AS seen in last week’s article, what’s happening is that the magnetic field from the coil attached to the battery is inducing electricity to flow through the second coil of wire. Move the coils apart and the needle will come to rest at zero. The strength of inductive coupling depends on several factors, one of them being the distance between the two conductors. Radio frequency identification (RFID) tags are one application of inductive coupling. This technology is a predecessor to NFC. With an RFID tag, an electronic reader generates a magnetic field. Bringing an RFID tag close to this field induces electricity within the RFID tag. The reader detects the new magnetic field from the RFID tag and registers it. Many transportation systems and security systems use this sort of technology, the RFID tag is in a card or fob that you must place near a reader to activate. This method is called passive RFID. Newer RFID technology adds the capacity to have a powered RFID tag, which we call active RFID. Active RFID tags can be used to improve the range of a tag and to store more information, among other applications. Near field communication builds on this technology; It allows for two-way communication between devices at a very short range. It uses inductive coupling the same way RFID tags do. It is like swiping.  What exactly happens when you tap two NFC-enabled devices together? It’s easier to understand with a concrete example, so let’s assume you’re walking down the street when you see a poster for an upcoming event, you want to check it out. You also see some text on the poster that says it has an NFC tag. You quickly whip out your smartphone and activate an NFC-reading app. activating the app sends a signal to the NFC chip inside your phone. Electricity flows through the circuitry of the chip, generating a weak magnetic field. This means your smartphone is an active NFC device it’s using power to generate a magnetic field. You hold your phone up to the appropriate spot on the poster. At this point, the weak magnetic field generated by your phone induces a magnetic field in the NFC tag within the poster. The magnetic field induces electricity in the NFC tag, which doesn’t have its own power supply   it’s a passive NFC tag. This creates a radio field. The radio field generated by the tag interacts with the field generated by your phone. The NFC chip in your phone detects and decodes the radio field. The information turns out to be a link to a video of the live event. The app gives you the option of visiting the link directly if you wish.