perpendicular magnetic film 297 on a central moveable member 295 to which is applied an input signal 242 when the frequency of the input signal is around the resonant frequency of device 295 vibration of the hard magnetic film 206 occurs next to the magnetic film 297 on fixed supports 291 and 292 are mounted a pair of cip gmr sensors 293 on either side of the film 297 other sensor types could alternatively be used the output voltage across the electrodes 294 of each sensor will vary proportionally to the perpendicular or vertical displacement of the hard magnetic film 297 to increase the signal to noise ratio of the output of the device 290 a differential signal detection method is implemented noise results from sources such as fluctuation to the voltage supply and thermal noise because the two sensors 293 x and 293 y are arranged on opposite sides of the hard magnetic film 297 they will detect opposite directions of the magnetic field m the directions of magnetisation of the pinned layers in each sensor are the same this results in a positive output voltage for a positive displacement of the magnetic film 297 for one sensor 293 x and a negative output voltage for the same displacement using the other sensor 293 y and vice versa by applying these outputs to a differential detector 299 the output is the combined output of the two sensors 293 x and 293 y the noise from the device 290 is also reduced due to cancelling of noise common to both sensors.