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.
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.
"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 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.
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.
Yup, on the order of below 100 Hz usually https://en.wikipedia.org/wiki/Extremely_low_frequency .
my first association here would be steering of torpedoes. the US Navy must have been on this for decades and very deep pockets.
Navies are known to use low frequency radio to send messages to submerged subs.
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.
But isn't torpedo steering still dependent on wire?
youd think optic fiber like Ukraine is diing would be viable to some extent.
The sea is a very hard place. Heavy Chains break all the time.
"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!)
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.