Behaviour of Magnetic Fields Underwater

In summary: The ocean is a very large body of water and its physical characteristics can have a big impact on the way magnetic fields behave. There are a lot of factors that can play into this, like the presence of currents, the salt content of the water, and so on.The decay rate of a magnetic field depends on a lot of different things, like the material it's located in, the shape of the field, the orientation of the field, and the magnetic field's strength.There are two main types of propagation in magnetic fields: longitudinal and transverse. Longitudinal propagation is the waves that move along the direction of the field, and transverse propagation is the waves that move perpendicular to the direction of the field.
  • #1
sjr
TL;DR Summary
Expected decay rate and speed of magnetic field changes underwater.
I've been trying to pick up the fundamentals of electromagnetic theory and I reckon I'm doing alright, but I've run into a some questions about how magnetic fields behave in an anisotropic fluid medium like the ocean. There is an awful lot of conflicting information online. Ultimately, I'd like to be able to detect magnetic field anomalies at a range of up to 100m under the water as accurately as possible.

A couple of questions:

1. The rate at which the strength of a magnetic field decays with distance remains somewhat unclear to me. I understand there are near field and far field implications, and in general the field strength will decay at a cubic rate. Can someone offer me a clear explanation of the expected rate of magnetic field decay with distance in a medium like the ocean, and how it's affected by conductivity, permittivity and permeability, and so on? This part I haven't figured out yet.

2. The 'propagation' of magnetic field changes in the ocean. Consider a basic problem. A point source ##O## lies in the ocean and directly ahead of it there is a sensor ##A## a range ##r##. We then activate a magnetic field at ##O##. Assuming it is capable of doing so, how long will it take the sensor ##A## to detect a resultant change or 'front' in its vicinity? I'm consistently reading very different answers to this question.

If you could offer me any guidance on this I'd really appreciate it :)
 
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  • #2
Welcome to PF.

sjr said:
I've been trying to pick up the fundamentals of electromagnetic theory and I reckon I'm doing alright, but I've run into a some questions about how magnetic fields behave in an anisotropic fluid medium like the ocean.
Why do you say that you think that conductive seawater is anisotropic with respect to magnetic fields? And are you expecting a strong interaction, or a weak interaction? :wink:

https://svs.gsfc.nasa.gov/12450
 
  • #3
I should have worded that line differently, I wasn't specifically referring to magnetism.

I'm interested in how physical characteristics of seawater may cause magnetic fields to behave slightly differently in the ocean than they would in free space. I'm not making any assumptions at all right now, I'm just trying to make sense of the all the conflicting stuff I'm reading.
 

FAQ: Behaviour of Magnetic Fields Underwater

Does water affect the strength of a magnetic field?

No, water does not significantly affect the strength of a magnetic field. Magnetic fields can pass through water just as they do through air because water is a non-magnetic material. The magnetic field strength remains nearly the same underwater as it is in air.

Can magnets work underwater?

Yes, magnets work underwater. The magnetic forces between magnets or between a magnet and a ferromagnetic material are not hindered by water. Magnets will attract or repel each other underwater just as they do in air.

Are there any changes in the behavior of magnetic fields in saltwater compared to freshwater?

While the magnetic field itself is not significantly affected by saltwater compared to freshwater, the conductivity of saltwater can lead to the generation of electric currents when a magnetic field is present. This is due to the motion of ions in the saltwater, which can interact with the magnetic field, but the magnetic field strength and direction remain largely unchanged.

Can magnetic fields be used for underwater navigation?

Yes, magnetic fields can be used for underwater navigation. Devices such as magnetic compasses work underwater because the Earth's magnetic field permeates through water. Additionally, underwater vehicles can use magnetic sensors to detect and navigate using magnetic anomalies on the seafloor.

How do underwater magnetic fields interact with marine life?

Some marine animals, such as sharks and rays, have the ability to sense magnetic fields through specialized organs. These animals use the Earth's magnetic field for navigation and hunting. However, typical magnetic fields generated by human activities underwater are generally too weak to have any significant impact on marine life.

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