When Kevin Ashton first mentioned the «Internet of Things» in his 1999 report, he meant something else than we invest in this term now. He was talking about radio tags that would help radically change the logistics of Procter & Gamble products. In his opinion, radio tags should have become the foundation of IoT. They had to connect things (with radio tags) to devices and the Internet. But even though the Internet of Things is associated by users and developers with something completely different these days, radio-frequency identification, or RFID for short, has entered our lives.
1. What is RFID?
We use RFID every day, regularly, but we just do not notice it in most cases.
Let's say we went to the store, picked up the goods, and paid at the checkout with a credit card. We came home, opened the door with a keycard. Along the way, we may have seen cats or dogs. Where is the RFID here, one may ask? Some items from the supermarket, if not all, have pasted stickers and some of those could also be sewn into clothing. If such items do not pass through the checkout, then at the exit through the gate the system will detect it and start signaling. These stickers are RFID. A credit card also has built-in RFID (well, it is near-field communication based on RFID, but still) for contactless payment. Most pets and stray animals are chipped or clipped for identification. Yes, it's also RFID. And the keycard with which some people get access to the workplace or their apartment is also built with RFID technology. And these are just a few examples of the application of the technology.
2. How does RFID technology work?
If a conductive circuit is placed in an external alternating electromagnetic field, an alternating electric current will occur. Obviously, this current generates its own electromagnetic field, which forms the response of the circuit. If the natural frequency of the circuit coincides with the frequency of the external field, the response is significantly enhanced by resonance. The resonant response of the circuit is noticeable against the background of other responses and can be determined. This effect was studied way back in the 1930s. The first mass devices, which used resonant circuit responses, appeared in the 1970s and led to the emergence of mass RFID systems in the 1990s.
The RFID system consists of readers and tags that are attached to objects. The reader must have a transmitter and receiver working at a certain operating frequency. It sends an electromagnetic signal and listens for responses from the tag.
The RFID tag itself consists of two parts: a mixed (digital-analog) integrated circuit and a resonant loop antenna. The size and shape of the antenna depend on the frequency at which the tag should operate. Modern transmitters-responders (readers) and tags operate at frequencies from 120 kHz to 5800 MHz. The work of RFID systems is regulated mainly by the international standard ISO / IEC 18000. Nowadays, there are tags designed to operate at frequencies even up to 10 GHz, but that’s outside the standard.
RFID tags can be passive, without their own power source, and active, with a built-in power supply. Passive tags receive energy from the reader's electromagnetic field, so they can be operational at significantly shorter distances than active tags. In addition, the working distance of the tag depends on the operating frequency. For example, RFIDs built into credit cards and keycards operate at low frequencies, so their operating distance is below 10 cm. Tags on store items operate at frequencies an order of magnitude higher, so they can be read at a distance of several meters. The system reads the response of a tag when they cross a detector (typically frame or gate). Ultra-high frequency tags can be identified at a distance of tens or even hundreds of meters.
The integrated circuit in the tag is used to store and process information, as well as is responsible for demodulation and modulation of the signal from the antenna. Depending on the type of memory used in the integrated circuit, some tags can be overwritten once or multiple times and tags cannot be re-programmed.
Under the action of the electromagnetic field of the reader at the resonant frequency electrical signal appears in the circuit connected to the antenna. Depending on the task, the chip can read the information encoded in this signal, process it, and emit the response. Normally, the signal generated by the tag has a significantly smaller modulation depth than that, transmitted from the reader. It is clear that the farther the tag is from the reader, the more difficult it will be to identify the response. Tags with built-in power can transmit a signal that can be recognized at a much greater distance because the signal attenuates less with increasing distance to the reader. But even the induced signal in passive tags/labels is sufficient to power up simple logic and energy-efficient sensors. For example, RFID-based sensors can be used to measure soil temperature or other parameters across a wide area. Such sensors can form the network for a smart field IoT system, in which water and fertilizers are added to plants depending on the measured parameters.
Embedded integrated circuits can be used for the encryption of transmitted information and various types of modulation, which provides an additional protection level for reading. Security allows using RFID in authentication and access systems.
As with any other, RFID technology has its drawbacks, too. Electromagnetic waves do not propagate smoothly in all environments. For example, water, especially saltwater, suppresses electromagnetic radiation at high and ultrahigh frequencies. Therefore, long-distance RFID tags designed for these frequencies will be ineffective at a water depth of 30-40 cm, even if they are in a sealed waterproof housing. Metal electromagnetic shields are also a problem. A tag closed in a metal box will not work either.
RFIDs are quite resistant to mechanical action, but even minor damage can reduce the antenna loop Q-factor, and thus reduce the distance at which the tag will be read. Mechanical rupture of the antenna will disable RFID, even if the electronic components are fully operational.
3. Trends on the RFID market
Commodity logistics. The most popular are the cheapest RFID tags, which are used for control and logistics of goods in supermarkets and malls. Large retailers such as Walmart, Auchan, and Metro AG order such labels in batches of a hundred million. This mass production and new approaches to manufacturing have reduced the cost of RFID tags to 2-3 cents per item (the price of active ultrahigh-frequency tags can reach 10-20 dollars). Automated systems stick them to product packaging at the manufacturing line. This simplifies the logistics of goods during production and on the way from the manufacturer to the seller. The main competitors of such labels are visual codes (barcodes and QR-codes). Barcodes cost less than RFID tags because they can be easily printed. But barcodes are harder to read, especially in large numbers and remotely. They are also easier to forge. Therefore, to reduce the cost of mass RFID tags and their application to the product, new technologies are being developed. For example, the possibility of printing RFID tags on the product packaging with a special conductive ink is considered now.
Payment for travel on toll roads. Currently, the only reliable method of fixing tolls on toll roads and highways with heavy car traffic is RFID. They can be read when the car passes through the gate without stopping the flow of traffic. Such systems significantly reduce the cost of maintenance.
Access to the premises. RFID-tagged cards and keychains are often used to access apartments in buildings, hotel rooms, and offices. But in the future, they may be partially replaced by fingerprint or retinal authentication. There are even projects that use RFID tags that are implanted under the human skin. This option has proven itself well but is criticized because of moral aspects.
Similar cards are used to pay for travel on public transport. They reduce the flow of cash and significantly speed up fundraising in high-traffic vehicles. However, in this case, the use of fingerprints as a rival technology is ineffective.
Microchipping animals. Implantation of RFID tags under the skin of pets to identify the owner has long been considered standard practice. Also, many wild animals (birds, fish, dolphins, etc.) are implanted with RFID microchips, for example, to determine the routes of their migration. Unfortunately, there is currently no single standard for labels of this type, so to detect and read them one may need to have readers from different manufacturers.
Biometric passports. Most modern passports have built-in RFID tags with information similar to that in the passport. Sometimes, embedded also is the information about fingerprints. Such passports speed up border crossing, as they reduce the possibility of human error, adding yet another element of passport protection. To protect against unauthorized RFID reading passports must have a built-in electromagnetic shield.
Credit cards. Credit cards have built-in specialized RFID tags with unreadable memory. They generate special keys in response to a request. They also contain the same information as on the card (number, CVV code, and expiration date of the card).
As mentioned above, the exact technology that cards use is NFC and it is a little different from RFID, being designed for short-distance operation at 13.56 MHz frequency. NFC tags are subject to the international RFID standard ISO / IEC 18000-3. NFC modules in smartphones emulate the response of a similar tag. The RFID tag market statistics include statistics for NFC tags thanks to the identity of technologies. Given that NFC technology has only just begun to be widely used (as compared to RFID), and is being actively advertised by smart device manufacturers, current market growth estimates may be somewhat understated.
Another interesting application is finding lost objects. Missing TV remote or the car keys? Searching for a cat's favorite toy, which constantly rolls somewhere? Did anyone see the second sock? Well, you probably can't do anything with a sock, because it's out there in a different universe, but with everything else… Now all these things can be found easily with, for example, an application on a smartphone. Some devices can be hung, for example, on a key. When the device disappears from the smartphone, a message arrives. But they require battery power and therefore have a limited lifecycle. Also, these devices are not cheap enough to be attached to everything in the house.
And what if RFID tags can be attached, just as it is done in supermarkets? Then, to find labels, readers will be needed. And tracking everything in the house requires that the signal from the reader is emitted constantly. But most people already have an electromagnetic signal at home that is constantly emitted: from Bluetooth and Wi-Fi transmitters. That is, we have everything to identify the label on the frequencies of these standards. Of course, not everything is that simple, because you need to get a response from a tag minimum from three sources (triangulation then gives the exact position of the tag). Reflected and absorbed signals must also be taken into account. But this application is very promising. Now several large companies are interested in this issue and are conducting research. Or maybe someone has already succeeded? Soon, we can expect to be able to use RFID to position tagged items if they are within a smart home. And this could be another part of the already large RFID market.
RFID systems have come a long way and are integrated into people's social lives. But most applications of radio tags involve the identification or counting of objects by automated systems. However, the development of technology allows finding all new applications of RFID. A new wave of energy-efficient microcontrollers and sensors increases the variety of their functions, and the well-established production reduces the cost of RFID. Therefore, they can be a driving force for global IoT and robotic systems eventually becoming a part of new smart solutions.