principal the acoustic wave travels through the ferromagnetic sensing material 80 and the ferrite core 88 of detection coil 84 which in turn creates an electrical current in the detection coil 84 when force or stress is applied to the ferromagnetic sensing material 80 the acoustic wave is affected by the change in strain in the material 80 as is the electrical current in the detection coil 84 the current or voltage is measured to determine the change the frequency and amplitude of the signals and the number of turns in the coils 82 84 will depend upon the particular application as well the materials of the cores 86 88 and the thickness texture and shape of the ferromagnetic sensing material 80 one of ordinary skilled in the art would be able to determine suitable parameters for a given design 0031 fig3 illustrates the rms voltage output from the force sensor 42 in fig2 for a given force preferably the ferromagnetic sensing material 80 fig2 is mechanically preloaded so that the output verses force input is in the linear region the threshold shown in fig3 could be for activation of the horn or other vehicle functions for the user activated switching system 22 of fig1 it should also be noted that the threshold can be easily changed by simply changing a software in the controller 26 thus the sensor 42 can used for various applications and in different vehicle and can be easily configured to activate at the proper threshold 0032 fig4 a f illustrate possible configurations of the force sensor 42 a on a steering wheel 32 a.