Are folded-beam suspensions really linear?

Folded-beam suspensions are designed to respond as linear springs. In this work we show that even if their design and construction is perfect, their response is linear only for static applications. We show that the dynamic response of perfect foldedbeam suspensions is inherently nonlinear. Surprisingly, the nonlinearity becomes dominant when the vibration amplitudes are on the order of the width of flexure beams (far less than 10% of the beam length). We show that this nonlinearity is not associated with large deformations or with electrostatic actuation, but is rather caused by inertial effects which induce membrane stiffening. We discuss considerations that would lead to a solution of the problem, and would enable the design of a dynamically-balanced folded-beam suspension.