Linear oscillatory dynamics of flexoelectric membranes embedded in viscoelastic media with applications to outer hair cells

Abstract

Membrane flexoelectricity is an electromechanical coupling effect between the membrane average curvature and macroscopic electric polarization. Flexolelectricity is a biological actuation mechanism involved in the functioning of hearing. This thesis uses theory and simulation to develop a fundamental understanding of flexolectricity of relevance to hearing processes by integrating membrane elasticity and flexolectricity with viscoelastic processes.

Actuation of flexoelectric membranes in viscoelastic fluids with applications to outer hair cells

“…As expected, the issues (i) and (ii) identified above depend on (a) the E-frequency ω [11] as well as on (b) the material properties of the bio-device components discussed below. The magnitude |F D (jw)| represents the system's tendency to amplify or attenuate the input signal.…”

“…The oscillating electric field E(t) distorts the membrane through the flexoelectric effect. The membrane elastic E m curvature distortions are transferred to contacting viscoelastic fluids and deliver mechanical power P. The combination of flexoelectric actuation and mechanical actuation is flexoelectric mechanics (adapted from [11]). …”

“…The key role of OHCs is sound amplification in the presence of viscous dissipation and elastic storage [10]. Hence, the full description and understanding of OHC functioning has to include the frequency response of flexoelectric membranes embedded in viscous and viscoelastic media due to an oscillating E field [11][12][13][14][15]. The field of flexoelectric membranes was pioneered and developed by Petrov and co-workers [2][3][4]10].…”

“…The generic and key features of the electrical to mechanical energy conversion system in OHCs are described in figure 1 (figure 3 shows additional details). The input oscillating E field, through the electromechanical flexoelectric effect, produces curvature oscillations in the elastic membrane that forms the OHC [11][12][13][14][15] and that is surrounded by viscoelastic media. In turn, the oscillating elastic membrane displaces the contacting viscoelastic liquids through the mechanical viscoelastoelasticity effect [11].…”

“…The combined effect that allows the electromechanical energy conversion is based on the integration of the flexoelectric effect (E field imposed on flexoelectric membrane) and the mechanical effect (membrane elasticity plus viscoelastic bulk fluid flow) [14,15]. The two key issues in this energy conversion device are (i) how much power P is eventually delivered to the contacting viscoelastic fluids from the imposed oscillating electric field E and how much stored membrane elastic energy E m is required to deliver that power and (ii) under which material conditions is a well-localized resonant power peak found (in the spectrum of P), as physiologically required [11].…”