Patent ID: 6972560
Filing Date: 2005-12-06
Classification: G01B,G01L,G01R

Abstract:
1. A method for detecting a change in permeability of a magnetostrictive object due to a change in strain in the object along a strain direction comprising the steps of: a) obtaining at least one first coil having a coil axis and a first number of total turns; b) obtaining at least one second coil having a second number of total turns; c) disposing the at-least-one first and second coils relative to the object such that the at-least-one first and second coils are substantially coaxially aligned, such that the object is spaced apart from the coil axis, such that the inductance of each of the at-least-one first and second coils simultaneously changes due to the change in strain in the object, such that magnetic flux lines induced by an electric current in the at-least-one first coil pass through at least one portion of the object in a direction substantially parallel to the strain direction, such that magnetic flux lines induced by an electric current in the at-least-one second coil pass through at least one portion of the object in a direction substantially parallel to the strain direction, and such that any electromagnetic interference sensed by the at-least-one first coil is sensed oppositely by the at-least-one second coil; d) measuring the total inductance of the disposed at-least-one first and second coils over time; and e) detecting a change in permeability of the object from a change in the measured total inductance over time.