Sensor element, particle sensor device and method for detecting a particulate matter density

A sensor element comprising:

• a membrane structure suspended on a frame structure, wherein the membrane structure comprises a membrane element and an actuator,
• wherein the membrane structure is deflectable in a first stable deflection state and in a second stable deflection state and is operable in a resonance mode in at least one of the first and the second stable deflection states, wherein the membrane structure is coupled by a frame structure at a coupled location, wherein the membrane structure comprises a first portion that is above the coupled location in the first stable deflection state, and wherein the membrane structure comprises a second portion that is below the coupled location in the second stable deflection state,
• wherein the actuator is configured to deflect the membrane structure in a first actuation state into one of the first and the second stable deflection states, and to operate the membrane structure in a second actuation state in a resonance mode having an associated resonance frequency,
• wherein the actuator comprises an actuator layer stack mechanically coupled to the membrane element, wherein the actuator layer stack comprises a piezoelectric functional layer in a sandwiched configuration between a first and second electrode structure,
• wherein at least one of the first and second electrode structures is segmented into at least four electrically separated quadrant-shaped or wedge-shaped electrode structure segments, and
• wherein the membrane structure is configured to operate in a self-cleaning state comprising switching the membrane structure between the first and the second stable deflection states.