The invention related to an ultrasound system comprising: an ultrasound array including at least one capacitive micromachined ultrasonic transducer device comprising a membrane coupled to a first electrode, a substrate opposing the membrane with a gas or vacuum cavity there between and coupled to a second and a third electrodes, wherein the second electrode opposes the first electrode in a peripheral region and the third electrode opposes the first electrode in a central region; at least one drive circuit coupled to the array. The system further comprises a high impedance resistor, which electrically couples to the second electrode and the third electrode and has an impedance value higher than an AC impedance between the first and the second electrodes, when the membrane of the CMUT device is in the collapsed state and the CMUT devices is activated at operating frequency.