Two-terminal cmut device

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 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 and adapted to (a) bring the membrane into a collapsed state in which the membrane is collapsed to the substrate in the central region, by applying a DC voltage over the first and the third electrodes of the at least one CMUT device, and (b) activate the CMUT device by applying an AC voltage having a CMUT operating frequency over the first and the second electrodes of the at least one said CMUT device;
• and
• wherein the third electrode of at least one capacitive micromachined ultrasonic transducer device of the array is electrically coupled to the second electrode via a high impedance resistor (R) having an impedance value higher than an AC impedance between the first and the second electrodes, when the membrane is in the collapsed state and the CMUT devices is activated at operating frequency.