Influence of the geometry on magnetic interactions in a retina fixator based on a magnetoactive elastomer seal

Abstract

Abstract.We study the effects the geometric configuration has on magnetic interactions between a magnetoactive elastomer (MAE) sample and various systems of permanent magnets for problems with both flat and curved geometry. MAEs consist of a silicone polymer matrix and iron filler microparticles embedded in it. Permanent magnets are cylindrical neodymium magnets arranged in a line on a flat or curved solid surfaces. We use computer simulations, namely the finite element method, in order to study the interaction force and magnetic pressure in a system with an MAE sample and permanent magnets. The model is based on classical Maxwell magnetostatics and two factors taking into account field dependence of MAE's magnetic properties and inhomogeneities caused by local demagnetization. We calculate magnetic pressure dependences on various geometric parameters of the system, namely, the diameter and the height of permanent magnets, the distance between the magnets and dimensions of MAE samples. This research aims to create a set of guidelines for choosing the geometric configuration of a retina fixator based on MAE seals to be used in eye surgery for retinal detachment treatment.

Development of magnetoactive elastomers for sealing eye retina detachments

“…Furthermore, the pressure is lower in the curved configuration in comparison with the flat one as it has been predicted theoretically in Ref. . Indeed, when the system is bent the direction of the interaction force changes.…”

“…The results on the flat geometry were promising but theoretical calculations performed in Ref. for curved configurations corresponding to real human eyes have revealed that the surface curvature introduces sensitive corrections into the average pressure realized in the magnetic system. The difference in pressures for flat and curved cases can reach 20% at the distance of 0.7 mm between the nearest faces of the magnetic components of the retina fixator; the value 0.7 mm corresponds to the average thickness of the human sclera together with retina and choroid .…”

A Cascading Mean-Field Approach to the Calculation of Magnetization Fields in Magnetoactive Elastomers

“…Hence, upon introducing the generalized effective susceptibility χ A eff in Equation ( 29) and passing over to Equation (30) this self-demagnetization is implicitly, and exactly, taken into account. Furthermore, by definition, see Equation (29), the components of χ A eff are bound to moderate values even though the components of the generalized susceptibility itself, χ A = ∇ A L(A), may become very large. In contrast to Equation (26), it is now χ A eff which is forming the prefactor in Equation ( 30), resp.…”

“…Nevertheless, we also note a fundamental drawback for magnetization functions L(•) beyond the 'true' linear magnetization scheme. Only in this case where M = χH, or general M = χ • H, the here defined χ A , Equation (28), and accordingly also the effective χ A eff , Equation (29), are pure material parameters. They simply become χ A = χ, resp.…”

“…Quite a variety of technical implementations and applications have been proposed and implemented so far. For example, MAEs can be used as a working part in actuators and sensors [20][21][22], energy harvesting devices [23][24][25], micro-robots [26] and -pumps [27], in prosthetic and orthotic devices [28], as well as in ophthalmologic magnetic fixators [29][30][31].…”