Transcript 10 -4

SQUID FOR CHARACTERIZATION
OF MATERIALS
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
10-7
Earth’s field
Line frequency and
harmonics
Lab noise
Field (T)
10-8
nT 10-9
10-10
MR sensors
fluxgate
10-11
pT10-12
10-13
MCG
MEG
10-14
SQUID
fT10-15
10-16
10-2 10-1 10-0 101 102 103
104
Frequency (Hz)
105
106
MAGNETIC SENSORS
noise threshold
105
Hall
Flux Density [pT/Hz1/2]
104
103
GMR
102
SDP
101
100
fluxgate
10-1
SQUID
10-2
0
5
10
15
Frequency [Hz]
20
25
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

WeakLink
Superconductor, 1
1 = |1(x)| ei1 ,
Superconductor, 1
2 = |2| ei2
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 Inspection
Acoustic Sounding
Surface Hardness method
Ultrasonic Testing
Impulse Response
Magnetic Methods
Resonant Frequency
Infrared Thermography
Radioactive 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.
BIOMAGNETIC IMAGING
Cardiac magnetic signal
Need ~1 picotesla sensitivity for real time
monitoring
19
APPLICATION OF SQUID TO MCG
Low-Tc dc SQUID
systems for MCG
application
CardioMag Imaging,
Inc., USA
BASIC MORPHOLOGIES OF MCG IS
EQUAL TO ECG
T
P
QRS
MAGNETIC MAPS OF HUMAN HEARTS - AT
A SEQUENCE OF TIMES WITHIN THE T- WAVE
Healthy heart
Abnormal
Measured by a 9-channel CMI-3609 system, CardioMag Imaging, Inc. USA
WHICH WOULD YOU CHOOSE?
Magnetocardiograph
ECG





Nuclear scan
Non-contact
Non-invasive
No radiation
Safe
Accurate
MCG
DEFECT DETECTION CAN PREVENT
CATASTROPHIC FAILURE
• Need non-destructive test
Optical
image
for corrosion, cracks, and
stress
• Eddy currents imaged with
scanned GMR reveal invisible
corrosion.
Field
image
“The crack was in the upper row of rivets along
The S-10L lap joint…”
excerpt from NTSB report
24
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 shielding
current 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