Apparatus and methods for obtaining increased sensitivity, selectivity and dynamic range in property measurement using magnetometers

• US 5,629,621 A
• Filed: 06/02/1995
• Issued: 05/13/1997
• Est. Priority Date: 12/06/1991
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Goldfine, Neil J., Melcher, deceased, James R.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US08/460,664
• Time in Patent Office: 711 Days
• Field of Search: 324/207.17, 324/207.18, 324/207.19, 324/207.26, 324/202, 324/225, 324/227, 324/229-233, 324/239-243, 364/571.07, 364/578
• US Class Current: 324/239
• CPC Class Codes: G01B 7/105 for measuring thickness of coating
• CPC Class Codes: G01N 27/72 by investigating magnetic variables
• CPC Class Codes: G01N 27/9046 by analysing electrical signals
• CPC Class Codes: G01R 33/1223 Measuring permeability, i.e. permeameters G01R33/14 takes precedence

Abstract

Apparatus and methods are disclosed which provide increased sensitivity, selectivity and dynamic range for non-contact measurement of actual physical and/or kinematic properties of conducting and magnetic materials. The apparatus and methods are based upon various methods for increasing sensitivity, selectivity and dynamic range through proper construction of a magnetometer sensor and for proper selection of operating point parameters for the application.

A measurement apparatus for measuring one or more MUT properties includes an electromagnetic winding structure which, when driven by an electric signal, imposes a magnetic field in the MUT and senses an electromagnetic response. An analyzer is provided for applying the electric signal to the winding structure. A property estimator is coupled to the winding structure and translates sensed electromagnetic responses into estimates of one or more preselected properties of the material.

Claims

1. A method for generating a property estimation grid for use with a magnetometer for measuring preselected properties of a material comprising the steps of:

a) defining physical and geometric properties for a material including preselected properties of the material;

b) defining operating point parameters and a winding geometry and winding configuration for the magnetometer;

c) inputting the material properties, the operating point parameters and the magnetometer winding geometry and configuration into a model to compute an input/output terminal relation value;

d) recording the terminal relation value as a property estimation grid point;

e) adjusting the preselected properties of the material and repeating steps c) and d).

2. A method as claimed in claim 1 wherein the terminal relation values are transinductance magnitude and phase values.

3. A method as claimed in claim 1 further comprising the step of plotting the terminal relation values on a single or multi-dimensional grid.

5. A method as claimed in claim 1 wherein step (b) comprises:

a) defining initial magnetometer operating point parameters, winding geometry and winding configuration;

b) inputting the material properties and the magnetometer operating point parameters, winding geometry and configuration into a model to compute an input/output terminal relation value;

c) adjusting the preselected properties of the material to compute another terminal relation value;

d) computing the Jacobian elements which are measures of the variation in said terminal relation values due to the variation in the preselected material properties;

e) computing a singular value decomposition for the Jacobian elements to obtain singular values, singular vectors and condition number of the Jacobian elements;

f) evaluating sensitivity, selectivity and dynamic range of the magnetometer winding structure and operating point using the singular values, singular vectors and condition numbers for material property estimate requirements; and

g) adjusting the magnetometer operating point parameters and winding geometry and configuration and repeating steps b-f until the material property estimate requirements are achieved.

6. A method as claimed in claim 5, wherein the singular values, singular vectors and condition number are stored with grid points to support a grid interpolation algorithm to obtain property estimates.

4. A method of selection of a magnetometer winding structure and operating point for measuring one or more preselected properties of a material comprising the steps of:

a) defining physical and geometric properties for the material including preselected properties of the material;

b) defining magnetometer operating point parameters, winding geometry and winding configuration;

c) inputting the material properties and the magnetometer operating point parameters, winding geometry and configuration into a model to compute an input/output terminal relation value;

d) adjusting the preselected properties of the material to compute another terminal relation value;

e) computing the Jacobian elements which are measures of the variation in said terminal relation values due to the variation in the preselected material properties;

f) computing a singular value decomposition for the Jacobian elements to obtain singular values, singular vectors and condition number of the Jacobian elements;

g) evaluating sensitivity, selectivity and dynamic range of the magnetometer winding structure and operating point using the singular values, singular vectors and condition numbers for material property estimate requirements;

h) repeating steps c-g with adjusted magnetometer operating point parameters and winding geometry and configuration until the material property estimate requirements are achieved.