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.
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.
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.
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.
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.
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.
"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!
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.
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" :).
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.
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]
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.
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.
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.
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.
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!)
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.
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" :).
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.
Page 13 shows the diagram of an undersea fiber network separating into durable heavy and lightweight wires.
https://sundowner.colorado.edu/seefeldt/ptc-2005_2016/2013_p...