This creates an acoustic wave...

T

tigerduck

Senior Member
Switzerland
German / Switzerland
Hello

Hello

I've read an article from NewScientist.com, but have difficulties in understanding it. It is about a system that transforms infrared light signals into sound. The system is used to detect and measure mustard gas or nerve agents.

Can somebody let me know what the This in the last sentence refers to?
What is it exactely that creates the acoustic wave?

Light from an infrared source is shone past a rotating chopper wheel, producing a pulsed beam of light, and through the window into the chamber. Any gas present absorbs infrared energy, causing the temperature in the chamber to rise very slightly. The chamber is sealed, so the increase in temperature causes an equivalent increase in pressure. Because the infrared light is pulsating, the increase in pressure fluctuates at the frequency of the chopper. This creates an acoustic wave which is sensed by two microphones in the walls of the chamber.

Thanks
 
    • "This" refers to the fact that the pressure fluctuates (goes up and down).

    (If you need a more detailed explanation I'd be happy to help :) )
     
    Because the infrared light is pulsating, the increase in pressure fluctuates at the frequency of the chopper. This creates an acoustic wave which is sensed by two microphones in the walls of the chamber.

    I believe "This" refers to the fluctuation in frequency caused by the increase in pressure...

    What do you think?
     
    The chopper wheel is rotating and that makes the infrared light pulsate following the pattern of the chopper wheel's rotation (in other words, since the chopper wheel rotates, the infrared light is not reaching the window in a continuous "line").

    Since the infrared light is pulsating, the pressure in the chamber goes up and down following the pattern of the pulse.

    This change in pressure creates acoustic waves which follow the pattern of the pressure's fluctuation.

    So, "this" could possibly refer to the whole experiment (from the point someone rigs the whole thing up till the wave is created) or, as I think most probable, to the pressure
     
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