Near Field Communications

Contactless Cards

Near field communication (NFC) relies on magnetic coupling of a reader and tag and operates over a range of a few cm. The tag contains a low powered microprocessor which runs the application. The processor is powered by rectification of the induced field to produce a dc voltage at a few mA and communicates with the reader by means of a digital technique called modulated backscatter.

NFC forms the basis of several systems in use, for example Oyster cards, Visa contactless and Mastercard Paypass and some keyless door entry systems. 

JWD carried out an investigation into whether such cards could be energised and read whilst still in the owner's pocket, without their knowledge. The project involved making a high powered transmitter and reader, with an intended range of 1m and being small enough to fit in a briefcase powered by a gell cell battery.

Wireless Charging

For small currents, in the order of less than a few Amps, wireless charging is a practical and useful replacement for charging leads and connectors. JWD has carried out research and developed a discrete charger for a single 450mAh Lithium Polymer cell. The photograph below shows an early prototype resonant charger at 100 kHz with a mosfet driver that can charge at 200 mA. The next stage is to develop a QI compliant device, at 13.56 MHz, to reduce the size of the coils.

At some stage in the future, wireless charging might be used in electric vehicles. However, to obtain a short charging time and suitable efficiency, there are still hurdles to be overcome.