Experimental Study On Giant Magnetoresistance Effect Of Polyurethane Based Magnetorheological Gels

Giant magnetoresistance effect is a physical phenomenon that changes the resistance value of the material in the external magnetic field.It is widely used in hard disk technology,magnetic field sensing and voltage isolation.In recent years,the giant magnetoresistance effect of magnetorheological materials has attracted the interest of many researchers.The external magnetic field will change the distance between the conductive particles in the magnetorheological material,thus affecting the conductivity of the magnetorheological material.Compared with magnetorheological fluids and magnetorheological elastomers,the giant magnetoresistance effect of magnetorheological gels has to be further studied because of the late discovery of materials.On the basis of previous research work,a preparation method and evaluation system of conductive magneticrheological gels were proposed.By setting up the resistance testing system,the principle of giant magnetoresistance of magnetorheological gels is explored and the influence factors of giant magnetoresistance effect are discussed.The main contents of the work are as follows:(1)The research status and physical mechanism of giant magnetoresistance material are described.The current status of giant magnetoresistance effect of magnetorheological materials is introduced.Then,from the classification and characteristics of magnetorheological materials,the reasons for the selection of magnetorheological gel as the carrier are discussed.(2)A phenomenological model for giant magnetoresistance effect of magnetorheological gel is established.The material selection,synthesis and preparation technology of magnetorheological gel were discussed.The basic properties and Micromorphology were characterized by IR and SEM.Finally,the magnetorheological magnetoresistance testing system was built.(3)The characteristic parameters of giant magnetoresistance effect of magnetorheological materials are presented,and the effects of matrix viscosity and carbonyl iron powders' mass fraction on giant magnetoresistance are discussed.When the mass ratio of castor oil and two phenyl methane diisocyanate is 20:1 and the mass fraction of carbonyl iron powder is 60%,the giant magnetoresistance effect of magnetorheological gel is the best: the sensitivity is 4.7%/mT and the giant magnetoresistance effect is 4111.29%.(4)In order to improve the magnetoresistance properties of magnetorheological gel,the influence of traditional conductive filler carbon black and nano conductive carbon nanotubes on giant magnetoresistance effect was investigated respectively.The experimental results show that the performance enhancement of carbon black is mainly reflected in the value and sensitivity of giant magnetoresistance.When the filling amount is 6wt%,the giant magnetoresistance effect is 50992.82% and the sensitivity is 50.99%/mT.The advantage of carbon nanotubes is that the low doping amount can improve the conductivity of the magnetorheological gel,and the giant magnetoresistance effect and sensitivity have nearly doubled.