A micro-electromechanical system for sensing flow of a fluid, the system comprising: a planar first layer comprising an upper side, a lower side, a plurality of paddles (34a-d) and a frame, wherein the frame surrounds and supports the plurality of paddles in cantilever fashion to enable independent deflection of the plurality of paddles in response to the fluid flow; a planar second layer comprising an upper side, a lower side, a plurality of vent holes (36f-i) and a plurality of cavities (36a-e) extending between the upper side and the lower side, the upper side of the planar second layer being positioned adjacent to the lower side of the planar first layer; and a planar third layer comprising an upper side, a lower side and: a plurality of openings (38f-i) being aligned with the plurality of vent holes of the planar second layer so as to allow fluid entering the package to escape through the lower side of the planar third layer, at least one light source for producing a signal directed towards an underside of at least one of the plurality paddles, the light source being arranged in a first cavity of the plurality of cavities of the planar second layer, and at least one receiver (38a-d) for receiving the signal reflected by the underside of the paddle, the receiver being arranged in a second cavity of the planar second layer, wherein the planar second layer is adapted to block direct transmission of light between at least one source and at least one receiver (38a-d); wherein the system further comprises a housing enclosing the planar first layer, the planar second layer, and the planar third layer, the housing comprising a plurality of openings (32a-d) exposing the plurality of paddles to the fluid. a planar first layer comprising an upper side, a lower side, a plurality of paddles (34a-d) and a frame, wherein the frame surrounds and supports the plurality of paddles in cantilever fashion to enable independent deflection of the plurality of paddles in response to the fluid flow; a planar second layer comprising an upper side, a lower side, a plurality of vent holes (36f-i) and a plurality of cavities (36a-e) extending between the upper side and the lower side, the upper side of the planar second layer being positioned adjacent to the lower side of the planar first layer; and a planar third layer comprising an upper side, a lower side and: a plurality of openings (38f-i) being aligned with the plurality of vent holes of the planar second layer so as to allow fluid entering the package to escape through the lower side of the planar third layer, at least one light source for producing a signal directed towards an underside of at least one of the plurality paddles, the light source being arranged in a first cavity of the plurality of cavities of the planar second layer, and at least one receiver (38a-d) for receiving the signal reflected by the underside of the paddle, the receiver being arranged in a second cavity of the planar second layer, a plurality of openings (38f-i) being aligned with the plurality of vent holes of the planar second layer so as to allow fluid entering the package to escape through the lower side of the planar third layer, at least one light source for producing a signal directed towards an underside of at least one of the plurality paddles, the light source being arranged in a first cavity of the plurality of cavities of the planar second layer, and at least one receiver (38a-d) for receiving the signal reflected by the underside of the paddle, the receiver being arranged in a second cavity of the planar second layer, wherein the planar second layer is adapted to block direct transmission of light between at least one source and at least one receiver (38a-d); wherein the system further comprises a housing enclosing the planar first layer, the planar second layer, and the planar third layer, the housing comprising a plurality of openings (32a-d) exposing the plurality of paddles to the fluid.