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I am relatively new to this field, and please understand if my question seems ridiculous.

As far as I know, the passive RFID tag is supposed to harvest energy from radio waves emitted from other devices. The radio waves are electromagnetic signals. The passive RFID tag has a coiled antenna that also serves as a filter, which selects signals of a certain range of frequencies (for example, from 13.46 to 13.66 MHz)

This is where my question rises. Even after filtering the signal received, the filtered signal may contain noises. I am guessing that power source does not have to be as sensitive as data communication between two devices. However, even so, I wonder if having noises in a signal doesn't have any effect on its role as a power source. Thank you.

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  • \$\begingroup\$ What is the influence of someone whispering during an opera? \$\endgroup\$
    – Harry Svensson
    Commented Nov 11, 2017 at 17:39
  • \$\begingroup\$ The receiver will rectify the AC signal and smooth it with a small filtering capacitor to power the on-board RFID chip. There should be no problem with power unless the noise somehow managed to destructively interfere with the RF source to cancel out for long enough that the RFID chip blacked out. Most likely it would repower and transmit the response. \$\endgroup\$
    – Transistor
    Commented Nov 11, 2017 at 17:39
  • \$\begingroup\$ @Transistor, thank you for the answer. Thanks to all, my curiosity's been solved. \$\endgroup\$
    – user167987
    Commented Nov 12, 2017 at 6:35

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RF noise doesn't affect power delivery - random noise can't cancel out the transmission power of the RF signal since the noise and the signal are uncorrelated. In fact, the power of the noise gets added to the power of the signal, although the noise power is very small compared to the signal and doesn't make a difference in reality. (There's many, many orders of magnitude between noise and signal. The hard part is getting enough power so the device can operate properly, not avoiding the noise.)

Also, most passively-powered RFID devices are coupled magnetically, effectively creating an air-core transformer between the RFID reader and card. It's very difficult to receive enough power via regular radio waves in order to power a microcontroller like in those cards.

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  • \$\begingroup\$ Thank you so much for the answer. I wonder why I couldn't thought of it. It seem too obvious now. \$\endgroup\$
    – user167987
    Commented Nov 12, 2017 at 6:36

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