Quiet Propeller using Carbon Nanotube Thin Film Thermophone

The GLSV and MTU team are proposing a novel acoustic method using carbon nanotube (CNT) thin film as a thermophone embedded into the tip and trailing edge of advanced unmanned aerial vehicles to actively reduce propeller noise.  The of CNT thermophones in active noise cancellation has been demonstrated by the team in engine exhaust applications as well as fan applications to date.  The application of this technology to rotor noise has the potential to offer significant noise reduction benefits without a significant weight penalty or a need to modify airfoil geometry.  Instead the thermophone can produce rapidly fluctuating temperatures in the thin film, which creates and unsteady pressure that can be used to counteract the unsteady pressures that act on the rotor blades to create noise.  The ability to reduce noise without a performance reduction is critical in the acceptance of eVTOL into commercial and recreational applications.  The unique ability of this novel acoustic method to reduce propeller noise without a performance degradation has equally critical implications in the defense space since it allows missions to be carried out at lower altitudes without acoustic detection.  This means better surveillance and more missions accomplished for the US Military.