4 ms·

Magnetoelectric antennas could transform how underwater robots talk

80 points by breve 4mo ago

cyanydeez 4mo ago
youd think optic fiber like Ukraine is diing would be viable to some extent.
- gonzo41 4mo ago
  The sea is a very hard place. Heavy Chains break all the time.
  - m4rtink 4mo ago
    Yeah, Deep Ones just can't stop chewing on things. :P
- miduil 4mo 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_pdf/PTC_2013_Whitcomb.pdf https://sundowner.colorado.edu/seefeldt/ptc-2005_2016/2013_p...
gus_massa 4mo 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 4mo 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.
  - zipy124 4mo ago
    Yup, on the order of below 100 Hz usually https://en.wikipedia.org/wiki/Extremely_low_frequency https://en.wikipedia.org/wiki/Extremely_low_frequency .
    - fc417fc802 4mo ago
      Below a certain point do you suppose my headphone jack can double as a transmitter?
      - ferdzo 4mo ago
        Technically, yes. Also a lot of people in the amateur radio community use the microphone in as a receiver for VLF transmissions.
- bobmcnamara 4mo ago
  Thank Shannon!
peter_d_sherman 4mo 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 4mo 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 4mo 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" :).
    - 4mo ago
raffael_de 4mo ago
my first association here would be steering of torpedoes. the US Navy must have been on this for decades and very deep pockets.
- 7952 4mo ago
  Navies are known to use low frequency radio to send messages to submerged subs.
  - raffael_de 4mo ago
    But isn't torpedo steering still dependent on wire?
    - XorNot 4mo 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 4mo 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.
        XorNot 4mo ago
        Right but they're heavier with far fewer weight concerns then an aircraft. Torpedos are large, heavy and expensive. The point is a very thin wire had a surprisingly long range - versus this system which has a very low bitrate much past 1km. For an active weapons system it's just not a great choice when you already have the wires and they work. But for sensors or vehicle meshing, where you can't lay wires in advance? Potentially huge.
aaron695 4mo ago
[dead]
DoctorOetker 4mo 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 4mo 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.
  - pineaux 4mo ago
    And a lot faster than on land. 5 times if I recollect correctly.
    - mpyne 4mo ago
      About right, but more importantly it's highly dependent on factors like pressure, temperature and salinity, all of which change in relevant ways in the ocean depths. People imagine sonar like it's radar, where you get clean bearings and distance readings, but it's so much noisier and hard to decipher. And yet it really does travel long distances which is both good and bad if you're a submariner.
      - 4mo ago
rpaddock 4mo 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 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 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.unusualresearch.com/Sutton/sutton.htm https://web.archive.org/web/20120722112702/http://www.unusua...
jcalvinowens 4mo ago
https://arxiv.org/pdf/2411.09241 https://arxiv.org/pdf/2411.09241

80 points by breve 4mo ago

cyanydeez 4mo ago

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

gonzo41 4mo ago
The sea is a very hard place. Heavy Chains break all the time.
- m4rtink 4mo ago
  Yeah, Deep Ones just can't stop chewing on things. :P
miduil 4mo 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_pdf/PTC_2013_Whitcomb.pdf https://sundowner.colorado.edu/seefeldt/ptc-2005_2016/2013_p...

gus_massa 4mo 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 4mo 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.
- zipy124 4mo ago
  Yup, on the order of below 100 Hz usually https://en.wikipedia.org/wiki/Extremely_low_frequency https://en.wikipedia.org/wiki/Extremely_low_frequency .
  - fc417fc802 4mo ago
    Below a certain point do you suppose my headphone jack can double as a transmitter?
    - ferdzo 4mo ago
      Technically, yes. Also a lot of people in the amateur radio community use the microphone in as a receiver for VLF transmissions.
bobmcnamara 4mo ago
Thank Shannon!

peter_d_sherman 4mo 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 4mo 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 4mo 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" :).
  - 4mo ago

raffael_de 4mo ago

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

7952 4mo ago
Navies are known to use low frequency radio to send messages to submerged subs.
- raffael_de 4mo ago
  But isn't torpedo steering still dependent on wire?
  - XorNot 4mo 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 4mo 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.
      - XorNot 4mo ago
        Right but they're heavier with far fewer weight concerns then an aircraft. Torpedos are large, heavy and expensive. The point is a very thin wire had a surprisingly long range - versus this system which has a very low bitrate much past 1km. For an active weapons system it's just not a great choice when you already have the wires and they work. But for sensors or vehicle meshing, where you can't lay wires in advance? Potentially huge.

aaron695 4mo ago

[dead]

DoctorOetker 4mo 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 4mo 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.
- pineaux 4mo ago
  And a lot faster than on land. 5 times if I recollect correctly.
  - mpyne 4mo ago
    About right, but more importantly it's highly dependent on factors like pressure, temperature and salinity, all of which change in relevant ways in the ocean depths. People imagine sonar like it's radar, where you get clean bearings and distance readings, but it's so much noisier and hard to decipher. And yet it really does travel long distances which is both good and bad if you're a submariner.
    - 4mo ago

rpaddock 4mo 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 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 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.unusualresearch.com/Sutton/sutton.htm https://web.archive.org/web/20120722112702/http://www.unusua...

jcalvinowens 4mo ago

https://arxiv.org/pdf/2411.09241 https://arxiv.org/pdf/2411.09241