Unfortunately this seems outside the bounds for ambient RF energy harvesting, even if you don’t mind dropping a few frames to charge back up if the capacitor ru

Unfortunately this seems outside the bounds for ambient RF energy harvesting, even if you don’t mind dropping a few frames to charge back up if the capacitor runs low. The rectenna would have to be much too large to produce anywhere near 25mW even at a 10% duty cycle. I suppose if you didn’t mind ramping the RF output power way up you could shrink the antenna size, but not much smaller than 1cm^2 I think.