Lorentz force based magnetic field sensor with optical readout

A miniaturized sensor capable for measuring high magnetic flux densities is presented. The magnetic flux density is converted into a movement of a micro machined U-shaped cantilever, which bears a thin film lead. The cantilever movement is accomplished by the Lorentz force acting on the electrical current. The cantilever poses as a deflecting mirror in an optical readout system. The ratio of the intensity of the light reflected by the front side of the cantilever to the intensity of the incident light is analyzed. The optical conversion principle was proven experimentally. It is well described by an optical near field model. To overcome measurement problems caused by the deformation due to mechanically prestressed cantilevers, an ac excitation was used for sensor characterization. A measurement range of the current-flux density product of 2.2 mA T was achieved by evaluating the peak light intensity. Beyond this limit more sophisticated signal analysis has to be applied. Depending on the rest position, a magnetic flux density of about 10 mT can be resolved with a current of 10 mA. The target of an upper limit of 50 T can be achieved by reducing the electrical current. (C) 2003 Elsevier B.V. All rights reserved.