frequency systems are short-range transmitters. Smaller readers can only read cards reliably if they are placed on the tag. Depending on the orientation angle between the card and the reader, larger cards support ranges of between 30 and 80cm. The high-frequency cards operating in the 13.56MHz frequency band – also known as near-field communication (NFC) – offer a longer range: between 1cm and 1m, depending on the reader. A classic application for NFC is passports, access doors, and exchanging data with smartphones.

Ultra-high frequency (UHF) cards are available in the 865-960MHz frequency range. These readers, which given sufficient quality and a correspondingly large antenna, can achieve ranges of 5m and even up to 30m in special cases. Whereas the high-frequency tags located in the 15MHz range can compete with low-frequency tags in terms of price, because of the sheer volumes on the market, UHF cards are comparatively expensive.

In the active tag field, the frequency band is either 433 or 915MHz. In general, 433MHz systems are considered to have a longer range, which makes them more popular. When it comes to the format of active tags, you are spoiled for choice. One interesting product (Figure 2) offers a group of buttons that can be used to send a message to the reader. In this case, the manufacturer also promises the tag will detect manipulation and send a warning to the reader.

Figure 2: Tags with their own batteries offer a longer range. RFID tags with buttons can send messages to the reader.

Another interesting aspect of working with RFID tags is the possibility of burning "physical" information on a chip in addition to the electronic information. The classic method is to add a QR code, a barcode, or a serial number that uniquely identifies the individual asset. When selecting a supplier, you should therefore consider whether it can print the tags, so the physical information can be read and basic operations still can be performed without a reader.

Read Correctly

Although in theory you would want the reader to have as long a range as possible, in practice, this proves problematic: Imagine a server room in which several hundred or even thousands of computers are crammed together in tight spaces. If the range of the reader is too large, problems can arise, and the location information can be lost.

One interesting solution is a highly directional reader with an antenna that only scans in a certain area. You could then drive around with a cart carrying a group of scanners that automatically discover where the respective devices are located.

Far more interesting is the question of where the reader is placed. A mobile reader is not necessarily part of the solution. Behind the concept of the "choke point" hides the relatively simple idea that readers are placed at critical points. In a hospital, for example, readers can be placed inconspicuously in entrances and exits to prevent the loss of expensive medical equipment. The logical consequence is that such a reader ideally should not be visible, because a variety of different solutions now can prevent or complicate the detection of RFID tags.

When rolling out RFID systems, people often have the misconception that active RFID readers lead to problems with servers. This is not the case: Servers are designed for far higher electromagnetic compatibility (EMC) loads [1] than those caused by reading the average RFID tag.

Missing Standards

RFID tags, like any other wireless technology, depend on their environment. Tags with a low working frequency, especially, react badly when applied to metallic surfaces. To overcome this problem, you can procure special tags, but the price is off-putting. A guide online [2] suggests ways to place tags efficiently on different types of network hardware.

A number of problems can slow the adoption of RFID usage, including concerns about investment and operating costs, difficulty in exploiting the benefits, a lack of standardization, and, to some extent, data protection.