The press release links the two publications: - http://www.mit.edu/~fadel/papers/VAB-paper.pdf - http://www.mit.edu/~fadel/papers/PAB-theory-paper.pdf

> ... fix the input electrical power to 150 W ... The 20 dB DI transducers push the uplink decoding range up to several kilometers.

That probably is close to a baby whale fart, but I doubt competing systems are running at 150,000,000 W, as the above comment suggests. In their test to get 60m, they used 1.8W. 1.8 MW seems unlikely, for the same distance, with competing tech.

There's a fundamental misunderstanding of what's going on here. But, that's to be expected, with how these press releases are written.

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.

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).

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

There's a second theory paper in that press release that discusses the range and verifies the model experimentally: http://www.mit.edu/~fadel/papers/PAB-theory-paper.pdf

This isn't a product that's already on the market, so what matters is how far it can get if actually commercialized - which is pretty impressive at such low power.

This is pretty cool! This has been an unsolved research problem since World War 1.

The tech still needs to be tested in oceans with waves though; most experiments were done in a swimming pool. Promising and exciting but too early to tell how practical it will be.