Using Sound to Read Discs, instead of EMRs.

[math_way]

Hi all,

I was just reading a bit on the disc reading. It was only then that this idea of using sound to read discs struck me. We know that sound too, behaves like light, in many situations(has a particular speed limit, both exhibit resonance, etc.). One very important difference being that light is an emr, while sound is a mechanical wave.

Infact, sound is not affected by magnetic or electric field. So now, why is it that we are not using sound to read discs? Or is it that this idea is already being researched, and not much progress had been made yet?

Thanking You,
math_way

(NOTE: I am a new user, hence if any changes are to be made in the way I've posted this thread, kindly send me a msg)

 

[Wolfgang2b]

On top of my head, I think this is not a practical solution wit h regards to resolution. The wave length of sound is very large compared to light (At 20 KHz, wavelength of sound is around 1 cm). So one bit in the HDD has to be atleast 1 cm away from the next one for resolution. So if you have 100 bits side by side we will have a 1 meter wide HDD. Wavelength of light is in micrometers. So u can pack more bits in the same space.

There might be many other reasons as well

 

[cmb]

Infact, sound is not affected by magnetic or electric field. So now, why is it that we are not using sound to read discs? Or is it that this idea is already being researched, and not much progress had been made yet?

I don't understand the question as it seems to have already been done - often called a '78', or 'single' or 'LP', in ancient days gone by.

In fact, the reverse has come to pass - old records that are too fragile to be played with turntable and stylus can now be scanned optically to provide a contact-less means of playing them.http://www.redorbit.com/news/technology/1315449/experts_uncover_worlds_oldest_recording/

 

[math_way]

Right! This was what i found on the website: "...Using high resolution optical scanning equipment..."

But my question was, why not use sound to read discs, rather than LASERS. I agree LASER is monochromatic. Therefore, it does not get dispersed. And as Wolfgang2b pointed out, there is this problem of space as well.

 

[cmb]

Light provides a high frequency, contact-less means to read and write to discs. It would be impossible to deliver anywhere near the data speeds, signal-noise ratios or reliability by mechanical means. It was to overcome these limitations that optical discs were created.

 

[math_way]

Right! and what about the future of CDs with the entry of Blue Ray discs. I understand that Violet light is used to read the CDs, instead of the exisisting Red light.

Red light has a higher frequency, and shorter wavelength, than Violet light, that makes it faster. Its obvious that Velocity of light is faster when wavelength is greater(keeping frequency const.). Hence, I learned that the disc can store more data in some space. Now as a concequence, disc reading speed will be faster as well right?

 

[cmb]

Blue light has the shorter wavelength, so as the frequency of the lasers used becomes blue-er then more data can be physically recorded into the same physical space. I don't know enough about this tech to say whether there is an optimum wavelength for optical media to maximise data transfer rates, though.

 

[chill_factor]

sound has a much lower frequency and much longer wavelength than light does and is billions of times slower.

another practical problem is that sound cannot be directed the way light can be directed with a fiber, energy dissipation of sound is much faster, and its wavelength can be changed in unpredictable ways by uncontrollable environmental fluctuations like temperature far easier than light can; in fact, it is extremely hard to change the wavelength of light appreciably without special equipment. in addition it is reflected in complex and unpredictable ways compared to light and gives up far more of its energy to the reflecting medium than light does in most cases.

sound is actually very bad for communication but for animals its great because it can travel around obstacles the size of other animals and is easy to make, whereas to create light is not as easy - try it without a lighter or electricity, its not so easy.

 

[PageAA2231]

http://www.subeducation.info/avatar5.jpg There might be many other reasons as well

 

[nasu]

In order to attain ultrasound wavelengths (in plastic) of the same order as the wavelength of light (0.5 microns) frequencies one need frequencies in the GHz range, which may be available even though not in common use.
However the air is a very bad coupling between ultrasound source and target and one needs to add some coupling agent (usually gel). So I suppose you will need to put some gel on the DVD before inserting in the ultrasound reader. Or maybe the whole unit will be immersed in water.

 

[chill_factor]

In order to attain ultrasound wavelengths (in plastic) of the same order as the wavelength of light (0.5 microns) frequencies one need frequencies in the GHz range, which may be available even though not in common use.
However the air is a very bad coupling between ultrasound source and target and one needs to add some coupling agent (usually gel). So I suppose you will need to put some gel on the DVD before inserting in the ultrasound reader. Or maybe the whole unit will be immersed in water.

harder to guide sound though. there's very little that's soundproof at the atomic scale - everything will vibrate. there's plenty of substances that are truly reflective though. nondissipative waveguides for sound do not exist.

 

[nasu]

harder to guide sound though. there's very little that's soundproof at the atomic scale - everything will vibrate. there's plenty of substances that are truly reflective though. nondissipative waveguides for sound do not exist.

I am not advocating the use of sound for DVD. Just pointing another point of difficulty (coupling medium).
Thinking about the differences is interesting, though.

I think that focusing and transmitting the sound are not the major problems, at least for reading the data. The scanning acoustic microscope can see details around 1 micron. I don't know if it has good enough resolution to see the details on a CD. Probably not.
Writing the data with ultrasound though may be even more difficult.

 

[chill_factor]

yep another reason not to use sound, i hadn't even thought of writing. that would be a nightmare.

if you're going to use mechanical means to read storage media... might as well go all the way and use an AFM to read it. ultraslow data recovery but you could theoretically get 1 bit of information = 1 nm wide X nm deep indentations, and you can write with the AFM by indenting the surface. that'd require some extreme precision machining and extreme stability though.

 

[nasu]

yep another reason not to use sound, i hadn't even thought of writing. that would be a nightmare.

if you're going to use mechanical means to read storage media... might as well go all the way and use an AFM to read it. ultraslow data recovery but you could theoretically get 1 bit of information = 1 nm wide X nm deep indentations, and you can write with the AFM by indenting the surface. that'd require some extreme precision machining and extreme stability though.

Actually there are people trying some variation of this. Or at least they did, in the early 2000's. There was a project at IBM Zurich along these lines. I mean, using a multiple AFM head to write and read data. They called it "millipede". Thermal AFM levers were used to control the position of the reading head relative to substrate.
I don't know what happened with it since then.

 

[math_way]

Right guys, that makes a lot of sense! And nasu, what exactly was this project conducted by IBM Zurich? Can you please elaborate a bit on it? Thank you.

 

[nasu]

Look up "millipede project IBM". There is a Wiki article on it too.
Or here, on their website:
http://www.zurich.ibm.com/st/storage/concept.html

 

[Borek]

This "size" thing mentioned at the very beginning means disks will have abstract sizes. The way I understand the situation the main difference between DVD and Blu-Ray is the laser color - switching from red to blue (shorter wavelength) allowed higher information density on the surface. Change the wavelength in the other direction, and your disk becomes size of the tennis field.

Blu-ray uses 405 nm lasers to read 12 cm disks. Let's say we will use 50 kHz sound to read the information - that means wavelength of 6.6 mm. Assuming naively that information density is just inversely proportional to the wavelength, using 50 kHz ultrasound we would obtain 16300 times lower information density on the disc, so we need 16300 times more surface. That means 15.3 m diameter of the disk. 50 feet.

 

[nasu]

I don't think this is the major problem. Or at least, is not so bad, from this point of view.
50 kHz is a very low frequency in ultrasound technology. 1 GHz is quite common. I don't know the speed of sound in the material that may satisfy all the reuirement for a possible sound recording technique. But using a "slow" medium like some plastics, wavelength can be of the order of a micron. Still larger than that of the blue light but not by much.
What I am trying to say is that the wavelength is not the major impediment.
The easiness and cheapness of producing, focusing and manipulating light beams compared with ultrasound beams I suppose is a more important factor.