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Abstract

An ultrasound array for acoustic wave transmission comprising at least one capacitive micro-machined ultrasound transducer (CMUT) cell (6), wherein the CMUT cell comprises a substrate (4) having a first electrode (7); a cell membrane (5) having a second electrode (7′), which opposes the first electrode with a cavity (8) there between, wherein the membrane is arranged to vibrate upon the cell activation; and an acoustic window layer (13), overlaying the cell membrane, and having an inner surface opposing the cell membrane and an outer surface; the acoustic window layer is in a direct contact with the cell membrane and comprises a first layer comprising molecules of antioxidant and a polymeric material, wherein the polymeric material consists of hydrogen and carbon atoms and has a density equal or 3 below 0.95 g/cm and an acoustic impedance equal or above 1.4 MRayl. The array may further comprise comprising at least one drive circuit coupled to the cell and adapted to (a) bring the membrane into a collapsed state in which the membrane is collapsed to the substrate in the central part, by applying a d.c. voltage over the first and the second electrodes of the at least one CMUT cell, and (b) activate the CMUT cell by applying an a.c. voltage having a CMUT operating frequency over the first and the second electrodes of the at least one said CMUT cell. This acoustic window layer provides an improved acoustic performance, such as wide bandwidth and low attenuation, in application with the CMUT based array, especially in the collapsed operation mode.

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