Artificial Gills (human)
Artificial gills are devices that exist in science fiction, and being developed in reality, to extract oxygen dissolved in water, thus allowing humans to survive underwater.
It is generally thought that they would be unwieldy and bulky, because of the massive amount of water that would have to be processed to extract enough oxygen to supply an active diver, as an alternative to a scuba set. However, Like-A-Fish is an ongoing attempt to develop such a system in the real world.
As sea water contains 7 ppm oxygen. 1,000,000 kg (1,000 tonnes) of sea water holds 7 kg (1,000 short tons holds 14 lb) of O2, the equivalent of 5,350 litres (1,400 U.S. gallons) of oxygen gas at atmospheric pressure. <p>An average diver with a fully closed-circuit rebreather needs 1 litre (roughly 1 quart) of oxygen per minute. As a result, at least 192 litres (51 gallons) of sea water per minute, or 3.2 liters (3.5 quarts) each second, would have to be passed through the system, and this system would not work in anoxic water.
Natural gills work because nearly all animals with gills are cold-blooded and so need much less oxygen than a warm-blooded animal the same size.
Like-A-Fish Technologies is an Israeli business, founded by Alan Bodner in 2001, that is developing a human artificial gill system; they have developed a prototype. Like-A-Fish's technology uses a centrifuge causing lower pressure at the center, where dissolved air comes out of the water.
The key issue remaining is battery life. Currently a one kilo battery would only last for one hour, whereas a regular scuba tank can last longer (depending on depth). The biggest possibilities lie in underwater habitats, which have access to electricity, but need constant refilling of air tanks. Additional possible uses include systems for scuba divers and submarines, among others.
Like-A-Fish currently holds patents in Europe for its system.
1. Lakshmi Sandhana. "Inventor develops 'artificial gills'", BBC News, 2006-01-31. Retrieved on 2007-09-14.
2. Iddo Genuth, Tomer Yaffe. "Like A Fish - Revolutionary Underwater Breathing System", IsraCast, 2005-12-14. Retrieved on 2007-09-14.
3. Open-circuit Self-contained Underwater Breathing Apparatus (WO0240343). European Patent Office. Retrieved on 2007-09-18.
4. Open-circuit Self-contained Underwater Breathing Apparatus (EP1343683). European Patent Office. Retrieved on 2007-09-18.
Longer Bottom Time
Air supply is not restricted to amount of air that can be contained in one tank, only on amount of batteries taken.
No Need for Refills
No need to refill air tanks with diving gas (save money and dependence on dive centers)
Higher Safety & Less Stop Stations
The composition of the air that is extracted from water is enriched with 34% Oxygen (similar to Nitrox), which minimizes the amount of Nitrogen that is inhaled during a dive and thus adds to the safety of a dive.
With conventional SCUBA gear, a diver's buoyancy changes throughout the dive, as he uses (and thus loses) approximately 4 Kg worth of air.
This is not the case with the Company's gear.
Like a Fish - Underwater Breathing System
December 14, 2005 on IsraCast.com
An Israeli Inventor has developed a breathing apparatus that will allow breathing underwater without the assistance of compressed air tanks. This new invention will use the relatively small amounts of air that already exist in water to supply oxygen to both scuba divers and submarines. The invention has already captured the interest of most major diving manufacturers as well as the Israeli Navy.
The idea of breathing underwater without cumbersome compressed air tanks has been the dream of science fiction writers for many years. In George Lucas movie "The Phantom Menace", Obi-Wan whips out a little Jedi underwater breathing apparatus and dives in. As things tend to happen in our world, yesterdays science fiction has turned into today's science fact due to one Israeli inventor with a dream.
There are a number of limitations to the existing compressed air tank underwater breathing method. The first is the amount of time a diver can stay underwater, which is the result of the compressed air tank capacity. Another limitation is the dependence on compressed air refueling facilities near the diving site which are costly to operate and are used to compress the gas into the tanks which might be dangerous if not handled properly. The final problem has to do with the actual use of compressed air tanks underwater. When these tanks are in use they empty out and change the balance of the diver in the water.
Engineers have tried to overcome these limitations for many years now. Nuclear submarines and the international space station use systems that generate Oxygen from water by performing 'Electrolysis', which is chemical separation of Oxygen from Hydrogen. These systems require very large amounts of energy to operate. For this reason, smaller, diesel fueled submarines cannot use these systems and are required to resurface to re-supply their air tanks every so often. Divers can't even consider carrying such large machines not to mention supplying them with energy. To overcome this limitation an Israeli inventor, Alon Bodner, turned to fish. Fish do not perform chemical separation of oxygen from water; instead they use the dissolved air that exists in the water in order to breathe. In the ocean the wind, waves and underwater currents help spread small amounts of air inside the water. Studies have shown that in a depth of 200m below the sea there is still about 1.5% of dissolved air. This might not sound like much but it is enough to allow both small and large fish to breathe comfortably underwater. Bodner's idea was to create an artificial system that will mimic the way fish use the air in the water thus allowing both smaller submarines and divers to get rid of the large, cumbersome compressed air tanks
The general structure of the system
The system developed by Bodner uses a well known physical law called the "Henry Law" which describes gas absorption in liquids. This law states that the amount of gas that can be dissolved in a liquid body is proportional to the pressure on the liquid body. The law works in both directionslowering the pressure will release more gas out of the liquid. This is done by a centrifuge which rotates rapidly thus creating under pressure inside a small sealed chamber containing sea water. The system will be powered by rechargeable batteries. Calculations showed that a one kilo Lithium battery can provide a diver with about one hour of diving time.
Bodner has already built and tested a laboratory model and he is on the path to building a full-scale prototype. Patents for the invention have already been granted in Europe and a similar one is currently pending examination in the U.S. Meetings have already been held with most major diving manufacturers as well as with the Israeli Navy. Initial financial support for the project has been given by Israel Ministry of Industry and Commerce and Bodner is currently looking for private investors to help complete his project.
If everything goes according to plan, in a few years the new tankless breathing system will be operational and will be attached to a diver in the form of a vest that will enable him to stay underwater for a period of many hours.
Transcript of the Interview with Alon Bodner:
Question: We are speaking now with engineer Alon Bodner. First of all I have to tell you that since we put up your report on IsraCast, we have been inundated with literally millions of people going into our website to find out about your invention. Just where did you get the idea sir?
Bodner: My seven years old son, Aviv, asked me some questions about the possibility of diving without tanks, maybe he was inspired by a Star Wars' movie, and then the wheels in my head started spinning. I knew that there is dissolved air in the water and that the fish breath this air so I thought, with all the technology in the world, why couldn't we also do it?
Question: But just how practical is your idea, have you actually tried to run through this prototype in a pool or that kind of thing?
Bodner: I call it a lab model it's not yet a prototype, it's in an aquarium which has a pump, a centrifuge, some hoses and a balloon, we cannot take it into the water yet, into the sea, but we tried it out with water and we saw that in principle it works.
Question: In principle it works. We've been getting inquiries from people all around the world, some are asking what about the quantity, the large quantities of water that might have to be processed in order to get an adequate amount of oxygen for a diver?
Bodner: I want to distinguish between open diving systems and closed diving systems. Usually when you go sports diving it's with open systems and this means that you inhale air from a tank and you exhale it into the water, and this requires a very large quantity of air. With closed systems, such as with breathers for individual divers or submarines or maybe in the future underwater habitats, the required water flow is much smaller, so this device is very suitable.
Question: In other words, it could be a portable apparatus?
Bodner: It is supposed to be a portable apparatus, yes.
Question: And when you speak of underwater habitats, just what do you have in mind?
Bodner: Well right now there exists several underwater habitats especially for research, off the coast of Florida there is one. It's like a Spacelab in the past, in which a few scientists live 10-20 meters underwater, they breath from compressed tanks and perform experiments. In the future, you can have a whole city or many people under a glass dome and breathing air straight from this device.
Question: What about the scientific community, have you yourself been approached by scientists and so forth?
Bodner: Well I have, a few people do not understand the concept, they assume that I separate oxygen from the water and they say correctly that it is toxic below a depth of seven meters and then they ask some technical questions. In this case I want to say again, the device can extract air from the water. It is dissolved air which contains oxygen and nitrogen and so on. It does not extract oxygen from hydrogen.
Question: And what are some of the technical problems that you have to overcome at this stage?
Bodner: The main concerns are the power of the batteries I suppose and the water flow. The batteries are evolving in a very good rate and we don't expect any problems right now. As I said the water flow can be a problem, especially if using open systems, if you want I can elaborate better calculations.
Question: If you could, please.
Bodner: The calculation is quite different for open or closed systems; I'll start with the calculations for open systems. A diver can consume about 25 liters per minute of air at the surface. Assuming that there's about 2 percent of dissolved air in the water, the calculations show the water flow requirement of 1,250 liters per minute. As you go deeper your lungs require more air. At 10 meters depth the air and water flow requirement is double than that on the surface so that means that you will need 2,500 litters per minute of water, and this is a lot. For closed systems, the
calculation is different. In these systems the air is re-circulated and returned to the diver after the carbon dioxide is removed. For this case we calculate the oxygen consumption rate and not the air consumption rate as before. Say a diver consumes one liter per minute of oxygen, and unlike the above calculation your body requires the same amount of oxygen at all depths. So, assume there is about half a percent of dissolved oxygen in the water, this result in the water flow requirement of only 200 liters per minute at all depths, which is not too bad, and we can make a compact machine for this.
Question: Engineer Bodner, you are a diver yourself?
Bodner: Yes, lately I dive mainly in the Red Sea in Eilat and in the Mediterranean Sea, in the past I also dived in the Bahamas and off California.
Question: So you can be a guinea pig for your own invention now?
Bodner: I'd love to, but there are also many other volunteers, I get lots of e-mail from people all over the world who want to volunteer, to be among the first to use the systems.
Question: OK, let's go to the big question now. How long do you estimate that it might take before your remarkable invention actually goes on the market, becomes marketable, in a finished product?
Bodner: I expect the complete work the complete working prototype in about two years; this is provided if I get more funding, a commercial product will be ready shortly thereafter.
Question: Well, what can we say, perhaps when the Wright brothers talked about people flying like birds in the air, you're following in their footsteps and talking about people that can swim like fish in the sea.
Bodner: Well I hope so but it's too early still to compare me with the Wright brothers but I appreciate the comparison.
Question: Have you had approaches from manufacturing companies and so forth?
Bodner: I have but the discussions are still at early stages so of course I cannot divulge which names I'm speaking to.
Iddo Genuth, Tomer Yaffe - IsraCast, Jerusalem
US Patent Application # 20040003811
Open-Circuit Self-Contained Underwater Breathing Apparatus
January 8, 2004
Abstract -- A self-contained open-circuit breathing apparatus for use within a body of water naturally containing dissolved air. The apparatus is adapted to provide breathable air to a diver. The apparatus comprises an inlet means for extracting a quantity of water from the body of water. It further comprises a separator for separating the dissolved air from the quantity of water, thereby obtaining the breathable air. The apparatus further comprises a first outlet means for expelling the separated water back into the body of water, and a second outlet means for removing the breathable air and supplying it for breathing. The air is supplied so as to enable all of it to be expelled back into the body of water after it has been breathed.
Inventors: Bodner, Alan-Izhar; (Zichron Yaakov, IL)
Correspondence Name and Address:
BROWDY AND NEIMARK, P.L.L.C.
624 Ninth Street, N.W.
Washington DC 20001 US
U.S. Current Class: 128/202.26; 128/201.27
U.S. Class at Publication: 128/202.26; 128/201.27
Intern'l Class: A61M 015/00; A61M 016/00
 The present application is a continuation-in-part of copending
parent application No. PCT/IB01/02142, filed Nov. 14, 2001, and claims
the benefit of U.S. Provisional Appln. No. 60/248,249, filed Nov. 15, 2000.
FIELD OF THE INVENTION
 This invention relates to self-contained underwater breathing
apparatus and methods.
BACKGROUND OF THE INVENTION
 Among known underwater respiration devices are those that supply air via a conduit from the Earth's atmosphere to a submerged user or, in the case of SCUBA, comprise a portable tank with breathable compressed gases including oxygen. In open-circuit SCUBA systems, the breathed, exhaust gas is discarded in the form of bubbles with each breath. Closed-circuit systems recycle the exhaust gas by adding oxygen to and removing carbon dioxide from exhaled breaths.
 U.S. Pat. No. 3,333,583 discloses a closed-circuit underwater respiration device which purifies and recycles a diver's exhaled breath. This purification is achieved by driving the exhaust breath through gas permeable tubes, which are surrounded by a current of seawater. Oxygen dissolved in the seawater then passively diffuses across the tubes into the exhaled breath while carbon dioxide similarly diffuses out. The breath is then supplied to the diver for breathing and the process is repeated indefinitely.
 U.S. Pat. No. 3,656,276 discloses a closed-circuit method and apparatus for reoxygenating and removing carbon dioxide from stale, breathed air in an underwater habitat by mixing it with seawater in intimate and agitated contact, and subsequently separating the refreshed air from the seawater.
SUMMARY OF THE INVENTION
 The present invention suggests a self-contained breathing apparatus that operates in an open-circuit SCUBA-like manner where the user's exhaled breath is expelled into the body of water in the form of bubbles. However, the apparatus of the present invention differs from conventional SCUBA in that it does not require a portable tank of breathable compressed gases.
 The apparatus of the present invention comprises an inlet means for extracting a quantity of water from said body of water, a separator for separating said dissolved air from said quantity of water thereby obtaining said breathable air, a first outlet means for expelling the separated water back into said body of water, and a second outlet means for removing said breathable air from the separator and supplying it for breathing.
 The apparatus is for use within any body of water that naturally contains dissolved air and it obtains breathable air directly from the surrounding water in which it is submerged. The body of water may be an ocean, lake, pond, river or any such body having breathing marine life such as fish.
 The present invention further suggests a method for providing breathable air from a body of water naturally containing dissolved air comprising the steps of drawing an amount of water from said body of water, separating said dissolved air from the drawn water and thereby obtaining said breathable air, expelling the separated water and supplying the separated air for breathing, and expelling the air back into said body of water after it has been breathed.
 An apparatus operating according to the method of the present invention may be relatively light and uncomplicated. It also eliminates the need to carry a set amount of breathing air, one of the primary factors normally limiting the amount of time that can be spent underwater. Also, since in the apparatus of the present invention, the separated air already meets a user's pressure requirements for breathing, the apparatus eliminates the need for a pressure regulator, which is necessary in SCUBA to lower the pressure of the compressed gases in the tank.
BRIEF DESCRIPTION OF THE DRAWINGS
 In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
 FIG. 1 shows an apparatus according to the present invention;
 FIG. 2 shows an embodiment of an apparatus according to the present invention;
 FIG. 3 is a functional diagram of the method by which the apparatus of FIG. 2 operates.
DETAILED DESCRIPTION OF THE INVENTION
 FIG. 1 schematically shows a self-contained breathing apparatus 2 according to the present invention. The apparatus 2 is adapted to provide breathable air and is designed for use within any body of water naturally containing dissolved air, such as an ocean, lake, pond, river and the like. As can be seen in FIG. 1, the apparatus 2 comprises two inlet means 4a and 4b for extracting a quantity of water from the body of water, but may have one or many such inlet means. The inlet means 4a, 4b may be any kind of conduit through which liquid can be conducted.
 The apparatus 2 further comprises a separator 6 for separating the dissolved air from the extracted quantity of water conducted thereto via the inlet means 4a and 4b. The separator 6 has a housing and also includes first outlet means 8a and 8b for expelling the separated water back into the body of water, and second outlet means 10a and 10b for conducting the separated air out from the separator 6. The separator 6 may include one or many first and second outlet means, which may be any kind of conduit through which fluids can be conducted.
 The second outlet means 10a and 10b may include valves that only permit air to be conducted further. These valves may be any kind of mechanism preventing the passage of water but allowing the passage of air. One possible option for such a mechanism includes providing a portion of the outlet means 10a and 10b that tapers to a smaller cross-sectional area and also includes a floating body, similar to a ping pong ball, for example, having a larger cross-sectional area and, consequently, being capable of blocking the movement of water without hindering the passage of air. Since the separated air in the separator 6 rises above the water, the separator 6 may be designed to ensure that the outlet means 10a and 10b and valves are located on the upper part of the separator 6. In addition, a plurality of outlets with valves can be positioned at various points on the separator 6, thereby ensuring that at least one of them is always pointing up and in contact with the rising separated air. In this way, the air rises towards the highest outlets 10a, 10b, which conduct the air further, either directly to a location for breathing or to an air bag 14, which serves as a storage reservoir for breathable air.
 The air bag 14 may be any kind of storage reservoir, and may also be part of another body such as a floatation jacket or depth-adjusting bladder, thereby simultaneously serving multiple purposes.
 The apparatus 2 further comprises a pump 16 to pump water into the separator 6 via the inlet means 4a and 4b. The pump 16 may be any mechanism creating a flow of water through the separator 6 such as by drawing water in via one or more of the inlet means 4a and 4b and/or ejecting water out via one or more of the outlet means 8a and 8b. The pump 16 is motorized and may be powered electrically, using batteries for example, or mechanically, such as by using the efforts of a user.
 The apparatus 2 and method by which it functions can be employed in a variety of settings to provide breathable air to living beings such as in submersible quarters, e.g. submarines or underwater habitats, as well as in diving gear for use by individuals. The apparatus 2 may further be used to provide such breathable air for uses other than breathing, e.g. for supplying air to combustion engines.
 FIG. 2 illustrates a specific use of the apparatus 2 according to the present invention designed for an individual diver 20 as in the case of SCUBA. In this use, the apparatus 2 includes batteries 17 to supply electrical power thereto, which are arranged on a belt 18 worn by the diver 20. The belt 18 may also carry lead diving weights to provide the diver 20 with the additional weight needed to counter his natural buoyancy, or alternatively, the batteries may also provide or contribute to this needed weight. The diver 20 also wears the air bag 14, which simultaneously serves as a thermal and flotation jacket.
 FIG. 3 is a functional diagram schematically illustrating how an apparatus 2 according to the present invention may operate for an individual diver in an ocean. Seawater from the ocean is drawn into the apparatus 2 via the inlet means (not shown) by the pump 16 and enters the separator 6.
 The separator 6 separates the dissolved air from the water by any known method of physical separation or combination thereof. Most such methods are based on passing the water across a pressure drop and examples include, but are not limited to, cavitation, volumetric increase, and the use of centrifugal force. Cavitation involves passing the water across a hydrofoil such as a propeller, which, due to its design, creates a lower pressure region on its trailing edge, resulting in the release of dissolved air. Volumetric increase entails passing the water from a smaller to a larger space, thus increasing the volume of the water and decreasing the pressure applied thereto, thereby causing the release of the dissolved air. The use of centrifugal force involves rotating the water at such a speed that the heavier water moves farther away from the axis of rotation than the lighter dissolved air, consequently resulting in its separation.
 The air-depleted seawater is expelled from the apparatus 2 back into the ocean via the first outlet means (not shown). The air released by separation is breathable and is, preferably, conducted to the air bag 14 via the second outlet means (not shown), wherefrom it is supplied to the diver. Having been breathed by the diver, the air is expelled into the ocean. If the diver requires less air than is conducted to the air bag 14 by the separator 6, the air bag 14 stores the air. When the air bag fills completely, the air separator 6 shuts down until the diver has
used a predetermined fraction of the air in the bag 14, at which point the separator 4 resumes supplying air to the air bag 14. In this way, the apparatus expends less power. In the case of an individual diver, it is preferable for the air bag 14 to be flexible and inflatable but at the same time made from a durable material to minimize its likelihood of being damaged since the diver draws his breath from the air bag 14. In the case of a submarine or underwater habitat, a storage reservoir such as an air bag 14 may not be necessary and the breathable air can be directly supplied to such spaces.
 Reverting back to FIG. 1, the separator 6 shown utilizes two propellers 12a and 12b to separate air from water by cavitation. The propellers 12a and 12b also contribute to separation by imparting a centrifugal force on the water. In addition, the propellers 12a and 12b drive the water through the separator 6, thereby acting as axial pumps, which may be used in place of or in conjunction with the pump 16. The separator 6 may also comprise air tubes 13 to attract rising bubbles of air as they are separated from the water and convey them to the outlets 10a and 10b. The air tubes 13 may be made of a material (e.g. stainless steel) adapted to attract air bubbles based on the coalescence effect.
 The amount of breathing air required by a diver depends on many factors such as diving depth and extent of physical exertion and also varies from one individual to the next. Nonetheless, most divers, even during their highest exertion, require no more than 25 liters of air per minute, and so the separator 6 is designed to provide at least this minimum amount of air at this rate. While the apparatus 2 may be of various sizes, one possible example for use by an individual diver includes the apparatus 2 having separator 6 cylindrical in shape and approximately 10 inches in diameter at its base and 20 inches long. For a separator 6 having these dimensions and two cavitating propellers spanning its inner diameter, at most depths, the pump 16 will need to provide about 2000 liters of average seawater per minute to the separator 6 in order to produce the aforementioned minimum amount of air required by the diver.
 As can be seen in FIGS. 2 and 3, the apparatus 2 according to the present invention may include a small reserve tank 22 of compressed breathable gases to be used in the case of a malfunction, which prevents or hinders the providing of air.
 Also, as shown in FIG. 3, the apparatus 2 may include an air purifying mechanism, such as a scrubber 24, as known in the art, adapted to reduce the amount of carbon dioxide and/or other undesirable gases present within the air bag 14 and to thereby enable delivery of a more healthy supply of breathable air to the diver 20.
 Reverting to FIG. 1, the apparatus 2 may also provide a diver or other submersible with propulsion by directing the flow of water via the first outlet means 8a and 8b in a desired manner. Provided with a means for varying their direction separately or in unison, the first outlet means 8a and 8b can be oriented to create thrust at a user's command and propel the diver or submersible in a desired direction. In this way, energy that would otherwise be expended to propel a diver or submersible is saved.
 It should be understood that the above described embodiments are only examples of a self-contained open-circuit underwater breathing apparatus and method for using same according to the present invention, and that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art. For example, the apparatus may be used in underwater drilling, where a supply of air may be necessary.