 "space transformer" is established when the coil windings or "antenna loops" of the two devices are brought into range (Figure 4-38). The effective range is comparable to the actual physical dimensions of the transmitting antenna loop. When the resonant circuit in the transmitting device is energised by a RF power source, the resulting magnetic flux linkage results in energy transfer between the two resonant coil windings. Inductive coupling is only effective in the near-field region of the transmitting antenna loop. In the far-field region, where the electromagnetic field separates from the antenna and propagates as an electromagnetic wave, it can no longer have a direct effect through inductive coupling. Chapter Four Filter Magnetic field Oscillator Active NFC transmitter Passive NFC responder Figure 4-38: Inductive Coupling Between NFC Antenna Loops Load Modulation When an NFC target device in passive mode is within range of an active NFC transmitter (or initiator) its resonant circuit draws energy from the magnetic field created by the initiating device. This additional consumption results in a voltage perturbation that can be measured in the resonant circuit of the initiator. If an additional load resistance in the target is periodically switched on and off, this has the effect of an amplitude modulation of the carrier wave voltage in the initiator. By using the data stream to be transmitted from the target device to control this load switching, the data stream is transferred from the target to the initiator. This technique is called load modulation. Load modulation creates amplitude modulated sidebands on the 13.56 MHz carrier frequency, and the data stream is recovered by demodulating these sidebands in the initiating device's RF signal processing circuits. CHAPTER Infrared Communication Basics The Ir Spectrum The infrared (Ir) part of the electromagnetic spectrum covers radiation having a wavelength in the range from roughly 0.78 um to 1000 um (1 mm). Infrared radiation takes over from extremely high fre