The Truth About Terahertz (2012) | Hacker News Reader

The Truth About Terahertz (2012)

spectrum.ieee.org

63 pointsCieplak21 comments

Though it’s non-ionizing, there is a paper out there about DNA resonance at mmW and THz. So I suppose you can still get cellular damage.

So a single photon is not ionizing, but I can certainly generate plasmas with lots of photons at lower energy. So the whole point of ionizing radiation is that it can induce cellular damage without killing the cell? So this can’t be done with non-ionizing radiation, even though it can certainly ionize with average energy?

> mmW

Did you mean micro Watt here?

millimeter-waves, like in the high frequency 5G-NR radio - around 50 GHz.

Reading this article, it seems that terahertz is only suited for space-based telecommunication.

Given its super high transfer rate, it would be perfect for a low orbit, internet-providing satellite constellation. cough starlink cough

It might be great for satellites talking to each other but as TFA points out, terahertz is basically completely absorbed by the atmosphere.

Attenuation in atmosphere is extreme. But this can be seen as a plus if you want to limit interference (try wifi in a crowded mall)

You don't have to go full terahertz for that. Just look at the difference between 2.4ghz and 5ghz wifi.

I had read a research wherein Terahertz was used to read the contents of a closed book. Wonder how far that research has progressed, or have they tried to make it applied, ready for some sort of operational results.

For reference I think you mean this, right? https://news.mit.edu/2016/computational-imaging-method-reads...

Right you are!

In the comments section:

"""

Terahertz Medicine • a year ago

This review would be different now in 2017.

"""

Any pointers?

The laws of physics didn't change, it's great but suffers most of the problems of IR communication, namely air diffraction/absorption (severely hurting range) and mostly line of sight communication. Through advanced modulation schemes one can reach gigabit speeds but it's such an extremely short range[1] it's no surprise there seems to be no commercial product.

Terahertz signal processing, though, has a much brighter (hah) future ahead, in medical and security imaging[2].

[1] http://www.embednet.com/Giga-IR_General.pdf

[2] https://codeburst.io/terahertz-thz-gap-tech-for-speedy-commu...

I'm aware of at least one research project[1] which is currently prototyping Terahertz communications in the range of several hundred Gbps over distances of several meters.

[1]https://www.ee.ucl.ac.uk/research/photonics/eu-2018beyond-5g...

What about interconnects inside a computer?

Physics is still a problem there as well. 1 THz = 10^12 Hz. The speed of light is ~3E10 m/s so at 1 THz light can only move ~0.0003 m/cyc = 300 um/cyc. Electric current moves slightly slower than the speed of light through copper and silicon but its close enough to approximate here. That means in a CPU running at 1 THz it would take multiple clock cycles for a signal to move from one side of the CPU to the other. You also have to take into account the switching speed of transistors and the distance from the CPU to memory. All together, you would just end up wasting a lot of clock cycles achieving nothing and driving the current required to run a CPU at those speeds would generate a lot of heat.

Comes down to another issue discussed in the article: extremely high power and current density, which require another greal deal of engineering to cool down and make sure things don't vaporize, melt or simply break down.

I’m just speculating. Theoretically if you have vacuum sealed CPU, it could work. This brings other problems. How would you remove heat released by the chips in vacuum if there is no airflow.

That does not make sense.

The distances are so short that you would not have much attenuation from air at normal pressure / humidity.

Also: (not that it matters), but you can remove heat from chips in vacuum through IR radiation and through heatpipes connected to the guts of the chips in the normal fashion (through a heatsink connected to the top of the device).

https://en.wikipedia.org/wiki/Nanoscale_vacuum-channel_trans...

Don’t we have Terahertz communication already? Fiber optics run on 100 THz light approximately, no?

From the article: "The terahertz regime is that promising yet vexing slice of the electromagnetic spectrum that lies between the microwave and the optical, corresponding to frequencies of about 300 billion hertz to 10 trillion hertz (or if you prefer, wavelengths of 1 millimeter down to 30 micrometers). "

So, no.

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