A high resolution imaging susceptometer

Abstract

High resolution magnetic susceptibility imaging is a new technique for investigating the composition of diamagnetic and paramagnetic objects. It might contribute to the nondestructive evaluation of critical components by identifying both surface and internal defects. In order to demonstrate the technique, we have attached magnetizing coils to our high resolution MicroSQUID magnetometer. With our present system, we can apply a nearly uniform field of 0.3 mT, 2.0-2.5 mm below the 3 mm diameter sensing coils. By placing a sample in this applied field and scanning, MicroSQUID measures the local magnetic field variations caused by the spatial distribution of magnetic susceptibility in the sample. The system has sufficient sensitivity to image susceptibility-induced field changes equal to 3 x of the applied field, in a 100 Hz bandwidth. We describe the concept of susceptibility imaging and present preliminary data.

Local magnetic probes of superconductors

“…Historically applications have focused on areas such as biomedical or military remote sensing which require extremely high magnetic ® eld sensitivity combined with rather coarse spatial resolution. The basic technology to build scanning SQUID systems has, however, long been available and it is perhaps surprising that, with one exception (Rogers 1983), the ® rst prototypes (Minami et al 1992, Black et al 1993, Ma et al 1993, Vu et al 1993, Kirtley et al 1995a) have only been developed in the last few years as part of the current explosion in scanning probe techniques.…”

Highly Sensitive Measurement of Moisture Content Using HTS-SQUID

“…When the magnetic field is applied, a secondary magnetic field from the subject is generated and its strength depends on the susceptibility. A high resolution imaging system detecting the magnetic susceptibility in the DC magnetic field was reported [10]. Our measuring method uses the volume effect in the AC magnetic property to detect the moisture content.…”

Magnetic property mapping system for analyzing three-dimensional magnetic components

“…21 For investigations of diamagnetic and paramagnetic objects, an imaging susceptometer based on SQUID that exposes an object to dc magnetic fields has been reported. 22,23 In the case of ferromagnetic metal NDE, the secondary magnetic field is caused not only by eddy currents but also by the focused magnetic flux based on high permeability. In order to distinguish between these phenomena, we have developed an imaging system capable of detecting and analyzing three-dimensional secondary magnetic field components utilizing a large area primary magnetic field exposure.…”