1

Design of a Remote Electrical Conductivity

Measurement Sensor Based on Pulsed

Eddy Current Technology

Ehsan Shameli, Ph.D, P.Eng.

Senior Associate February 2012

2

Who We Are

Exponent is a multi-disciplinary consulting firm

dedicated to solving important science, engineering and

regulatory issues

for clients

3

Masters

30%

Doctorates

54%

Bachelors

16%

Consulting Staff

4

Harrogate

Derby

Düsseldorf Hangzhou

Boston: Maynard

Natick

Winchester Chicago: Lisle

Wood Dale Denver

Detroit

Houston

Miami

New York

Philadelphia

Phoenix

Seattle

Southern California: Irvine

Los Angeles

Washington, DC: District of Columbia

Maryland

Virginia

San Francisco Bay Area: Menlo Park

Oakland

Basel

Exponent Offices

5

6

Emerging Opportunities

Defense

Technology

Development

Design Support

Energy

Health

Transportation

Safety

7

Overview

Introduction of Eddy Current Testing

Pulsed Eddy Currents

Principal of Operation

Design Principles

Experimental Results

Conclusion

8

Current State of the Art

Continuous Eddy Current Testing Works based on principles of electromagnetic induction

Uses a continuous, sinusoidal excitation signal

Applications Defect detection

Monitoring heat and surface treatment

Alloy characterization and material sorting

Disadvantages Narrow band signal

High sensitivity to lift-off distance

Low penetration depth into the test targets

Thermal drift

High power consumption

9

Pulsed Eddy Current Testing

10

Pulsed Eddy Current

Wide band signals with more information

Deeper penetration into the test sample

Insensitive to lift-off distance

Energy efficiency

Less thermal drift

11

Applications of PE Technique

Conductivity measurement of objects

Thick layer of coating

Measurement targets with elevated temperatures

Molten metals

Measurements through conductive layers

12

Theoretical Principle

L

Din

Dout

dl

I

R

P(R)

Biot-Savart Law

13

Define coil aspect ratios

Calculate the current as a function of power supplied to the coil

Substitute the calculated current in the field equation

Collect all the geometry related terms into a geometry factor

Select optimal aspect ratios that maximize

Using the selected aspect ratios, select the inner diameter

Design Procedure – Driver Coil

Geometry

Factor

14

Driver Coil Design – Selection of Aspect Ratios

15

Considerations for Selection of and

Larger and smaller increase the field amplitude

Increasing the will grow the sensing footprint of the

transducer

Decreasing the makes the coil very thin and structurally

compromised

Larger coils have higher inductive and capacitive resistance

and slower dynamics

16

Driver Coil Design – Selection of Inner Diameter

Electric Current

Limitation Zone

17

Receiver Coil Geometry

S. Tumanski, “Induction Coil Sensors – a Review”

18

Receiver Coil Design

0.37 ( l=2.4 Di )

19

Experimental Setup

Driver Receiver

• Max. Lift-off Distance: 65mm

• Test Targets: Aluminum and

Copper sheets

• Coil Separation: 50mm

20

Driver and Pickup Signals

21

Signal Characteristics

23%

Signal Statistics – 500 Cycles of Measurement

Material Aluminum Copper

Normalized mean of maximum signal amplitude 1.00 0.667

Normalized STD of maximum signal amplitude

0.0098 0.0146

22

Summary

A Remote Conductivity Measurement System was designed and

prototyped

The system can operate at lift-off distance up to 65mm

There is a 23% contrast between the signal levels obtained from

aluminum and copper samples

Standard deviation of measurements is less than 2.5%

23

Thanks