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Amir Abdollahi's picture

Flexoelectricity in Bones: A nanophenomenon that triggers the bone-repair process

Bones generate electricity under pressure, and this electromechanical behavior is thought to be essential for bone's self-repair and remodeling properties. The origin of this response is attributed to the piezoelectricity of collagen, which is the main structural protein of bones. In theory, however, any material can also generate voltages in response to strain gradients, thanks to the property known as flexoelectricity.'s picture

A level-set based IGA formulation for topology optimization of flexoelectric materials


This paper presents a design methodology based on a combination of isogeometric analysis (IGA),

level set and point wise density mapping techniques for topology optimization of piezoelectric /

flexoelectric materials. The fourth order partial differential equations (PDEs) of flexoelectricity,

which require at least C 1 continuous approximations, are discretized using Non-Uniform Rational

B-spline (NURBS). The point wise density mapping technique with consistent derivatives is

Amir Abdollahi's picture

Fracture toughening and toughness asymmetry induced by flexoelectricity

Cracks generate the largest strain gradients that any material can withstand. Flexoelectricity (coupling between strain gradient and polarization) must therefore play an important role in fracture physics. Here we use a self-consistent continuum model to evidence two consequences of flexoelectricity in fracture: the resistance to fracture increases as structural size decreases, and it becomes asymmetric with respect to the sign of polarization. The latter phenomenon manifests itself in a range of intermediate sizes where piezo- and flexoelectricity compete.

Amir Abdollahi's picture

Constructive and Destructive Interplay between Piezoelectricity and Flexoelectricity in Flexural Sensors and Actuators

Flexoelectricity is an electromechanical effect coupling polarization to strain gradients. It fundamentally differs from piezoelectricity because of its size-dependence and symmetry. Flexoelectricity is generally perceived as a small effect noticeable only at the nanoscale. Since ferroelectric ceramics have a particularly high flexoelectric coefficient, however, it may play a significant role as piezoelectric transducers shrink to the sub-micrometer scale.

Amir Abdollahi's picture

A computational study of flexoelectricity

Flexoelectricity is a size-dependent electromechanical mechanism coupling polarization and strain gradient. It exists in a wide variety of materials, and is most noticeable for nanoscale objects, where strain gradients are higher. Simulations are important to understand flexoelectricity because experiments at very small scales are difficult, and analytical solutions are scarce.

Piezoelectricity above the Curie temperature? Combining flexoelectricity and functional grading to enable high-temperature elect

Most technologically relevant ferroelectrics typically lose piezoelectricity above the Curie temperature. This limits their use to relatively low temperatures. In this Letter, exploiting a combination of flexoelectricity and simple functional grading, we propose a strategy for high-temperature electromechanical coupling in a standard thin film configuration.

On the Possibility of Piezoelectric Nanocomposites without using Piezoelectric Materials

In a piezoelectric material an applied uniform strain can induce an electric polarization (or vice-versa). Crystallographic considerations restrict this technologically important property to non-centrosymmetric systems. It can be shown both mathematically and physically, that a non-uniform strain can potentially break the inversion symmetry and induce polarization even in non-piezoelectric dielectrics.

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