Noise reduction for an acoustic cooling system

Abstract

The present invention relates to an acoustic cooling system ( 1 ) arranged for cooling by generating sound waves, said system ( 1 ) comprising a transducer ( 2 ) and a control unit ( 6 ) configured to generate a drive signal (S 1 ) for exciting said transducer ( 2 ), wherein said drive signal is a multi-harmonic drive signal comprising at least one higher harmonic (A 2 -A 5 ) selected to reduce the presence of at least one corresponding higher harmonic (B 2 -B 5 ) comprised in the sound waves. The system is advantageous in that noise-reduction can be achieved without the need of incorporating a second transducer, thereby enabling a compact acoustic cooling system at a low cost.

1 . An acoustic cooling system arranged for cooling by generating sound waves, said system comprising:
 a transducer; and   a control unit configured to generate a drive signal for exciting said transducer, wherein said drive signal is a multi-harmonic drive signal comprising at least one higher harmonic selected to reduce the presence of at least one corresponding higher harmonic comprised in the sound waves.   
     
     
         2 . Acoustic cooling system according to  claim 1 , further comprising a sensor configured to detect sound waves generated by the system and to provide a sound signal (S sound ) related to the detected sound waves to said control unit, wherein the control unit is further configured to select the at least one higher harmonic of the drive signal based on said sound signal (S sound ). 
     
     
         3 . Acoustic cooling system according to  claim 1 , further comprising a sensor configured to measure at least one of an induced voltage and an induced current in the transducer as an indication of the sound waves generated by the system and to provide information related to at least one of the induced voltage and the induced current to said control unit, wherein the control unit is further configured to select the at least one higher harmonic of the drive signal based on said information. 
     
     
         4 . A method for determining a multi-harmonic drive signal for an acoustic cooling system arranged for cooling by generating sound waves, the method comprising the steps of:
 providing a drive signal to a transducer;   acquiring a sound signal (S sound ) relating to sound waves generated by the system in response to the drive signal;   determining a sound power spectrum for said sound signal (S sound ); and   transforming said drive signal by introducing at least one higher harmonic selected such that at least one corresponding higher harmonic in the sound power spectrum is reduced.   
     
     
         5 . A method according to  claim 4 , wherein at least one of an amplitude and a phase for said at least one higher harmonic in the drive signal is selected such that a corresponding higher harmonic in the sound power spectrum is reduced. 
     
     
         6 . A method according to  claim 4 , wherein the multi-harmonic drive signal is determined by a procedure that iteratively introduces increasingly higher harmonics to the drive signal, starting with the second harmonic. 
     
     
         7 . An illumination device comprising:
 a light emitting device; and   an acoustic cooling system according to  claim 1  arranged for cooling said light emitting device.