Dielectric/Magnetic Probe A Unique NDT Sensor for Magnetic Material - - PowerPoint PPT Presentation

Dielectric/Magnetic Probe

A Unique NDT Sensor for Magnetic Material Quality Assurance Mark D. A. Rosen, Ph.D. General Applied Physics Solutions

Approach

• Simple, cost effective measurement techniques
• Measure parameters directly related to performance
• Ability to measure local variations (spatial mapping)
• Adaptable to automation (if needed)

• Eddy Current and Interdigital Patterned Sensors

Can be sensitive to dielectric and magnetic properties but limited to frequencies less than HF (<30 MHz)

• Open-Ended Transmission Line

Determine ε by the interaction of a material with the fringing field at the end of an open transmission line

• Free-space (NRL Arch; Radar Range*)

Measure the reflection and/or transmission of a plane wave in free space using a flat panel (NRL arch or range), fabricated component (range) or final assembled part

*including non-anechoic impulse imaging radar

NDT for Measuring Electromagnetic Properties

Open-Ended Coaxial Dielectric Probe

Material (ε, µ)

• Both the electric and magnetic field components interact

with the sample and affect the magnitude and phase of the reflected wave

• Altering the magnetic character (µ) in a controlled way can

change the reflected wave’s amplitude and phase

Effect of Applied Magnetic Field on Permeability

Y3Al0.66Fe4.34O12

From: G. G. Bush, J. Appl. Phys. 64 (1988), 5653

Plessey 1634 MagRAM

36 mils

8 10 12 14 16 18 20 22 24

Probe Response ( ε ')

4 8 12 16 20

Frequency (GHz)

With field 1 2 3 4 5 6 4

Probe Response ( ε ")

8 12 16 20

Frequency (GHz)

With field

Feasibility Test of Concept

HP Probe Plessey Material Ground Plane (Al) Magnet

Effect of Applied Magnetic Field on Probe Response

Dielectric/Magnetic Probe Modified Open-Ended Coaxial Probe

• Addition of an axial coil for applying an external

magnetic field

• External field can alter the contribution of the

material’s magnetic spins (dipoles)

• Difference in the probe response with and without

the field is related to µ of the material

• Patented

Dielectric/Magnetic Probe Design

Soft Magnetic Sleeve Magnetic Field Coil Pure Iron Center Conductor Non-magnetic Metal Teflon Spacer Beryllium Copper Outer Conductor

Prototype Probes

Measurement Problem

Lack of reproducible measurement due to contact variations with the sample:

• operator dependent
• sample surface dependent (not flat and/or

rough)

Conformal Tip

• Use of custom designed

spring loaded test pins

• Pins adjust to surface

imperfections (roughness and/or curvature)

• Pins allow wave to

propagate to surface so that fringing field interacts with sample (eliminates air gap effect)

• Patented

First Prototype (7mm Probe)

Dielectric/Magnetic Probe Modeling Tools

High Frequency Structure Simulator (HFSS) High Frequency Structure Simulator (HFSS)

Source: Hewlett-Packard Company Computes S-parameters for passive 3D structures by finite element solution of Maxwell’s equations Powerful tool for modeling the response of our probe (S11, reflected wave amplitude and phase)

Magneto Magneto

Source: Integrated Engineering Software, Inc. Software for solving magnetostatic problems using boundary element method Used to optimize magnetic field coupling to sample volume sensed by probe

Comparison Between Measurement and Modeling

Difference indicates that the applied magnetic field was not able to completely turn off the magnetic permeability (µ)

• 0.25
• 0.2
• 0.15
• 0.1
• 0.05

1 1.5 2 2.5 3 3.5 4

HFSS Calculations

Mag(µ=1)-Mag(µ=µ

m)

µ'

Freq = 2.0 GHz

• 0.05
• 0.04
• 0.03
• 0.02
• 0.01

1 1.5 2 2.5 3 3.5 4

GrumProbe™ Measurements

Mag(w/field)-Mag(w/o field)

µ'

Material: FeAl composite Freq= 2.0 GHz

Probe Frequency Response (Signature)

Signature is influenced by: (1) ε & µ (2) Structure (3) Physical defects

• 0.7
• 0.6
• 0.5
• 0.4
• 0.3
• 0.2
• 0.1

0.1

Magnitude Difference Phase Difference

• 3
• 2.5
• 2
• 1.5
• 1
• 0.5

0.5 2 4 6 8

Frequency (GHz)

10 ASD QC Sample

CL4 56mils

Effect of Thickness on 7mm Probe Response

1.2 1.4 1.6 1.8 2 2.2 2.4

Position of Freq Peak (GHz)

10 20 30 40 50 60

Thickness (mils)

PR2407-CL4

Probe is sensitive to the thickness as well as to the electromagnetic properties

Dielectric/Magnetic Probe

A New Unique NDT Sensor for Magnetic Material Quality Assurance

• Sensor is sensitive to both ε & µ
• Very Broadband
• Easily Addresses the very difficult to measure frequency

range below 4 GHz

• Can provide

– Spatial Mapping – Depth Profile of Structures

• Provides Processing Control