Near Field versus Far Field

Near field communication can be considered the twin of far field communication. Both terms describes certain areas within an electromagnetic field formed around an antenna. In addition to the near and far field regions, a transition zone between the two also exists. Near field, as the name suggests, is very close to the antenna while far field is further away. The distance the region is from an antenna creates very different properties in how the electromagnetic field reacts. By taking advantage of these properties in the near field region, near field communication is possible.

The far field region of an electromagnetic field starts approximately two wavelengths from the antenna and extends outward. As the distance increases, the strength of the electromagnetic field decreases equal to the square of the distance the field is from the antenna. If the signal is picked up by another antenna this has no effect on the original antenna signal. 

Between the near and far field zones exists the transition zone, which retains properties of both near and far field communication depending on the distance. No exact distance exists for the transition zone. Its region changes based on several factors, such as the strength of the signal sent by the transmitting antenna.

In contrast to the far field region, the near field region is found one wavelength or less from the transmitting antenna. The strength of the signal decreases rapidly the further it travels from the antenna. Unlike far field communication, the receiving antenna affects the transmitting antenna. This unique characteristic of the near field region allows near field communication to create a signal between a transmitting device and the receiving NF tag where the tag’s field is powered by the transmitter and the tag’s field can communicate back to the transmitter to send information. This set-up requires the reader, such as a NFC compatible smartphone, and the NFC tag it is interacting with to be approximately 4cm or less from each other to work properly.

The short distance prevents accidental payments and offers protect against eavesdroppers trying to “overhear” the communication between reader and tag, though encryption of the data is still advised. When two devices need to communicate over longer distances, NFC technology can create a connection and switch to Bluetooth so the users can move further away without breaking the data transfer or communication connection.

Near and Far Field