RFID technology allows contactless transfer of information (much like the bar code we are familiar with), making it effective in production environments and other harsh environments where bar code labels cannot survive. See how it works and what are the pros and cons.
Radio Frequency Identification (RFID) is the use of electromagnetic or electrostatic coupling in the radio frequency portion of the radio frequency identification electromagnetic spectrum to uniquely identify objects, animals or people. With its ability to track moving objects, it has established itself in a wide range of markets including livestock identification and automatic vehicle identification. This technology has also become a major component of automated data collection, identification and analysis systems around the world.
The Architecture and Working Principle of Radio Frequency Identification Technology
An RFID system consists of three parts: a transceiver (usually combined with a reader), some kind of data processing equipment (such as a computer), and a transponder (tag). A typical RFID system is shown in Figure 1.
Figure 1: Structure and working principle of
RFID system RFID tags, commonly referred to as transponders, act as both a transmitter and a receiver in an RFID system. The three basic components of an RFID tag are the antenna, the microchip (memory), and the packaging material.
In a typical system, tags are attached to objects. Each tag has a certain amount of internal memory (EEPROM), which stores information about the object, such as its unique ID (serial) number, or in some cases more details, including production date and product composition.
As these tokens pass through reader-generated fields, they pass this information back to the reader, thereby identifying the object. The antenna uses radio frequency waves to transmit the signal, which activates the transponder. When activated, the tag transmits data back to the antenna. These data are used to inform the programmable controller that action should be taken. Operations can be as simple as opening an access door, or as complex as connecting to a database for currency transactions.
Low frequency (30-500 kHz) RFID systems have shorter transmission distances (generally less than 1.8 meters). High frequency (850-950 MHz and 2.4-2.5 GHz) RFID systems have longer transmission distances (over 27 meters). In general, the higher the frequency, the more expensive the system. RFID is sometimes referred to as dedicated short-range communication.
There are two types of RFID tags
Read-only tags and read-write tags. In read-only tags, the microchip or memory is written only once during the manufacturing process. This information and the serial number on the read-only tag can never be changed. In read-write tags, only the serial number is written during the manufacturing process. The remaining blocks can be overwritten by the user.
Until recently, the focus of RFID technology was mainly on tags and readers, which were used in systems with relatively small amounts of data. This is changing now, as RFID in the supply chain is expected to generate huge amounts of data that will have to be filtered and routed to back-end IT systems. To solve this problem, the company has developed a special software package, called "scholar," which acts as a buffer between the RFID front-end and the IT back-end. Academics are equivalent to middleware in the IT industry.
RFID reader
An RFID reader is a device used to send and receive information from RFID tags. It is also called "Interrogator". It includes sensors capable of reading nearby RFID tags. The reader sends an information request to the tag. The tags respond with their respective information, which the reader then forwards to the data processing device. The tag and reader communicate with each other via radio channels. In some systems, the connection between the reader and the computer is wireless.
supporting infrastructure. The supporting infrastructure includes the associated software and hardware required for the RFID system. The software manages the interaction between RFID readers and RFID tags.
letter of agreement
The communication process between reader and tag is managed and controlled by one of several protocols, such as ISO 15693 and ISO 18000-3 for HF, ISO 18000-6 and EPC 18000-6 for UHF . Basically, when the reader is turned on, it starts transmitting in the selected frequency band (specifically UHF at 860-915 MHz or HF at 13.56 MHz). A reader with any corresponding tag in the vicinity will detect the signal and use energy to wake up from it and provide operational power to its internal circuitry. Once the marker encodes the signal as valid, it returns
anti-collision
If there are many tags, they will all reply at the same time. On the reader side, this is seen as an indication of signal collisions and multiple markers. The reader manages this problem by using an anti-collision algorithm that allows tags to be sorted and selected individually. There are many different types of algorithms (binary trees, aloha, etc.) defined as part of the protocol standard.
The number of identifiable tags depends on the frequency and protocol used, typically ranging from 50 tags/s for HF to 200 tags/s for UHF. Once a marker is selected, the reader is able to perform operations such as reading the marker. This process continues under the control of the anti-collision algorithm until all labels are selected.
Inductively Coupled RFID Tag
These original tags were complex systems of metal coils, antennas and glass. Inductively coupled RFID tags are driven by a magnetic field generated by an RFID reader. Electric current has an electronic component and a magnetic component, i.e. it is electromagnetic. The name "inductive coupling" comes from the magnetic field induced by the current in the wire.
Advantages of RFID tags
- RFID tags are durable and can work in harsh temperatures and environments. Even under harsh conditions, RFID systems can work at very high speeds.
- RFID tags come in different shapes, sizes, types and materials. Information on read-only tags cannot be altered or copied. Read and write tags can be reused. RFID tags are always read without any errors.
- No direct physical contact is required between the tag and reader, and radio frequency technology is used for communication.
- Multiple RFID tags can be read simultaneously. RFID tags can read 10 to 100 tags at a time. Reading labels is automatic and requires no labor.
- RFID systems can identify and track unique items, unlike barcode systems that only identify manufacturer and product type.
- The entire RFID system is very reliable, and RFID tags can be used for security purposes.
- RFID tags have more storage capacity than any other automatic identification and tracking system.
Disadvantages of RFID tags
- Compared to other automatic identification systems, RFID systems are costly. If the RFID system is designed for a specific application, the cost will increase further.
- Compared to barcode systems, labels are larger in size and weight. Electronic components such as antennas, memory and other parts of the tag make them bulky.
- While tags work in harsh environments, the signals they emit can be affected when certain types of tags come into close contact with certain metals or liquids. Reading such marks becomes difficult and sometimes the data read is wrong.
- There is no way to track down damaged labels and replace them with undamaged ones.
- While tags do not require line-of-sight communication, they can only be read within a specified range.
Capacitively Coupled Labels
These tags are designed to reduce the cost of the technology. These are disposable labels that can be applied to less expensive items and make as common bar codes. Capacitively coupled tags use conductive carbon ink instead of metal coils to transmit data. The ink is printed on paper labels, which are scanned by the reader.
Motorola's BiStatix RFID Tag
They are the frontrunners in this technology. They used a silicon chip just 3mm wide to store 96 bits of information. The technology didn't catch on with retailers, and BiStatix was shut down in 2001.
Inductively coupled and capacitively coupled RFID tags are not as commonly used as they are today due to their expensive and bulky size. New innovations in the RFID industry include active, semi-active and passive RFID tags. These tags can store up to 2 kilobytes of data and consist of a microchip, an antenna and, in the case of active and semi-passive tags, a battery. The components of the tag are encapsulated in plastic, silicon or sometimes glass. Table i gives an overview of the performance of passive markers at different frequencies.
Active and passive tags
When considering labels, the first basic choice is between passive, semi-passive, and active. Passive tags can be read from a distance of 4 to 5 meters using the UHF band, while other types of tags (semi-passive and active) can achieve longer communication distances, up to 100 meters for semi-passive and active up to several kilometers. The large variance in communication performance can be explained by the following reasons:
- Passive tags use the reader field as a source of energy for the chip and for communication with the reader. The available power from the reader field not only decreases rapidly with distance, but is also controlled by strict regulations, resulting in limited communication distances of only 4-5 meters when using the UHF band (860-930 MHz).
- Semi-passive (battery-assisted backscatter) tags have built-in batteries and therefore do not require the reader's power to drive the chip. This allows them to operate at much lower signal power levels, allowing them to reach distances of up to 100 meters. The distance is limited mainly because the tag does not have an integrated transmitter and must also use the reader field to communicate back to the reader. An active tag is a battery-operated device with a built-in active transmitter. Unlike passive tags, these tags generate radio frequency energy and apply it to wireless antennas. This autonomy from readers means they can communicate over distances of more than a few kilometers.
- HF and UHF are best suited for supply chains. UHF, due to its superior read range, will be the dominant frequency. Low frequencies and microwaves cannot be used in some cases
Integrated Circuits for Labeling
RFID tag integrated circuits are designed and manufactured using some of the most advanced and smallest geometric silicon processes available. The results are impressive when you consider that UHF tag chips are about 0.3 mm2 in size.
In terms of computing power, RFID tags are very unwieldy, containing only basic logic and state machines capable of decoding simple instructions. That doesn't mean their design is simple. In fact, very real challenges exist such as achieving very low power consumption, managing noisy RF signals and staying within strict emission regulations.
Other important circuits allow the chip to transfer power from the reader signal area and convert it to a supply voltage through a rectifier. The chip clock is also usually extracted from the reader signal.
Figure 3: Example of HF (13.56 MHz) tag
Figure 4: Example of a UHF (860-930MHz) tag
The amount of data stored on a tag depends on the chip's specification and can range from a simple identification number of about 96 bits to a product containing 32 kbits of more information. However, larger data capacity and storage (memory size) results in larger chip size and therefore more expensive tags.
In 1999, the AUTO-ID Center (now EPC Global) headquartered at the Massachusetts Institute of Technology in the United States, together with some large companies, came up with the idea of a unique electronic identification code called Electronic Product Code (EPC). EPC is conceptually similar to the Universal Product Code used in barcodes today.
Figure 5: Basic tag integrated circuit structure
If there is only a simple 256-bit code, the chip size will be smaller and the tag cost will be reduced, which is considered a key factor for the widespread adoption of RFID in the supply chain. Tags that store ID numbers are often called license plate tags.
category of label
One of the main ways to classify RFID tags is based on their ability to read and write data. This leads to the following four categories:
Class 0 (read only, factory programmed)
These are the simplest types of tags, where the data (usually a simple ID number (EPC)) is written to the tag only once during manufacture. Then disable memory for any further updates. Class 0 is also used to define a class of tags called electronic article surveillance or anti-theft devices, which have no ID and only reveal their presence when passed through the antenna field.
Type 1 (write-once read-only, factory or user programmed)
In this case, no data was written to memory when the mark was manufactured. The data can then be written once by the marker manufacturer or by the user. After this time, no further writes are allowed, and only the tag can be read. This type of token usually acts as a simple identifier.
Category 2 (read-write)
These are the most flexible tag types and users can access read and write data in tag memory. They are often used as data loggers and therefore contain more memory than a simple ID number would require.
Category 3 (read and write with on-board sensors)
These tags contain onboard sensors that record parameters such as temperature, pressure and motion by writing to the tag's memory. Since sensor readings must be taken without a reader, tags are either semi-passive or active.
Category 4 (read and write with integrated transmitter)
These are like tiny radios that can communicate with other tags and devices without the need for a reader. This means that they are fully active with their own battery power.
How to choose a marker
Selecting the correct label for a specific RFID application is an important consideration, and a number of factors listed below should be considered:
- Size and form factor — where does the label have to go?
- How close are the labels?
- Durability — Does the label need to have a strong exterior protection against constant wear and tear?
- Are tags reusable?
- Resistant to harsh (corrosive, wet, etc.) environments
- Polarization — the orientation of the tag in the reader field
- exposure to different temperature ranges
- Communication distance
- Influence of materials such as metals and liquids
- Environment (electrical noise, other radio equipment and equipment)
- Operating frequency (LF, HF or UHF)
- Supports communication standards and protocols (ISO, EPC)
- Regional (United States, Europe and Asia) Regulations
- Does the tag need to store more than an ID number like EPC?
- Anti-collision — how many tags in the field must be detected at the same time, and how fast?
- How fast does the label move in the reader field?
- Reader Support — Which reader products are able to read labels?
- Does the label need to be secure?
Figure 6: Two different ways of energy and information transfer between reader and tag
How labels communicate
To receive energy and communicate with the reader, passive tags use one of the following two methods shown in Figure 6. These techniques include near-field techniques, which use the inductive coupling of the tag combined with a magnetic field (such as a transformer) circulating around the reader antenna, and far-field techniques, which use a radar-like technique (backscatter reflection) coupled with an electric field .
The near field is typically used for RFID systems in the low and high frequency bands, and the far field is used for reading UHF and microwave RFID systems over long distances. The theoretical boundary between the two fields depends on the frequency used, and is in fact proportional to l/2p, where "l" is the wavelength. For example, a high frequency system is about 3.5 meters and an ultra-high frequency is about 5 centimeters, both of which are further reduced if other factors are taken into account.
Figure 7: HF tag orientation for different antenna structures
Label Orientation (Polarization)
How the tags are placed in terms of the reader's field polarization can have a significant impact on the communication distance for HF and UHF tags. This can result in a 50% reduction in the operating range, and if the label is displaced by 90° (see Figure 7), the label cannot be read.
The best orientation for HF tags is when the two antenna coils (reader and tag) are parallel to each other, as shown in Figure 7. UHF tags are even more sensitive to polarization, due to the directional dipole field. The problem of polarization can be largely overcome by different technologies implemented on the reader or tag, as shown in Table IV.
future
Advances in RFID technology continue to yield larger memory capacities, wider reading ranges, and faster processing. However, there is little chance that the technology will eventually replace barcodes. Even with inevitable reductions in raw materials, coupled with economies of scale, integrated circuits in RF tags will never be as cost-effective as barcode tags. Still, RFID will continue to grow in areas where barcoding and other optical technologies are ineffective, such as chemical containers and animal husbandry.
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Mr. Bai Jilong has been engaged in the electronics industry for 15 years. He has developed more than 100 products so far, and most of them have been mass-produced.
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It took 5 years since 2018 to record thousands of practical-level electronic engineer series courses, from components to core modules to complete products
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Lao Bai's original intention is "May the world's engineers not take detours" Among them, there are courses explaining MOS tubes and IGBTs in detail