Researchers in Japan observed the transverse Thomson effect for the very first time, a thermoelectric phenomenon that allows the control of the direction of heating and cooling flows by changing the direction of the magnetic field.
The scientific understanding of how heat and electricity interact stems from the 19th century. At the time, physicists only theorized the existence of a transverse Thomson effect, which refers to the direction in which an electric current and temperature gradient flow. Now, for the very first time, Japanese physicists proved that it indeed exists.
Imagine a device that could actively switch between heating and cooling a targeted area by changing a magnetic field, rather than needing to separate heating and cooling units, or reversing the current direction as with Peltier coolers. It could be revolutionary.
It’s all about the angle
In a study published in Nature Physics, a team of researchers led by Atsushi Takahagi from Nagoya University and Ken-ichi Uchida from the University of Tokyo reported “the observation of the transverse Thomson effect in a semi-metallic Bi88Sb12 alloy with thermoelectric imaging.”
“Our experiments and analyses reveal the essential difference between the conventional and transverse Thomson effects,” study authors continued.
“Whereas the former depends solely on the temperature derivative of the Seebeck coefficient, the latter depends on the temperature derivative and the magnitude of the Nernst coefficient. The observation of the transverse Thomson effect provides a new concept for active thermal management technologies.”
Physicists had trouble observing the transverse Thomson effect because competing thermal Peltier and Ettingshausen effects interfered, Phys continued.
Changing the material
However, researchers used a semimetal bismuth and antimony conductor, which partially explains why the effect hadn’t been achieved in the past, according to IFLScience. They selected it because of its strong Nernst effect around room temperature, as per Phys.
They observed the heating and cooling in a sheet of Bi88Sb12 by applying an electric current and magnetic field at perpendicular angles. This material, in particular, was well-suited to finally achieving the desired effects. As the current flows lengthwise in the material, they applied heat to a side, not the ends, and they directed the magnetic field from above.
To bypass the problem of signal isolation, Japanese researchers told Phys that they used an infrared camera to observe the thermal response of the sample when they applied the periodic electric current.
“By extracting the temperature modulation component that oscillates at the same frequency as the applied current from the taken thermal images, we were able to isolate the thermoelectric signals from the Joule heating.”
Once they recognized that the spatial distribution of the transverse Thomson effect differs from other competing effects, they were able to perform measurements with and without a temperature gradient, Phys continued. “Then they subtracted the results to isolate the pure transverse Thomson signal.”
They found that they could switch between heating and cooling by changing the magnetic field direction, which surprised them, and it could improve the performance of transverse thermoelectric cooling devices.
Now, the researchers intend to continue finding the materials most conducive to producing the transverse Thomson effect, which researchers concluded to Phys, will be “an important avenue for future research.”