Gelatine-Coated Carbonyl Iron Particles and Their Utilization in Magnetorheological Suspensions

This study demonstrates the formation of biocompatible magnetic particles into organized structures upon the application of an external magnetic field. The capability to create the structures was examined in silicone-oil suspensions and in a gelatine solution, which is commonly used as a blood plasma expander. Firstly, the carbonyl iron particles were successfully coated with gelatine, mixed with a liquid medium in order to form a magnetorheological suspension, and subsequently the possibility of controlling their rheological parameters via a magnetic field was observed using a rotational rheometer with an external magnetic cell. Scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis confirmed the successful coating process. The prepared magnetorheological suspensions exhibited a transition from pseudoplastic to Bingham behavior, which confirms their capability to create chain-like structures upon application of a magnetic field, which thus prevents the liquid medium from flowing. The observed dynamic yield stresses were calculated using Robertson–Stiff model, which fit the flow curves of the prepared magnetorheological suspensions well.

Magnetodielectric Effects in Magnetorheological Elastomers Based on Polymer Fabric, Silicone Rubber, and Magnetorheological Suspension

We fabricate a hybrid magnetorheological elastomer (hMRE) based on a microfiber cloth soaked with a mixture containing magnetorheological suspension (MRS) and silicone rubber (SR). Two parallel copper electrodes are attached to the hMRE and the capacitance C is measured as a function of time t, for fixed values of magnetic flux density B. We show that C is stable in time and is sensibly influenced by B, while the relative dielectric permittivity increases up to two orders of magnitude when B reaches 340 mT. We explain the physical mechanism which leads to the observed magnetodielectric effects. The obtained results can be used for various biomedical applications such as in fabrication of active biomagnetic membranes used in dental implantology.

Magnetic spring effect on the force characteristics of the electromechanical magnetic liquid damper

The effect of a magnetic spring is observed in electromechanical devices with limited pole sizes. Simultane-ous changing of the system magnetic conductivity after a relative displacement of the poles causes mag-netic tension forces. These forces in electromechanical magnetic fluid dampers have their own specific characteristics which have not been studied before. All this requires studying the effect of a magnetic spring on the damper power characteristics, estimating the effect of the properties of a magnetorheological suspension on the magnetic spring strength, nature of its change and combination of the action of magnetic forces and viscosity resistance to the piston movement. To do that, it is important to analyze the effect of a magnetic spring in statics, at a slow movement of the piston and its dynamic oscillations. The studies were based on the theory of natural experiment and methods of processing experimental results. We have obtained and analyzed dependences of the resistance force of the electromechanical magnetic fluid damper for different vibration frequencies and magnetic inductions. The effect of magnetic spring forces on the damper power characteristic has been investigated. It has been found how the damper resistance force is affected by the magnetic and hydrodynamic components. The use of a damper with alternating elements with high and low magnetic conductivities makes it possible to change the strength characteristic of electromechanical magnetic fluid dampers. The proportion of the force controlled by the magnetic field reaches 75 % of the total effort. The use of the magnetic spring effect allows increasing the damping efficiency at small amplitudes and vibration frequencies. Increasing the magnetic properties of a magnetorheological suspension enhances the effect of a magnetic spring if the piston is non-magnetic, and weakens it if it is a magnetic one. When the magnetic induction rises, the effect of the magnetic spring increases. By changing the initial piston position, it is possible to obtain an asymmetrical power characteristic, for example, without using valves and spools, to increase the rebound force and to reduce the compressive force. If there are no moving parts, the damper reliability increases.