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When an electric field is applied to an electrical insulator, that insulator might deform or change shape in some way. This property of the electrical insulator is called electrostriction. Specifically, electrostriction is the coupling between strain and electric field, or between strain and polarization; this coupling takes place only when an electric field is applied to the material. Electrostrictive materials can be used to construct actuators, which can be used in control circuits where a small amount of force is required to turn on the circuit. These materials also react to electric fields very quickly, which makes these materials suitable for high-speed control circuits.
Electrostriction occurs in certain materials that are poor conductors of electrical current. When a voltage differential is applied to electrostrictive materials, these materials undergo a temporary change in shape. Materials that are electrostrictive change shape because of the electrostatic attraction of free charges on the electrodes that are applied to the electrostrictive material.
Electrostrictive materials are unlike magnetic materials in that electrostrictive materials will not reverse the direction of the deformation if the electric field is reversed. Unlike magnetostriction, which is linear in nature, it is necessary to use quadratic equations to calculate the forces at work in electrostriction. This nonlinear property of electrostriction allows the electrostrictive materials to exhibit a reproducible strain response to electric fields without the losses to hysteresis — and the resulting waste heat — that magnetic materials produce.
An electrostrictive actuator is often made of electrostrictive polymer materials. Each polymer exhibits electrostriction differently. For example, silicone polymers might exhibit high strain performance when compared with other electrostrictive polymers.
A polymer that has high strain performance is better suited to an environment in which mechanical strain might be an issue than a polymer with low strain performance. Other electrostrictive polymers — such as polyurethane — are capable of producing more force under the same electrical conditions than other polymers. Such a polymer allows more of the input electrical energy to be converted into mechanical work.
Electrostrictive materials have a high response speed — often less than 10 milliseconds — when an electric field is applied to the material. Quick-response electrostrictive materials can be used in mechanical and electromechanical devices that require ultrafast circuit response times, such as precision instruments. Electrostrictive materials are often used in mechanical applications such as microangle adjusting devices, oil pressure servovalves and field-tunable piezoelectric transducers.