Abstract: A transducer array (10) is disclosed comprising a plurality of CMUT cells (100, 100, 100?), each CMUT cell comprising a first electrode (110) supported by a substrate (101) and a second electrode (120) supported by a membrane suspended over a cavity (105) between the first electrode and the second electrode, the plurality of CMUT cells comprising a first group of CMUT cells (100) each having a membrane comprising a first layer stack (130); and a second group of CMUT cells (100?) each having membrane comprising a second layer stack (130?), the second layer stack including a layer (135) of a material having a higher density than any of the layers in the first layer stack. Also disclosed is a device comprising such a transducer array, an ultrasound imaging system including such a transducer array and a method of operating such an ultrasound imaging system.