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.