Monochrome interference microphone

  • Thread starter poor mystic
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In summary, the idea is to create a microphone that uses a monochrome light source and a reflective membrane to track the position of gold leaf. The detector consists of a monochrome source, a reflective membrane, and several randomly-placed detectors. The idea is that as the membrane moves towards or away from the source and detectors, each detector will be excited at different times, when constructive interference exists between the light reflected from the moving membrane and the light reflected from the static reflectors. With 'towards' and 'away' discrimination provided by the sequence discriminator, a count can be incremented or decremented respectively. The count therefore shows the position of the gold leaf.
  • #1
poor mystic
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Idea for a microphone.

Hi People!
I've had an idea for a monochrome light microphone, which I have rendered as a drawing, attached.
The detector consists of a monochrome source (l.e.d.), a reflective membrane (gold leaf) some distance from the source, a static reflective element, and several randomly-placed detectors, 3 of which are shown.
The idea is that as the membrane moves towards or away from the plane of the source and detectors, each detector will be excited at different times, when constructive interference exists between the light reflected from the moving membrane and the light reflected from the static reflectors.
As a sound wave pushes the membrane towards the detectors, the detectors will tend to be excited in some characteristic repeating sequence, I hope; the order will be reversed when the membrane is moving away from the detectors.
With 'towards' and 'away' discrimination provided by the sequence discriminator, a count can be incremented or decremented respectively. The count therefore shows the position of the gold leaf.
Questions & Problems
First, I wonder whether this has been tried before, and then I'm looking for any ideas on how to train some kind of sequence discriminator to recognise "toward" and "away" movements of the membrane.
The biggest problem is the light. I think I'd be a lot better off using a low infrared monochrome source than a visible light source. This is because there are so horrendously many wavelengths of visible light per millimeter. It would be better to use a wavelength of hundreds of nanometers, if practicable.

Still, it's just an idea at this stage... any thoughts?
 

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  • #2
poor mystic said:
Idea for a microphone.

Hi People!
I've had an idea for a monochrome light microphone, which I have rendered as a drawing, attached.
The detector consists of a monochrome source (l.e.d.), a reflective membrane (gold leaf) some distance from the source, a static reflective element, and several randomly-placed detectors, 3 of which are shown.
The idea is that as the membrane moves towards or away from the plane of the source and detectors, each detector will be excited at different times, when constructive interference exists between the light reflected from the moving membrane and the light reflected from the static reflectors.
As a sound wave pushes the membrane towards the detectors, the detectors will tend to be excited in some characteristic repeating sequence, I hope; the order will be reversed when the membrane is moving away from the detectors.
With 'towards' and 'away' discrimination provided by the sequence discriminator, a count can be incremented or decremented respectively. The count therefore shows the position of the gold leaf.
Questions & Problems
First, I wonder whether this has been tried before, and then I'm looking for any ideas on how to train some kind of sequence discriminator to recognise "toward" and "away" movements of the membrane.
The biggest problem is the light. I think I'd be a lot better off using a low infrared monochrome source than a visible light source. This is because there are so horrendously many wavelengths of visible light per millimeter. It would be better to use a wavelength of hundreds of nanometers, if practicable.

Still, it's just an idea at this stage... any thoughts?

One variation of your idea that exists today for position measurement is the laser interferometer systems like these from Agilent:

http://www.home.agilent.com/agilent/product.jspx?nid=-536900386.0.00&lc=eng&cc=US

So instead of using multiple detectors to figure out movement, you use the changes in intensity from constructive/destructive interference to tell you how many wavelengths the distance has changed.

You might be able to make a small version of this for your microphone, using a laser diode. I'm not sure what the coherence length of a typical low-cost laser diode is, though. You could use a laser pointer's diode for initial experimentation (but please wear laser eye protection if you start working with laser diodes).
 
  • #3
Thanks Berkeman!
Still, I'm sure the professional systems use more than 1 detector, otherwise they wouldn't be able to detect the sense of any movement - whether it is towards or away from the detector.
I've made a small advance in understanding. If just 2 detectors are 1/4 wavelength apart the order in which they detect the changeing sums of interfering waves shows the sense of the movement.
 
Last edited:
  • #4
Further question:
I've been turning this over and over in my mind and I just don't see why a laser should be required. It seems to me that a Young's double slit should work just as well, with no dangerous lasers. Perhaps I got that wrong?
 
  • #5


As a fellow scientist, I find your idea for a monochrome interference microphone to be very interesting. I am not aware of any previous attempts at creating such a device, but I believe it has potential for further exploration and development.

In terms of training a sequence discriminator, one approach could be to use machine learning techniques. By feeding the detector readings from different sound wave frequencies and amplitudes, the algorithm could learn to differentiate between "toward" and "away" movements of the membrane.

I agree that using a low infrared monochrome source would be more practical and efficient for this type of microphone. It would also be important to carefully select the wavelength to ensure minimal interference from ambient light sources.

Overall, I think your idea has great potential and could potentially offer new advancements in microphone technology. I look forward to seeing how it progresses in the future.
 

1. What is a monochrome interference microphone?

A monochrome interference microphone is a type of microphone that uses a single color of light to detect sound waves. It works by converting the sound waves into variations in the intensity of the light, which can then be measured and converted into an electrical signal.

2. How does a monochrome interference microphone work?

A monochrome interference microphone works by using a thin membrane that vibrates in response to sound waves. This membrane is placed in front of a light source, and as it moves, it creates variations in the intensity of the light. These variations are then detected by a photodetector and converted into an electrical signal.

3. What are the advantages of using a monochrome interference microphone?

One of the main advantages of a monochrome interference microphone is its high sensitivity, as it is able to detect very small variations in light intensity. It also has a wide frequency range and is less susceptible to external noise compared to other types of microphones.

4. What are some common applications of monochrome interference microphones?

Monochrome interference microphones are commonly used in scientific research, specifically in acoustics and vibration studies. They are also used in audio recording and broadcasting, as well as in the medical field for measuring heart and lung sounds.

5. Are there any limitations to using a monochrome interference microphone?

One limitation of using a monochrome interference microphone is that it is sensitive to ambient light, which can affect its accuracy. It also requires a stable light source, making it less portable compared to other types of microphones. Additionally, it is not suitable for high-pressure or high-temperature environments.

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