Microssensores magnéticos tipo fluxgate planar utilizando ligas de NiFe eletrodepositadas / Planar microfluxgates using NiFe eletrodeposited cores.




This work present the development of fluxgate magnetic field sensors based on planar technology. The material for the core of the device is based on early works that determined the best NiFe electrodeposition parameters for this application. Functional devices were created proving the usability of the alloy. Also 4 new layouts were proposed in order to build more sensitivity, cheaper, less power consumption and better resolution sensors. Firstly, only macro scale devices were created using printed circuit board as substrate and a laser printer toner based lithography. This process is very simple and allows a fast way from sketch to macro scale prototypes with no need of special equipments. Unlike the conventional macrofluxgates, these devices can be directly scalonable. This prototypes characterization data will be used to produce optimized microsensors. Some finite element simulations computed the magnetic field produced by a square planar coil to predict the intensity that the core is immersed on. At small distances from the coils plane, smaller than the separation between wires, where the core stands, the field is very influenced by the periodicity of the coil giving rise to periodic profiles. The effects of this high inhomogeneity is not well known. Using the measured hysteresis curve from the NiFe films, the simulated response of a fluxgate sensor was obtained. The simulated sensitivity and linear range as a function of the excitation field amplitude showed some unexpected results. While the sensitivity has a maximum with excitation fields just above the core saturation values decreasing later on, the linear range shows a high peak in low field region. The first were confirmed by the experimental data that also showed strong evidences of the existence of the second one. The 4 new layouts are basically 2 with a double version each. That is, stacking two identical coil layers in order to multiply by 1.41 the excitation field using the same power, double the number of pick-up coils and minimize the undesired perpendicular magnetic field produce by planar coils. The new layout prototypes had better sensitivity, up to eight times higher, related to the reference one taken from literature. Also the noise measured was smaller in the double layers version. The best one presented more then three times less noise than the reference for a power of Wrms. But all of them presented smaller linear range. All this sensors characteristics where also studied as a function of the applied power, that is directly related to the excitation field.


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