Upload
emma-patterson
View
225
Download
1
Embed Size (px)
DESCRIPTION
Theory of SQUIDs Superconducting QUantum Interference Device Measure tiny magnetic fields (threshold is around T where 1T=10000Gauss. ) Magnetic field of heart= T
Citation preview
Image Processing for HTS SQUID probe microscope
Advanced Image Processing Seminar
Colin Bothwell0570063
General Discussion of Paper
Use High Temp SQUID probe microscope Probe allows high spatial resolution of
measurement of samples even at room temp
Aim to produce magnetic field images Improve images using Image Processing
Theory of SQUIDs Superconducting QUantum Interference Device
Measure tiny magnetic fields (threshold is around 10-14 T where 1T=10000Gauss. )
Magnetic field of heart=10-10T
Theory of SQUIDs To understand
SQUIDs need to know basic principles
Superconductivity-no resistance
Josephson Effect- current flow carried by cooper pairs
Theory of SQUIDs Josephson
Junction-a junction of 2 S/C materials divided by non-S/C material (oxide)
With these principles, SQUID was designed
Theory of SQUIDs SQUID has two
Josephson Junctions
Apply current to SQUID
Voltage will oscillate
Oscillations depend on magnetic flux
Experimental Set-Up Developed HTS
SQUID probe microscope using fine permalloy needle as flux guide
Images the magnetic field by means of raster scan
Experimental Set-up
Separation of probe and SQUID adjusted by viewing through glass window
PC used to control SQUID
Magnetic Image-Deficiencies Resultant images are noisy and
unclear because of Background Noise Drifting Data Jumping So…
Image Processing! Background Noise Use image processing
algorithm Calculate mean and
standard deviation of power spectrum
Threshold value=Pm + αPs
Apply this to each scan line in same way
Drift between Lines Drift of flux bias
point of SQUID Treated with
another algorithm Drift calculated as
difference in the mean value of magnetic field for each scan line
Data Jumping Artifacts due to a
jump in the flux bias point in SQUID by flux trapping or unexpected noise
Jump causes change dynamic range of magnetic field to become larger
Data Jumping
Small changes can no longer be detected
IP detects line with jump by derivation of line data (higher derivation considered to contain jump) so is interpolated with neighbouring lines
Conclusion
Used high-permeability needle to enable high spatial resolution measurement of samples.
Developed IP algorithms for magnetic field data obtained from SQUID probe microscope.
Algorithms can remove problems of background noise, drifting and jump data.