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.