a diaphragm structure with a first substrate including a first surface with an annular groove therein and a second opposing surface with an annular groove on each side of annular groove in the first surface defining a first diaphragm . a second substrate also includes a first surface with an annular groove therein and a second opposing surface with an annular groove on each side of the annular groove in the first surface defining a second diaphragm . a diaphragm overload stop is located behind the first and second diaphragms .