Computers

Thermal diode could lead to space-faring computers that run on heat instead of electricity

Thermal diode could lead to sp...
A thermal diode, an electronic component that runs on heat instead of electricity, could lead to the creation of heat-resistant computers
A thermal diode, an electronic component that runs on heat instead of electricity, could lead to the creation of heat-resistant computers
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Mahmoud Elzouka, left, and Sidy Ndao, right, developed the thermal diode
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Mahmoud Elzouka, left, and Sidy Ndao, right, developed the thermal diode
A thermal diode, an electronic component that runs on heat instead of electricity, could lead to the creation of heat-resistant computers
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A thermal diode, an electronic component that runs on heat instead of electricity, could lead to the creation of heat-resistant computers

Electronic systems don't work well in heat – which is a problem, because apart from a few exceptions, heat is a normal byproduct of electricity. Researchers have now developed a thermal diode: a computer component that runs on heat instead of electricity. This could be the first step towards making heat-resistant computers that can function in extremely hot places, like on Venus or deep inside the Earth, without breaking a sweat.

A regular diode is a key logic component in electronic circuits that allows electricity to flow freely in one direction but blocks it from moving back the other way. These crucial components often fail under high temperatures or when exposed to ionizing radiation, so to help make hardier computer systems, a team at the University of Nebraska-Lincoln have developed thermal diodes, powered by heat instead of electricity.

"If you think about it, whatever you do with electricity you should (also) be able to do with heat, because they are similar in many ways," says Sidy Ndao, co-author of the study. "In principle, they are both energy carriers. If you could control heat, you could use it to do computing and avoid the problem of overheating."

The team's thermal diode is made up of pairs of surfaces, where one is fixed and the other can be moved towards or away from its stationary partner. That movement is handled automatically by the system to maximize the transfer of heat: when the moving surface is hotter than the still one, it will actuate inwards, and increase the rate that heat moves to the cooler surface.

When performed at temperatures between 215° and 494° F (102° and 257° C), the thermal diode hit a peak heat transfer rate of about 11 percent, but the team reported that the device was able to function at temperatures as high as 620° F (327° C). Ndao believes that future versions could even operate at up to 1,300° F (704° C), potentially leading to computers that can work under extreme heat conditions.

Mahmoud Elzouka, left, and Sidy Ndao, right, developed the thermal diode
Mahmoud Elzouka, left, and Sidy Ndao, right, developed the thermal diode

"We are basically creating a thermal computer," says Ndao. "It could be used in space exploration, for exploring the core of the Earth, for oil drilling, (for) many applications. It could allow us to do calculations and process data in real time in places where we haven't been able to do so before."

Even when they're not running in the molten core of the planet, electronics can overheat and damage themselves if they aren't properly cooled by fans or water circulation systems. As heftier tasks are handed off to computers, more elaborate cooling tactics are needed, and to that end Lockheed Martin has tinkered with embedding microscopic water droplets inside chips, IBM developed the counter-intuitive technique of cooling with warm water, and Microsoft has turned to the power of the ocean itself to cool a large data center.

Using components like thermal diodes, the researchers say some of that wasted heat could instead be fed back into the system as an alternative energy source, improving its energy efficiency.

"It is said now that nearly 60 percent of the energy produced for consumption in the United States is wasted in heat," says Ndao. "If you could harness this heat and use it for energy in these devices, you could obviously cut down on waste and the cost of energy."

The researchers are now working on improving their thermal diode's efficiency. But since diodes aren't the only component in electronics, a true thermal computer would need the rest of its system to be able to withstand those temperatures as well.

"If we can achieve high efficiency, show that we can do computations and run a logic system experimentally, then we can have a proof-of-concept," Mahmoud Elzouka, co-author of the study. "(That) is when we can think about the future."

The research was published in the journal Scientific Reports.

Source: University of Nebraska-Lincoln

2 comments
wle
it must be SSSSLLLLLOOOOOOWWWWWWW though...... wle
GiovanniDimaggio
While it is true that electricity and thermal energy have some things in common (both transport energy and flow from a "source" of higher potential to a "sink" of lower potential) they have very different basic properties. While electric potentials propagate very fast (in vacuum with the speed of light, in wires and electronic circuits with a significant fraction of this), "heat" (understood as the energy state of matter) propagates very slowly in materials. Thermal energy can also propagate in the form of infrared electromagnetic waves which travel at the speed of light in vacuum. In the discussed invention, heat is transported this way over a small gap which changes its length, depending on the location of a heat source. The "diode" effect (i.e. the difference in conductivity depending on the direction of the heat flow), is caused by a change of the length (expansion/retraction) of a piece of material which then reduces or enlarges this gap between source and sink. A larger gap causes a higher thermal resistance. Heat brought to one of the "diode" sides causes a larger gap and thus a higher thermal resistance than heat brought to the other side. This is similar to the higher or lower electrical resistance of a semiconductor diode depending on the polarity of the voltage applied to it or to the behavior of a non return valve for water or air. But the similarities end here. Obviously it takes significant more time than a few nano or even microseconds to cause significant mechanical elongation of any piece of material by heating it, even if these elements are sized in the sub mm range (an image in the original publication shows elements of the size of 500 um (1/2 mm). Besides being intrinsically slow, the rectification factor (resistance in one direction in relation to resistance in the opposite direction) of the "heat diode" is only around 5-11% (0.05 - 0.11). Opposite to this, electronic diodes (and even good valves) have rectification factors in the range of millions of times higher. I cannot see how these ratios could be improved significantly, which would certainly be necessary for any creation of "thermal logic". The authors say that "thermal rectification (is) increasing with decreasing initial separation gap, suggesting that the thermal rectification can be further augmented through design optimization" (actually the "gap" is around 3 um). This is is easily understandable because the same absolute change of the gap length (caused by the elongation of the heated material) will have a higher relative (%) impact when the initial gap is smaller. But there are obviously limits for the precision of thermally/mechanically moving parts and it will hardly be possible to increase the ratio to 1000:1 or even 1000000:1. Equally important as the rectification factor is the reaction time. The authors don't say a word about it. While semiconductor ("electronic") diodes can switch from off to on in nanoseconds and even faster, thermal diodes would probably have switching times in the millisecond range or more for meaningful rectification factors because switching means the previously hot pole must cool down and the other one heat up and the moving element (the "gap") must expand or shrink due to the temperature change. Faster switching would reduce the rectification factor further. I can't see how thermal potentials can be used meaningfully for calculations when changes of states of thermal energy take so much longer and the difference in the states (rectification factor) is so small. And let's not forget that "diodes" alone do not allow to build circuits that keep their state once it has changed ("flipflop") which is condition sine qua non for storing ones and zeros. Diodes only allow to calculate simple boolean operations like "AND" and "OR". While I can imagine the use of light or quantum states instead of electron flow for future computers, in my opinion there is no way that this invention will ever lead to a useful computing system.