tailieunhanh - Ebook The electrical engineering handbook: Part 2

(BQ) Part 1 book "The electrical engineering handbook" has contents: Electrostriction, piezoresistivity, the hall effect, superconductivity, power systems, energy, electrical machines, communications, digital devices, computer engineering,.and other contenrs. | 50 Electrostriction Introduction Defining Equations V. Sundar and . Newnham Intercollege Materials Research Laboratory, The Pennsylvania State University Piezoelectricity and Electrostriction • Electrostriction and Compliance Matrices • Magnitudes and Signs of Electrostrictive Coefficients PMN–PT — A Prototype Electrostrictive Material Applications Summary Introduction Electrostriction is the basic electromechanical coupling mechanism in centric crystals and amorphous solids. It has been recognized as the primary electromechanical coupling in centric materials since early in the 20th century [Cady, 1929]. Electrostriction is the quadratic coupling between the strain developed in a material and the electric field applied, and it exists in all insulating materials. Piezoelectricity is a better-known linear coupling mechanism that exists only in materials without a center of symmetry. Electrostriction is a second-order property that is tunable and nonlinear. Electrostrictive materials exhibit a reproducible, nonhysteretic, and tunable strain response to electric fields, which gives them an advantage over piezoelectrics in micropositioning applications. While most electrostrictive actuator materials are perovskite ceramics, there has been much interest in large electrostriction effects in such polymer materials as polyvinylidene fluoride (PVDF) copolymers recently. This chapter discusses the three electrostrictive effects and their applications. A discussion of the sizes of these effects and typical electrostrictive coefficients is followed by an examination of lead magnesium niobate (PMN) as a prototype electrostrictive material. The electromechanical properties of some common electrostrictive materials are also compared. A few common criteria used to select relaxor ferroelectrics for electrostrictive applications are also outlined. Defining Equations Electrostriction is defined as the quadratic coupling between strain (x) and .