The 0.7 Tesla magnet, developed by Federico Casanova and his colleagues at the RWTH Aachen University’s department of macromolecular chemistry, is about the size of a standard D battery and weighs 500 grams.
Today bulky and expensive superconducting magnets are used to generate the strong magnetic fields (about seven tesla) needed for precision NMR (nuclear magnetic resonance). While portable magnets have been made before, the new one enables NMR measurements that are just as precise as the large commercial magnets.
The portable magnet could make possible sensitive, high-resolution NMR devices that can be taken to an archaeological dig to identify artifacts and to a factory to detect contamination in products. It could be used in doctors’ offices to spot blood clots, bacteria, or cancer proteins in a patient’s blood. It could also allow portable NMR machines to monitor the production of drugs and chemicals in-line instead of taking chemical samples to NMR labs for analysis. Even better magnets might be possible by fine-tuning the design, the researchers say. While the magnet’s field strength is 0.7 tesla right now, increasing the outer diameter of the magnet should make it possible to generate 1.5 tesla, the researchers say. What is more, using magnets made of other materials such as neodymium, as much as two tesla could be generated.
As the size of a permanent magnet shrinks, it generates magnetic fields that are uniform over a smaller volume because of tiny imperfections in its material and shape. This means less of a material sample can be used, making the NMR measurements almost a thousand times less sensitive than if a superconducting magnet were used. The NMR signal then becomes comparable to the electronic noise, and the device can miss chemicals that are present in very small quantities.
The new magnet generates a 0.7 tesla magnetic field, but it generates an extremely homogenous field. As a result, it is the first portable magnet that works with the conventional five-millimeter tubes in which NMR samples are placed. “The goal of our work was to take this tube, keep the volume constant, and build the smallest magnet with the desired homogeneity,” Casanova says. “The important thing we did is to correct the inhomogeneity that comes from imperfections in the magnet.”