An aerosol-generator (100; 200; 400) for an aerosol-generating device , the aerosol-generator comprising: a surface acoustic wave atomiser comprising: at least one substrate comprising an active surface defining at least one atomisation region ; a first transducer positioned on the active surface of the at least one substrate ; and a second transducer positioned on the active surface of the at least one substrate ; a first supply element arranged to supply a first liquid aerosol-forming substrate to the at least one atomisation region ; a second supply element arranged to supply a second liquid aerosol-forming substrate to the at least one atomisation region ; and a controller , wherein the controller is configured to provide a first drive signal to the first transducer for generating surface acoustic waves on the active surface of the at least one substrate , wherein the controller is configured to provide a second drive signal to the second transducer for generating surface acoustic waves on the active surface of the at least one substrate , wherein the controller is configured to provide the first drive signal to the first transducer only when the first liquid aerosol-forming substrate is supplied to the at least one atomisation region by the first supply element , and wherein the controller is configured to provide the second drive signal to the second transducer only when the second liquid aerosol-forming substrate is supplied to the at least one atomisation region by the second supply element . a surface acoustic wave atomiser comprising: at least one substrate comprising an active surface defining at least one atomisation region ; a first transducer positioned on the active surface of the at least one substrate ; and a second transducer positioned on the active surface of the at least one substrate ; at least one substrate comprising an active surface defining at least one atomisation region ; a first transducer positioned on the active surface of the at least one substrate ; and a second transducer positioned on the active surface of the at least one substrate ; a first supply element arranged to supply a first liquid aerosol-forming substrate to the at least one atomisation region ; a second supply element arranged to supply a second liquid aerosol-forming substrate to the at least one atomisation region ; and a controller , wherein the controller is configured to provide a first drive signal to the first transducer for generating surface acoustic waves on the active surface of the at least one substrate , wherein the controller is configured to provide a second drive signal to the second transducer for generating surface acoustic waves on the active surface of the at least one substrate , wherein the controller is configured to provide the first drive signal to the first transducer only when the first liquid aerosol-forming substrate is supplied to the at least one atomisation region by the first supply element , and wherein the controller is configured to provide the second drive signal to the second transducer only when the second liquid aerosol-forming substrate is supplied to the at least one atomisation region by the second supply element . <EOS>