NIST Works the Thermal MagIC

The next big milestone will be the first measurement over a temperature gradient, which would allow Thermal MagIC to graduate to a true temperature imaging system.

In the current study, researchers found that measuring higher harmonics (the harmonic signals with higher frequencies) rather than lower harmonics gave them better spatial resolution—that is, they were able to distinguish the four wells from each other, even when they were spaced quite closely (see graphic below). Measuring the ratio of a higher harmonic to a lower harmonic gave them an even clearer picture.

Sometimes, the imager could pick out each of the four wells distinctly. Other times, the foursome merged into one or two blobs. The researchers tested which parts of the signal best distinguished the wells from each other.

Harmonics in the magnetic signals from the nanoparticles in Thermal MagIC work in a similar way. In this case, though, the main frequency isn’t sound waves but a pulsing magnetic signal produced by the nanoparticles. The harmonics are pulsing magnetic signals of higher frequencies, produced by a unique recipe of materials and conditions in the system.

Published: Tuesday, January 16, 2024 – 12:01

Four years and many milestones into the project, the research team has just published a paper fully characterizing the temperature sensitivity and spatial resolution of their imaging system, a necessary step toward making a reliable “thermometry camera.” The paper was published recently in Scientific Reports.

Close-up of the quartz glass cube that holds the magnetic nanoparticles in solution. Credit: Jennifer Lauren Lee/NIST.

Thermal MagIC consists of two systems working together.

The paper’s authors include Thinh Bui, Mark-Alexander Henn, Weston Tew, Megan Catterton, and Solomon Woods.

The second part comprises the instrument that excites the tiny spheres magnetically and then reads out their signal. (See animation.)

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One key part of the signal researchers can pick up in their Thermal MagIC system is its harmonics.

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NIST Works the Thermal MagIC

Digging into the details of an ambitious new ‘thermometry camera’

With this setup, they were able to assess temperature differences to within just 500 millikelvin (thousandths of a kelvin) in a volume of just 63 nanoliters (billionths of a liter).

Those with musical training might already be familiar with the term. A single note played with a clarinet has one primary frequency of sound—the main note, say an A flat. But that tone also contains a series of other, fainter frequencies—harmonics of the main note—that give the clarinet its distinctive sound quality. A clarinet and an oboe might be playing the same note, but they sound distinct from one another due to their different harmonics, which arise from differences in the instruments’ shapes and sizes and the materials used to make them.

Close-up of the quartz glass cube that holds the magnetic nanoparticles solution. The brown liquid is the solution of nanoparticles. Credit: Thinh Bui/NIST.

“So far, I’ve measured a sample of nanoparticles at one single temperature at a time,” Bui says. “True thermal imaging requires a system that has many temperatures across different local regions, and then quantifying and imaging the variations across the local regions. And that’s what we’re endeavoring to do in the coming months.”