| The tunnel magnetoresistive(TMR)sensor has the advantages of high sensitivity,low power consumption,and wide linear range.It has been widely used in aerospace,automotive electronics,non-destructive testing,biomedical fields and other industrial fields.However,at present,the measurement level of TMR characteristics is still relatively lower and thus cannot meet the practical requirements of diverse applications.This brings about an unavoidable restriction for further application of TMR sensors.In order to make full advantage of the TMR sensor's superiority,it is necessary to conduct comprehensive measurement and analysis of the TMR sensor's performances according to different and specific applications.Usually,the TMR sensor's performances are measured in a standard magnetic field generator(SMFG).A conducting straight wire produces magnetic field with low uniformity,while a solenoid has limited inner space for measurement;the magnetic field calculation of a saddle-shaped coil is rather complicated,while the circular Helmholtz coil requires strict manufacturing process and precise positioning.All the above conventional SMFG apparatus are incapable of tackling the measurement of TMR sensors.In this thesis,a standard magnetic field generator based on the Merritt coil structure is proposed to measure the characteristics of the TMR sensor.The main research contents are as follows:(1)The development of sensing technology and the application of TMR sensors were briefly summarized.The existing testing methods of TMR sensor's characteristics and their downsides were analyzed,and afterwards,the idea of measuring TMR sensor's characteristics based on the standard magnetic field generators was put forward.(2)The working principle of the TMR sensor and the relevant physical meaning of each its parameters were elaborated.After that,there types of TMR sensors-TMR2103,TMR2505 and TMR2701 manufactured by Jiangsu Multidimensional Technology Co.,Ltd.were selected as the test objects and their working specifications were preliminarily analyzed.(3)The uniformity of magnetic field generated by common magnetic field generating coils were compared and analyzed using finite element analysis,and the Merritt coil was selected as the core of our SMFG prototype.Then,the analytical expression of the magnetic field in the coil axis was derived,and consequently the coil design was accomplished using1% deviation of the magnetic flux density at the coil centre as the threshold.After that,the position regulator and coil guide of the measurement apparatus were designed and manufactured,to guarantee the position accuracy of the TMR sensor under test.(4)The experiment platform for measuring TMR sensor performance was established.The characteristics of input-output,magnetic hysteresis,sensitivity axis,repeatability and stability of the selected three types of TMR sensors were studied.Results show that: the sensor output is in direct proportion to the magnetic flux density,and the sensitivity is inversely proportional to the supply voltage;the effect of magnetic hysteresis is relatively low in linear range;the sensor output reaches maximum when the angle between the sensitivity axis and magnetic field direction is zero;all three sensors show good repeatability and stability.Among the three sensors,TMR2701 has the highest sensitivity but the error of magnetic hysteresis is up to 1.52%,while TMR2505 exhibits the best repeatability.(5)Multiple repeat measurements were performed on the three TMR sensors under the same measurement conditions and the error analysis of test results indicated that the standard deviation was within 1.84 m V.On this basis,the uncertainty source of the test results was analyzed and the uncertainty of the testing system was calculated.The results showed that the repeatability measurement was the main source of the uncertainty.Therefore,it is proved that the scheme of using Merritt coil as the magnetic field generator to measure the characteristics of TMR sensor is feasible and effective. |
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