3D simulation of a magneto-resistice sensor.

Dear Matlab users.

I am trying to perform a simulation where I used "AMR" magneto-resistive sensor for gear tooth sensing where extract the sensor output in function of time. as in the following image:

I do not have any clue from where to begin, I have the stl file of the gear tooth and the dimension and data sheet of the chip only so I would highly apreciate any of your feedback