MR Fluid & MR Powder

The secret behind our haptic feedback technology

MRM (MR materials or magnetorheological materials) are smart materials consisting of fine, magnetizable particles (typically iron) whose rheological properties change through the application of a magnetic field.

This change occurs in less than 0,5 milliseconds, more than 200 times faster than the blink of an eye. Once the magnetic field is removed, the MR material (MR fluid or MR powder) reverts to its unlinked state.

MR fluid in a petri dish exposed to a magnetic field from below with a permanent magnet. You can see how the particles link together, forming spikes that grow larger towards the center where the magnet is located.

The characteristics of MR materials

Fully adjustable & incredibly accurate

The degree of change the MR materials undergo when exposed to a magnetic field is related to the magnetic field’s strength. The stronger the magnetic field, the higher the yield stress of the material. Therefore, the MRM’s level of stress resistance can be controlled very accurately by varying the magnetic field’s intensity. A high level of control over the MR fluid or MR powder is the key to our technology’s flexibility and accuracy. Its fast response time allows us to switch between haptic patterns in perfect sync with your user interface, making the operation simple, safe, and intuitive.

Even though MR materials are new to most people, MR technologies have proven themselves for over 20 years in the automotive industry in suspensions or steering systems.

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The graph illustrates, how, with increasing strength of the magnetic field (kA/m), the yield stress of the MR fluid increases as well.

Yield Stress vs. Magnetic Field Strength

Carefully selected

For intricate haptic feedback

For our HAPTICORE technology, we use both MR powder (MRP or magnetorheological powder) as well as MR fluid (MRF or magnetorheological fluid), a mixture of MR powder, and a carrier fluid (e.g., oil or glycol). Based on our many years of experience, we test different MR material variations to generate haptic feedback tailored to the specific use cases of various fields of applications and use cases.

After using MR fluid for many years, we have since developed our haptic technology further and also use pure MR iron powder for certain applications. While the operating principle of MR fluid and MR powder is the same, the use of different variations of the smart materials allows us to tailor factors such as base torque precisely to our customer’s requirements.

We have published a comprehensive blog post about smart materials. Learn more about their special properties and applications.

Smart Materials
Both MR (magnetorheological) fluid and powder in a glass cylinder in their unlinked (liquid/powdered) state.

Frequently asked questions about MR materials

Magnetorheological or MR materials (MR fluid, MR powder, MR elastomers – You can learn more about MREs here) are a type of smart material that can change their rheological properties in response to an external magnetic field. These materials consist of tiny magnetic particles suspended in a carrier material.

Rheological properties: The way in which materials deform or flow in response to applied forces or stresses.

For MR fluids, this carrier typically is oil. The magnetic particles are usually made of ferromagnetic or paramagnetic materials, such as iron or iron oxide. In the absence of a magnetic field, the suspended particles move freely, allowing the material to flow and deform uninhibited. However, when a magnetic field is applied, the particles align themselves along the lines of magnetic force, forming chains or clusters that restrict the flow/deformation of the material. As a result, the material transforms into a semi-solid or solid-like state with increased viscosity and stiffness.

Magnetorheological (MR) materials are used for a wide range of applications where controlled changes in material properties are desired. Some of the common uses of magnetorheological materials include:

  • Dampers and shock absorbers: MR fluids are extensively used in dampers and shock absorbers in automotive, aerospace, and engineering applications. By adjusting the magnetic field, the viscosity, and stiffness of the material can be changed, allowing for real-time control of vibration and impact absorption. Learn more about our adaptive MR damping system RHEOSHOX.
  • Clutches and brakes: MR materials find application in clutches and brakes to provide variable torque transmission and control. By adjusting the magnetic field strength, the engagement and disengagement of the clutch or brake can be precisely controlled.
  • Haptic devices: For our HAPTICORE technology, we use an operating principle comparable to that of MR brakes. By changing the viscosity and stiffness of the smart material, we create mechanical haptic feedback for the simple, safe, and intuitive operation of HMIs.

Our parent company INVENTUS Development is specialized in the development of innovative MR technologies and possesses more than 20 years of experience in this field. Visit their website to learn more about other applications of MR materials.

Magnetorheological (MR) fluids are suspensions that typically contain two main components: magnetic particles and a carrier fluid. The combination of these components allows MR fluids to exhibit their unique rheological properties.

  • Magnetic particles: MR materials contain tiny magnetic particles that are typically made of ferromagnetic or paramagnetic materials. Common examples include (carbonyl) iron, iron oxide, or nickel-based particles. These particles are dispersed within the carrier fluid and are responsible for the response to the applied magnetic field. The size, shape, and magnetic properties of the particles influence the behavior and performance of the MR fluid.
  • Carrier fluid: The magnetic particles are usually suspended within a carrier fluid, which acts as a medium to hold and disperse the particles. The carrier fluid can be a liquid or a semi-liquid material, depending on the desired application and the required viscosity range. Common carrier fluids used in MR fluids include mineral oil, silicone oil, water, or a mixture of these fluids. The choice of carrier fluid depends on factors such as temperature range, desired viscosity, stability, and compatibility with the surrounding materials.
  • Stabilizers and additives: MR fluids may also contain stabilizers and additives to enhance their performance and stability. These can include surfactants or dispersing agents that help to prevent agglomeration or settling of the magnetic particles, thus ensuring a consistent suspension. Other additives can be incorporated to improve the thermal stability, lubricity, or anti-corrosive properties of the MR fluid, depending on the specific application requirements.

Based on our many years of experience, we now also use pure MR powder for our HAPTICORE technology and no longer necessarily need a carrier fluid.

We source our MR materials from selected, long-term partners. Besides the manipulation of the magnetic field, the know-how about the exact composition and the specific material characteristics allows us to generate intricate haptic feedback. Magnetorheological materials are usually produced through a formulation process in which magnetic particles are dispersed in a carrier liquid. This process usually looks like this:

  • Selecting the magnetic particles: The first step is to choose the appropriate magnetic particles based on the desired properties and application requirements. Factors like particle size, shape, and magnetic properties are considered during selection.
  • Preparing the carrier fluid: The carrier fluid is selected based on factors like desired viscosity range, temperature stability, and compatibility with the application environment. The carrier fluid is typically preprocessed to remove impurities and ensure it meets the desired specifications.
  • Mixing the magnetic particles and the carrier fluid: The magnetic particles are added to the carrier fluid in a controlled environment. The mixing process helps to ensure the particles are evenly dispersed throughout the carrier fluid.
  • Stabilization and additive incorporation: Stabilizers and additives may be introduced to enhance the stability and performance of the MR fluid. These additives prevent particle agglomeration, settling, or oxidation. The specific additives and their concentrations depend on the desired properties and the application requirements.
  • Quality control and testing: The prepared MR material is subjected to extensive quality controls to ensure consistency and meet our high-quality requirements. This may involve testing the fluid’s rheological properties, viscosity, magnetic response, stability over time, and compatibility with materials it will come into contact with.
  • Packaging and storage: After the MR material is tested and approved, it is filled into suitable containers such as bottles or drums and stored under appropriate conditions to maintain its stability until it is ready for use.

Magnetorheological (MR) materials offer several advantages that make them valuable for various applications. Here are some examples:

  • Real-time controllability: One of the significant advantages of MR materials is their ability to undergo rapid and reversible changes in their rheological properties in response to an applied magnetic field.
  • Wide range of tunability: MR materials offer a wide range of tunability, allowing for fine control over their rheological properties. By adjusting the strength of the magnetic field, the viscosity, stiffness, and damping behavior of the material can be tailored to meet specific industry requirements.
  • Simple and compact design: MR-based components, such as dampers, clutches, or brakes can be more compact and lightweight compared to traditional mechanical counterparts. This advantage is particularly beneficial in industries where space and weight constraints are crucial.
  • Energy efficiency: MR materials can provide energy-efficient solutions by dynamically adjusting their damping properties. MR technologies allow for efficient energy consumption by absorbing and dissipating energy only when needed.
  • Robustness and durability: MR materials are known for their robustness and long service life. They can withstand high loads, temperature variations, and harsh environmental conditions without significant degradation in performance.
  • Versatility of applications: MR materials find applications in various industries, including automotive, aerospace, robotics, consumer electronics, and more.

The main difference between magnetorheological (MR) fluid and ferrofluid lies in their composition and behavior. The biggest difference is in the size of the particles: While MR materials contain particles on a micrometer scale, ferrofluid particles are on a nanometer scale and thus about 1000 times smaller.

MR fluid consists of magnetic particles dispersed in a carrier fluid, and its rheological properties, such as viscosity and stiffness, change in response to an applied magnetic field. The alignment of magnetic particles in the field leads to increased viscosity and stiffness. On the other hand, ferrofluid is a colloidal suspension of magnetic nanoparticles coated with a surfactant, dispersed in a carrier liquid. Even when a magnetic field is applied, ferrofluid remains fluid-like and forms distinct spike-like structures.

While MR fluid is commonly used for its controllable rheological properties, ferrofluid is known for its unique response to magnetic fields and is often employed in applications such as sealing, heat transfer, or damping. However, in contrast to MR damping technologies, ferrofluids are typically employed in specialized damping applications that require fine control over small-scale movements and vibrations. Examples include loudspeakers, but also other precision instruments, and microelectromechanical systems.

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