How do NFC tags and readers work?

　　NFC, or Near Field Communication, is a popular wireless technology that allows you to transfer data between two devices that are close to each other. For some short-distance applications, such as mobile payments, it is usually a faster and safer alternative than QR codes. In fact, there is nothing special about this technology, as long as you have a reading device, you can read data from various NFC tags.

　　NFC tags are versatile, and they are often useful when you want to transfer a small amount of data effortlessly. After all, compared to using Bluetooth pairing or other traditional wireless communication methods, it takes less time and effort to touch the surface. For example, digital cameras and headsets have embedded NFC tags, you can click on it to quickly start the connection with the device.

　　Even so, do you know how they work? Now, let’s take a look.

　　How does NFC tag work

　　NFC tags come in various shapes and sizes. The simplest ones are usually made in the form of square or round stickers. The structure of this type of tag is extremely simple: it consists of a thin copper coil and a small storage space on a microchip. .

　　The 　　 coil allows the tag to wirelessly receive power from the NFC reader through a process called electromagnetic induction. Essentially, whenever you bring a powered NFC reader close to the tag, the latter will power up and transfer any data stored in its microchip to the device. If sensitive data is involved, the label can also be encrypted with a public key to prevent malicious attacks.

　　Since the basic structure of the NFC tag is very simple, you can fit the required hardware into a large number of external dimensions. Take hotel key cards or general access control cards as an example. These are usually made into a plastic card with some copper wires and some microchip memory on it. The same principle applies to NFC-equipped credit and debit cards, which contain thin copper wires that extend along the perimeter of the card.

　　It is worth noting that powered NFC devices like smart phones and tablets can also be used as NFC tags. Unlike RFID, which only supports one-way communication, NFC can facilitate two-way data transmission. For example, this allows your phone to emulate an embedded NFC tag, such as a tag used for contactless payments. Of course, these are more advanced equipment, but the basic operating mode is still the same.

　　What types of NFC tags are there

　　Most NFC tags follow the ISO 14443 based short-range data transmission standard, but there are also five sub-types, which are labeled 1 to 5 for convenience. Type 1 tags are the least advanced because they can only store less than one kilobyte The data is just a few hundred characters of text. So such a tag has enough memory to store a URL or Wi-Fi password, but it is not enough to store other information. The transmission speed is not particularly large, about 100kbps.

　　The 5 type NFC tag can hold 32KB of memory. Their data transmission speed is approximately 4 times that of Type 1 tags. Compared with a typical microSD card of the same physical size, this is still not a lot of data. However, this is sufficient for use cases such as ticketing and access control. These types of tags may also provide additional features, such as tamper resistance and improved interference handling capabilities.

　　However, as expected, more advanced NFC tags are more expensive to manufacture. Considering that the data transmitted through this medium is very small, most applications provide adequate services by more primitive types. Type 1 and Type 2 tags are more common, and if purchased in bulk, the cost is only a few cents.

　　NFC tags are usually readable and writable, so you can reuse them according to your needs. This further reduces deployment costs in large-scale use cases.

　　How does NFC reader work

　　NFC reader provides power for passive tags and reads data. To achieve this, the NFC reader needs a power source to pass current through its own coil, which will generate an alternating magnetic field near the reader. Due to Faraday's law of induction, bringing the tag into the range of this magnetic field eventually leads to inductive coupling between the two coils.

　　Once the tag is powered on, the actual data transmission process is quite simple. The reader can detect how the NFC tag modulates the electromagnetic field. A technique called Manchester encoding is used to determine binary values (0 and 1) from electromagnetic pulses. Finally, these binary values are converted into human-readable text.

　　Contactless payment terminals are probably the most widely used NFC readers, followed by public transportation cards. In both cases, you will get a unique NFC tag in the form of a card or token with your balance or account information stored on it. At the same time, readers are usually fixed devices that are actively connected to power and data, and sometimes connected via battery and Wi-Fi respectively.

　　NFC tag: how to read and write data

　　As mentioned earlier, most mid-range and high-end smartphones nowadays include NFC hardware. This makes it very easy to read an existing NFC tag, just use the back of the smartphone to make physical contact with it. According to the content of the label, a pop-up window will automatically appear on your device and prompt you to complete an action. For example, a tag with a URL may surface in a web browser, and a tag embedded in a pair of headphones will automatically initiate Bluetooth pairing.

　　As for writing or overwriting data, it should be noted that not all NFC tags can be read and written. Certain tags, such as those designed for access control, may have write protection features to prevent tampering or unauthorized modification. And some unbranded NFC stickers and cards can rewrite NFC tag data.

　　With a rewritable NFC tag, you can program it to do whatever you want. Applications like NFC tools will allow you to write contacts, Bluetooth pairing information, website links or Wi-Fi configuration on the tag. For a more advanced example, you can combine NFC tags with automated applications, such as Tasker for Android or Shortcuts for iOS, to perform actions such as turning on lights.