A density and viscosity sensor 1 for measuring density and viscosity of fluid F, the sensor 1 comprising: a resonating element 3, 3A, 3B, 3C, 3D, 3E, 3F, 3G arranged to be immersed in the fluid F, an actuating/detecting element 4, 4A, 4B coupled to the resonating element, a connector 7 for coupling to the actuating/detecting element 4, 4A, 4B, a housing 2 defining a chamber 8A isolated from the fluid F, the housing 2 comprising an area of reduced thickness defining a membrane 9 separating the chamber 8A from the fluid F, the membrane 9 having a thickness enabling transfer of mechanical vibration between the actuating/detecting element 4, 4A, 4B and the resonating element 3, 3A, 3B, 3C, 3D, 3E, 3F, 3G, the actuating/detecting element 4, 4A, 4B is positioned within the chamber so as to be isolated from the fluid F and mechanically coupled to the membrane 9, the resonating element 3, 3A, 3B, 3C, 3D, 3E, 3F, 3G arranged to be immersed in the fluid F is mechanically coupled to the membrane 9, wherein the resonating element 3, 3A, 3B, 3C, 3D, 3E, 3F, 3G has a shape defining a first resonance mode and a second resonance mode characterized by different resonant frequencies F1, F2 and different quality factors Q1, Q2, the first resonance mode moving a volume of fluid, the second mode shearing a surrounding fluid.