Global Positioning System Reference
In-Depth Information
coil has been flattened to allow it to be printed (or more likely etched) onto a
plastic film. The energy and communications are handled by a custom low-power
microcontroller chip.
Figure 6.7
Near-field communications using electric fields and capacitors.
If the electric field is used, and this is rare, plates or conducting surfaces are
used for both tag transmitter and receiver. The range of magnetic NFC is greater
than for electrostatic NFC. Figure 6.7 shows a capacitor with an air gap at the left-
hand side of the diagram and an RFID tag system using the electric field on the
right. (The tag and tag readers have double capacitors that would be working on
opposite phases of the AC signal.)
Backscattering is a longer range approach used by some tags that use the far
field where the tag essentially interferes with the radio field, which is detected at
the transceiver (note that the term transceiver is used for an integrated transmitter
and receiver).
6.1.5
Communications and Sensing
Radio was initially used solely for communications but the reflective nature of
metallic objects such as aircraft and ships led to the development of radio
detection and ranging or RADAR (explained in the historical Section 1.4.1). The
technique can be used to track the position of moving targets by measuring the
