A study that contradicts the general assumption of physics, researchers at the University of Michigan arranged a light emitting diode (LED) with electrodes to cool another device that was only nanometers.
This method could lead to a new solid-state cooling technology for future microprocessors that will have so many transistors packed in a small space so that current methods can not remove heat quickly enough.
"We have shown a second method of using photons to open devices," said Pramod Reddy, who jointly led the work with Edgar Meyhofer, both mechanical engineering professors.
The first – known as laser cooling – is based on Arthur's main work, Ashkin, who shared the Nobel Prize in Physics in 2018.
Instead, scientists have used the chemical potential of thermal radiation, a term used more often to explain how the battery works.
"Even today, many assume that the chemical potential of radiation is zero," Meyhofer said. "But the theoretical work that goes back to the 1980s shows that this is not the case under certain conditions."
For example, the chemical potential of a battery causes electric current when placed in a device. Inside the battery, the metal ions want to flow to the other side as they can get rid of some energy – chemical potential energy – and we use that energy as electricity. Electromagnetic radiation, including visible light and infrared radiation, usually does not have this type of potential.
"Normally, the intensity of thermal radiation depends only on temperature, but we have an additional knob to control this radiation, so cooling is possible," said Linxiao Zhu, a mechanical engineering research fellow.
This handle is electric. Theoretically, the withdrawal of the positive and negative electrical connections of the infrared LEDs not only stops its radiation, but actually suppresses the thermal radiation that it should produce just because it is at room temperature.
with this reverse trend behaves as if it were at a lower temperature, said Reddy.
However, measuring this cooling and proving something interesting is difficult
To get enough infrared light flow from the object to the LED, both should be very close to each other – less than one infrared light wavelength . This is necessary to use the effects of the "near field" or "changing coupling" that allow more infrared photons or light particles to cross from the cooling object to the LED.
The Reddy and Meyhofer teams had legs, as they were already heated and cooled by nanoselectric devices, arranged to be just a few tens of nanometers, or less than a thousand hair widths. At this close distance, a photon can escape to the LED that would not have escaped from the cool object, as if there was no gap between them. In addition, the team had access to an ultra-low vibration laboratory that can measure the measurements of nanometer-separated objects, as vibrations, such as from the footprint of others in the building, are significantly reduced
. Minimal calorimeter, which is a device for measuring energy changes, and near that small LED, about the size of rice grain. These two consistently spread and received thermal photons from each other and elsewhere in their environment.
"Any object at room temperature emits light. The night vision camera basically captures the infrared light that the warm body receives." Meyhofer said.
However, when the LED is inverted, it started to function as a very low temperature object by absorbing photons from the calorimeter. At the same time, the gap prevents the heat from moving back to the calorimeter through the conduction that causes the cooling effect
The team showed that cooling was 6 watts per meter. Theoretically, this effect can cause cooling to 1000 watts per meter, or solar energy on the Earth's surface.
This may be important for future smartphones and other computers. With higher computing power in smaller and smaller devices, heat removal from the microprocessor begins to limit how much energy can be pressed into a particular space.
By improving the efficiency and cooling speed of this new approach, the team envisions this phenomenon as a way to quickly remove heat from microprocessor devices. It could even resist the abuse of smartphones, as nanoparticulate gaskets can provide a separation between microprocessors and LEDs.
The study should be published in a journal Nature 2019. "Near field photon cooling for controlling photon chemical potential".
Interference as a new method for cooling quantum devices
Photonic cooling near the field, controlling the photon's chemical potential, Nature (2019). DOI: 10.1038 / s41586-019-0918-8, https://www.nature.com/articles/s41586-019-0918-8