In a small Petri dish sits a droplet of liquid the size of a pinhead. An ordinary scanner wouldn't even notice it: the signal is too weak. But bring a tiny magnetic field sensor close to the droplet, and the picture changes.
A team of researchers placed a commercial optically pumped magnetometer, a device where a laser reads the oscillations of atoms in alkali metal vapor, right next to the sample. No intermediate coils, just direct contact. They set the magnetic field to 10 microtesla, about five times weaker than Earth's field. That was enough to produce two-dimensional images with a field of view larger than a centimeter and resolution below a millimeter. The sharpness was limited only by the signal acquisition time: that's just how the physics works.
This approach works like a portable microscope for the magnetic properties of matter. It promises rapid analysis of fluids and biological tissues without bulky superconducting magnets. And it also provides a precise map of the sensor's own sensitivity, which will come in handy for engineers.
Earth's magnetic field, which we don't feel, is 50 times stronger than the field used in this experiment. Yet the sensor detected signals a billion times weaker.
In the iconic series Star Trek, the medical tricorder diagnosed in seconds by scanning the body without contact. The new method is a step toward real portable scanners that see tissue chemistry through magnetic fields.