SQUID FOR CHARACTERIZATIONOF MATERIALS

Nasser S. AlzayedPhysics & Astronomy

Dept.King Saud UniversityRiyadh, Saudi Arabianalzayed@ksu.edu.sa

OUTLINE.…

Briefing about SQUID

General Applications

Our Application to NDT in Aluminum

Plates

SQUIDS OUTLINE SQUID stands for: Superconducting

Quantum Interference Device SQUID is a very sensitive Magnetic Flux

detector SQUID is Flux-To-Voltage Transducer Output of Voltage of SQUID is periodic with

Flux Quantum Period фo=h/2e=2.07x10-15 Web

So far, SQUID is the most sensitive device.

10-4

Field

(T)

SQUID

106

Line frequency and harmonics

Frequency (Hz)

fluxgate

10-2 10-1 10-0 101 102 103 104 105

Lab noise

10-16

10-15

10-14

10-13

10-12

10-11

10-10

10-9

10-8

10-7

fT

pT

nT

MR sensors

MCGMEG

Earth’s field

MAGNETIC SENSORS

10-2

10-1

100

101

102

103

104

105

0 5 10 15 20 25Frequency [Hz]

Flu

x D

en

sit

y [

pT/H

z1/2]

Hall

GMR

SDP

fluxg

ate SQUID

noise threshold

SQUID FOR APPLICATIONS

In principle: SQUID can measure any thing that can provide magnetic flux:

Current Brain Signals Heart Signals Magnetization None-Destructive Testing Geophysics Astrophysics

SQUID combines few Physical Phenomena: Flux Quantization (in a Closed Sup.

Loop) electron-pair wave coherence Josephson Tunneling

Two Types of SQUIDs available: DC- SQUID (Biased using DC current) RF- SQUID (Biased using rf current)

TYPES OF MEASUREMENTS:

Single Channel Magnetometer

Single Channel Gradiometer

Multichannel Scanning System

SQUID: SIMPLY SUPERCONDUCTING RING WITH ONE OR MORE WEAKLINKS

DIFFERENT SHAPE OF SQUID

Bulk RF-SQUID Gradiometer (Hand made)

PRINCIPLE OF OPERATION

Applying External Mag. field to the Ring

Phase Change across the Links

1 = |1(x)| ei1 , 2 = |2| ei2

Superconductor, 1

WeakLink

Superconductor, 1

Also a current i will loop around the ring

This current shall cancel the Bext

But this does not happen because of the critical current across the Link

Total Phase Change must = 2πn Total Phase change due to applied

Mag. Field:

Tota Phase Change = 2πn a phase due to current i is made to

justfy the total phase change:

Current moves clockwise or (counterclockwise)

the magnitude of i increases to a maximum

Result is: Circulating current is periodic with

applied magnetic field. The period is Фo

FEW KNOWN INSPECTION METHODS

Visual InspectionAcoustic SoundingSurface Hardness methodUltrasonic TestingImpulse

ResponseMagnetic MethodsResonant

FrequencyInfrared ThermographyRadioactive

Testing

SQUID SYSTEM FOR NDT

Evaluating cracks in metals no matter how deep

Evaluating Corrosion in concrete without contact

Output can be contour like for more details of defect.

19

BIOMAGNETIC IMAGING

Need ~1 picotesla sensitivity for real time monitoring

Cardiac magnetic signal

Low-Tc dc SQUID systems for MCG application

CardioMag Imaging, Inc., USA

APPLICATION OF SQUID TO MCG

P

QRS

T

BASIC MORPHOLOGIES OF MCG IS EQUAL TO ECG

Healthy heart Abnormal

Measured by a 9-channel CMI-3609 system, CardioMag Imaging, Inc. USA

MAGNETIC MAPS OF HUMAN HEARTS - AT A SEQUENCE OF TIMES WITHIN THE T- WAVE

WHICH WOULD YOU CHOOSE?

Non-contact Non-invasive No radiation Safe Accurate

MCG

ECG

Nuclear scan

Magnetocardiograph

24

DEFECT DETECTION CAN PREVENT CATASTROPHIC FAILURE

• Need non-destructive test for corrosion, cracks, and stress • Eddy currents imaged with scanned GMR reveal invisible corrosion.

Field image

Optical image

“The crack was in the upper row of rivets along The S-10L lap joint”…

excerpt from NTSB report

TYPICAL SQUID SIGNALS FOR NDT

Scan of 1, 3, 5, and 10 mm holes in a steel plate

Solving Maxwell Equations for the Applied magnetic field in the Near zone only:

The measured field signal is described by a vector. The vector magnitude and angle represent the amplitude and phase angle of the detected signal respectively

In terms of the field amplitudes, the result shows that the attenuation of a magnetic dipole field through a metal is significantly less than the calculated attenuation of plane wave given by the Equation:

The reason of less attenuation is ascribed to the fact that usually the attenuation of the field is caused by the shielding effect of the induced current which is normally in opposite phase to the source current. However, the low frequency small circular shieldingcurrent induced by a magnetic dipole has a different phase shift. Hence, the orthogonal component of that shielding current causes no significant shielding effect.Thus, attenuation is less than that calculated for a plane magnetic wave. This better attenuation property of a dipole field inside a metal can be applied beneficially for the NDT.

CONCLUSIONS

SQUID has been successfully used for: Biomagnetic Applications Non-Destructive Evaluation (NDE) Geophysical Applications Scanning SQUID Microscope