Theoretical And Experimental Study On Horizontal Magnetic Fluid Micro-pressure Sensor

Magnetic fluid is a new functional nanomaterial which exhibits simultaneously liquidity of liquid and superparamagnetism of solid material.The unique properties of magnetic fluid include surface instability under magnetic field gradient and second-order buoyancy,which makes it have a broad application prospect in sensors field.The manufacture standard and technology of micro-pressure sensor with high precision in China is far away from abroad(10-3Pa),which is urgent to be solved by adopting new materials,procedures and structures to sensors.A novel inductance magnetic fluid micro-pressure sensor based on the principle of magnetic fluid second-order buoyancy(including kerosene based,engine oil based,water based and diester based magnetic fluid)is proposed in this paper.In theory aspect,the formula of restoring force between the permanent magnets on the compound magnetic core and the restoring magnets is derived,including the sinking distance formula of the compound magnetic core.The relationship between the anti-pressure capability of the magnetic pressure sensor and the unilateral gap of the compound magnetic core away from the transparent glass pipe is also proposed.The flmction relationship between the displacement of the compound magnetic core and the change of the inductance coils is deduced too.What's more,the in-out characteristics of static measurement of the magnetic fluid micro-pressure sensor is provided,together with the second order system transfer function of dynamic measurement;In architecture design aspect,different design models of sensing element and transition element are put forward,and the final parameters of all elements are determined according to theoretical analysis,simulation research and experimental measurement;In simulation aspect,the simulation restoring force is given along with the sinking distance of the compound magnetic core and the anti-pressure capability of magnetic fluid ring according to ANSYS finite element analysis.In particular,the optimal design of the dimension parameters of the magnetic fluid micro-pressure sensor is carried out by using MATLAB,and the dynamic output characteristics of the second order system under step pressure is discussed too;In experiment aspect,the linear fitting formula of the restoring force between the permanent magnets is determined together with the final measuring range of the sensor.In addition,the static in-out characteristics of the sensor are deeply researched,such as the linearity,sensitivity,accuracy,resolution,hysteresis,repeatability,stability and so on.Some preliminary considerations on the influence factors of dynamic characteristics of the sensor in terms of magnetic fluid viscosity are also included.According to the comparison between the experimental results and the simulation results,the reason of the difference is analyzed.The novel conclusions are shown as follows:(1)Novel horizontal magnetic fluid micro-pressure sensor is designed,whose measuring range is ± 1000Pa,accuracy is ?ma= 10Pa,linearity is ef = 2.5%,sensitivity is S=0.1mV/Pa,resolution is 0.6%F.S.,hysteresis is ?H=±1.25%;(2)The measuring range of the magnetic fluid pressure sensor is determined by two factors:one is the anti-pressure capability of the magnetic fluid ring;another one is allowable compound magnetic core displacement decided by the linearity interval of the restoring force between the permanent magnets.The final measuring range is determined by the smaller one of the two factors;(3)The empirical formula of sinking distance of the compound magnetic core in the transparent glass pipe is proposed according to the second-order buoyancy principle and simulation results.The formula indicates that the sinking distance is concerned with the weight of the compound magnetic core and the saturation magnetization,which provides theoretical foundation for the anti-pressure capability research of the magnetic fluid seal ring in the magnetic fluid micro-pressure sensor;(4)The influence of magnetic fluid viscosity on the static characteristics of the magnetic fluid micro-pressure sensor could be ignored,but there is significant influence on dynamic response.The dynamic parameters,such as rise time,overshoot,oscillation times,settling time and so on,are all influenced by magnetic fluid viscosity;(5)The non-linear programming model according to the magnetic fluid micro-pressure sensor is proposed along with the optimal dimension parameters of the sensor;(6)The compound magnetic core could be treated as a mass block,the restoring force between permanent magnets could be treated as spring term,and the Newton internal friction between magnetic fluid and transparent glass pipe could be treated as damping term.Then the magnetic fluid pressure sensor could be treated as a second-order dynamic system,based on which the transfer function of the sensor is derived.The influence of the parameters to the dynamic response of the sensor is analyzed,which provided theoretical foundation for the dynamic parameter design of magnetic fluid micro-pressure sensor.