Device for detecting breathing

Claim 1

A breathing detection apparatus comprising: (A) an airbag including: (a) a sponge body having pores therein for containing air, said sponge body being expandable and contractable in response to contractive and expansive motions of a body part of a person; (b) a sponge cover enclosing said sponge body for preventing air contained in the pores of said sponge body from escaping therefrom; (c) an air guide tube having one end connected to an opening in said sponge cover, said air guide tube guiding an air stream to and from said sponge cover caused by expansion and contraction of said sponge body; and (d) a flange provided integrally with a peripheral edge of said sponge body; and (B) a detector coupled to another end of said air guide tube for converting said air stream to a variable voltage, a level of said variable voltage being proportional to a flow rate and direction of said air stream, said detector including: (a) an open-ended housing, said air guide tube being connected to a closed end of said housing; (b) an electret capacitor microphone closing said open-end of said housing, said electret capacitor microphone comprising: (1) a housing having an aperture therein opening into said open-ended housing; (2) an oscillating film spaced from and opposite to said aperture, said film forming a seal with sides of said housing; (3) a back electrode spaced behind said oscillating film, said back electrode and said oscillating film having an electrostatic capacitance which varies with movement of said oscillating film; (4) a field-effect transistor connected to said back electrode for converting changes in said electrostatic capacitance to said variable voltage, and (c) a pressure reduction film mounted in said open-ended housing between said microphone and said closed end of said open-ended housing, said pressure reduction film being a continuous air impermeable membrane and forming an airtight seal with sides of said open-ended housing; whereby movement of said air stream causes pressure changes in said housing which, in turn, cause said oscillating film to deflect changing the electrostatic capacitance of the oscillating film and the back electrode, this change in capacitance being converted into the variable voltage by said field effect transistor, and whereby a resistance to flexing of said pressure reduction film reduces the pressure exerted on said oscillating film thereby preventing saturation of said oscillating film.