Artificial Gills were breathing devices that extracted oxygen out of water. It allowed unlimited underwater breathing for humans.
(Note: The background section of this page uses most of the same words as Terra Futura's page on liquid breathing rigs to save time.)
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In the 1940s, during World War II, French naval officer Jacques Cousteau invented the Aqua-Lung. This was the first scuba gear. Jacques Cousteau continued to improve the throughout World War II. This led to the first open circuit scuba diving technology. The word scuba was short for "Self-Contained Underwater Breathing Apparatus". It was coined in 1952 by Major Christian Lambertsen who invented the rebreather. However, rebreathers did not become common in civilian use until after the Cold War ended. The tank was usually full of air like what we have at the surface. But there was a problem. Humans could metabolize oxygen, but not nitrogen. At a certain depth, narcosis could. And if a person rose from the water too quickly, he or she would get what was known as the bends or decompression sickness. One solution to this problem was a liquid breathing rig.
Liquid breathing experimented on in the 1960s. Animal testing was a success. Liquid breathing was prominently featured in the sci-fi movie The Abyss. In one scene of the movie, a rat is shown submerged in perflourocarbon liquid and breathing normally. This was no special effect. It was real. Perflourocarbons could hold 25 times more oxygen than human blood. Although PFCs were heavier and more viscous than gasses, the lungs could still work normally. Liquid breathing rigs could go down to 1,000 meters or so, but there was a problem. Not only did a person feel like he was drowning all the time, but an artificial respiration went down the trachea because PFCs were not good at handling carbon dioxide. This caused people to gag at first. Though cheaper than an atmospheric diving suit, it was still more expensive than normal diving equipment. Artificial gills were cheaper.
There were two kinds of artificial gills: Dissolved Oxygen Artificial Gills and Oxygen Cracking Artificial Gills.
Dissolved Oxygen Artificial Gills
Tech Level: 11
Dissolved Oxygen Artificial Gills were in 2001 in Israel by a man named Alon Bodner who founded Like-A-Fish Technologies. It was like a soda can in that it extracted oxygen out of the water. This was done by a centrifuge. Water went in. Oxygen was extracted. Water went out. I could never run out of air as long as there was enough power. However, 200 liters of water had to be processed to provide enough oxygen. Biosensors were used to decide how much, but there was need for more power. The centrifuge system was in a backpack unit with an air tank and rebreather because of bulk. A second centrifuge was used to prevent progressional instability. The air tank was there in case dead or depleted zones. Due to large large power requirements this was best deployed in underwater habitats. Oxygen Cracking Artificial Gills were preferred for personal breathing rigs.
Oxygen Cracking Artificial Gills
Tech Level: 11
Oxygen Cracking Artificial Gills worked by breaking the bonds between hydrogen and oxygen in water molecules. Instead of a centrifuge, this type of artificial gills used a semi-permeable membrane which expelled hydrogen but retained oxygen. The oxygen was then sent into an air tank. Combined with air or nitrox, the oxygen is breathable. Mask-only systems had a maximum depth of 9 meters. Below that and pure oxygen was toxic. Another semi-permeable membrane allowed carbon dioxide. Superconducting batteries provided enough power to keep the artificial gills working indefinitely. The oxygen tanks were reduced in size as a result.
Artificial gills became common during the 21st century. However, in some cases, they became obsolete for people who modified themselves genetically to have gills.