The optimal frequency for penetrating 1 meter of seawater using radio waves is approximately 540 kHz, as this frequency minimizes attenuation in saline conditions. Research indicates that at this frequency, the skin depth is about 1 meter, allowing for effective communication and detection. The discussion also highlights the challenges of using fractal antennas for single-frequency transmitters and suggests that optical methods, such as LiDAR, may be more effective for underwater imaging. The target for detection is an aluminum canister filled with finely cut aluminum powder, which presents unique challenges due to its particle size and potential oxidation.
PREREQUISITESEngineers, researchers, and developers involved in underwater communication, imaging technology, and radio frequency applications, particularly in marine environments.
Will you radiate from air into water, or underwater to underwater.chemisthypnos said:We are attempting to penetrate 1m of water featuring dissolved ions ( assume salinity of sea water) using radio waves.
1 meter? Seriously? Just blink your flashlight.chemisthypnos said:We are attempting to penetrate 1m of water featuring dissolved ions ( assume salinity of sea water) using radio waves. Aside for using wavelengths of very low frequency radio or below, what would be the best frequency for achieving this task?
It would be used for air to water and it would be for underwater imaging. That graph was very helpful. I think that we are going to try for 540 kHz wavelength. This should minimize the attenuation. We are trying to find out how large of an antenna we would need and how much power that would take if we used electrical loading and fractal antenna design for it. I see that there is a small one on Walmart for 1MHz and it seems pretty small.Baluncore said:Will you radiate from air into water, or underwater to underwater.
Why? Imaging? Will you look at the reflection?
How much attenuation can you tolerate?
https://www.researchgate.net/profil...6400134714/RF-attenuation-in-sea-water-41.png
What will you be imaging?chemisthypnos said:It would be used for air to water and it would be for underwater imaging.
There will be a problem with the beamwidth required of your antenna array.chemisthypnos said:We are trying to find out how large of an antenna we would need and how much power that would take if we used electrical loading and fractal antenna design for it.
This problem of underwater imaging has been solved many times over the last century. Radio and optical systems are employed from many different types of vehicles.Vanadium 50 said:This is hopeless.
If there is mud, algae or fish in the water, first take a look at this 460 page book; "Light Absorption in Sea Water", by Bogdan Wozniak, Jerzy Dera (auth.) Springer-Verlag New York (2007)DaveE said:LiDAR is what you want for this application, I think.
If there are fish that can be imaged with 500 kHz radar, I think I want to let them be. Holy Jonah!Baluncore said:fish in the water
We are attempting to image an aluminum target at the base of the pond at 1m depth. The resolution does not particularly matter as we are looking for a binary outcome ( either object is detected or the object cannot be detected). That is a very good point about the 540 kHz antenna length. We were thinking of using a 1MHz wavelength and using electric shortening to about 1/100th ( it should get the size of the antenna down to about 1m or so). Do you think this could work?Baluncore said:What will you be imaging?
What resolution?
At what depth?
There will be a problem with the beamwidth required of your antenna array.
Beamwidth in degrees = 57° / wavelength in metres.
If you use 100 MHz which has a wavelength of 3 metres, then to get a 5.7° beam, your antenna array will need to be 30 metres across.
To do the same at 540 kHz where the wavelength is 555 metres, your antenna array will need to be 5.555 km across.
At 1 GHz with a wavelength of 300 mm, the array will be only 3 metres across. That is a good reason for using shorter wavelengths.
The target ( aluminum) should be shiny in the radio spectrum. Visible light cannot be used in this scenario as the pond is opaque to visible light.hutchphd said:Is the target (optically) shiny?
Are you trying this as a prototype for some more difficult problem?
A modulated optical source and synchronous detector should have no trouble with this. $102
What am I missing?
This is a detection, not an imaging exercise. Aluminium is a very good conductor, independent of colour or finish.chemisthypnos said:We are attempting to image an aluminum target at the base of the pond at 1m depth.
The dimensions of the target can be regarded as a 1 meter long glass canister full of aluminum finely cut to a powder for which each particle's diameter is 5 nanometers. Assume that the bottom/sides of the pond are made of a material that is transparent to radio light.Baluncore said:This is a detection, not an imaging exercise. Aluminium is a very good conductor, independent of colour or finish.
What are the physical dimensions of the aluminium target?
What material forms the bottom and sides of the pond?
Is the pond filled with seawater or with freshwater?
Why is the seawater opaque to "light"?chemisthypnos said:The dimensions of the target can be regarded as a 1 meter long glass canister full of aluminum finely cut to a powder for which each particle's diameter is 5 nanometers. Assume that the bottom/sides of the pond are made of a material that is transparent to radio light.
The pond is filled with seawater.
Are the canister contents conductive from end to end, like a 150 MHz dipole, or are the 5 nanometre spheres oxidised and insulated, like in a paint?chemisthypnos said:The dimensions of the target can be regarded as a 1 meter long glass canister full of aluminum finely cut to a powder for which each particle's diameter is 5 nanometers.
Nanometers? That changes everything.chemisthypnos said:5 nanometers.
The pond seawater is opaque to visible light because it is a simplifying assumption of the thought experiment and helps focus attention on the radio aspect of the problem..hutchphd said:Why is the seawater opaque to "light"?
The canister is not assumed to behave like a dipole. I think that 5nm aluminum powder would still be conductive. For the sake of the thought experiment, assume that the aluminum is not oxidized. Paint would be a good analogy.Baluncore said:Are the canister contents conductive from end to end, like a 150 MHz dipole, or are the 5 nanometre spheres oxidised and insulated, like in a paint?
It should be a reasonably good conductor even at that size as experiments with nano chaff have shown: https://iopscience.iop.org/article/10.1088/1742-6596/1176/6/062002/pdfVanadium 50 said:Nanometers? That changes everything.
This is not aluminum like people think of it. It's not even a powder like people think it is. It's more like dust. Each particle has maybe a few thousand atoms.
I doubt this is a good conductor, as the surfaces will have oxidized. At 5nm it may all have oxidized, which will make it safer. As it is, it is highly, highly flammable. Possibly explosively so.
For safety's sake I would start with a much, much, much smaller setup. I'd also look really hard for alternative materials.
Why don't you tell us the real problem, and we can stop with the twenty questions.chemisthypnos said:This is a prototype for a more difficult problem.
Vanadium 50 said:It is of course difficult to help someone who is keeping secrets.
Thread paused for Moderation...hutchphd said:Why don't you tell us the real problem, and we can stop with the twenty questions.
Please check your Private Messages (PMs). If you want this thread reopened to get assistance with your project, you will need to much more open in your posts here, especially when we have safety concerns. Thank you.chemisthypnos said:Having aluminum of that size would be very explosive. In the real world, it will not be ( for very good reasons) so do not be concerned about that detail. I would ignore that detail for the sake of the thought experiment.