LARGE ARRAY SQUID MAGNETOMETER FOR NON-DESTRUCTIVE EVALUATION

AN IMPROVED METHOD FOR NON-DESTRUCTIVE EVALUATION (NDE) OF METALLIC STRUCTURES AND MICROCIRCUITS IS BEING DEVELOPED USING HIGH-RESOLUTION MAGNETIC SOURCE IMAGING. EXISTING NDETECHNOLOGIES ARE NOT ALWAYS ABLE TO DETECT EARLY-STAGE METALFATIGUE, CORROSION, OR STRESS-INDUCED FLAWS IN METALLIC STRUCTURES OR ADEQUATELY LOCALIZE FAULT CURRENTS IN VLSI ANDHYBRID MICROCIRCUITS. MAGNETIC SOURCE IMAGING CAN POTENTIALLY SOLVE MEASUREMENT CAPABILITY, MUCH ENHANCED SPATIAL RESOLUTION, AND FASTER DATA ACQUISITION THAN EXISTING NDE TECHNOLOGIES. TO ACCOMPLISH THIS FOR METALLIC STRUCTURES, CURRENTS ARE INDUCED OR INJECTED INTO THE TEST SPECIMEN AND THE RESULTING MAGNETIC FIELD PATTERNS ARE MEASURED TO IDENTIFY AND CHARACTERIZE THE FLAWS. SIMILARLY,ABNORMAL CURRENT DISTRIBUTION IN VLSI AND HYBRID MICROCIRCUITS PRODUCE AN ABNORMAL MAGNETIC FIELD AROUND THE TEST STRUCTURE WHICH CAN BE MEASURED. THE EXISTANCE AND PROPERTIES OF THE FLAW CAN BE DETERMINED USING ALGORITHMS SIMILAR TO THOSE FOR IMGING BIOMAGNETIC SOURCES. THE OBJECTIVE OF THIS EFFORT IS TO DEVELOP THE PERFORMANCE SPECIFICATION AND PRELIMINARY DESIGN FOR A LARGE ARRAY OF MINIATURE SQUID MAGNETIC SENSORS TO BE USED AS THE IMAGING INSTRUMENT. THIS RESEARCH MAY LEAD TO A SIGNIFICANT COMMERCIAL ROLE FOR SUPERCONDUCTING SQUID MAGNETOMETERS IN QUALITY CONTROL AND IN-SERVICE INSPECTION.