Integrating Piezoelectric Loudspeakers into Aircraft Engines to Reduce Noise

One of the main aircraft engine noises comes from the compression of air between the rotors, mobile parts of the motor, and stators, consisting of static blades. A technology being developed in the framework of a European project, and currently being tested in the Swiss Federal Institute of Technology in Lausanne's Electromagnetics and Acoustics Laboratory (LEMA), aims to integrate piezoelectric speakers into the blades of the stator. They function due to the property of certain materials to deform when an electric voltage is applied. A set of small microphones also placed in the engine captures the incident acoustic wave. They send the information to an electronic controller that calculates the signal to send to each of the loudspeakers integrated into the thirty blades to counter the wave coming from the reactor. "When they work together, the sound of the plane can be reduced by 1.5 to 2 decibel the noise percived by the human ear," notes Hervé Lissek, head of the acoustic group of LEMA.