Following on from our look at Near Field Communication, we’re going to take a closer look at the counterpart NFC tag technology, which is used to power interactive advertisements, public transport cards, and is even used in wristband technologies, just to name a few.
You may have noticed small NFC tags next to advertisements near bus stops, stickers in shops, or may have even come across the clever idea of using NFC enabled business cards. These tags can store wide ranges of information, from short lines of text, such as a web address or contact details, to links to apps in the Google Play Store.
NFC tags have the potential to replace many existing technologies, from bar and QI codes to the Bluetooth wireless standard, but how does it all work?
How it works
NFC tags are considered passive devices, which means that they operate without a power supply of their own and are reliant on an active device to come into range before they are activated. The trade-off here is that these devices can’t really do any processing of their own, instead they are simply used to transfer information to an active device, such as a smartphone.
In order to power these NFC tags, electromagnetic induction is used to create a current in the passive device. We won’t get too technical on this, but the basic principle is that coils of wire can be used to produce electromagnetic waves, which can then be picked up and turned back into current by a another coil of wire. This is very similar to the techniques used for wireless charging technologies, such as Qi or A4WP.
The active devices, such as your smartphone, are responsible for generating the magnetic field. This is done with a simple coil of wire, which produces magnetic fields perpendicular to the flow of the alternating current in the wire. The strength of the magnetic field can be adjusted by varying the number of turns in the wire coil, or increasing the current flowing through the wire. However, more current obviously requires more energy, and very high power requirements would not be desirable for use in battery powered mobile technologies. Hence why NFC operates over just a few inches, rather than the many meters that we’re used to with other types of wireless communication.
The passive device works in the same way, just in reverse. Once the passive device is in range of the active device’s magnetic field, the electrons in the receiving coil of wire begin to produce a current that matches that in the transmitting smartphone. There is always some power lost during transmission through the air, but over short distances the current generated is enough to power the circuitry in the NFC tag.
These circuits are fine tuned to a certain frequency, which increases the device’s sensitivity to signals at a specific frequency. This allows for a maximum transfer of energy across the air.
Different Tag Types
NFC tags communicate using the ISO 14443 type A and B wireless standards, which is the international standard for contactless smartcards, used on many public transportation systems. This is why NFC devices can be used with existing contactless technologies, such as card payment points.
There are a range of different tag types available, each offering different storage levels and transfer speeds. Tag types 1 and 2 come with capacities between just a tiny 48 bytes and 2 kilobytes of data, and can transmit that information at just 106 kbit/s. Although that may sound quite small, especially compared to your typical SD card, that’s enough data for some very simple pieces of information, such as a website URL, and is all you need for most basic NFC tags. These tags are designed to be highly cost effective, and can also be re-used if you want to change the data stored on them.
Type 3 uses a different Sony Felica standard, and can transfer data at a slightly faster 212 kbit/s. These tend to be used for more complicated applications, but sadly can’t be rewritten. Similarly, type 4 is again read-only, but has a larger memory capacity of up to 32 kbytes and communication speeds of between 106 kbit/s and the maximum NFC 424 kbit/s. Tag type 4 works with both type A and B of the ISO14443 standard.
Cheap and effective
The strongest argument in favour of NFC, over other forms of short range wireless communication, is that tags are incredibly cheap to make and maintain, but can still be used for a wide range of applications. With very simply circuitry and very few components, NFC tags can be produced on mass for very low unit costs.
Combine low costs with the absence of any power requirements, and you have a cheap yet effective way of quickly communicating with other smart devices. From launching applications, to exchanging web addresses and purchasing a rail ticket, NFC aims to make our lives that little bit more convenient just by using our smartphones.
Don’t be surprised if you see more and more of these little tags popping up over the next few years.