Artificial Muscles were materials that worked like human muscles. They revolutionized powered exoskeletons and robots.
(Note: The background section of this page uses most of the same words as Terra Futura's page on piezoelectric ceramics to save time.)
The story of piezoelectricity started with the pyroelectric effect. The pyroelectric effect, in which electric current depends on temperature, was discovered in the mid-18th century by scientists Carl Linnaeus and Franz Aepinus. Years later, in 1820, two French scientists, René Just Haüy and Antoine César Becquerel, predicted a relationship between electric current and mechanical stress based on their knowledge of pyroelectricity. The direct piezoelectric effect, which is what was described in the previous sentence, was discovered in 1880 by the Curie brothers. One year later, the converse piezoelectric effect was discovered by Gabriel Lippeman and confirmed by the Curies brothers. The first application of piezoelectricity was sonar. During World War I, German U-boats were attacking ships. British scientists created sonar to detect submarines. The success of sonar during World War I allowed for the development of more devices that used piezoelectricity. Then, during World War II, American, Soviet, and Japanese scientists discovered ferro electric materials which combined pyroelectricity and piezoelectricity. Japan was much more successful in that market. This created new sensors. Later, it would revolutionize air travel.
Birds were more efficient flyers than airplanes because they had a flexible shape-changing wing. Scientists decided to replicate this wing design for future planes. Scientists at Virginia Tech came up with the idea of using piezoelectric ceramics in flexible wings. The test was a success. By the mid-21st century, this had been scaled up. The trailing edge of the wing was now bending. It was more like a bird than ever before. Piezoelectric ceramics revolutionized other things, too. These included vibration reduction and surgery. It was an innovation for all the world. Piezoelectric ceramics were the first artificial muscle.
There were three types of artificial muscles that followed piezoelectric ceramics.
Pneumatic Artificial Muscles
Tech Level: 10
Pneumatic artificial muscles were first proposed in the 1950s for use in artificial limbs. They required pressurized air filling a pneumatic bladder. Around the same time that piezoelectric ceramics were coming out in sensors, these pneumatic artificial muscles were still experimental. These were comercialized in the 1980s by the Japanese company Bridgestone. In the early 21st century, scientists started using them for robots (Hence, the tech level.). The Shadow Dextrous Hand was developed in 2004 by The Shadow Robot Company in London. Using 40 air muscles (That's what the company calls them.), the Shadow Dextrous Hand could move like a human hand or close to it. The Shadow Dextrous Hand was used in the Robonaut by NASA to better work with humans. It worked, but pneumatic artificial muscles were not the only artificial muscles. There were also electroactive polymers.
Tech Level: 10
Electroactive polymers (EAPs) were polymers that changed size and shape when reacting to electricity. In the late '90s, it was discovered that they could hold up to 380% strain. That was more than any piezoelectric ceramic. They had been used in robots during the early 21st century. They were used in microelectromechanical systems to produce artificial muscles that were smarter than pneumatic ones. There was one problem. EAPs were not waterproof. The solution was a water permeable surface. This used metal vapor desposition to protect EAPs from water. This allowed EAPs to be used in water and other liquids. By the mid-21st century, however, EAPs were replaced by shape-memory alloys.
Tech Level: 10-11
Shape-memory alloys or SMAs, like Nickel-titanium alloy, were metals that when bent could revert back to their original shape through heat. They were investigated for use in spying during the early 21st century. During World War III, spying machines that looked like jellyfish were used by the USA to spy on enemy activity underwater. The enemy did not know that some jellyfish they saw were not jellyfish at all. This helped the USA win the war. At the same time, they revolutionized powered exoskeletons. This increased a person's strength. This also helped the USA win World War III. This also helped the paralyzed to walk. SMAs also revolutionized construction. Society was changing.