tag perhaps even in real time presently available rfdi systems operate in both low frequency less than 100 megahertz and high frequency greater than 100 megahertz modes unlike their low frequency counterparts high frequency tags can have their data read at distances of greater than one meter even while closely spaced together new data can also be transmitted to the tags in the low frequency system an integrated circuit sends a signal to an oscillator which creates an alternating current in the reader 39 s coil that current in turn generates an alternating magnetic field that serves as a power source for the tag the field interacts with the coil in the tag which induces a current that causes charge to flow into a capacitor where it is trapped by the diode as charge accumulates in the capacitor the voltage across it also increases and activates the tag 39 s integrated circuit which then transmits its identifier code high and low levels of a digital signal corresponding to the ones and zeros encoding the identifier number turn a transistor on and off variations in the resistance of the circuit a result of the transistor turning on and off cause the tag to generate its own varying magnetic field which interacts with the reader 39 s magnetic field in this technique called load modulation magnetic fluctuations cause changes in current flow from the reader to its coil in the same pattern as the ones and zeros transmitted by the tag the variations in the current flow in the reader coil are sensed by a device that converts this pattern to a digital signal the reader 39 s.