An ultrasound system is disclosed comprising a probe (10) including an array (110) of CMUT (capacitive micromachined ultrasound transducer) cells (100), each cell comprising a substrate (112) carrying a first electrode (122) of an electrode arrangement, the substrate being spatially separated from a flexible membrane (114) including a second electrode (120) of said electrode arrangement by a gap (118), the flexible membrane comprising a mass element (140) in a central region (17, 17′) and a voltage supply (45) coupled to said probe and adapted to, in a transmission mode of the ultrasound system, provide the respective electrode arrangements of at least some of the CMUT cells with a voltage including a bias voltage component driving the at least some of the CMUT cells into a collapsed state in which a central part of the flexible membrane contacts the substrate, said central part including the central region and a stimulus component having a set frequency for resonating the respective flexible membranes of the at least some of the CMUT cells in said collapsed state, wherein the mass element of each of the at least some CMUT cells forces at least the central region of the flexible membrane of said cell to remain in contact with the substrate during said resonating. A pulse transmission method for such a system is also disclosed.
