Measuring vibrations in a variable speed wind turbine using light might sound a little abstract, but when you take these vibrations convert them to sound and speed them up some 44 times, it suddenly becomes concrete. This is exactly what has been done using the optical MEMS accelerometers from CEKO Sensors based on refractive index modulation™. Approximately 10 minutes of vibration turned into 13 seconds of sound – see (and listen!) to the result here:
What happens is that wind makes the wind turbine vibrate slightly. Optical MEMS accelerometers inside the wind turbine detect this vibration. Inside the accelerometers light is propagating, but due to the vibrations the speed at which light propagetes in the accelerometers varies. This is seen as color changes in the light. Taking these color changes and transforming them to variations in sound pressure produced by a loud speaker you can hear the wind turbine whistling. The graph shows the frequency as function of time.