P.A. Voltairas

Hydrodynamics of magnetic drug targeting

Among the proposed techniques for delivering drugs to specific locations within the human body, magnetic drug targeting surpasses due to its non-invasive character and its high targeting efficiency. Although the method has been proposed almost 30 years ago, the technical problems obstruct possible applications. It is the aim of the present work to classify the emerging problems and propose satisfactory answers. A general phenomenological theory is developed and a model case is studied, which incorporates all the physical parameters of the problem.

A theoretical study of the hyperelasticity of electro‐gels

The continuum theory of electro‐elasticity is used in order to describe the large deformations observed in gels endowed with electric properties when they are placed in electric fields. The analytical solution of the properly constructed boundary‐value problem agrees quantitatively with available experimental data.

Estimation of exchange constant A and g factor for CoxNi1−x microspheres from size-dependent ferromagnetic resonance modes

Abstract The exchange constants A and the g factors for Co x Ni 1− x microspheres are estimated by comparing theoretical calculations of size-dependent resonance modes with the experimental data of spherical monodisperse Co–Ni particles. Only cylindrically symmetric modes are studied. The deviation from previously reported values is presented.

Elastic stability of silicone ferrofluid internal tamponade (SFIT) in retinal detachment surgery

Abstract It has been argued that silicone ferrofluid internal tamponade (SFIT) can provide (360°) tamponade of the retina in retinal detachment surgery. Provided that the produced SFIT is biocompatible, exact knowledge is needed of its elastic stability in the magnetic field produced by the semi-solid magnetic silicon band (MSB) used as a scleral buckle. We propose a quantitative, phenomenological model to estimate the critical magnetic field produced by the MSB that ‘closes’ retinal tears and results in the reattachment of the retina. The magnetic ‘deformation’ of SFIT is modeled in accordance with the deformation of a ferrofluid droplet in an external magnetic field.

Mode mixing in ferromagnetic resonance in magnetic microspheres

The problem of ferromagnetic resonance in magnetic microspheres is revisited due to related experiments in this size range. The eigenfrequency spectrum is examined more rationally compared to previous numerical computations, due to proper selection of the radial dependence of the solution. The cylindrically symmetric modes studied agree with experiments on Ni micrometer-size particles for an exchange constant A=2×10−7 erg/cm, while the error is less than 9% for the well-known value of A=3.4×10−7 erg/cm.

Modeling the hyperelasticity of magnetic field sensitive gels

The continuum theory, previously developed to quantitatively account for the large deformations observed in gels endowed with electric properties, is extended to magnetic field sensitive gels (ferromagnetic or diamagnetic in origin). The derived analytical formula for the dependence of the gel displacement on the magnetic field can be applied either to control recently developed biomimetic valves and possible artificial muscles constructions or to interpret similar phenomena in biophysics.

The role of material parameters and mechanical stresses on magnetic and magnetostrictive hysteresis

The proposed micromagnetic model (Voltairas et al., Int. J. Engng. Sci., accepted for publication) is extended to account for shearing strains. We assume that the ferromagnetic material is a single cubic crystal, the magnetization reverses coherently and the strains are uniform. The equilibrium field equations are derived from the free energy functional. The role of the material parameters and the applied stresses (inverse magnetostriction effect) on the magnetization and magnetostriction curves is examined in detail.

Magnetization reversal in thin ferromagnetic films under mechanical stress

Abstract A simple micromagnetic model is presented to study the effect of stress on the magnetization reversal in thin ferromagnetic films (well-known as inverse magnetostrictive effect). To simplify the calculations the plane strains are confined to be uniform. The externally applied magnetic field is oriented either, parallel or perpendicular to the stress direction. For coherent magnetization reversal, analytical relations between coercivity and stress and remanence and stress were obtained. The nucleation modes and fields for non-uniform, one-dimensional magnetization reversal were calculated. From our analysis we conclude that the stress dependence of coercivity is qualitatively the same with related experiments.

Size-dependent resonance modes in ferromagnetic spheres

Abstract In the present work we deal with the size-dependent resonances in small ferromagnetic spheres. The analysis is based on the theory of micromagnetism, the work of Aharoni, and an optimization technique. Numerical results are presented for the resonance field, as well as for the resonances mode and the magnetization configuration in the material. The role of parameters entering into the problem is extensively discussed.

Non-uniform magnetization reversal in stressed thin ferromagnetic films

Abstract The effect of applied mechanical stresses on the magnetization reversal, well known as inverse magnetostriction effect, is studied for thin ferromagnetic films. The model used, is a micromagnetic one proposed in (Voltairas et al., Int. J. Eng. Sci., in press). Numerical non-uniform (NU) solutions for the Brown’ s magnetoelastic equations are presented and compared with uniform Stoner–Wolfarth (SW) ones. We study only the case where the applied stresses are oriented perpendicular to the fields direction (Case 1 of (Voltairas et al., Int. J. Eng. Sci., in press)). The dependence of coercivity and remanence on applied stress and thin film thickness is discussed. The framework for stability analysis is developed, but it is applied only to the saturation solutions of the NU modes, which are proved to be unstable. Energy considerations confirm that the NU modes are unfavorable ones throughout the magnetization reversal.