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I think the question is clear. I only need a reference value, like is it in the range of 1mW or 10mW or 100mW. Clearly this will vary among smartphones. Also do you think it is possible to set the transmitter power from an app on android?

The only real reference I found is this article that states, that during each read event, the phone radiates about 200 milliwatts of power

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  • \$\begingroup\$ More in the range of zilch. \$\endgroup\$ – PlasmaHH Mar 23 '18 at 12:32
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    \$\begingroup\$ RF Energy Harvesting question previously asked - it may be of some relevance. \$\endgroup\$ – Andy aka Mar 23 '18 at 13:00
  • \$\begingroup\$ electronics.stackexchange.com/questions/268441/… \$\endgroup\$ – Bruce Abbott Mar 23 '18 at 16:26
  • \$\begingroup\$ Probably worth reading the documentation of NFC chips capable of energy harvesting to see if they give any figures. Variability is definitely likely; even just looking at the signaling pattern over time (from a separately powered NFC chip), I recall seeing very different patterns between different Android phones. \$\endgroup\$ – Chris Stratton Mar 23 '18 at 19:02
  • \$\begingroup\$ The ST24DVxxK datasheet is not very specific at all, only something along the energy harvesting element is capable "to deliver µW of power when external conditions make it possible" is mentioned. \$\endgroup\$ – Andy Ef Mar 23 '18 at 19:36
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A test series with an Huawei Mate 7 and an ST25DV development board was conducted by myself. The ST25DV has an energy harvesting output pin, on which different resistor values where applied. Meanwhile the field was observed with a simple loop antenna and an oscilloscope. The smartphone was attached directly on the ST25 board, making sure the 2 coils are coupled in an optimal way. Here is the recorded I(U) characteristic of the energy harvesting pin:

Characteristic of ST25DV and Huawei Mate 7

As you can see the maximum power that can be drawn from the tag is around 750 µW, at a current of 200µA. Trying to draw more energy out of the field resulted in the field breaking down, or rather beeing disabled by the smartphone.

After that another air coil with 20 turns was build and placed between a NFC card and the smartphone. When the I(U)-characteristic of this coil was recorded, the field was monitored with an oscilloscope. It was found, that the field broke down when 800 µW of power where drawn out of the coil.

So we can conclude:

The maximum power which can be drawn from the NFC-field of an Huawei Mate 7 is around 800 µW. This may vary among smartphones.

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    \$\begingroup\$ Very interesting test. However, it is unclear who conducted the test. If it's you, you should state it clearly, if it's somebody else, you should provide references in your answer. \$\endgroup\$ – juhist Apr 27 '18 at 16:35
  • \$\begingroup\$ good point. It was indeed me. \$\endgroup\$ – Andy Ef Apr 27 '18 at 17:01

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