Study On The Levitation Characteristics Of Magnetic Fluid And Its Application In Inertial Sensor

The stable levitation of a permanent magnet whose density is greater than that of magnetic fluid in magnetic fluid is one of the special properties of magnetic fluid,and the theory to study this phenomenon is called the buoyancy levitation of the second kind principle of magnetic fluid which has great research value and wide application field.The magnetic fluid inertial sensor is one of the important application fields of buoyancy levitation of the second kind characteristic of magnetic fluid,it has the outstanding advantages such as simple structure,high reliability and long service life,and the research value of magnetic fluid inertial sensor is important.This paper focuses on the application of the self-levitation phenomenon of permanent magnets in magnetic fluids in magnetic fluid inertial sensors,and the research is carried out in two steps.First,the buoyancy levitation of the second kind principle of magnetic fluids（the self-levitation of permanent magnets in magnetic fluids）is studied.Then,a magnetic fluid inertial sensor is designed and used to measure the tilt angle based on the research results of levitation principle.The main research work is as follows:（1）In the aspect of theoretical research of buoyant levitation of the second kind of magnetic fluid:The calculation formula for the levitation force of the permanent magnet immersed in the magnetic fluid under the magnetic field generated by itself is obtained based on the stress tensor of the magnetic fluid,and the formula focuses on the boundary interface between the magnetic fluid and the external environment.The relationship between the surface instability appearing over the boundary interface of magnetic fluid and air and the magnetic fluid levitation force experienced by the permanent magnet is studied,and the interaction model between the surface instability of magnetic fluid and the levitation force received by the permanent magnet is established.The calculation formula of the levitation force received by the permanent magnet in magnetic fluid is analyzed,and a simplified calculation formula of the levitation force is obtained.The self-levitation phenomenon of a combination of permanent magnets,nonmagnetic substances,and soft ferromagnetic substances in magnetic fluids is studied,and a method for analyzing the influence of nonmagnetic substances and soft ferromagnetic substances on the levitation force is obtained.（2）In the aspect of theoretical and experimental research of self-levitation of permanent magnet in magnetic fluids:Two experimental schemes for studying the levitation force of permanent magnets in magnetic fluid are proposed,the effects of the"self-sealing"effect on the experiments are demonstrated,and the relevant parameters of the experiments are determined.The relationship between the levitation force received by the magnet,the mass of the magnetic fluid and the levitation height of the magnet is studied experimentally,the stage change model of magnetic fluid levitation force is proposed and verified,the interaction model between the levitation force received by the magnet and the surface instability of the magnetic fluid is verified,and the influence of air in the magnetic fluid on the levitation force is studied.The model studying the experimental error caused by nonmagnetic rods is established,and the correctness of the error model is verified by nonmagnetic rods with different diameters.Two simple physical models are proposed to simulate the levitation force received by the magnet immersed in magnetic fluid,and the simulation results of levitation forces are consistent with that of experimental measurement.（3）In the aspect of theoretical and experimental research on the self-levitation phenomenon of a combination of permanent magnets,nonmagnetic substances and soft ferromagnetic substances in magnetic fluids:The levitation force of the ring permanent magnet with axial magnetization and the inner core in magnetic fluids is studied,and the influence of the quantity and relative position of the soft magnetic inner core on the levitation force is demonstrated.The levitation force of a cylindrical permanent magnet and shells in magnetic fluid is studied,the influence of the position of the soft magnetic shell and the magnetization direction of the permanent magnet on the levitation force is demonstrated.The levitation force of the ring permanent magnet with axial magnetization,inner core,and shell in magnetic liquid is studied,and the influence of the inner core and shell on the levitation force is demonstrated.Using the soft magnetic shell and the soft magnetic inner core can reduce the levitation force of the combination.Taking the cylindrical permanent magnet with axial magnetization and shell as an example,the influence of the container radius on the magnetic fluid levitation force is studied and demonstrated.（4）In the aspect of model design of magnetic fluid inertial sensors:The working principle of the magnetic fluid inertial sensor is explained,and the theoretical analysis shows that both the magnetic effect and eddy current effect of the inertia mass can affect the output characteristics of the inertial sensor.The calculation formula for the inductance of the coil is deduced,and the influence of inertia mass and magnetic fluid on the inductance of the coil is studied.The influence of the inertia mass with different structures on the inductance of the coil is studied,the design criterion for the inertia mass is determined,and the results show that the soft magnetic material in the inertia mass should be far away from the pole of the permanent magnet.The influence of the axial length of the inertia mass and the outer diameter of the soft magnetic side shell on the inductance of the coil is studied,and the results show that increasing the axial length of the permanent magnet and the outer diameter of the soft magnetic side shell can increase the influence of the inertia mass on the inductance of the coil.The influence of the magnetic fluid on the inductance of the coil depends on the inertia mass,and the magnetic fluid can reduce the change rate of the inductance by about 2%.（5）In the experimental study of magnetic fluid inertial sensors:The magnetic fluid levitation forces of different inertial masses are studied,the combination of ring permanent magnet,inner core and outer shell is selected as the inertial mass to measure the tilt angle.The influence of the axial length of the inertia mass and the outer diameter of the soft magnetic side shell on the levitation force is studied,the results show that increasing the length of the inertia mass can slightly increase the levitation force,and the influence of the outer diameter of the soft magnetic side shell on the levitation force can be ignored;The influence of the frequency of signal source and the series connection way of coil on the sensor output voltage is studied,and the frequency of signal source and the series connection way of coil are determined.The influence of the size of the inertia mass and eddy current effect on the output voltage of the sensor is studied,the results show that increasing the length and diameter of inertia mass can increase the output voltage of the sensor,and the effect of eddy current effect of mass on the output voltage is far less than that of magnetic effect.The performance of the magnetic fluid inertial sensor for static acceleration（tilt angle）measurement is studied,the linearity between the output voltage and the static acceleration of the sensor is good,when the acceleration range is 0～8.66m/s²,the linearity is 5.16%,the hysteresis and repeatability error of the sensor is less than 1%,and the sensitivity is 0.03v/ms^-2 which increases by about 100 times.