Coulomb-actuated microbeams revisited: experimental and numerical modal decomposition of the saddle-node bifurcation

Electrostatic micromechanical actuators have numerous applicati ons in scie nee and technology.In many applications,they are operated in a narrow frequency range close to resonanee and at a drive voltage of low variation.Recently,new applications,such as microelectromechanical systems(MEMS)microspeakers(μSpeakers),have emerged that require operation over a wide frequency and dynamic range.Simulating the dynamic performance under such circumstances is still highly cumbersome.State-of-the-art finite element analysis struggles with pull-in instability and does not deliver the necessary in formation about un stable equilibrium states accordingly.Convincing lumped-parameter models amenable to direct physical interpretation are missing.This inhibits the in dispensable in-depth analysis of the dynamic stability of such systems.In this paper,we take a major step towards mending the situation.By combining the finite element method(FEM)with an arc-length solver,we obtain the full bifurcation diagram for electrostatic actuators based on prismatic Euler-Bernoulli beams.A subsequent modal analysis then shows that within very narrow error margins,it is exclusively the lowest Euler-Bernoulli eigenmode that dominates the beam physics over the entire relevant drive voltage range.An experiment directly recording the deflection profile of a MEMS microbeam is performed and confirms the numerical findings with astonishing precision.This enables modeling the system using a single spatial degree of freedom.

The push-pull principle:an electrostatic actuator concept for low distortion acoustic transducers

Electrostatic actuators are of particular interest for microsystems(MEMS),and in particular for MEMS audio transducers for use in advanced true wireless applications.They are attractive because of their typically low electrical capacitance and because they can be fabricated from materials that are compatible with standard complementary metal-oxide semiconductor(CMOS)technology.For high audio performance and in particular low harmonic distortion(THD)the implementation of the push-pull principle provides strong benefits.With an arrangement of three electrodes in a conjunct moving configuration on a beam,we demonstrate here for the first time a balanced bending actuator incarnating the push-pull principle operating at low voltages.Our first design already exhibits a harmonic distortion as low as 1.2%at 79 dB using a signal voltage of only 6 V_(p) and a constant voltage of only±10 V_(dc) in a standard acoustic measurement setup.Thus,exceeding our previously reported approach in all three key performance indications at the same time.We expect that our novel electrode configurations will stimulate innovative electrostatic actuator developments for a broad range of applications.In this paper we report the basic theory,the fabrication and the performance of our novel actuator design acting as an audio transducer.