Magnetoelectric antennas could transform how underwater robots talk

65 pointsposted 3 days ago
by breve
(newatlas.com)

26 Comments

DoctorOetker

2 hours ago

this transduces between magnetic <-> acoustic <-> electric domains, via acoustic pressure.

does this result in some acoustic side channel emissions? can an adversary track subs by correlating acoustic with EM noise if this were employed on second strike submarines?

conceptually its like a 3 port device: a magnetic port, an electric port and an acoustic port.

One would be especially interested in the scattering parameters S_mag-acou , S_acou-mag , S_elec-acou, S_acou-elec at the used frequencies, for passive detection, and for wider frequency range for active detection...

vitally3643

2 hours ago

One of the most challenging thing about submarine communications is that EM waves don't propagate through water. To communicate from the surface to a submarine, we use radio waves on the order of 100Hz, with incredibly large antennas running at very high power. Submarines cannot communicate back without sending a more conventional antenna up to the surface.

Acoustics is the entire game under water. You can only detect nearby objects with visible light or sound. A great deal of submarine design goes into minimizing the amount of sound emitted into the environment because water is astonishingly good at transmitting sound waves very long distances with little loss.

gus_massa

3 days ago

I was wondering how this could make sense until:

The result is an antenna that operates at very low frequencies, around 35–36 kHz, while remaining far more compact than the conventional electrical antennas that work at those same frequencies.

They are using a super low frequency.

adrian_b

6 hours ago

Very low frequency radio waves is the traditional means of communication with military submarines, while submerged.

However, this required huge antennas and very high power transmitters, so this was used mainly to transmit short messages from a terrestrial station to submarines, for instance instructing them to send an antenna to the surface, for bidirectional communication at high speed.

The innovation here is the use of a new kind of antenna, which can work well under water despite small dimensions, and with which a low-power transmitter is sufficient for communication with other submarines or with a surface boat, up to a few hundred meters.

raffael_de

7 hours ago

my first association here would be steering of torpedoes. the US Navy must have been on this for decades and very deep pockets.

Klaus23

5 hours ago

Torpedoes are usually steered using fibre-optic wires, like the fibre-optic drones in Ukraine today, so there is no need for problematic low-frequency radio.

m4rtink

3 hours ago

Terminal homing phase sub-torpedo drone swarm use case for this ? ;-)

Klaus23

an hour ago

As funny as your comment sounds, I wouldn't rule out the Ukrainians actually doing it. At least for sea+air and air+air, sub-drones are already a reality.

7952

6 hours ago

Navies are known to use low frequency radio to send messages to submerged subs.

adrian_b

6 hours ago

This uses the same principle, but the traditional method required immense antennas and very high power radio transmitters.

Such antennas and transmitters cannot be installed in a small submarine.

Here a new kind of antenna is used, which is efficient under water even at small dimensions, so it can be installed in small submarines, for communication at distances of up to a few hundred meter.

raffael_de

6 hours ago

But isn't torpedo steering still dependent on wire?

XorNot

3 hours ago

The issue is it doesn't really matter and radio isn't much benefit: you get much higher bandwidth, better reliability, immunity to ECM, and fiber-optic wires in Ukraine are over 50km long.

The exact application for this is autonomous underwater vehicles where what you would like to do is communicate quickly and without a tether in arbitrary scenarios - i.e. think a bunch of autonomous vehicles which might need to relay a message or communicate with dropped assets. Using radio in those scenarios solves the problem of a consumable (the wire), and also the problems associated with sonar like fouling of the array.

raffael_de

3 hours ago

fair enough but afaik torpedoes aren't tethered by a fiber optic cable like drones. it's a much thicker cable that possibly contains a fiber optic cable.

peter_d_sherman

7 hours ago

"At 36 kHz, the wavelength shrinks from roughly 8,327 m (27,320 ft) in air to just 170 m (558 ft) in freshwater..."

Yes, waves apparently compress or expand depending on the medium they are in...

I'm curious as to what the extremes of potential medium might be... on one end, we might have the densest of heavy metals and on the other, we might have the vacuum of outer space...

Also, what role does/would temperature play?

If a heavy metal was frozen and its temperature brought as close to absolute zero as possible, then would that shrink or expand any propagated waves through it, if even by the smallest amount?

Also, if so, might there be a definable relationship between that phenomena, if it exists, and superconductivity?

Anyway, great article, and it's interesting to learn about Magnetoelectric Antennas!

(I had never heard about them before!)

adrian_b

6 hours ago

When a wave passes through different media, its frequency remains the same, but its velocity changes.

The wavelength is the ratio between velocity and frequency, so it changes proportionally.

If you multiply 36 kHz by 8326 m, you get a value only slightly less than the speed of light in vacuum, which is true for the propagation of electromagnetic waves in most gases.

On the other hand, with 170 m, you will get a speed of VLF radio waves in sea water that is much lower than in vacuum.

The speed of electromagnetic waves in most media depends strongly on frequency.

At frequencies corresponding with visible light, only in few materials the speed is lower than half of the speed in vacuum (i.e. the refractive index is greater than 2).

On the other hand, for low frequency radio waves, speeds that are 10 times slower or even 100 times slower than in vacuum are not unusual.

mcswell

4 hours ago

I tried to do a little (web) research on this. It is of course the reason a prism separates white light into its components. I didn't find out much about sea water, though.

And then there's "slow glass", in which the passage of light through half an inch of glass takes years; the subject of the short story "Light of Other Days" :).

ninalanyon

3 hours ago

One of my favourite stories, heartbreaking though it is.

Arthur C. Clarke and Stephen Baxter wrote a novel of with the same title, but the two stories have nothing in common. It's worth a read in these surveillance heavy times.

cyanydeez

3 days ago

youd think optic fiber like Ukraine is diing would be viable to some extent.

miduil

3 hours ago

I was just looking into the topic recently, there is a decent graphic explaining how fiber is already used for submarine communication for quite some time.

Page 13 shows the diagram of an undersea fiber network separating into durable heavy and lightweight wires.

    Sea surface
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
        |
        | near-surface armored cable
        |
     [Depressor]
          \
           \  fiber cable
            \  0.010 inch diameter
             \ up to 40 km long
              \
            [Float pack]
                 \
                  \ 50 m secondary cable
                   \
                 [Vehicle]
https://sundowner.colorado.edu/seefeldt/ptc-2005_2016/2013_p...

gonzo41

7 hours ago

The sea is a very hard place. Heavy Chains break all the time.

m4rtink

3 hours ago

Yeah, Deep Ones just can't stop chewing on things. :P

rpaddock

2 hours ago

In World-War-One J.H.Rogers invented and patented an antenna that worked well underground or underwater. It was used to communicate with Subs at the time.

According to the late, and somewhat controversial, T.E.Bearden the Rogers system has been rediscovered and then "lost" at least five times since WW1.

"James H. ROGERS Underground & Underwater Radio ( Static-free Reception & Transmission Underwater & Underground )"

https://www.rexresearch.com/rogers/1rogers.htm

There is also

Wallace MINTO Hydronic Radiation Transmitter

Radio-Electronics (May, 1967), p. 37-38.

“Build a Hydronic-Radiation Transmitter”

by Jack Althouse

“Scientists in Florida have discovered a new form of electromagnetic radiation which propagates under water as well as radio does in air”.

https://www.rexresearch.com/hydronics/hydronics.htm

While not indented for water use the Sutton & Spaniol et.al.'s "Black Hole" Antenna is always of interest when it comes to VLF/ELF. This work was done for NASA. Dr Sutton described it to me this way:

"Re: ACTIVE ANTENNA From: John and Helen Date: 10/02/05 10:54 pm

Hi Bob,

The synchronous detectors were used in temperature monitors and temperature controllers designed to control temperatures on spacecraft at 60 milliKelvin +/- a few ucroKelvin. The preamplifier had to have a gain of 10E5 after which the demodulated signal had to be converted by a 16 bit ADC, with +/- 1LSB allowable error.... so of course, you can see that we were working with extremely small signals buried in the noise, and we had to go all out in an effort to beat down the noise. That's why we had to use a new improved synchronous demodulator. This project was as close to being impossible as you can get! I still have trouble believing that we actually made it work.

The active ("Black Hole") antenna was developed in another project, where we didn't want to transport a two meter long antenna that weighed 200 pounds.....so we miniaturized the hardware while simultaneously expanding the antenna field cross section. We wanted to receive the entire ELF-VLF bands all at once, so we had to have an extremely broadband antenna....like four decades of bandwidth or more. You wouldn't believe the arguments I had with the reviewer at Physics Essays. He just couldn't believe that one could do what we did....and if it was indeed true, then why hadn't someone done it years ago?.., "and what makes you so smart", .so, of course, "this must be nonsense, etc....." Progress in physics is so bloody difficult because most physicists think that everything worthwhile has already been discovered....so they expect nothing new. This is negative feedback which, of course, makes the system stable, I suppose.

The one text book that includes diagrams of the antenna-external field interaction is listed as one of the references in the Physics Essays paper. Sorry, I can't remember the name of the author or the title.

John Sutton, Ph.D."

https://web.archive.org/web/20120722112702/http://www.unusua...