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NFC is used every day, but do you know the principle?

2022-06-25

 As the English abbreviation of near field communication, NFC can exchange data when they are close to each other. It is evolved from the integration of contactless radio frequency identification (RFID) and interconnection technology. By integrating the functions of inductive card reader, inductive card and point-to-point communication on a single chip, NFC uses mobile terminals to realize mobile payment, electronic ticketing, access control, mobile identity recognition Anti counterfeiting and other applications.

"Near field" in the Chinese name of NFC refers to radio waves adjacent to electromagnetic fields. Because radio waves are actually electromagnetic waves, they follow Maxwell's equation. The electric field and magnetic field will carry out energy conversion alternately in the process of transmitting from the transmitting antenna to the receiving antenna, and enhance each other during the conversion. For example, the radio signals used by our mobile phones use this principle to spread, which is called far-field communication. Within 10 wavelengths of electromagnetic wave, the electric field and magnetic field are independent of each other. At this time, the electric field has little significance, but the magnetic field can be used for short-distance communication, which we call near-field communication.

The application of NFC technology has been widely concerned all over the world. Different roles such as telecom operators and mobile phone manufacturers at home and abroad have carried out application pilot projects, and some international associations and organizations have also actively carried out standardization work. According to the prediction of relevant institutions in the industry, mobile applications based on near-field communication technology will become the next killer application of mobile value-added services.

In order to be compatible with contactless smart cards, NFC standard specifies a flexible gateway system, which is specifically divided into three working modes: point-to-point communication mode, reader writer mode and NFC card simulation mode.

1. Point to point form

Point to point mode, in which two NFC devices can exchange data. For example, several digital cameras and mobile phones with NFC function can use NFC technology for wireless interconnection to realize data exchange such as virtual business cards or digital photos.

For the point-to-point form, the key is to connect two devices with NFC function, so that the data transmission between points can be realized. By taking the point-to-point form as the premise, mobile phones and computers with NFC function can truly achieve point-to-point wireless connection and data transmission, and in subsequent associated applications, it can be not only local applications, but also network applications. Therefore, the application of point-to-point form plays a very important role in the rapid Bluetooth connection between different devices and its communication data transmission.

2. Reader mode

Read / write mode, in which NFC device is used as a contactless reader. For example, NFC enabled mobile phones play the role of readers and writers when interacting with tags, and NFC enabled mobile phones can read and write tags that support NFC data format standards.

NFC communication in card reader mode is used as a non-contact card reader, which can read relevant information from electronic labels of exhibition information, movie posters, advertising pages, etc. NFC mobile phones in card reader mode can collect data resources from tag and complete information processing functions according to certain application requirements. Some application functions can be completed directly locally, and some need to be completed in combination with TD-LTE and other mobile communication networks. NFC application fields based on card reader mode include advertisement reading, ticket reading, cinema ticket sales, etc. for example, there is a tag tag behind the movie poster. At this time, users can carry a mobile phone that supports NFC protocol to obtain movie information, and can also connect to buy movie tickets. NFC mode of card reader can also support the acquisition of bus stop information and map information of tourist attractions, and improve the convenience of people's tourism transportation.

3. Card analog form

Analog card mode, which simulates a device with NFC function as a tag or contactless card. For example, mobile phones that support NFC can be read as access cards, bank cards, etc.

The key of card simulation mode is to simulate the equipment with NFC function and turn it into a non-contact card mode, such as bank card and access control card. This form is mainly used in contactless mobile payment such as shopping malls or transportation. In the specific application process, users only need to put their mobile phones or other relevant electronic devices close to the card reader, and enter the corresponding password to make the transaction. For the card in the card simulation form, the key is to implement power supply processing in the RF domain of the contactless card reader, so that the NFC device can continue to work even if there is no power. In addition, for the application of card simulation form, it can also collect data in relevant equipment with NFC function, and then transmit the data to the corresponding processing system for relevant processing. Moreover, this form can also be applied to various aspects such as prohibition system and local payment.

Comparison between NFC and RFID

First, the working mode is different. NFC integrates point-to-point communication function, reader function and contactless card function into one chip, while RFID is composed of reader and tag. NFC technology can read or write, while RFID can only read and determine information.

Second, the transmission distance is different. The transmission distance of NFC is much smaller than that of RFID. The transmission distance of NFC is only 10 cm, and the transmission distance of RFID can reach several meters or even tens of meters. NFC is a close and private communication method. Compared with RFID, NFC has the characteristics of close distance, high bandwidth, low energy consumption and high security.

Third, the application fields are different. NFC is more used in the field of consumer electronics, and plays a huge role in the fields of access control, public transportation, mobile payment, etc; RFID is better at long-distance identification and is more used in production, logistics, tracking and asset management.

Comparison between NFC and Bluetooth

NFC and Bluetooth are short-range communication technologies. Compared with Bluetooth, which has been integrated into mobile phones for a long time and has been popularized, NFC has only been integrated into mobile phones in recent years, and so far it has only been integrated into a few mobile phones.

First, the establishment time is different. The NFC communication setup procedure is simple, and the communication establishment time is very short, only about 0.1s; The Bluetooth communication setup procedure is relatively complex, and the communication establishment time is long, which takes about 6S.

Second, the transmission distance is different. NFC transmission distance is only 10cm, while Bluetooth transmission distance can reach 10m. However, NFC is slightly better than Bluetooth in terms of transmission power consumption and security.

Third, the transmission speed and working frequency are different. The NFC working frequency is 13.56MHz, and the maximum transmission speed is 424 kbit / s, while the Bluetooth working frequency is 2.4GHz, and the transmission speed can reach 2.1 Mbit / s.

Comparison between NFC and infrared

Compared with infrared transmission, NFC has the same transmission distance, but it is faster than infrared transmission. The maximum transmission speed of NFC can reach 424 kbit / s, while the infrared transmission speed is about 100kbit / s. The establishment time of NFC is slightly faster than that of infrared. The establishment time of NFC is 0.1s, and the establishment time of infrared transmission is 0.5s. Infrared transmission must be strictly aligned to transmit data, and there must be no obstacles in the middle, while NFC has no such restrictions; In addition, NFC is safer and more reliable than infrared.

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