Development of finite element design simulation tool for proximity sensor coils with ferrite cores

In the development of inductive proximity sensors, a great deal of time and effort is spent in the design of the sensor coil, which is typically used with a ferrite core for increased Q (quality factor). Computer simulation of the sensor coil could shorten this design process by eliminating the need for extensive building and testing of prototypes. Analytical solutions require extensive information about the material properties of the ferrite core, which is not readily available. While there are software packages commercially available that use the finite element method to simulate magnetic fields, these packages require extensive user training, and they involve lengthy run times. In this work, a linear minimal node finite element model of a proximity sensor coil is developed, serving as a rapid design simulation tool that requires little operator training. Using this minimal node model, a rapidly converging Pascal program is created to calculate the Q of a coil vs. frequency and vs. temperature. Measured and simulated data are presented for coils having a 22mm x 6.8mm core. Because this model is linear and uses a minimal number of nodes, errors do exist between measured and simulated data. The simulated Q curves are still reasonable representations of the measured Q curves however, indicating that the model can be used as a rapid design tool to reduce the flowtime of new coil designs.