NFC stands for Near Field Communication
So what does that mean?. 
Below is a simplistic explanation of the term and some of the principles involved.
Radio Waves
Radio communication occurs because the voltage along an aerial wire, creates a magnetic field.
This field reacts with the earths magnetic field and as the changes occur so does the magnetic interference.
At the receiving end, this change in magnetic field induces a voltage on the aerial. The 'magic smoke' bits inside the receiver, convert this back to it's original form (more or less).
There is a non maths explanation here
http://www.antenna-theory.com/basics/whyantennasradiate.php
It can be refered to as EM or Electro Magnetic radiation but the true conversion doesn't occur until several wavelengths away from the source.
Image source Near and far field - Wikipedia, the free encyclopedia
Within the near field reactive region, any conductive objects can cause the antenna can be detuned.
This is why the art of tuning antennas can be likened to ("non white magic" ... the correct term trips the blacklist ) (not NZ's America cup yacht) but the dark arts, since you can't see it, and often can't measure it, but the effect is there.
Somewhere along the line someone discovered that they could use this and the most common use is to pass small amounts of data.
NFC
I've never heard of it or used it.
Until the later cellphones and credit cards with 'Tap and Go' the term NFC wasn't widely used.
I don't have one of those phones. 
Some people may have a Proximity Tag for access control into buildings, and these use the same principle.
Don't work in one of those buildings. 
Anyone that has a modern car probably hasn't realised there is a tag inside their key, which is registered in the cars Engine Management Computer.
Image source Google search various multiple finds
My car doesn't have one of those keys. 
If your pet is micro-chipped, they have a tag using the same technology inserted under the skin.
Image source Google search various multiple finds
No still not convinced I've used it. 
Well if you've ever been shopping you will have.
Many of the stores use security tags inside the products you buy.
While they may not contain data, they work on the principle of detuning the antenna at the shop entrance.
I don't have access to the technology they use (and it's not important here), but the reality is you will have experienced it somewhere.
So you may have using NFC technology for some time without realising it.
How does it work.
Contrary to popular belief the tags do not transmit.
The reader sends out a signal at the designed frequency (usually 125 KHz, 134 KHz, 13.5 MHz) and when a tag is within range it captures that energy.
This provides sufficient energy to power the chip inside which then will short the antenna in a particular manner.
The shorted antenna will detune the readers antenna, resulting in a difference. (a shorted antenna acts like a large metal object)
The reader electronics will translate that pattern of 'shorts' and 'non-shorts' into data.
How the reader handles the resultant data depends on the design of the system.
These tags are referred to as 'passive', and for some inventory control an 'active' (powered) tag can be used.
Is it secure
That is a good question. 
It has been alleged that some credit cards used for 'tap and go' applications have shown that it may be possible to skim them, without the owner knowing.
(You can find various conspiracy theories on the internet ... they are all true) ... 
In the past it required a physical swipe of the magnetic strip in order to collect the data, and you also needed a pin number, but with NFC unless there is a security handshake, the card/tag will give up its identity quite easily.
Some vendors have no pin required for transactions up to $80 ... meaning someone can do some damage to your account.
How can I protect myself.
Since the card requires to be within a readers field, the application of metal either side of the card, renders it's performance extremely poor.
This has resulted in another industry for wallet protectors.
image source Protect Your Credit Cards | Credit Card RFID Wallet - Full Sheild Protection
I've also heard of a piece of foil used inside your favourite wallet, but whatever is used, the idea is to prevent the tags getting a signal so it can respond.
Now that I've introduced you to what NFC is, the next blog will look at some of the uses, and how you can play with it.
Mark
edit
Next blog
