SQUID FOR CHARACTERIZATIONOF MATERIALS
Nasser S. AlzayedPhysics & Astronomy
Dept.King Saud UniversityRiyadh, Saudi [email protected]
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.
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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
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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