A magnetorheological damper with a variable cross-section piston structure

Abstract

This invention relates to a magnetorheological damper with a variable cross-section piston structure, comprising a shell filled with magnetorheological fluid, a piston disposed within the shell, a piston rod connected to the piston, and a permanent magnet sleeved outside the shell; one end of the shell has a through hole, and one end of the piston rod extends through the through hole into the shell and connects to the piston, the piston rod driving the piston to move linearly within the shell; the piston comprises a hollow shell and a telescopic rod disposed within the hollow shell, the hollow shell comprising several telescopic segments slidably connected in sequence, the telescopic rod extending and retracting controls the relative sliding of the telescopic segments, adjusting the cross-sectional dimensions of the piston, thereby adjusting the output damping force. This damper can achieve the effect of adjusting the output range by only changing the internal structure of the damper, without requiring modification and reconstruction of the overall dimensions.

Description

Technical Field

[0001] This invention relates to a magnetorheological damper with a variable cross-section piston structure, belonging to the field of magnetorheological vibration reduction. Background Technology

[0002] Magnetorheological fluids (MRFs), a novel type of smart material, are composed of a carrier fluid, ferromagnetic particles, and various additives. Under an applied magnetic field, they can transform from a Newtonian fluid to a non-Newtonian fluid within milliseconds, thereby altering the yield stress of the MRF. Magnetorheological dampers are vibration absorbers that utilize the properties of MRFs to change their stiffness in real time according to the input current. Due to their advantages such as simple mechanical structure, wide dynamic range, fast response speed, low power consumption, and large output damping force, MRF dampers have been widely researched and applied in vibration control fields such as vehicle suspension, prosthetic knee joints, and earthquake mitigation.

[0003] However, traditional magnetorheological dampers typically use a single excitation coil or permanent magnet to generate a magnetic field, which results in uneven magnetic field distribution, leading to poor damping force stability; the damping force adjustment range is limited, making it difficult to meet the requirements of high dynamic response; and the magnetorheological fluid is prone to sedimentation after long-term standing, reducing performance and increasing maintenance costs. Summary of the Invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a magnetorheological damper that can adjust the damping force by changing the piston cross-sectional size.

[0005] To achieve the above objectives, the technical solution proposed in this invention is as follows: a magnetorheological damper with a variable cross-section piston structure, comprising a shell filled with magnetorheological fluid, a piston disposed within the shell, a piston rod connected to the piston, and a permanent magnet sleeved outside the shell; one end of the shell is provided with a through hole, and one end of the piston rod extends through the through hole into the shell and connects to the piston, the piston rod driving the piston to move linearly within the shell; the piston comprises a hollow shell and a telescopic rod disposed within the hollow shell, the hollow shell comprising a plurality of telescopic segments slidably connected in sequence, the telescopic rod extending and retracting controls the relative sliding of the plurality of telescopic segments, adjusting the cross-sectional dimensions of the piston, thereby adjusting the output damping force.

[0006] A further design of the above technical solution is as follows: the outer shell is provided with a sealing cover plate corresponding to the through hole, the sealing cover plate is provided with sealing filler, and one end of the piston rod passes through the sealing cover plate and extends into the outer shell through the through hole to connect with the piston.

[0007] The hollow shell further includes two fixed sidewalls, two sliding sidewalls, a fixed top plate, and a fixed bottom plate. The two sliding sidewalls are slidably connected between the two fixed sidewalls to form a telescopic frame of the hollow shell. The telescopic rod is fixedly connected to the two sliding sidewalls at both ends. The fixed top plate and the fixed bottom plate are fixedly connected between the two fixed sidewalls. Several telescopic segments are symmetrically arranged on both sides of the fixed top plate to form a telescopic top plate of the hollow shell. Several telescopic segments are symmetrically arranged on both sides of the fixed bottom plate to form a telescopic bottom plate of the hollow shell. The two ends of the telescopic segments are slidably connected to the two fixed sidewalls, and the piston rod is connected to the fixed top plate.

[0008] The fixed sidewall is provided with a sliding groove arranged along the piston extension direction, and the sliding sidewall and the two ends of the extension segment are provided with sliders that cooperate with the sliding groove.

[0009] The top of the telescopic segment is provided with a guide groove arranged along the piston telescopic direction, and the bottom is provided with a guide rod that cooperates with the guide groove. Adjacent telescopic segments are slidably connected through the cooperation of the guide rod and the guide groove.

[0010] The piston is filled with sealing packing.

[0011] The sealing filler is hydrophilic polyurethane.

[0012] The telescopic rod is equipped with a displacement sensor at its end.

[0013] The outer shell is provided with several excitation coils. When the excitation coils are energized, they generate a magnetic field, which adjusts the viscosity of the magnetorheological fluid, thereby adjusting the output damping force.

[0014] The magnetorheological fluid is an oil-based ferrorheological fluid, the carrier liquid is synthetic hydrocarbon, the magnetic powder volume percentage is 40%, the magnetic powder weight percentage is 86%, and the density is 3.65 g / cm³. 3 .

[0015] The beneficial effects of this invention are as follows:

[0016] The damper of the present invention can adjust the output damping force by adjusting the cross-sectional size of the piston through the telescopic rod. The effect of adjusting the output range can be achieved by simply changing the internal structure of the damper, without the need to modify or reconstruct the overall size.

[0017] This invention utilizes the response of magnetorheological fluid to a magnetic field to set up several excitation coils, which can form a multi-level magnetic field adjustment scheme, significantly improving the utilization rate of the magnetic field and enhancing the adjustment accuracy of the damping force. For specific output damping force requirements, controllable adjustment can be achieved by controlling the magnetic field in conjunction with a variable cross-section piston damper, realizing the automation and controllability of magnetorheological vibration reduction, and expanding the adjustment range of the output damping force.

[0018] This invention incorporates a permanent magnet, which effectively solves the problem of performance degradation caused by sedimentation of the magnetorheological fluid in a long-term stored magnetorheological damper, thus maintaining the damper at a high operating level. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the invention;

[0020] Figure 2 for Figure 1 Schematic diagram of the piston structure;

[0021] Figure 3 for Figure 2 Schematic diagram of the connection between adjacent expansion joints;

[0022] Figure 4 This is a schematic diagram of the structure of Embodiment 2 of the invention;

[0023] Figure 5 This is the control circuit diagram for the excitation coil;

[0024] Figure 6 Damping force curves for different piston cross-sectional dimensions;

[0025] Figure 7 The damping force curves are for different magnetic fields;

[0026] 1-Sealing packing, 2-Piston rod, 3-Sealing cover plate, 4-Housing shell, 41-Patch sensor, 5-Piston, 51-Fixed side plate, 52-Sliding side plate, 53-Fixed top plate, 54-Fixed bottom plate, 55-Telescopic segment, 551-Guide groove, 552-Guide rod, 56-Telescopic rod, 57-Control unit, 58-External control system, 6-Permanent magnet, 7-Magnetorheological fluid, 8-Excitation coil. Detailed Implementation

[0027] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Example 1

[0028] like Figure 1 As shown, the magnetorheological damper with a variable cross-section piston structure in this embodiment includes a housing 4, which is filled with magnetorheological fluid 7. A piston 5 is disposed inside the housing, and a piston rod 2 is connected to the piston 5. The upper end of the piston rod 2 has an opening design to facilitate connection of a drive device to drive the telescopic rod 2, and the lower end has a threaded design. The piston 5 has a corresponding threaded hole for connection to the lower end of the piston rod 2, which facilitates replacement and cleaning. A permanent magnet 6 is fitted over the housing. The permanent magnet can generate a magnetic field without an external energy supply and is responsible for providing a stable background magnetic field. To avoid the influence of the external magnetic field on the piston, both the piston 5 and the piston rod 2 are made of non-magnetic rigid material.

[0029] In this embodiment, a through hole is provided at one end of the outer shell 4, and a sealing cover plate 3 is provided at the corresponding location of the through hole. One end of the piston rod 2 passes through the sealing cover plate 3 and extends into the outer shell 4 through the through hole to connect with the piston 5. The piston rod 2 drives the piston 3 to move linearly within the outer shell 4. The piston includes a hollow shell and a telescopic rod disposed within the hollow shell. The hollow shell includes several telescopic segments that are slidably connected in sequence. The telescopic rod controls the relative sliding of the several telescopic segments, adjusting the cross-sectional dimensions of the piston, thereby adjusting the output damping force.

[0030] Combination Figure 2 As shown, piston 2 includes a hollow shell and a telescopic rod 56 disposed within the hollow shell. The hollow shell includes two fixed sidewalls 51, two sliding sidewalls 52, a fixed top plate 53, a fixed bottom plate 54, and several telescopic segments 55. The two sliding sidewalls 52 are slidably connected between the two fixed sidewalls 51, forming a telescopic quadrilateral frame of the hollow shell. The two ends of the telescopic rod 56 are fixedly connected to the two sliding sidewalls 52. The fixed top plate 53 and the fixed bottom plate 54 are fixedly connected between the two fixed sidewalls 51, and several telescopic segments 55 are symmetrically arranged on both sides of the fixed top plate 53. The telescopic segments 55 are arranged in a series. The two ends of the integral structure formed by these telescopic segments are connected to the corresponding sides of the fixed top plate 53 and the corresponding sliding sidewalls 52, respectively, forming a telescopic top plate of a hollow shell. Similarly, a series of telescopic segments 55 are symmetrically arranged on both sides of the fixed bottom plate 54 and are slidably connected in sequence. The two ends of the integral structure formed by these telescopic segments are connected to the corresponding sides of the fixed bottom plate 54 and the corresponding sliding sidewalls 52, respectively, forming a telescopic bottom plate of a hollow shell. The two ends of the telescopic segments are slidably connected to the two fixed sidewalls, and the piston rod 2 is connected to the fixed top plate. In this embodiment, the fixed sidewall 51 is provided with a groove arranged along the piston telescopic direction. The sliding sidewall 52 and the telescopic segments 55 are provided with sliders that cooperate with the grooves at both ends, thereby facilitating the sliding of the sliding sidewall 52 and the telescopic segments 55 relative to the fixed sidewall 51 and realizing the variable cross-section of the piston. In this embodiment, since the sliding sidewall 52 and the telescopic segment 55 are stacked axially on the piston, the fixed sidewall 51 is provided with a groove in the axial direction corresponding to the sliding sidewall 52 and each telescopic segment 55, thus limiting the telescopic range of each telescopic segment 55. Figure 3 As shown, the top of the telescopic segment 55 is provided with a guide groove 551 arranged along the piston telescopic direction, and the bottom is provided with a guide rod 552 that cooperates with the guide groove. Adjacent telescopic segments are stacked one on top of the other and are slidably connected by the cooperation of the guide rod and the guide groove to realize the relative sliding of adjacent telescopic segments 55. In this embodiment, both the sliding sidewall 52 and the telescopic segment 55 are rectangular or arc-shaped sheet structures that can be stacked on top of each other during sliding.

[0031] The telescopic rod 56 is an electric telescopic rod. The telescopic rod is equipped with a control unit 57, which is used to control the extension and retraction of the telescopic rod 56. The magnetorheological damper is equipped with an external control system 58, which is connected to the control unit and is used to send control commands to the control unit. The control unit controls the extension and retraction of the telescopic rod, pushes / pulls the telescopic segment and the sliding side wall to move, and realizes the cross-section adjustment of the piston.

[0032] Displacement sensors are also installed at both ends of the telescopic rod to monitor changes in the dimensions of the piston cross section.

[0033] The piston 5 is filled with sealing packing and has a sealed structure; or it is not filled with sealing packing and has an unsealed structure. Example 2

[0034] A further design feature of this embodiment is that both the interior of the piston 5 and the interior of the sealing cover plate 3 are filled with sealing filler. The sealing filler 1 is hydrophilic polyurethane, which, while achieving a seal, can deform to always fill the interior of the piston as the inner cavity contracts / expands during piston adjustment, achieving a relative seal. Even if a small amount of magnetorheological fluid enters the piston, it will not affect the performance, or the magnetorheological fluid can be replenished by a fluid replenishment method. The threaded hole of the piston 5 is provided on the fixed top plate 53 and communicates with the hollow structure inside the piston for adding sealing filler.

[0035] In this embodiment, the magnetorheological fluid 7 is an oil-based ferrorheological fluid, the carrier liquid is synthetic hydrocarbon, the magnetic powder volume percentage is 40%, the magnetic powder weight percentage is 86%, and the density is 3.65 g / cm³. 3 .

[0036] In this embodiment, the magnetorheological damper is assembled as follows: First, the piston rod 2 and piston 5 are screwed together to ensure a tight, integrated assembly, allowing for stable displacement during use. When assembling the sealing cover, an appropriate amount of sealing filler is evenly filled between the cover plates, ensuring the filler completely fills the internal cavity of the sealing cover to provide a good seal and prevent liquid leakage or air ingress. The sealing cover 3 is then firmly bonded to the upper cover of the housing 4, ensuring a stable, closed structure and preventing loosening due to vibration or external force. The assembled piston rod 2 is then passed through the pre-drilled openings in the sealing cover 3 and the upper cover of the housing 4, connecting these components into a single unit to ensure smooth and coordinated operation of all parts. Magnetorheological fluid is injected into the housing until the fluid level reaches 60% of the housing height. Then, the piston 5 is slowly immersed in the magnetorheological fluid within the housing until it is completely submerged. Magnetorheological fluid is then injected again into the upper part of the housing using a syringe until the remaining space is filled, ensuring no gaps remain. Securely bond the top cover plate of housing 4 to the rest of the housing, ensuring a tight seal and stability between the top cover plate and the housing. Allow the assembled device to stand for a period of time until it is firmly bonded, preventing loosening or leakage during use. Finally, place a ring-shaped permanent magnet at the lower edge of the housing to generate a constant magnetic field, providing a suitable magnetic field environment for the magnetorheological fluid.

[0037] Piston 5 is initially in its maximum extended state (maximum cross-section), with all segments in the extended position. At this point, the piston's effective force-bearing area is at its maximum, resulting in the strongest damping effect on the fluid. This is suitable for low-speed, high-damping conditions (such as buffer braking and low-speed stability control). Based on actual conditions, remote control is achieved via an external control system. Upon receiving the command, the telescopic rod gradually retracts some segments, reducing the piston's effective force-bearing area. Due to the segment movement, the dimensions of the fluid channel change, affecting fluid flow resistance and achieving dynamic damping adjustment. When all variable segments are fully retracted, the piston cross-section decreases, and the piston is in its minimum cross-section state, reducing the damping effect. This is suitable for high-speed, low-damping conditions (such as high-frequency vibration absorption and rapid response adjustment). Example 3

[0038] This embodiment is a further design based on Embodiment 1, specifically, a plurality of excitation coils 8 are provided outside the outer casing 4, such as... Figure 4As shown, the excitation coil 8 generates a magnetic field when energized, adjusting the viscosity of the magnetorheological fluid and thus regulating the output damping force. Several damping forces are divided into two groups, with the excitation coils of each group distributed along the axial direction of the damper. In this embodiment, four excitation coils are provided, labeled L1, L2, L3, and L4. Each coil can independently control the magnitude and direction of the current, thereby adjusting the local magnetic field strength. The permanent magnet, labeled M, provides a uniform and stable magnetic field, alternating with the excitation coils to form a composite magnetic field source. The permanent magnet provides a stable background magnetic field, ensuring that the magnetorheological fluid within the damper remains in an active state, preventing sedimentation that could affect the fluid's performance.

[0039] like Figure 5 As shown, the multi-stage magnetic field adjustment of the damper in this embodiment is specifically manifested as follows: When the system is connected to a 24V power supply and the main control switch F1 is open, the excitation coils L1, L2, L3, and L4 do not generate a magnetic field. The overall magnetic field of the device is emitted by the permanent magnet M. At this time, the magnetic field generated by the permanent magnet M can be used under low magnetic field conditions and can also maintain the magnetorheological fluid in an active state, preventing the magnetorheological fluid from settling and affecting the damper performance. When the damping force demand increases, control switches F1 and S2 are opened to energize the excitation coils L3 and L4 and generate an induced magnetic field, increasing the magnetic field strength around the damper and improving the output damping force. When the damping force demand further increases, control switch S2 is closed and control switch S1 is opened. Because the excitation coils L3 and L4 are farther from the magnetorheological fluid, while the excitation coils L1 and L2 are closer to the magnetorheological fluid, L1 and L2 can provide a stronger magnetic field, providing a greater damping force compared to opening L3 and L4. When the damping force requirement is greater, control switches F1, S1, and S2 are turned on simultaneously, so that excitation coils L1, L2, L3, and L4 are all in working condition. At this time, the damper can provide the maximum induced magnetic field and maximize the output damping force.

[0040] This embodiment of the multi-stage magnetic field adjustment device, composed of multiple excitation coils and permanent magnets, can achieve a gradient distribution of the magnetic field. It primarily allows for five levels of step adjustment. In the first stage, control switch F1 is closed, removing the permanent magnet. At this point, the entire device is in a magnetic field-free state, and the magnetorheological fluid remains unaffected by the magnetic field, maintaining its liquid properties. In the second stage, control switch F1 is closed, and permanent magnet M is added. At this point, only the permanent magnet outputs a magnetic field, and the magnetorheological fluid changes from a liquid to a near-solid state, exhibiting a certain damping effect. The uniform and stable magnetic field emitted by the permanent magnet also maintains the state of the magnetorheological fluid, keeping it in an active state for a long time and preventing sedimentation that could affect the damper's performance. In the third stage, control switches F1 and S2 are opened, controlling... When control switch S1 is closed, the two excitation coils L3 and L4, which are farther from the magnetorheological fluid, begin to work under the influence of the input current, providing a magnetic field and strengthening the magnetic field strength in the second-stage step, thus improving the damper performance. When control switches F1 and S1 are opened and control switch S2 is closed, the two excitation coils L1 and L2, which are closer to the magnetorheological fluid, begin to work under the influence of the input current, providing a magnetic field. Because they are closer to the magnetorheological fluid, more magnetic field lines can pass through it, resulting in a larger overall induced magnetic field output compared to the third-stage device. When control switches F1, S1, and S2 are all opened in the fifth stage, the permanent magnet M and excitation coils L1, L2, L3, and L4 begin to work simultaneously, generating the maximum magnetic field value. Through multi-stage magnetic field adjustment, the utilization rate of the magnetic field can be significantly improved, the adjustment accuracy of the damping force can be enhanced, and the adjustment range of the damping force can be further expanded.

[0041] In this embodiment, a patch sensing device is provided inside the housing 4, which consists of a patch sensor 41 and a pressure display module. The two are connected via Bluetooth. The patch sensor 41 is a thin-film pressure sensor, and the pressure display module is equipped with a high-definition display screen, which can display the measured pressure value in real time and intuitively, making it convenient for users to monitor.

[0042] Magnetorheological dampers with pistons of different cross-sectional dimensions were tested, and damping force, cross-sectional dimensions, and magnetic field data were collected. The output damping force of each structure under different magnetic field strengths was determined, and a mathematical relationship function between damping force, piston structure, and magnetic field was fitted. This relationship can be quickly queried and calculated via a processing terminal. When a specific damping force needs to be maintained, the required damping force can be input into the processing terminal. The terminal matches the required magnetic field strength according to the settings and sends commands to the electromagnet device, causing the system to dynamically adjust the magnetic field strength to maintain a constant output damping force. When a specific magnetic field strength is required, the desired constant magnetic field value can be input into the processing terminal. The terminal analyzes the data in the database and displays the output damping force of each piston cross-section under that magnetic field, allowing the user to select according to their needs.

[0043] Comparative Example

[0044] The comparative sample uses the distance between the two sliding sidewalls of the piston. D Five variable cross-section pistons with diameters of 8mm, 12mm, 16mm, 20mm, and 24mm, respectively, all with a piston length of 10mm, were obtained using the preparation process described in Example 1. The compression rate was 5mm / min, and the stretching rate was 5mm / min. The comparative effect is as follows:

[0045] 1. Variable cross-sectional dimensions D piston

[0046] Compression under an applied magnetic field can reflect the magnitude of the output damping force of a magnetorheological damper. This invention compares five piston magnetorheological dampers with varying cross-sectional dimensions under applied magnetic fields. After multiple experiments with a controlled magnetic field strength of 0.5T, the following results were obtained. Figure 6 The curves shown in the figure illustrate the relationship between output damping capacity and output damping capacity. As can be seen from the figure, the output damping capacity decreases with piston diameters of D=24 mm, D=20 mm, D=16 mm, D=12 mm, and D=8 mm, respectively. This means that the larger the piston cross-sectional size D, the greater the output damping force. The variable cross-section piston design proposed in this embodiment can effectively control the piston's cross-sectional changes and allow the system's output force to be adjusted within a certain range.

[0047] 2. Output damping force under multi-stage magnetic field adjustment

[0048] Different magnetic field strengths were set using a multi-stage magnetic field adjustment method: the first stage had a magnetic field strength of 0 T, the second stage 0.5 T, the third stage 0.6 T, the fourth stage 0.7 T, and the fifth stage 0.8 T. Taking a variable cross-section piston magnetorheological damper with ds=24, D=24, and h 10 and 12 mm respectively as an example, the output damping force of the sample under multi-stage magnetic field adjustment varied with the stage as follows: Figure 7 As shown, the output damping force increases with the increase of the number of multi-stage magnetic field adjustment levels. This demonstrates that the multi-stage magnetic field adjustment device provided by this invention can indeed increase the output damping force by adjusting the number of stages.

[0049] The technical solutions of the present invention are not limited to the above embodiments. All technical solutions obtained by equivalent substitution fall within the scope of protection claimed by the present invention.

Claims

1. A magnetorheological damper with a variable cross-section piston structure, characterized in that: It includes an outer shell filled with magnetorheological fluid, a piston disposed inside the outer shell, a piston rod connected to the piston, and a permanent magnet sleeved outside the outer shell; One end of the outer shell is provided with a through hole, and one end of the piston rod passes through the through hole and extends into the outer shell to connect with the piston. The piston rod drives the piston to move linearly inside the outer shell. The piston includes a hollow shell and a telescopic rod disposed inside the hollow shell. The hollow shell includes several telescopic segments that are slidably connected in sequence. The telescopic rod controls the relative sliding of the several telescopic segments to adjust the cross-sectional dimensions of the piston, thereby adjusting the output damping force. The outer casing is provided with a sealing cover plate corresponding to the through hole, and the sealing cover plate is provided with sealing filler. One end of the piston rod passes through the sealing cover plate and extends into the outer casing through the through hole to connect with the piston. The hollow shell also includes two fixed sidewalls, two sliding sidewalls, a fixed top plate and a fixed bottom plate. The two sliding sidewalls are slidably connected between the two fixed sidewalls to form a telescopic frame of the hollow shell. The telescopic rod is fixedly connected to the two sliding sidewalls at both ends. The fixed top plate and the fixed bottom plate are respectively fixedly connected between the two fixed side walls. The fixed top plate has several telescopic segments symmetrically arranged on both sides to form a telescopic top plate with a hollow shell. The fixed bottom plate has several telescopic segments symmetrically arranged on both sides to form a telescopic bottom plate with a hollow shell. The two ends of the telescopic segments are slidably connected to the two fixed side walls respectively. The piston rod is connected to the fixed top plate.

2. The magnetorheological damper with a variable cross-section piston structure according to claim 1, characterized in that: The fixed sidewall is provided with a sliding groove arranged along the piston extension direction, and the sliding sidewall and the two ends of the extension segment are provided with sliders that cooperate with the sliding groove.

3. The magnetorheological damper with a variable cross-section piston structure according to claim 2, characterized in that: The top of the telescopic segment is provided with a guide groove arranged along the piston telescopic direction, and the bottom is provided with a guide rod that cooperates with the guide groove. Adjacent telescopic segments are slidably connected through the cooperation of the guide rod and the guide groove.

4. The magnetorheological damper with a variable cross-section piston structure according to any one of claims 1 to 3, characterized in that: The piston is filled with sealing packing.

5. The magnetorheological damper with a variable cross-section piston structure according to claim 4, characterized in that: The sealing filler is hydrophilic polyurethane.

6. The magnetorheological damper with a variable cross-section piston structure according to claim 5, characterized in that: The telescopic rod is equipped with a displacement sensor at its end.

7. The magnetorheological damper with a variable cross-section piston structure according to claim 6, characterized in that: The outer shell is provided with several excitation coils. When the excitation coils are energized, they generate a magnetic field, which adjusts the viscosity of the magnetorheological fluid, thereby adjusting the output damping force.

8. The magnetorheological damper with a variable cross-section piston structure according to claim 7, characterized in that: The magnetorheological fluid is an oil-based ferrorheological fluid, the carrier liquid is synthetic hydrocarbon, the magnetic powder volume percentage is 40%, the magnetic powder weight percentage is 86%, and the density is 3.65 g / cm³. 3 .

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