Although NFC is similar to RFID in many respects and is based on RFID, it is an independent concept. In the case of RFID with passive and active tags, active tags can be read from a relatively long distance, while NFC, as its name implies, works in the near-field region of the electromagnetic field.
RFID still exists and will be in the foreseeable future. NFC is a direct development of RFID, and you might consider parallel branches. At the most basic level, NFC is usually two inductively coupled devices whose communication is performed by modulating the power absorbed by the passive device. Passive RFID absorbs RF power and then uses it to transmit data back to the reader-Active RFID can use its own power source to transmit data back to the reader. As with NFC, there are always exceptions to the rule-5 NFC tags have a longer working distance (up to 1 meter).
In the most typical implementation of NFC, a device is an active device, acting as a master device in communication and creating a modulated RF near field that will power passive slave devices. Active devices usually use the name of the reader, while passive devices are called tags. Common examples of tags include stickers and embedded systems. The most common NFC readers you might see in your daily life are smartphones or payment terminals.
Near Field Communication
In a typical RF communication, a transmitting antenna transmits RF signals into free space, and an antenna with at least λ/4 (quarter wavelength) is required to be effective. When the distance between two RF devices exceeds 2λ (two wavelengths), for example, about 245 mm (10 inches) for 2.4 GHz signals, they can usually communicate with each other.
Instead, NFC communicates in a spatial near-field area below λ/2 (less than half of the wavelength). Two near-field devices are used as two coils of a coupled inductor or transformer wound on a common magnetic core.
NFC technical parameters
Since NFC tags operate in the near field, the technical features and specifications are completely different from the more traditional far-field-based wireless technologies that you may be more familiar with. Let's look at some interesting technical data related to NFC and how to compare it with far-field wireless technology.
Working distance
Although a dedicated point-to-point device can reach more than 100Km in compliance with the standard, it is estimated that the typical maximum outdoor range of a 2.4GHz WiFi device is about 50 to 75 meters. When a Bluetooth device runs on the same 2.4GHz WiFi, it will trade off bandwidth to increase power consumption, and expand to more than 300 meters for version 5.0. The range of LoRa equipment can exceed 10Km, its power consumption is much lower than these two technologies, and the bandwidth is very limited.
NFC is limited by design to a maximum of 10 cm.
Near-field magnetic induction communication systems (such as NFC) have very strict power density. The power density decays at a rate proportional to the reciprocal of the sixth power range. This is much larger than far-field communication, so that at the end of the near-field region of 13.56MHz (the most common frequency of NFC), its energy level is 10,000 to 1,000,000 times lower than far-field communication (-40dB to -60dB) ). The equivalent deliberate far-field transmitter.
Like any good rule, there are exceptions. NFC Type 5 tags using the ISO-15693 protocol can be read by dedicated hardware at a distance of up to one meter; however, in fact, if not all, most smart phones can only comply with the 10 cm limit. Some high-performance NFC antennas allow tags up to 15 cm to be read, while on the other side of the spectrum, some smaller tags limit the distance to around 2 cm.
The reduced distance causes the user to require explicit physical actions for the protocol to work. Contrary to the always-on characteristics of WiFi and Bluetooth, NFC is the only widespread wireless communication protocol that requires users to take conscious actions to use.
Frequency
MHz is a unit of measurement that one cannot expect to find in the wireless specifications of modern smartphones. iPhone 11 has a communication frequency of up to 8GHz, and 60GHz WiGig devices are becoming more and more popular in the market. NFC uses a different method to reduce power consumption, range, price and frequency.
Compared with a wide range of high-speed connections, the limited frequency and short distance make the implementation of NFC antennas relatively stress-free. For reasons of simplicity or inexperience, wise designers may wish to use modules with integrated antennas for Bluetooth or WiFi. In the NFC field, if you follow the IC’s recommendations, your design may perform well regardless of small manufacturing differences or nearby objects (for example, at microwave frequencies).
Data rate
The maximum bandwidth supported by the NFC standard is 424Kbit/s, which is about eight times the speed of a traditional dial-up 56K connection. This limitation makes the standard comparable in performance to Bluetooth, which is about half the data rate of version 4.0. Unfortunately, the standard has a lot of overhead, and most devices usually run at 50Kbit/s. Even if the data rate on the connection is so limited, and there is some ingenuity and creativity, the applications are endless. Since the memory on most tags is relatively limited, there is almost no need for higher data rates.
Memory
Most models of NFC tags contain 100 bytes to 1KB of memory, although the available models have a memory capacity of up to 64 KB. These larger storage capacities are usually used for smart cards.
Although this storage volume sounds a bit limited, it allows a large number of 8-16 bit (1-2 bytes) sensor readings or data about the contents of the tag attached.
Current draw
Many NFC ICs provide energy harvesting output, which can provide about 5mA of current under better conditions. The following are no special suggestions for processing methods less than 5mA:
Supply power to external sensors and analog circuits. In terms of temperature sensing, NFC ICs with embedded temperature sensors have been widely used to track perishable goods.
For external storage, its capacity is greater than that provided by the NFC IC.
Update the electronic ink display.
Charge a small lithium battery.
Charge the super capacitor (electrolytic double layer capacitor)
Price
NFC tags, tags and basic ICs are widely used for asset tracking and therefore need to be very affordable. If NFC tags are affixed to every item in a supermarket, or every piece of clothing in a clothing store, even 50c per tag, it will quickly become unpopular. Fortunately, the simplicity of NFC makes the production of tags and basic tags easy, and each tag costs between 10c and 50c, depending on the volume.
When you read the NFC standards, you will find that they have been built to support multiple existing standards and applications. Fortunately, out of our sanity, almost all electronic engineers who are not engaged in mainstream NFC implementation work need to understand the depth of NFC tag types. All modern smartphones must support each tag type to comply with the NFC standard. The data sheet will clearly explain the functions and characteristics of each NFC IC, whether it is active or passive, tag or reader, sticker or the entire SoC.
Mark Type 2 can satisfy most NFC cards, stickers and asset tags of NFC Forum Mark Type 2. Basic information storage and retrieval can be performed through NFC communication or the I2C interface used to connect to the microcontroller.
Tag type 4 mainly supports functions that perform calculations on the basis of storage and retrieval, as well as advanced security functions. Finally, if you need to read for a long time and allow users to interact with the tag through a smartphone, you will need tag type 5.
The part 2 of the depth of NFC tag types
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