Deep Dive into the Deep Sea with WPT
Let’s talk about where the sun don’t shine.
…the deep sea.
Duh.
It might not be immediately obvious, but our understanding of the deep sea plays a role in everything from the air, weather, and long-term climate patterns.
What’s crazy is that we’ve only discovered 5% of the Earth’s oceans.
The deep-sea starts where sunlight begins to fade which is about 200m below the surface. Then there’s a twilight zone with partial light that reaches down to 1000m. Beyond that is the midnight zone where the water is cold, has very little oxygen, and there’s nearly no light.
We’ve even found Archaea in the deep sea — the most ancient form of life — the one most closely related to the first instance of life on Earth. They are single-celled prokaryotes (organisms lacking a cell nucleus).
We’re relying on deeper waters more and more for food, energy, and other resources.
Until very recently, we believed that all life on Earth needed the sun to survive. However, over the last 30 years or so we’ve discovered several deep-sea ecosystems that use an alternative source of energy. 🤯
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These systems function using the concept of chemosynthesis, which describes how specialized bacteria can create energy from hydrogen sulphide.
This gas is toxic to most land-based life, but deep-sea life has used it to survive without sunlight. The bacteria form the bottom level of the food chain in vent ecosystems.
To better understand chemosynthesis, let’s look at the formula for photosynthesis.
In words, the process turns carbon dioxide + water into sugar + oxygen. The sugar is the energy.
Now, let’s take a look at the process for chemosynthesis. The formula has a few differences.
What’s interesting about chemosynthesis is that the formula can differ because the gas being vented can differ. Instead of carbon dioxide, it can sometimes be methane CH4 or hydrogen gas H2.
In this case, carbon dioxide, hydrogen sulphide and oxygen gas combine to form water, pure sulphur and energy (CH2O).
The chemosynthetic bacteria use chemicals rather than sunlight to produce glucose.
Where these bacteria live is another super cool secret of the deep sea. Hydrothermal vents are chimney looking tunnels along the bottom of the ocean floor. They form due to volcanic activity.
The water coming through the cracks in the Earth’s crust is super hot (can reach 400C) and comes out in geysers. When the geyser hits the cool water of the deep-sea, the dissolved metals and minerals from the Earth’s core immediately precipitate and form a tunnel around the vent.
Vent life consists of organisms like giant tubeworms, crabs, shrimp, slugs, fish and anemones. All of these species survive temperatures up to 113C — the highest recorded temperature at which an organism can live. They all rely on the hydrogen sulphide I mentioned earlier.
To toss a bone to space here…if other planets have similar environments, there may be life out there. 🤯
There’s more to the energy piece I mentioned too.
We’ve come up with a new source of energy.
Hawaii was the first to create an Ocean Thermal Energy Conversion Plant or OTEC. The process draws in warm surface water to vaporize ammonia, which boils and creates steam to generate electricity via a turbine. Then, cool water from the deep sea is used to cool and condense the ammonia back to liquid form before it’s recycled in the closed-loop system.
The OTEC process mist use deep-sea cool water because the difference in temperature between the cooling water and warm water intake needs to be at least 20C.
What of exploration?
The most obvious reason why ocean literacy is important is for exploration and resource management.
“The bottom of the ocean…contains the largest mountain range on earth, canyons far grander the Grand Canyon and towering vertical cliffs rising up three miles.” — Robert D Ballard (discovered wreck of the Titanic, part of the team who discovered chemosynthesis, all around legend.)
Information we gather from the deep sea can help us to predict earthquakes and tsunamis by studying things like underwater landslides. Some of these exist between the Bahamas and Florida.
Also, our topography right now could use some improvement. To take a page from Mr. Ballard’s book again (and paraphrase):
Our current mapping of the seafloor relies on satellites and the estimates are kind of like throwing a wet blanket over a dinner. You can see the outlines of things but that’s really it. We only have a rough idea of what lies deep beneath the surface.
What’s even worse than terra incognita is the potential hazards we open ourselves to. Things like shipwrecks can pose dangers to our modern endeavours — things like shipping lanes or commercial fishing or gas drilling.
We only have one federal organization dedicated or exploring the ocean (the NOAA Office of Ocean Exploration and Research).
What?
Deep-sea exploration is incredibly important for so many reasons. So, what is it that we should do now?
Well, Ruhani, you said it yourself already. We need to explore more.
But how?
Using autonomous underwater vehicles (AUVs).
These are computer-controlled systems that can operate underwater. It’s kind of like the Curiosity rover that NASA uses on Mars — but for the ocean.
These AUVs have no physical connection to an operator and can self-guide to stop, hover and move. They’re also self-powered.
A lot of AUVs are designed to carry power onboard. Most use specialized batteries but some have used fuel cells and rechargeable solar power. The energy lets the propellers and thrusters move the AUV and to operate sensors on it.
AUV design lets them minimize their energy use by taking advantage of gravity and buoyancy when possible. They’re less expensive than research vessels, collect and process data and produce high-resolution maps. They could be used to record environmental information, track what humans leave behind and identify larger hazards that might harm bigger research vessels.
The only problem is…they die. 💀
AUV’s are limited due to human dependency. The energy components have to be replaced by an operator. Humans still must replenish the power supply. While small AUVs can last several hours and large ones for several days — we are severely limited by something as trivial as dying batteries.
What if they could replenish their batteries?
I’m glad you asked.
Using high-frequency wireless power transfer, we can fully autonomize AUVs and conduct more subsea exploration.
There are many different types of wireless energy transfer. For this use-case, the AUV would be charging by induction. Highly resonant wireless power, transfer or HR-WPT, supports the transfer of kilowatts of power even through sea or saltwater.
AUVs would be recharged by navigating towards a docking station located on the seafloor.
This diagram requires an understanding of charging by induction.
But first, a recap of concepts you need to know to understand induction.
Electric Field: we all know that like charges repel and opposite charges attract. How do we know what the force of the attraction/repulsion is between two charged particles? How do we measure the electrostatic force?
Coulomb’s Law tells us that the strength of the electrostatic force between two charges, q1 and q2, is equal to the absolute value of their product. K represents the electrostatic constant (about 8.987551….) and the force is inversely proportional to the square of the distance between q1 and q2, represented by r2.
An electric field is an effect created by any charged object. Fields carry the energy and transfer it to other materials with a net charge by exerting electric force.
Coulomb’s Law comes back here. If Q represents an existing charge with an electric field and q represents a second charge entering the electric field of Q, the law will define F(e) the force between the two charges, as K multiplied by Q2 divided by r2.
This defines an electric field at a given point. To define the electric field in general, we get this.
Now, a magnetic field is the region around a magnet where attraction and repulsion happen. In mathematical terms, it is also sometimes called the vector field.
Moving charges surround themselves with a magnetic field. when more charge is put in more motion, strength increases.
Using yet another law, Lorentz Force Law, this can be described as a fixed amount of charge, q, moving at a constant velocity v, in a uniform magnetic field b to find the magnetic force F.
Now for electromagnetism. When electrically charged particles start to move — the field becomes a flowing electric current and forms a magnetic field around it.
Now that we’ve got the background, inductive charging occurs when two conductors are inductively coupled. A change in current through one wire will induce a voltage across the other wire.
If you put a second coil of wire in the magnetic field, the field can induce a current in the second coil of wire.
When electrical current moves through a wire, it creates a circular magnetic field around the wire. Bending the wire into a coil amplifies this magnetic field. More loops = bigger field. If you put a second coil of wire in the magnetic field, the field can induce a current in the second coil of wire.
How induction will work for AUVs is a two-part process.
First, the docking station will generate AC energy from wave and tidal movement. The circuit inside will convert the AC into DC for storage.
Then, the same process of induction will take place when the AUV comes to dock and wirelessly charge. It’s important to note the difference in eddy current loss too. WPT based on electromagnetic theory generates a type of loss due to EMG induced currents.
I won’t get into the specifics of ECL right now, but all you need to know is that the AUV’s system uses something called a shielding coil to weaken the EMG in seawater and reduce this loss to improve efficiency.
However, WPT in the ocean environment is still very much under research. The ocean is stochastic, so transferring energy wirelessly is more difficult than through air. Some of the factors we’ve found that help overcome saltwater include using a heavier primary coil, adjusting the coil shape according to the shape of the AUV, and use of extra resonator circuits. The shape of the coil is dependent on AUV design — for an example of this tailoring, check out the “Coils” section of this study.
In the end, the same study found that the HR-WPT system for AUV’s was able to produce a 72% efficiency rate in transfer with a 100 W output. For context, typical wireless charging has a 75–8-% efficiency rate on land, so that’s a really good rate given the environment.
There are four specific properties of coils that determine how efficient the WPT system is — and these become way more important when you shift the environment from air to water.
- Self Inductance: the property of a coil that causes opposition to changes in current flowing through it
- Capacitance: the ability of the coil to store an electric charge (ratio between change in electric charge to the change in electric potential)
- Parasitic Resistance: unintended and unwanted resistance found in a circuit post-design — a consequence of manufacturing
- Best Coil Shape: tailored by design, but typically circular coils have the best misalignment tolerance and largest magnetic fields — works even better when the primary and secondary coils are the same size
Ocean exploration improves ocean literacy. Exploring the deep sea and the resources it has will help us manage them sustainably. The challenges that we face in trying to explore more of it is what provides the basis we need to encourage new tech and engineering innovations.
I think we need more hype around the deep sea. From learning about a new process that describes life to learning about extremist organisms, there’s so much more to learn.
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