# Use of solid materials as medium for data transfer

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1. Nov 4, 2016

### Austincr48

Really odd question for you guys but I'm curious about your input, and apologies if it's a foolish question to ask anyway(I'm a CS student and this came up in a discussion with a classmate of mine).

So I know this is a fairly odd thought and not likely practical in any real world scenario, but I was curious what input you guys might have(other than it being horribly inefficient The use of fiber optic cables has been used more often lately in enterprise deployments to make transferring large amounts of data faster. This got me thinking about the use of different mediums for transferring data.
Ultimately here's my scenario:
The speed of light is 188~k miles per second, this makes fiber optic cabling preferable to copper/electricity(Only in terms of speed/performance).

If one were to take a 100 mile stretch of land(assuming flatland) and ran a fiber optic cable across it, and then a solid steel beam(theoretical scenario, 100 mile steel beam wouldn't be practical anywhere else obviously). If a machine were pushing and pulling(representing 1s and 0s), what would be faster for data transfer(aside from the obvious momentum and force needed to push and pull this massive beam).

I understand this isn't exactly an electrical question, but I didn't think any of the other forums would've dealt with scenarios like this.

Perhaps the material's flex/bend/impurities would account for some minor distortion in what would receive the signal, but I would assume a physical object being moved in realtime would be faster than photons being shot through fiber cabling, but I might be wrong.

2. Nov 4, 2016

### Averagesupernova

In the case of the steel beam you would be limited by the speed of sound in steel. Are you under the impression that the signal speed of electricity in a wire is slower than light in an optical fiber?

3. Nov 4, 2016

### Austincr48

No I wasn't actually thinking of using electricity as the medium but the actual physical object that is the steel beam.

Pretty bad example image, but basically using a sensor to detect if the beam is in front of it would be the encoding(from the "analog" medium to digital). Just speaking plainly, if I were to push on the beam and have it move on the other end, would it trigger at the same(faster/slower?) speed as if I sent a signal over the fiber?

I know I posted under the "electrical" forum, but my intent wasn't to use the steel beam for electrical data transfer but actually using the physical beam as the medium.

Instead of shooting a photon or pushing electrons, would it be faster to push the actual object's atoms?

4. Nov 4, 2016

### CaptainJonathanNorth

I suspect not. If you intend to move the beam itself, there is inertia to overcome. And solids don't support compression waves the way gasses do. There are two distinct ways of doing what you are describing; Pushing the whole beam back and forth, and sending some form of compression wave down the beam. One is no go, the other is a slight maybe, you would really have to experiment. But the question as to speed, the light fiber travels very close to the speed of light, so it seems pretty unlikely that if you are not using electricity, any other form of compression wave would be waaaaaay slower.

But don't give up just yet. Consider this: never underestimate the bandwidth of a station wagon packed full of DVDs hurtling down the highway at 65 MPH. If the car had 15,000 movies on disk, and was headed to a destination one hour away, you might not be able to download 15,000 movies over a wire that fast. I would urge you to try and define your metrics. What sort of information do you want to transmit? As you can see with the station wagon, the actual speed at which the information is moving (60 MPH), may not be the bottleneck. Does that help?

5. Nov 4, 2016

### Ryan_m_b

Staff Emeritus
@Averagesupernova nailed the answer, any compression wave travelling through an object is limited by the speed of sound within that object. The speed of sound in steel is ~6km/s, which is 50,000x slower than fiber optic cable.

A similar question that often comes up is whether or not pushing and pulling a long rod will send information faster than light, it wont and we have an FAQ on why:
https://www.physicsforums.com/insights/can-i-send-a-signal-faster-than-light-by-pushing-a-rigid-rod/

6. Nov 4, 2016

NICE! LOL

7. Nov 4, 2016

### Austincr48

@Ryan_m_b Sorry about that, I wasn't aware of that so when I read his post I didn't know how it applied to the situation. Thanks for elaborating on that for me!

8. Nov 4, 2016

9. Nov 4, 2016

### Baluncore

Data rate comes down to the bandwidth of the channel multiplied by the number of independent parallel channels you can operate at one time. At this time, a bundle of optic fibres, each fibre carrying many different optical wavelengths will outperform all other systems.

10. Nov 4, 2016

### rbelli1

Glass has a refractive index if about 1.5 so it has a velocity factor of about 67%. This is the same as much of your standard communication cabling. However cables with much higher factors are available. For instance http://www.alphawire.com/Home/Products/Cable/Alpha-Essentials/Coaxial-Cable/9823?device=pdf is 78%.

So it is actually often the other way around.

BoB

Edit: If you could figure out how to traverse the north Atlantic with high velocity copper you would end up extremely rich.

11. Nov 4, 2016

### Baluncore

A two wire transmission line in air, without insulation on the wires, has a velocity factor above 99% and very low losses.

Optic fibres have a graded RI with a faster surface material that guides the light along the low loss central part of the fibre.
The opposite is the case with compression waves in a metal rod, energy will escape the surface of the rod and be lost into the lower velocity air.

12. Nov 4, 2016

### Staff: Mentor

With respect to bandwidths, there's a funny story of how Time magazine would fly a courier from NYC to Hong Kong with a old massive mainframe disk pack 30 lbs or so once a week.

He had a great time racking up airline mileage and seeing the sites of Hong Kong until someone thought of transmitting the same info over the wire. The end result was that the trips were reinstated when they discivered it took a whole week to transmit the data on the disk. Things were a bit slower then.

Anecdotal story told in a 1970's data communications class.

Last edited: Nov 4, 2016