A catheter (700, 800, 1206) comprising: a shaft with distal (808, 906, 1004, 1208) and proximal ends (1006), wherein the distal end comprises at least one array of capacitive micromachined ultrasound transducers (308, 402, 404, 500, 512, 600, 604, 802, 1008) with an adjustable focus for controllably heating a target zone (806, 1014, 1210); and a connector (1012) at the proximal end for supplying the at least one array of capacitive micromachined ultrasound transducers with electrical power and for controlling the adjustable focus.