What’s a MagneRheo Damper?

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A magnetorheological damper is a damping device that works by placing a magnetic field on a mixture of liquid oil and iron particles. The iron particles are attracted to the magnetic field and line up along the magnetic field lines that pass through the liquid. This creates a thick liquid that resists movement and can help reduce vibration and shock in a variety of applications. These fluids are sometimes referred to as smart fluids, because they change properties as the magnetic field is added or changed.

Rheology is the study of the effects of liquids and solids when exposed to motion or pressure. In liquids, the primary characteristics that can be useful for vibration control are viscosity and shear stress. Viscosity refers to the thickness of a liquid and how well it can resist movement or flow. Shear stress is a measure of how well a liquid resists being suddenly separated or moved, and also how well materials placed in the liquid can move if rapidly pulled in any direction.

A shock absorber is a term for a device used to reduce vibrations, which is similar to a shock absorber used on vehicles to reduce suspension movement due to uneven road surfaces. Many shock absorbers and shock absorbers use oils of various thicknesses to reduce movement and protect the equipment. When small iron particles are added to oils, magnetic fields can affect the iron particles and change the properties of the liquid.

By adding the iron-oil mixture inside a standard damper and creating a magnetic field with an electric current, a magnetorheological damper will be created. As the magnetic field increases, the iron particles will increasingly resist movement and create higher levels of vibration damping. If an electrical controller is added along with software to control the magnetic field, a variable magnetorheological damper can be used to rapidly reduce vibrations and protect structures or vehicles.

The iron particles in shock absorbers are often coated with a polymer to prevent them from sticking together. Keeping the particles very small helps keep them suspended in the oil and prevents them from settling to the bottom of the shock. When the magnetic field is created, the mixture becomes more like a solid than a liquid and is very resistant to flow or movement. If oil is pushed with a piston inside a cylinder, the high viscosity can reduce the movement of the oil through small holes in the piston.

Shear stress can be utilized by replacing the piston with a series of plates immersed in oil. The plates move back and forth in the liquid and when the magnetic field is activated, the iron-oil mixture thickens rapidly and becomes very resistant to shear. If the plates are connected to a solid shaft extending from the shock absorber, the shaft can be attached to a vehicle or building foundation and provide a damping system.

Earthquake protection became an area of ​​increased research in the late 20th century as human development grew into areas where the potential for damage to buildings was high. One technique was to separate the building from the ground with rubber or other cushioning materials, which allowed for some movement of the building during an earthquake. Without some form of damping, however, building movement could be extreme and damage or complete failure could occur. Adding a magnetorheological shock absorber system to the base of the building gave the architects a way to reduce the building’s movement with a controllable system.

Vehicles were another area of ​​interest for magnetic damping systems in the 20th century. Interest in passenger comfort and a higher level of safety systems has led to shock absorbers that use magnetorheological damper technology to provide variable suspension. The driver can choose a level of driving comfort using a dial, which tells the controller how much magnetic field to create when vibration is sensed. Additionally, safety systems could detect skidding or a possible rollover situation and modify suspension behavior to counteract it.

Military weaponry was another area where magnetorheological dampers could provide an advantage. When mounted on a large gun, the muzzle brake could detect the firing of a shell and activate to reduce recoil. Not only did this reduce wear on the weapon, but in mobile tanks or guns, shock reduction could reduce the fatigue of soldiers firing the weapons.

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