[wirelessR]

This is asymmetric communication. The node itself uses backscatter thus operates at few micro-Watts. The remote acoustic projector is the 1.8W, and can communicate with 100s/1000s(?) of micro-watt power nodes - similar to RFIDs, but this tech works underwater.

[nomel]

I understanding that, but claiming that the backscatter energy, or the nodes power usage, is all the ocean life (the context of this comment chain) will see is incorrect, as the previous comment did. They primarily see the excitation energy, which appears to be ~23db greater (harvesting efficiency) than the backscatter, at the node. This is the same as something sitting between an RFID chip and the reader would.

So, the sea life near the transmitter would still have a bad time. The sea life near the nodes would see 23db more* than an active node, assuming the same power could be used to transmit from the node. Correct? This seems logical, since the energy harvesting will come at a coupling and efficiency cost, which means significantly more energy in the water at that node. If you had a battery powered node, you wouldn't need all the extra energy, and instead could just transmit.

All these numbers being thrown around are the power usage of the node, not what the sea life actually sees.

* Maybe more, since the signal path is twice as short, meaning your SNR starts higher at the midpoint (node).

[nomel]

And note, 1.8W is for the dock test. Their paper suggests 150W will be required for km ranges, with 20db directionality.