Cannula assembly and ambulatory infusion system with a pressure sensor made of stacked coplanar layers

The invention is directed towards a cannula assembly (40), comprising: an infusion cannula (20) and a hub (40), the hub (40) comprising a pressure sensor with a fluid channel (115), the fluid channel (115) being fluidically arranged upstream of the infusion cannula, the pressure sensor comprising a stack of coplanar layers, the stack of coplanar layers comprising: a) a rigid top layer (110) and a rigid base layer (102), b) a resilient metallic electrode layer (106) and a metallic counter-electrode layer (108), the electrode layer (106) and the counter-electrode layer (108) being electrodes of a sensing capacitor, c) a spacer layer (109) which has a through cut-out, the through cut-out defining an electrode cavity (112), wherein the fluid channel (115) is coupled to the electrode layer (106) such that a positive fluidic pressure of the drug in the fluid channel (115) causes the electrode layer (106) to bend into the electrode cavity (112), thus modifying the capacitance of the sensing capacitor. The invention is further directed towards an ambulatory infusion system comprising such a pressure sensor.