CHARACTERISATION AND MEDICAL APPLICATIONS OF

MAGNETORHEOLOGICAL FLUIDS

Javier Echavarri Otero, Andrés Díaz Lantada, Pilar Lafont Morgado, Juan Manuel Munoz-Guijosa

José Luis Muñoz Sanz, Héctor Lorenzo-Yustos and Julio Muñoz-García

Grupo de Investigación en Ingeniería de Máquinas, E.T.S.I. Industriales, Universidad Politécnica de Madrid

c/ José Gutiérrez Abascal, nº 2. 28006, Madrid, Spain

Keywords: Magnetorheology, Damper, Characterisation, Application, Medical.

Abstract: Magnetorheological fluids are composed by magnetic particles suspended within a carrier fluid which allow

to change their rheology when subjected to a magnetic field. This property can be controlled very accurately

by varying the magnetic field intensity which provides a rapid and effective system to control the response

of very diverse fluid-mechanical devices.The characterisation of two new magnethoreological fluids is

presented. The force response when the magnetic field varies is studied in static and dynamic

conditions.This paper sets out some of the opportunities and advantages provided by this fluids both for

medical and non-medical applications.

1 INTRODUCTION TO THE

MAGNETORHEOLOGICAL

FLUIDS

Magnetorheological fluids (MR-fluids) are capable

to change their rheology when subjected to a

magnetic field. This property can be controlled very

accurately by varying the magnetic field intensity,

which provides a rapid and effective system to

control the response of very diverse fluid-

mechanical devices.

These kinds of fluids are composed by magnetic

particles suspended within a carrier fluid. Thus, they

are typically composed by micrometer or nanometer

scale spheres distributed in a mineral oil.

The response of the magnetorheological fluids is

the result of the induced distribution of the magnetic

suspension particles (usually in the 0.1-10 µm range)

within the fluid when an external magnetic field is

applied (usually about 100 mT in air). The

microscopic particles align themselves along the

lines of magnetic flux. Thus, the resulting chains of

particles restrict the movement perpendicular to the

direction of the lines of flux, leading to an

anisotropic behaviour and to an increase in the

viscosity of the fluid (Torcuato, 2006).

This phenomenon is considered completely

reversible and almost instantaneous (response time

is about 10 milliseconds) for these fluids.

The magnetically controllable properties of

magnetorheological fluids depend on the carrier

fluid and its additives, the magnetic field applied,

the working condition and the size, shape,

concentration, density and distribution of the

particles.

The first patent related to MR-technology was

issued to inventor Jacob Rabinow in the 1940s,

though this technology remained with little practical

use. However, in the last twenty years there is a

serious research in this field, especially when other

technologies began to converge that made their use

practical and a real possibility.

Numerous research efforts have been carried out

in order to improve the magnetorheological fluids, in

specialised companies like Lord, Repsol-YPF and in

different universities.

Although MR-fluids have many potential

applications, they are limited by aspects like their

high density and wear in materials due to presence

of iron, very high cost or precipitation of particles.

437

Echavarri Otero J., Díaz Lantada A., Lafont Morgado P., Munoz-Guijosa J., Muñoz Sanz J., Lorenzo-Yustos H. and Muñoz-García J. (2009).

CHARACTERISATION AND MEDICAL APPLICATIONS OF MAGNETORHEOLOGICAL FLUIDS.

In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 437-440

DOI: 10.5220/0001815004370440

 SciTePress

2 CHARACTERISATION OF NEW

MAGNETORHEOLOGICAL

FLUIDS

The Machines Engineering Division (DIM)

belonging to the Technical University of Madrid

(UPM) has collaborated with the company Repsol-

YPF and the Applied Physics Department of the

University of Granada in the development and

characterisation of new magnetorheological fluids

for shock-absorbers used for different applications.

Two oils have been developed: MR-Lub1 and

MR-Lub2. The carrier fluid is the same for both of

them but the second one includes a higher

percentage of magnetic particles. The cited

characterisation was carried out in a commercial

damper mounted in a MTS damper test system

shown in figure 1.

Figure 1: MTS Damper Test System.

The first characterisation includes an static test

(velocity of the damper below 1mm/s) to determine

the effect of the electric intensity (which produces a

magnetic field) in the increase of the damping force

in the damper.

The results for MR-Lub1 are depicted in figure

2, which shows a non-linear behaviour.

Figure 2: Damping force vs. Intensity for MR-Lub1.

The reversible magnetorheological behaviour is

shown in figure 3, obtained for a of the damper at a

velocity of 130mm/s and a stroke of 25mm. The

traction and compression cycles are depicted for the

MR-Lub1. The force obtained at each point when

the intensity is growing is very similar to the force

measured when intensity is decreasing.

Nevertheless, the results show a slight remaining

magnetisation when low intensities around 1A are

applied.

Figure 3: Static force vs. Intensity for MR-Lub1 in traction

and compression cycles.

Figure 4 shows a comparison between dynamic

tests in the shock absorber with MR-Lub1, MR-

Lub2 and two commercial fluids by Lord at a

velocity of 1m/s. The higher quantity of magnetic

particles in MR-Lub2 than in MR-Lub1 leads to an

increase in the sum of the traction (T) and

compression (C) forces. A similar Force-intensity

behaviour is observed in all the tests performed.

Figure 4: Dynamic force vs. Intensity.

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3 POSSIBLE NON-MEDICAL

APPLICATIONS FOR

MR-FLUIDS

Nowadays, the main manufacturers of

Magnetorheological fluids (Lord, 2008) offer

specific solutions for many applications mainly

within the following sectors:

-Suspension systems

-Fan Clutches

-Crash-protection systems

-Buildings and bridges

-Medical applications

In the near future many other applications are

expected to be available, because their possibilities

are almost endless.

The most extended application for the fluids

developed is the use in a magnetorheological

suspension, where a controllable fluid replaces

traditional hydraulic oil in each shock absorber. As

sensors monitor road and vehicle conditions, a

controller modifies the intensity applied and

therefore the damping characteristics are adjusted in

real-time. This enables remarkable improvements in

both ride comfort and handling.

Magnetorheology has had a large role in recent

advances in military and automotive industries. The

called MR-Technology has been integrated not only

in military tactical and combat vehicles but also in

primary suspension systems of high performance

vehicles designed by Cadillac, Audi, Ferrari, Honda

and others. In addition, these new technologies are

used in seat and cab suspension designs of

agricultural and other off-highway vehicles in order

to improve operation environment.

Apart from the use for suspension applications,

there are a lot of patents concerning MR-fluids for

fan clutches. The main aims of these inventions are

to provide smooth, efficient torque-transfer in clutch

devices. The designs include a large range of

applications in order to improve the controllability

and the high off-state drag.

Another present application for MR-fluids is

obtained by combining the variable control

magnetorheology with advanced sensors in

passenger protection systems. In these cases, the

protection systems can be adjusted to provide the

perfect resistance based on the impact severity and

the passenger size.

There is also a civil and structural application in

skyscrapers and long bridges protection, which are

susceptible to vibrations induced by high winds and

seismic activity. In order to mitigate their effect,

large dampers are built into their design, which

protect against shocks through a continuously

controllable and cost-effective solution. Figure 5

shows a Rheonetic Seismic Damper by Lord.

Figure 5: Example of a Rheonetic Seismic Damper,

obtained from Lord’s website.

4 SOME POSSIBLE MEDICAL

APPLICATIONS FOR

MR-FLUIDS

The main medical applications for MR-fluids are

considered haptic devices, new prothesis

development and innovative cancer therapies.

4.1 Haptic Devices

Tactile and force feedback systems are used in

surgery training assisted by computer. Active

dampers have been developed based on MR-fluids

and their utilization in haptic systems provides a

very precise control which enhances the skills of the

surgeons (Bar-Cohen, Mavroidis et al., 2001;

Neelakantan, 2002; Rizzo, 2007).

In particular, by using sensorized surgical

instruments, suitable signals could be acquired and

used for controlling the haptic device. The surgeons

could use the surgical instruments to interact with

biological tissues and organs during a simulated

operation and, probe their compliance by touching

the haptic device (Scilingo, Sgambelluri et al, 2003).

4.2 Prosthetic and Rehabilitation

The company Lord, in collaboration with

Biedermann Motech, manufacturer of prosthetic

components, has developed a device that improves

the mobility of leg amputees. The new design,

shown in figure 6, is based in MR-dampers and

produces an increase in gait balance, stability and

energy efficiency.

CHARACTERISATION AND MEDICAL APPLICATIONS OF MAGNETORHEOLOGICAL FLUIDS

439

Figure 6: New prosthesis for leg amputees, obtained from

Lord’s website.

Other medical systems based on similar active

control elements are used in training devices for

rehabilitation purposes which allow an adjustable

resistance to the movement according to the

evolution of the patient (Dong, 2005).

4.3 Cancer Therapy

The biocompatibility and tolerability by humans and

animals to magnetorheological materials have been

tested successfully (Sheng, Flores and Liu, 1999).

Some techniques developed for cancer therapies

target chemotherapeutic agents to the tumor sites

employing magnetic nanoparticles as carriers is a

promising cancer treatment reducing side effects of

conventional chemotherapy.

Electron microscope investigations show that the

ferrofluids can be enriched in tumour tissue and

tumour cells (Alexiou, 2006). Therefore, these

studies show a remarkable improvement to the

conventional cancer therapy but still causes toxicity

to the body.

Other interesting studies are based in MR-fluids

introduced into the blood vessels supplying the

tumor. When a magnetic field is applied a seal is

formed, which blocks the blood flow and cut the

alimentation in oxygen, leading to tumor necrosis.

There are interesting in-vitro investigations on these

therapies (Sheng, Flores and Liu, 1999) concerning

the study of the seal kinetics and pressure

resistibility of the formed seal.

5 CONCLUSIONS

In this paper the characterisation of two new

magnethoreological fluids in a damper is presented.

The force response when the magnetic field varies is

studied both in static and dynamic conditions. The

remaining magnetisation when the external field

stops is analysed.

Different possible applications for the two fluids

developed are indicated for medical or non medical

purposes. In the future, the new possibilities of the

magnetorheological fluids are incalculable.

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