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But new technologies will eventually make artificial muscles smaller and even more powerful than normal ones. Here are some man-made actuator technologies that are the most promising for future developments of artificial muscle:
Electromagnetic Actuators – are specially designed electromagnets that consist of a coil and a movable iron core called the armature. When current flows through a wire, a magnetic field is set up around the wire. When the coil of the solenoid is energized with current, the core moves to increase the flux linkage by closing the air gap between the cores. The movable core is usually spring-loaded to allow the core to retract when the current is switched off. The force generated is approximately proportional to the square of the current and inversely proportional to the square of the length of the air gap. Unlike hydraulic pistons, this actuator is totally silent and extremely smooth.
Piezoelectric Actuators – have a very high electric field corresponding to only tiny changes in the width of a piezo crystal, this width can be changed with better-than-micrometer precision, making piezo crystals the most important tool for positioning objects with extreme accuracy. There are two kinds of these actuators: direct piezo actuators and amplified piezo actuators.
Shape Memory Alloy – is an alloy that "remembers" its original, cold, forged shape, and which returns to that shape after being deformed by applying heat. This material is a lightweight, solid-state alternative to conventional actuators.
Magnetostrictive Actuators – are made from materials that exhibit a strain when exposed to a magnetic field. In other words, magnetostrictive materials undergo a deformation when a magnetic field is present. These materials are referred to as the Rare-Earth's. Rare-Earth materials typically consist of the lanthanides group in the transition metals on the periodic table.
Electrostatic Actuators – are comprised of parallel plate electrodes where one or both are being moved by an electrostatic coulomb force between them.
And the winner is:
Dielectric Elastomers – are electroactive polymers in which actuation is caused by electrostatic forces between two electrodes which squeeze the polymer. Dielectric elastomers are capable of very high strains and are fundamentally a capacitor that changes capacitance when voltage is applied by allowing the polymer to compress in thickness and expand in area due to the electric field. They have low power consumption and are considered to exhibit the closest behavior to natural muscle.
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