Patent ID: 8198992

Claim:
A seat belt warning system comprising a sensor mat having a surface and adapted for detecting a force acting upon the surface in a direction, said sensor mat comprising a first conductive layer, a second conductive layer and a third conductive layer disposed in parallel, spaced relationship; a first dielectric layer interposed between the first conductive layer and the second conductive layer and having a first compressibility in response to the force, said first conductive layer, said first dielectric layer and said second conductive layer forming a first electrical capacitor acted upon by the force and characterized by a first capacitance that varies dependent upon the force; and a second dielectric layer interposed between the second conductive layer and the third conductive layer and having a second compressibility in response to the force, said second compressibility being different from the first compressibility, said second conductive layer, said second dielectric layer and said third conductive layer forming a second electrical capacitor acted upon by the force and characterized by a second capacitance that varies dependent upon the force different from the first capacitance.