An interesting application is an 'elephant ear' for detecting infra-sound produced by wind turbines.
You need a sturdy 1mX1m frame with a plastic membrane stretched across it. Use an ultrasonic distance measuring device (e.g. HC-SR04) to capture membrane vibration. Software controls ultrasonic TX pulse rate and use a FFT algorithm to separate RX vibration data into wind turbine infra-sound components and random wind speed components.
