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Excess heat given off by smartphones, laptops and other electronic devices can be annoying, but beyond that it contributes to malfunctions and, in extreme cases, can even cause lithium batteries to explode. To guard against such ills, engineers often insert glass, plastic or even layers of air as insulation to prevent heat-generating components like microprocessors from causing damage or discomforting users.
Now, Stanford researchers have shown that a few layers of atomically thin materials, stacked like sheets of paper atop hot spots, can provide the same insulation as a sheet of glass 100 times thicker. In the near term, thinner heat shields will enable engineers to make electronic devices even more compact than those we have today, said Eric Pop, professor of electrical engineering and senior author of a paper published Aug. 16 in Science Advances.
"We're looking at the heat in electronic devices in an entirely new way," Pop said.
The heat we feel from smartphones or laptops is actually an inaudible form of high-frequency sound. If that seems crazy, consider the underlying physics. Electricity flows through wires as a stream of electrons. As these electrons move, they collide with the atoms of the materials through which they pass. With each such collision an electron causes an atom to vibrate, and the more current flows, the more collisions occur, until electrons are beating on atoms like so many hammers on so many bells -- except that this cacophony of vibrations moves through the solid material at frequencies far above the threshold of hearing, generating energy that we feel as heat.
Thinking about heat as a form of sound inspired the Stanford researchers to borrow some principles from the physical world. From his days as a radio DJ at Stanford's KZSU 90.1 FM, Pop knew that music recording studios are quiet thanks to thick glass windows that block the exterior sound. A similar principle applies to the heat shields in today's electronics. If better insulation were their only concern, the researchers could simply borrow the music studio principle and thicken their heat barriers. But that would frustrate efforts to make electronics thinner. Their solution was to borrow a trick from homeowners, who install multi-paned windows -- usually, layers of air between sheets of glass with varying thickness -- to make interiors warmer and quieter.
"We adapted that idea by creating an insulator that used several layers of atomically thin materials instead of a thick mass of glass," said postdoctoral scholar Sam Vaziri, the lead author on the paper.
Atomically thin materials are a relatively recent discovery. It was only 15 years ago that scientists were able to isolate some materials into such thin layers. The first example discovered was graphene, which is a single layer of carbon atoms and, ever since it was found, scientists have been looking for, and experimenting with, other sheet-like materials. The Stanford team used a layer of graphene and three other sheet-like materials -- each three atoms thick -- to create a four-layered insulator just 10 atoms deep. Despite its thinness, the insulator is effective because the atomic heat vibrations are dampened and lose much of their energy as they pass through each layer.
(Score: 3, Insightful) by bzipitidoo on Friday August 23 2019, @05:09PM (9 children)
Just 10 atoms thick? Must be incredibly fragile. I'd guess the material has to be physically bonded to something thicker and stronger.
I always find it easier to think of electricity in wires as analogous to water flowing through garden hoses. A capacitor is a storage tank, a resistor is a narrow spot in the hose, and an inductor is, well, I'm not sure. A very long coil of hose? DC is like water flowing in one direction through the hose, and AC is like water alternating directions in the hose. Making this mental connection between heat and sound is similar, and awesome. To me, it's one of those things that in hindsight seems obvious.
(Score: 2) by DannyB on Friday August 23 2019, @05:21PM (1 child)
Maybe: a resistor is a narrow spot in the hose for voltage. Some current through the resistor is dissipated as heat. So not an exact analogy. Did I mention light emitting resistors, uh, nevermind.
Maybe: A capacitor resists a change in voltage when wired in parallel across that voltage. When the voltage that charged the capacitor is removed, the capacitor 'resists' the change in voltage by supplying current at that voltage for a short time. An inductor simiilarly resists a change in current flow when wired in series with that current flow. If the current flow is stopped the inductor produces a 'kick' of current momentarily, trying to keep the current flowing.
Don't take my word, I'm a software guy. Not my field. If I could do it with all software and NO HARDWARE -- I would! Hardware is a necessary evil. For now. Always beware a software developer carrying a screwdriver into a server room to 'fix some minor problem'.
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(Score: 2) by DannyB on Friday August 23 2019, @05:30PM
I would point out, the act of charging a capacitor is also resisting a change in voltage. This pair of wires is at zero volts potential. Apply voltage, the capacitor charges while soaking all the current keeping the voltage low until capacitor can no longer resist change in voltage.
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(Score: 2) by DannyB on Friday August 23 2019, @05:28PM (5 children)
A thing I have always thought funny about the electricity as water analogy, which I sometimes think of myself, is the units we measure in. With water it would be volume per time, eg, gallons per minute. That would be like current 'amps'. But we don't measure current in something per second -- although at the base most units, it seems it must be electrons per time. (coulombs per second?) Voltage is like water pressure. A narrow spot in the hose rather than being a resistor is a transformer. It trades voltage / current like a transformer. Higher water speed at lower pressure. Wide spot in hose is lower water speed at higher pressure? Not sure. When that wide spot in hose ends, you're back to the original water speed / pressure it seems.
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(Score: 3, Informative) by maxwell demon on Friday August 23 2019, @05:43PM (2 children)
Amperes are Coulombs per second.
Electrons per time would be an impractical measure for two reasons: First, it would give impractically large numbers for everyday currents (even the SI prefixes would not suffice to describe them). And second, while in most cases, the charge flow is carried by electrons, sometimes (particularly in batteries) it is carried by ions instead.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 2) by DannyB on Friday August 23 2019, @06:03PM
Thank you!
I sort of vaguely remembered that from my DC Circuits class in, what was it?, oh, 1979! And I still have the textbook, somewhere.
Thevenizing, Nortonizing, AC Circuits where voltage and current are out of phase, oh my!
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(Score: 2, Informative) by Anonymous Coward on Friday August 23 2019, @09:03PM
Well there's also the little nuance that moving electrons does not, in and of itself, result in an electric current.
Pick up an object and move it somewhere else on the desk. All the electrons (negative charge) in that object just moved, but there is no electric current as a result, because an equal amount of positive charge in that object moved in the same direction. An asymmetry in charge movement is required to have electric current.
The idea that "electric current is the movement of electrons" is really a property of metals (and some other materials); solid metals in particular, where the positively-charged nuclei form rigid crystaline structures and zillions of electrons are "loose" and easily move around the material.
(Score: 0) by Anonymous Coward on Friday August 23 2019, @10:23PM (1 child)
Voltage is not at all like pressure in the hydraulic analogy. Water pressure represents electric potential. So the analogue of voltage (which is a difference in electric potential) is a pressure difference.
E.g. on either side of a kink you have a difference in pressure -> analogous to the voltage across a resistor (the kink).
(Score: 3, Informative) by shortscreen on Saturday August 24 2019, @01:24AM
That's true although generally (not always) when people talk about pressure they are talking about relative pressure. When the gauge on the air compressor reads 0 it doesn't mean there's a vacuum inside, it's 0 relative to atmospheric.
(Score: 3, Insightful) by Rupert Pupnick on Friday August 23 2019, @07:58PM
In the water hose analogy, voltage is pressure, and current is water flow rate. A pressurized storage tank is a good analogue for a capacitor. For the inductor analogy, you could think of the kinetic energy of the moving water as the stored energy, so maybe something like an impeller in the hose that is attached to a flywheel that spins in proportion to the rate of water flow. A high inductance is like a flywheel with a bigger mass or moment of inertia.