What is RF?
Radio frequency — electricity that wiggles fast enough to leave the wire.
Push electrons back and forth in a wire and you make a changing electric and magnetic field around it. Do it fast enough — thousands to billions of times a second — and that field stops hugging the wire and starts travelling. That's radio, and "RF" (radio frequency) is just the umbrella name for it.
Two numbers describe any radio signal:
- Frequency — how many times per second it wiggles, in hertz (Hz). 125 kHz is 125,000 wiggles a second. 915 MHz is 915 million.
- Wavelength — how far the wave travels during one wiggle. Radio moves at the speed of light, so higher frequency means shorter waves.
That trade-off is the whole story of RFID in miniature: the frequency a tag uses decides how big its antenna is, how far away it can be read, whether it works next to metal or water, and how much data it can move. More in LF, HF, UHF.
#The trick that makes RFID work
A passive RFID tag has no battery. The reader's field doesn't just carry data — it carries the power. The tag's antenna harvests a tiny bit of energy from the field, wakes up its chip, and answers.
How the tag answers depends on the distance in wavelengths; that's near field vs far field.