High Contribution Node Selection for Cognitive Radio Networks

In the simplest embodiment of the invention, the apparatus holds the edge of the magnetized film to be measured close to, and above, a linearly biased magnetoresistive (MR) element. Magnetic poles appearing at the magnetic discontinuity at the edge of the film generate a magnetic field which is incident on the MR element, and which results in a measurable change in the element's resistivity. In a preferred embodiment, a pair of MR elements are placed so that they are both linearly biased by a magnet; only one of the MR elements being in close proximity to, and influenced by the magnetic field emanating from the edge of the magnetized film. The second MR element, selected for matched characteristics with the first MR element, is located out of the field of the magnetized film, but still subject to the same temperature environment and field noise as the first MR element. The two MR elements are configured with associated resistors as arms of a Wheatstone bridge so that the common mode fields and thermal drift signals experienced by both MR elements are canceled to the first order, and the output of the bridge is proportional to the change in resistance in the first MR element due only to the field of the magnetized film.