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100 hz display device with very low electromagnetic emissions needed - LCD? Shielding on CRT?

Posted on 2008-11-10
Medium Priority
Last Modified: 2013-11-06
Greetings All.

I need a monitor with very low electromagnetic emissions that will refresh an image at 100Hz or higher. Why? Read on macduff, there is some detail:

I am a scientist working in the area of brain research. We are measuring neural oscillations with EEG equipment. We are looking at brain oscillations that occur when people socially cooperate with each other. We've found some - now we're developing a machine version of a human so that we can manipulate the brain rhythms with a simulated partner to better understand whats happening in the brain.

we need a low energy display device *desperately*, that fulfills certain constraints. why?

Your brain gives off very very small (microvolt range) electromagnetic signals which we can read by placing electrodes on the scalp. We'd prefer to drill them into your head to get a better signal, but apparently there are ethical issues with this and the university won;t allow it.

[skip next para if you don't care about the experiment details]

The experiment involves real-time interaction with a computer display. The subject's behavior is relayed into a computer, and a clever set of equations (not devised by me) simulate what the behavior of another human would be. The behavior of the equations is then used to drive an animation so that as the human behaves, s/he alters the simulated human, who in turn alters the behavior of the real human. we can change the behavior of the equations; hence measure how the brain reacts to different social coordination situations.

At the moment, we've had great success with this system, but we have not done any EEG (brain) recording, just behavioral recording. The brain recordings so far have been done between two real people, rather than a person and a machine.

So, we have been able to use CRT monitors. These monitors have a refresh rate of 100Hz. That means that the WHOLE system operates at 100Hz; data acquisition, recording, display and so on. And through directX, I can use the monitor refresh cycle to guarantee the timing of the whole system. This is:

CRUCIAL!! for a scientific experiment. The timing must be PERFECT. 100Hz is ok, as long as we know that everything is in sync. In an ideal world, it would be 1000 or 10000 Hz, but it is the sync that is crucial.

It could be 60 - BUT 60Hz is too slow - the human brain begins (subconsciously, in an area called V1 - primary visual cortex) to discern the frames changing. We need at least 100.

Now: the problem: CRT's give off a ton of electromagnetic radiation. And these one's are going to do it at 100Hz - exactly where we don't want it

This will screw our brain readings.

So, we need some other display technology that can refresh the screen at 100Hz or more without giving off too much electromagnetic energy,

I've asked all over the scientific community, No one knows of such a thing. I've seen LCD/PLASMA TV's that claim to update at 100Hz - but apparently the *image* is not really being updated at 100Hz.

Does anyone know of a technology, maybe even quite an expensive one, that might fulfill my needs:

100Hz+ image refresh
very little electromagnetic radiation.
this could be some kind of shielded CRT?

it need not be 100Hz refresh - it needs to be 100Hz *image update*

hoping for some expert advice; I'm clueless about display technology.

Question by:zatak
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LVL 93

Expert Comment

ID: 22928813
can you not use a beamer, to display the crt screen on a wall, and keep the crt some rooms away, and shielded?

Author Comment

ID: 22932297
the environment is full of electromagnetic noise from many sources.

So the experiment takes place inside a Faraday chamber, and one cannot cut a hole in that even if one wants to

Really, I think we need an LCD of some sort
LVL 32

Accepted Solution

aleghart earned 1600 total points
ID: 22937366
Have you talked to your room designer about shielding the existing monitors?

Some things to look at:

1. fine mesh window
2. polyester shield coating

3. custom monitor with EMI sheilding:

The LCD route may be a no-go.  I don't know of any monitors that go above 75-85Hz.  Even the medial models from Eizo and Barco, which run from $2K to $10K+.

Have you tried contacting Barco Medical Imaging?  I know some of their greyscale monitors for imaging display (xray, crt, mri) go up to 120Hz:  http://www.barco.com/barcoview/downloads/MVGD1318.pdf

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Author Comment

ID: 22937399
There is not a room designer, there is a very expensive custom built isolated Faraday chamber (complete with airlock) that cannot be altered, at least not just for this one experiment. Obviously my experiment is the most important experiment in the history of science, but my superiors need convincing of that :) Anyway, we can't alter the chamber and thats' that - and it was not built by us.

But it seems to me that shielding the CRT may be the way to go. I'm not really much of an expert on all this, but it seems to me that some wire mesh around the back of the monitor is not going to be good enough - do you know of an expert you could recommend who could give advice on hard-core shielding of a CRT?

One thing is that I *love* the CRT system - it works really well in the non-EEG pilots I've done, and interfaces with my directx code pretty well. The apparatus is tight as it stands in terms of timing.

I don't understand LCD, and I don't believe that the actual *image* would refresh at 100Hz even if the claim was that the monitor refresh rate was 100Hz.

below 100Hz the human visual system begins to detect the image flips, even if one does not consciously experience this.100ms is kind of a magic timescale in the brain.

I will follow your links (*very* gratefully received) and see what's what.


Author Comment

ID: 22937433
what about this:


it says 120Hz vertical scan freq
LVL 93

Assisted Solution

nobus earned 400 total points
ID: 22937516

Author Comment

ID: 22937538
I'm excited about the link I posted above for the 120hz lcd from barco. But the CRT shield does look good.

In any case, the information you've provided has been excellent - thank you very much. I may contact you in the future if that is ok. The Neuroscience 2008 conference in washington starts on the 15th; everything is on hold till then.

I'll pass these links to colleagues, and see what they think.

thanks again.
LVL 93

Expert Comment

ID: 22937700
please, review your points assignment; atleast-  assign some to aleqhart, who posted that idea !
you can do this by clickin "request attention" in your original question

Author Comment

ID: 22941917
oops - he was the one I thought I was giving points to in the first place -  how do I change the points?
LVL 93

Expert Comment

ID: 22942155
you should read the help files, all is in there;
but if you READ my post, i posted it already !
LVL 32

Expert Comment

ID: 22944193
>you should read the help files
umm...  Guilty.  I haven't read those yet, either.

So, click on "Request Attention" at the bottom of the original question.
I'll have to remember that.

Author Closing Comment

ID: 31515350
a complete solution is not possible in this case at present

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