Spectrographic material analysis using multi-frequency inductive sensing

Patent metadata

Field	Value
Publication number	US-9733231-B2
Application number	US-201514614234-A
Country	US
Kind code	B2
Filing date	Feb 4, 2015
Priority date	Feb 4, 2015
Publication date	Aug 15, 2017
Grant date	Aug 15, 2017

Abstract

A multi-frequency inductive sensing system can be used for spectrographic material analysis of a conductive target material (such as tissue) based on electrical impedance spectroscopy. An inductive sensor can be driven with an excitation current at multiple sensor excitation frequencies (ω) to project a time-varying magnetic field into a sensing area on the surface of the target material, inducing eddy currents within the target material. The inductive sensor can be characterized by a sensor impedance Z(ω) as a function of the sensor excitation frequency (ω), and the resulting induced eddy currents. Multiple sensor impedance Zs(ω) measurements, at the multiple sensor excitation frequencies (ω), can be determined, which represent electromagnetic properties of the target material (such as permittivity ε, permeability μ, and resistivity ρ), based on the induced eddy currents. The multiple sensor excitation frequencies (ω), and corresponding multiple sensor impedance Zs(ω) measurements, can be selected for particular target penetration depths.

First claim

The invention claimed is:

1. An inductive sensing system, suitable for spectrographic material analysis based on electrical impedance spectroscopy, comprising:
an inductive sensing circuit; and
a conductive target material under test;
the inductive sensing circuit configured to project a time-varying magnetic field into a sensing area on the surface of the target material, inducing eddy currents within the target material, and including
a sensor including an inductor coil, and characterized by a sensor impedance Z(ω) that is a function of a sensor excitation frequency (ω), and the resulting eddy currents induced within the target material; and
sensor electronics configured
to drive the sensor inductor coil with an excitation current at a sensor excitation frequency (ω), generating a corresponding time-varying magnetic field projected to the target material; and
to determine, for multiple sensor excitation frequencies (ω), corresponding multiple sensor impedance Zs(ω) measurements that represent electromagnetic properties of the target material based on the induced eddy currents;
wherein each sensor impedance measurement Zs(ω) is a function of the induced eddy current and associated target penetration depth:

δ
=

(

1
ω

)

⁢

{

(

με
2

)

⁡

[

(

1
+

(

1
ρωε

)

2

)

1
⁢

/

⁢
2

-
1

]

}

-
1

⁢

/

⁢
2

which is a function of sensor excitation frequency (ω), and electromagnetic properties of the target material: electrical permittivity ε, magnetic permeability μ, and electrical resistivity ρ (the inverse of the conductivity σ).

2. The system of claim 1 , wherein the electromagnetic properties are at least one of: permittivity ε, permeability and resistivity ρ (or its inverse conductivity σ).

3. The system of claim 1 , wherein the multiple sensor excitation frequencies (ω), and corresponding multiple sensor impedance Zs(ω) measurements, are selected for a target penetration depth, which represent electromagnetic properties of the target material at the target penetration depth.

4. The system of claim 1 , wherein the inductive sensing circuit is a resonant inductive sensing circuit, including:
a sensor resonator including a coil inductor, and characterized by a sensor impedance Rp=L/(C*Rs); and
an inductance-to-digital conversion (IDC) unit configured
to drive the sensor resonator with a sensor excitation current at a sensor excitation frequency (ω); and
to generate a negative impedance that counterbalances sensor resonator impedance Rp, such that the generated negative impedance is a function of the eddy currents induced in the target material (which are reflected in sensor resonator impedance Rp); and
to convert the generated negative impedance into sensor response data corresponding to the sensor resonator impedance Zs(ω) measurements.

5. The system of claim 1 , wherein the target material is tissue.

6. A resonant inductive sensing system, suitable for spectrographic material analysis based on electrical impedance spectroscopy, comprising:
a resonant inductive sensing circuit; and
a conductive target material under test;
the resonant inductive sensing circuit configured to project a time-varying magnetic field into a sensing area on the surface of the target material, inducing eddy currents within the target material, and including
a sensor resonator including a coil inductor, and characterized by a sensor impedance Rp=L/(C*Rs) that is a function of a sensor excitation frequency (ω), and the resulting eddy currents induced within the target material; and
an inductance-to-digital conversion (IDC) unit configured
to drive the sensor resonator with an excitation current at the sensor excitation frequency (ω), generating the corresponding time-varying magnetic field projected to the target material;
to generate, for multiple sensor excitation frequencies (ω), a negative impedance that counterbalances sensor resonator impedance Rp, such that the generated negative impedance is a function of the eddy currents induced in the target material (which are reflected in sensor resonator impedance Rp); and
to convert, for the multiple sensor excitation frequencies (ω), the corresponding generated negative impedance into multiple sensor impedance Zs(ω) measurements that represent electromagnetic properties of the target material based on the induced eddy currents;
wherein each sensor impedance measurement Zs(ω) is a function of the induced eddy current and associated target penetration depth:

δ
=

(

1
ω

)

⁢

{

(

με
2

)

⁡

[

(

1
+

(

1
ρωε

Assignees

• Texas Instruments Inc

Inventors

• Reitsma George Pieter

Classifications

• A61B5/0531

  Measuring skin impedance · CPC title

• A61B5/053

  Measuring electrical impedance or conductance of a portion of the body · CPC title

• G01N33/483 Primary

  Physical analysis of biological material · CPC title