We present an electrostatic transducer in which voltage remains constant while charge is stored or extracted from the device. We achieve this by designing a nonlinear mechanical spring, which exactly counteracts the nonlinearity associated with electrostatic attraction forces. In essence, the new device responds like a rechargeable battery, only that here we store electric energy in elastic deformation, whereas in common batteries, electric energy is stored as chemical potential. The capacitance of the presented test devices is currently too small to be practical, and we are not, by any means, suggesting that this transducer can replace chemical rechargeable batteries. Nevertheless, some necessary steps toward constructing a more viable device with larger energy density are discussed.

We show that nonlinear elastic springs can be used to counteract the nonlinearity of electrostatic forces in gap-closing electrostatic actuators. We demonstrate this in two types of devices. In the first, we use a nonlinear spring to extend the stable range of the parallel-plates actuator, and to ensure that the response in this extended range is linear by design. In the second device, we use a nonlinear spring to ensure that beyond what would have been the pull-in point, voltage remains constant and independent of charge. In effect, this second device is a rechargeable mechanical battery.

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 folded- beam 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.