Radio Frequency Iden­ti­fi­ca­tion (RFID)

RFID (short for Radio Frequency Iden­ti­fi­ca­tion) describes trans­mis­sion tech­nol­o­gy based on elec­tro­mag­net­ic waves, which serves con­tact­less data exchange in sender-recipient systems.

RFID systems consist of at least one RFID reader and any number of RFID transpon­ders which work primarily as mobile data stores. Fur­ther­more, a computer, which records and evaluates the sorted data, is required. Data trans­mis­sion is con­tact­less via the medium of air. We therefore speak of a so-called air interface between sender and recipient. The de­vel­op­ment of the basic technical com­po­nents, the range of functions and the un­der­ly­ing operating frequency differ con­sid­er­ably at times, according to the field of ap­pli­ca­tion of the RFID system.

An RFID reader is a tech­no­log­i­cal apparatus, which, depending on its design and purpose, either produces a magnetic al­ter­nat­ing field of low range or high frequency radio waves.

If an RFID transpon­der gets into the elec­tro­mag­net­ic field produced by the reader, coupling will take place with the reader, which enables the RFID transpon­der to be read out. The reading process is con­trolled by software on the reader. This usually has in­ter­faces to other computer systems. Depending on the design, it is also possible to describe transpon­ders and thereby modify in­for­ma­tion saved on the chip.

Modern RFID readers are able to read several transpon­ders at the same time. This group capacity is a central advantage of RFID tech­nol­o­gy compared to other processes for iden­ti­fy­ing objects – for example, iden­ti­fi­ca­tion via a barcode.

To enable RFID readers to com­mu­ni­cate with several tags at the same time, various anti-collision processes have been developed, in which transpon­ders are allocated different access times or fre­quen­cies, for example. This should prevent in­ter­fer­ence of the signals.

An RFID transpon­der is a radio com­mu­ni­ca­tion device that receives the incoming signals and responds au­to­mat­i­cal­ly. The de­scrip­tion transpon­der is a com­bi­na­tion of the terms trans­mit­ter and responder. The smallest types are just a few mil­lime­ters long. There are different types of transpon­der:

• passive
• active
• semi-active

The basic com­po­nents of any RFID transpon­ders are a microchip and an antenna (usually in the shape of a coil). The microchip of a standard transpon­der offers a storage capacity from a few bits up to several kilobytes, based on the design. Depending on the version, the storage capacity can be suf­fi­cient for a single sequence of numbers that serves as a unique ID to identify the chip, up to data sets with a scope of several type­writ­ten pages.

The RFID chip forms the so-called inlay, along with a printed, su­per­im­posed or etched antenna. This is highly sensitive and has only limited re­silience. RFID inlays are therefore mostly laminated – for example, self-adhesive labels (smart labels): so-called RFID tags. If the transpon­der is to sustain greater loads, the elec­tron­ics can be in­te­grat­ed into a plastic card or protected with a plastic casing.

If it involves passive or semi-active transpon­ders, the read RFID chip itself does not produce an elec­tro­mag­net­ic field. Instead the al­ter­nat­ing field of the reader is modified to transmit the retrieved data. Active transpon­ders are fitted with their own trans­mit­ter.

• Passive RFID transpon­ders have neither their own energy source nor are they able to transmit signals in­de­pen­dent­ly. The microchip of a passive transpon­der is tem­porar­i­ly supplied with elec­tric­i­ty via a capacitor (usually in­te­grat­ed) via its coupling with the reader. The coupling is carried out via induction in most cases.
• Active and semi-active RFID transpon­ders have an energy source in the form of a backup battery and are therefore somewhat larger. In passive RFID transpon­ders, data trans­mis­sion is limited to a few meters. Active and semi-active transpon­ders extend the reach of an RFID system to several hundred meters. The coupling is carried out via induction or elec­tro­mag­net­i­cal­ly.

For standard RFID systems, trans­mis­sion fre­quen­cies of the license-free ISM frequency bands are used, which can be deployed free of charge and without approval by high-frequency devices in industry, science and medicine, as well as in the domestic field. Dif­fer­en­ti­a­tion is made between RFID systems which work in the frequency ranges low frequency (LF), high frequency (HF), ultra-high frequency (UHF), and super-high frequency (SHF). These differ con­sid­er­ably with regard to range and trans­mis­sion rate. There is no in­ter­na­tion­al RFID standard that stip­u­lates the use of specific fre­quen­cies.

• Low frequency, LF: For LF RFID systems, long waves are used in the frequency range between 125 kHz and 135 kHz. Reading distances are con­sid­er­ably higher than one meter. The trans­mis­sion rate is com­pa­ra­bly low. RFID systems with a frequency of 125 kHz have es­tab­lished them­selves in areas of ap­pli­ca­tion such as pro­duc­tion, in­stal­la­tion, and access control, as well as in animal marking. Passive RFID transpon­ders in the low frequency range are supplied with energy via inductive coupling.
• High Frequency, HF: HF RFID systems use short waves with a working frequency of 6.78 MHz, 13.56 MHz or 27.125 MHz and dis­tin­guish them­selves thanks to a high trans­mis­sion rate. The maximum reading or writing distance is up to 3 meters. HF transpon­ders manage with fewer antenna windings. This enables smaller designs. For smart labels in logistics, a frequency of 13.56 MHz has been es­tab­lished as a standard worldwide.
• Ultra-high frequency, UHF: RFID systems in the UHF range enable a high reach and trans­mis­sion speed. The maximum reading or writing distance is 10 meters. For systems with active transpon­ders, a range of up to 100 meters is possible. A dipole is suf­fi­cient as an antenna due to the low wave­length. In Europe, a frequency range around 868 MHz has es­tab­lished itself as a standard for UHF transpon­ders. The common frequency of 915 MHz in the USA is not permitted in Europe for RFID systems. Building sections, objects and other obstacles lead to a sig­nif­i­cant damping and re­flec­tion of UHF waves.
• Super-high frequency, SHF (mi­crowaves): With fre­quen­cies of 2.45 GHz and 5.8 GHz, ISM bands in the microwave range are also used in RFID tech­nol­o­gy. RFID systems in the SHF range dis­tin­guish them­selves through a very high trans­mis­sion rate. The range of passive SHF transpon­ders is up to 3 meters, and with active transpon­ders, distances of up to 300 meters can be spanned. As with UHF waves, mi­crowaves are also greatly damped by physical obstacles.

The following table offers a summary of the frequency bands used in RFID systems and their char­ac­ter­is­tics.

The coupling of the reading device and transpon­der is carried out in practice using one of the following pro­ce­dures.

• Close-coupling: Close-coupling systems are im­ple­ment­ed in such a way that the distance between reading device and transpon­der is a maximum of one cen­time­ter. This is possible in all frequency ranges in principle. Data trans­mis­sion is usually carried out via induction. Cor­re­spond­ing systems are used in areas with high security re­quire­ments. Classic fields of ap­pli­ca­tion are con­tact­less payment with chip cards or au­then­ti­ca­tion for locking systems. Due to the small distance, passive transpon­ders are suf­fi­cient.
• Remote coupling: The remote coupling procedure enables data trans­mis­sion with a distance of up to one meter. The coupling can usually be carried out in­duc­tive­ly for this process, too. The standard fre­quen­cies are 135 kHz (LF) or 13.56 MHz (HF). Passive transpon­ders are also used for the remote coupling procedure. The trans­mis­sion process can be used in the field of storage and logistics as well as in in­dus­tri­al au­toma­tion.
• Long-range systems: RFID systems in the long range field usually work in the ultra-high frequency range (868 MHz or 915 MHz) and offer a reading/writing distance of several hundred meters. Long-range systems in the microwave range have still been in the de­vel­op­ment stage up to now. To enable as high a range as possible, active RFID transpon­ders with their own energy supply are used. A potential field of ap­pli­ca­tion for long-range systems is vehicle iden­ti­fi­ca­tion in the context of traffic payment systems.

The basic function of an RFID system is the iden­ti­fi­ca­tion of a transpon­der by reading the unique ID. Writable transpon­ders are used for more complex ap­pli­ca­tion scenarios. Three types of transpon­der are dis­tin­guished in this context:

• Read-only: The simplest RFID transpon­ders are written uniquely by the man­u­fac­tur­er and can then be read as often as required. Adding, over­writ­ing or deleting in­for­ma­tion is no longer possible retroac­tive­ly.
• Write once, read many (WORM): WORM transpon­ders are supplied unwritten by the man­u­fac­tur­er and can be equipped with data once by users. These can then be read as often as possible.
• Read and write: RFID transpon­ders in this category can be re-written. This enables writing and reading access as often as required, whereby data can be added, modified, or deleted. Writing access can also be re­strict­ed with this type of transpon­der if necessary.

RFID transpon­ders can be equipped with various ad­di­tion­al features, depending on the design.

RFID tags that are equipped with a so-called “kill code” are per­ma­nent­ly de­ac­ti­vat­ed after receiving a specific signal. This function can be used for RFID-supported mer­chan­dise pro­tec­tion, among other things, and prevents products equipped with transpon­ders being handled and read outside the shop area.

If sensitive in­for­ma­tion is stored on RFID chips, for example, access codes for locking systems or bank details, en­cryp­tion is available. Fur­ther­more, transpon­der chips are sometimes pro­grammed in such a way that com­mu­ni­ca­tion with the reader requires a secret password. Cor­re­spond­ing transpon­ders first check the identity of the reader before they allow reading access to the memory.

RFID systems are used in logistics and retail in par­tic­u­lar nowadays. However, ap­pli­ca­tion options are also to be found in pro­duc­tion, warehouse and stock man­age­ment, vehicle iden­ti­fi­ca­tion, combating product piracy and animal marking. Users fre­quent­ly come into contact with RFID tech­nol­o­gy in the context of cashless payment systems. The use of RFID transpon­ders is also common when recording working hours and for elec­tron­ic locking systems. RFID chips are also deployed in personal iden­ti­fi­ca­tion, in­te­grat­ed into personal IDs and passports.

RFID tech­nol­o­gy is also used as an al­ter­na­tive to the barcode in logistics. RFID transpon­ders enable unique iden­ti­fi­ca­tion of goods across the entire supply chain and thus the trans­par­ent tracking of goods flow. Central fields of ap­pli­ca­tion are the tracking of movements, object iden­ti­fi­ca­tion and locating goods. There are also op­por­tu­ni­ties for op­ti­miz­ing the process using RFID in the field of stock­tak­ing, container man­age­ment and quality control – for example, in mon­i­tor­ing the chill chain. Remote coupling systems are also common. The transpon­ders are usually secured directly to the goods packaging or transport pallet for this. Reading is carried out using hand-held readers, as well as via sensors – for example in door frames or in the forks of forklift trucks.

RFID tags have also proven them­selves in the context of goods and stock man­age­ment in the library sector as well as in retail. One advantage of RFID tech­nol­o­gy compared to tra­di­tion­al recording systems via barcode is the op­por­tu­ni­ty to read several RFID transpon­ders at the same time via bulk recording. This is what is used for book returns at libraries, for example. Bulk recording allows all books in a batch to be iden­ti­fied uniquely without each book having to be scanned in­di­vid­u­al­ly. RFID systems are also used in sales areas – for example, to trace the flow of goods, for au­tomat­ing re­order­ing or to monitor the use-by date for per­ish­able products. These have been used ex­ten­sive­ly in retail up to now, but not anymore – for reasons of data pro­tec­tion, among other things.

In retail, RFID systems are used in mer­chan­dise man­age­ment as well as in the field of goods sur­veil­lance. RFID tech­nol­o­gy is widely used in the textile industry. RFID transpon­ders are sewn into items of clothing as flexible labels, or are attached elsewhere. RFID tags for goods sur­veil­lance are generally already in­te­grat­ed into the pro­duc­tion process and are therefore less obtrusive, more efficient and less expensive than other elec­tron­ic goods sur­veil­lance pro­ce­dures. However, RFID-based goods sur­veil­lance systems are crit­i­cized by those dealing with data pro­tec­tion, as cor­re­spond­ing chips in products can also be read after being purchased by the customer.

There are ap­pli­ca­tion options for the use of RFID systems in pro­duc­tion in the field of goods and material tracking as well as in the au­toma­tion of pro­duc­tion lines. The use of RFID tech­nol­o­gy is not only aimed at ac­cel­er­at­ing pro­duc­tion processes but at oc­cu­pa­tion­al safety and quality control. The basic idea is that each product (part) is fitted with a chip, which not only iden­ti­fies this uniquely but also provides in­for­ma­tion on pro­cess­ing, in­stal­la­tion, main­te­nance, or disposal. RFID tech­nol­o­gy, together with the IoT (the Internet of Things), is one of the basic building blocks of a smart factory according to the vision of Industry 4.0.

One possible field of ap­pli­ca­tion for RFID systems in the long-range area is vehicle iden­ti­fi­ca­tion – for example, in the context of access control, toll systems, speed mea­sure­ment, car-sharing offers, or parking space man­age­ment. Motor vehicle license plate numbers with RFID chips (so-called e-plates) could present an al­ter­na­tive to camera-based license plate recog­ni­tion, or could com­ple­ment this. Payment at gas stations or toll­booths could also be handled via an RFID chip in the license plate, almost while driving by.

In the fight against product piracy, it is possible that RFID tech­nol­o­gy could be used as an al­ter­na­tive or a com­ple­ment to other security measures – such as optical holograms. Brand recog­ni­tion is common, where passive RFID transpon­ders are in­te­grat­ed un­ob­tru­sive­ly into the product during man­u­fac­ture. Such chips enable brand products to be clearly iden­ti­fied, and verified if necessary, across the entire supply chain, thereby con­firm­ing the au­then­tic­i­ty of the item. If a bulk-enabled RFID system is used, even large quan­ti­ties of goods can be verified quickly with minimum effort. To prevent fal­si­fi­ca­tion of the in­for­ma­tion saved on the transpon­der chip, en­cryp­tion processes should be used. Checking by the end user is possible, for example using a smart­phone.

In the context of animal marking, RFID transpon­ders are used in the form of glass in­jec­tates, using an ap­pli­ca­tion device for direct injection into the body of the livestock or pet to be marked. RFID tech­nol­o­gy is used here as an al­ter­na­tive to pet collars or ear tags.

RFID is the un­der­ly­ing tech­nol­o­gy for con­tact­less payment pro­ce­dures via chip card or smart device. Data trans­mis­sion is carried out as a close coupling process for security reasons. Near field com­mu­ni­ca­tion (NFC) has es­tab­lished itself as an in­ter­na­tion­al trans­mis­sion standard. The most common cashless payment pro­ce­dures using NFC include Girogo, Paypass, Visa PayWave, Apple Pay and Google Pay.

RFID systems are fre­quent­ly found in the context of time recording – for example, as a re­place­ment for punch card systems to record working hours. Instead of clocking in, employees simply hold their transpon­der up to the relevant terminal to register the starting or finishing time or break times. The data is then analyzed in the back­ground by a computer system, and is processed as plus or minus hours in the working time account. RFID is also used to record times in the field of sports. Relevant transpon­ders are attached to the running shoes of track athletes, to racing bikes or to sports cars, to record them crossing the finish line as precisely as possible.

In the form of key fobs or chip cards, RFID transpon­ders enable iden­ti­fi­ca­tion at elec­tron­ic locking systems. This type of entry control has a major advantage compared to key-based pro­ce­dures. If an employee loses their transpon­der, only their ID has to be blocked. The cost-intensive changing of the lock, which is required when a key is lost, is un­nec­es­sary. RFID-based security controls for user au­then­ti­ca­tion are also possible for access to work­places, devices, tools or vehicles.

ID documents can also be extended to include functions for the simple elec­tron­ic reading of personal data using RFID tech­nol­o­gy. Many passports have been fitted with an RFID chip as standard since 2005. In the future, ap­pli­ca­tion of relevant ID chips under people’s skin is con­ceiv­able. Not only could these make personal data available, but also life-saving emergency in­for­ma­tion such as allergies and in­tol­er­ances, pre-existing con­di­tions, or med­ica­tions.

The ad­van­tages and dis­ad­van­tages of RFID systems are usually discussed under con­sid­er­a­tion of other pro­ce­dures for con­tact­less iden­ti­fi­ca­tion. Other processes enabling optical iden­ti­fi­ca­tion via the use of barcodes or QR codes can often be used in place of RFID systems for the above-mentioned fields of ap­pli­ca­tion. By com­par­i­son, the following ad­van­tages and dis­ad­van­tages of RFID tech­nol­o­gy can be singled out.