CWRU physicists invent "supershielding" for MRI devices

July 19, 1999

CLEVELAND--The work of a thief is not the only way to rob you of the use of your credit cards and computers. Magnetic fields can zap the power from life's modern conveniences.

Robert Brown and Shmaryu Shvartsman, physicists in the College of Arts and Sciences at Case Western Reserve University, have created an armor they call "supershielding." The physicists will report on their new invention in the article, "Supershielding: Confinement of Magnetic and Electric Fields," tentatively scheduled for an August issue of Physical Review Letters.

The shielding completely contains magnetic fields as large as 10,000 times the Earth's natural magnetic field. Some of today's important technologies produce fields this great and wreak havoc with the identification codes on credit cards, wipe out computer memories, and become a mini-radio station, giving off a strong signal that interferes with commercial television and radio stations.

Brown, the Institute Professor of Physics, and Shvartsman, senior research scientist in CWRU's Department of Physics, recently made a joint application with Picker International to the U.S. Patent Office for a patent on supershielding. Michael Morich and Labros Petropoulos, Picker engineering scientists and Brown's former students, are also named on the patent application, along with another former graduate student, Hiroyuki Fujita.

The researchers have designed a method that can remarkably suppress the magnetic fields outside high-tech devices such as magnetic resonance imaging (MRI) machines.

Previously, the suppression has been carried out by positioning an iron barrier or a set of secondary coils outside the main coil that produces the original unshielded field. In each case, the field is left alive inside where it is needed to do its work.

Brown says that Picker International, a pioneer in computerized axial tomography (CAT scans) and magnetic resonance technology, and other manufacturers of imaging equipment are attempting to make smaller machines that are less claustrophobic for the patient. As the need for shorter and more open systems has grown, along with the desire for higher-quality shielding, the old methods of shielding have not kept pace.

Two years ago, Picker posed a shielding question to Brown and his research group at CWRU. Morich and Petropoulos formulated the specific problem. In response, the CWRU researchers came up with a surprising theoretical solution.

Brown explains that a shielding coil is used again, but the secondary and primary currents have to "dance" together to achieve supershielding, where the opposing coil currents cancel out the magnetic forces emitted.

He likens the results to a dam with a hole in it. "Instead of plugging the hole with a finger to stop the leakage, the dam can be discarded and the finger holds everything back by itself," Brown says.

"We couldn't believe it when we first did the mathematics. We found with a short and open outside shield, we could get the same perfect suppression obtained by an infinite shield," he adds. "We had a zero magnetic field everywhere outside, even in those regions where there was no secondary coil."

Trapping magnetic fields in a closed container presents no problem, but to be able to trap them with an open-coil system is what shocked the CWRU research physicists. Shvartsman adds that every time they describe the result to experts, the initial reaction is disbelief.

Upon patent approval, Picker will have rights to the medical diagnostics, while CWRU will have the rights to use the shielding concept in all other applications, such as electronic microscopes or microelectromechanical systems (MEMS).

"Everyone is trying to take smaller and smaller computer chips and pack them closer and closer together. The need to shield them from each other becomes more acute," says Brown.

The supershielding concept can also be applied to electric fields. By turning the shielding around, it can protect interior regions from an external field.

The magnetic and electric field shielding demands of future technology may well be met by protective, but open helmets of electric current and electric charges, adds Brown. "With only partial screening, a magnetic field system, as with Perseus in his Helmet of Hades, can be made invisible to outsiders."

Case Western Reserve University

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