@misc{MelnikovSchenkMonsalveetal., author = {Melnikov, Anton and Schenk, Hermann A. G. and Monsalve, Jorge Mario and Wall, Franziska and Stolz, Michael and Mrosk, Andreas and Langa, Sergiu and Kaiser, Bert}, title = {Coulomb-actuated microbeams revisited: experimental and numerical modal decomposition of the saddle-node bifurcation}, series = {Microsystems \& Nanoengineering}, volume = {7}, journal = {Microsystems \& Nanoengineering}, number = {1}, issn = {2055-7434}, doi = {10.1038/s41378-021-00265-y}, abstract = {Electrostatic micromechanical actuators have numerous applications in science and technology. In many applications, they are operated in a narrow frequency range close to resonance 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 information about unstable equilibrium states accordingly. Convincing lumped-parameter models amenable to direct physical interpretation are missing. This inhibits the indispensable 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.}, language = {en} } @misc{MonsalveMelnikovStolzetal., author = {Monsalve, Jorge Mario and Melnikov, Anton and Stolz, Michael and Mrosk, Andreas and Jongmanns, Marcel and Wall, Franziska and Langa, Sergiu and Marica-Bercu, Ioana and Br{\"a}ndel, Tim and Kircher, Marco and Schenk, Hermann A. G. and Kaiser, Bert and Schenk, Harald}, title = {Proof of concept of an air-coupled electrostatic ultrasonic transducer based on lateral motion}, series = {Sensors and Actuators A: Physical}, volume = {Vol. 345}, journal = {Sensors and Actuators A: Physical}, issn = {1873-3069}, doi = {10.1016/j.sna.2022.113813}, abstract = {An alternative implementation of an electrostatic MUT (Micromachined Ultrasonic Transducer), relying on multiple beams that displace along the chip's surface instead of a single membrane displacing perpendicular to it, is presented in this work. With this approach, a design requiring a low bias voltage (24 V) and occupying a small area (3.3×3.3 mm², 2D/λ≈0.77) was shown to generate a sound pressure level of 82 dB (re. 20 µPa-rms) at 40 kHz and a distance of 8.9 cm. The high level of damping allows this transducer to operate in a wide frequency range (35-63 kHz). The operation of this device as an ultrasonic receiver was also proven. An implementation of this transducer as a rangefinder requires a strong reduction in the noise level, particularly coming from radio-frequency interference, in order to increase its detection range.}, language = {en} } @misc{KaiserSchenkEhrigetal., author = {Kaiser, Bert and Schenk, Hermann A. G. and Ehrig, Lutz and Wall, Franziska and Monsalve, Jorge Mario and Langa, Sergiu and Stolz, Michael and Melnikov, Anton and Conrad, Holger and Schuffenhauer, David and Schenk, Harald}, title = {The push-pull principle: an electrostatic actuator concept for low distortion acoustic transducers}, series = {Microsystems \& Nanoengineering}, volume = {Vol. 8}, journal = {Microsystems \& Nanoengineering}, issn = {2055-7434}, doi = {10.1038/s41378-022-00458-z}, abstract = {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 Vp and a constant voltage of only ±10 Vdc 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.}, language = {en} } @misc{SchenkMelnikovStolzetal., author = {Schenk, Harald and Melnikov, Anton and Stolz, Michael and Wall, Franziska and Kaiser, Bert and Mrosk, Andreas and Schuffenhauer, David and Monsalve, Jorge Mario and Langa, Sergiu and Schenk, Hermann and Ehrig, Lutz and Conrad, Holger and Ahnert, Maik}, title = {Nonlinearity of balanced MEMS loudspeakers: optical experiments and numerical modeling using time-harmonic signals}, series = {27th International Congress on Sound and Vibration, Annual Congress of International Institute of Acoustics and Vibration (IIAV)}, journal = {27th International Congress on Sound and Vibration, Annual Congress of International Institute of Acoustics and Vibration (IIAV)}, pages = {7}, abstract = {A recently introduced novel actuator class, called the nano electrostatic drive (NED), uses the elec-trostatic actuation to generate large deflections of elastic structures. The NED principle was recently successfully applied to create an all silicon loudspeaker based on micro-electro-mechanical systems (MEMS) technology. Such MEMS audio transducers cover the full frequency range required for high fidelity audio applications. High fidelity audio reproduction also demands minimizing harmonic distortions substantially below 1 \%. A major advance in this direction is combining the NED principle with a push-pull driving scheme in a balanced design (BNED), eliminating even harmonics. The practical implementation of a BNED design is however demanding. The nature of the Coulomb force, the impact of stress stiffening and the large deformations required for generating high sound pressures, to name a few aspects, potentially contribute to the harmonic distortion and therefore need advanced experimental methods and simulation models to allow for an apt design. In this paper, we report first results of an experimental technique, combining an optical microscope with a high-speed camera, capable of analyzing the local details of the actuator movement at frame rates of 50,000 frames per second. Dynamic features, such as the excitation of harmonics and intermodulations become clearly visible. These experimental results are then used to scrutinize and refine our multi physics FEM simulations.}, language = {en} } @misc{MonsalveMelnikovKaiseretal., author = {Monsalve, Jorge Mario and Melnikov, Anton and Kaiser, Bert and Schuffenhauer, David and Stolz, Michael and Ehrig, Lutz and Schenk, Hermann and Conrad, Holger and Schenk, Harald}, title = {Large-Signal Equivalent-Circuit Model of Asymmetric Electrostatic Transducers}, series = {IEEE/ASME Transactions on Mechatronics}, volume = {7}, journal = {IEEE/ASME Transactions on Mechatronics}, number = {5}, issn = {1083-4435}, doi = {10.1109/TMECH.2021.3112267}, pages = {2612 -- 2622}, abstract = {This article presents a circuit model that is able to capture the full nonlinear behavior of an asymmetric electrostatic transducer whose dynamics are governed by a single degree of freedom. Effects such as stress-stiffening and pull-in are accounted for. The simulation of a displacement-dependent capacitor and a nonlinear spring is accomplished with arbitrary behavioral sources, which are a standard component of circuit simulators. As an application example, the parameters of the model were fitted to emulate the behavior of an electrostatic MEMS loudspeaker whose finite-element (FEM) simulations and acoustic characterisation where already reported in the literature. The obtained waveforms show good agreement with the amplitude and distortion that was reported both in the transient FEM simulations and in the experimental measurements. This model is also used to predict the performance of this device as a microphone, coupling it to a two-stage charge amplifier. Additional complex behaviors can be introduced to this network model if it is required.}, language = {en} } @misc{RuffertSchenkKaiseretal., author = {Ruffert, Christine and Schenk, Hermann A. G. and Kaiser, Bert and Ehrig, Lutz and Monsalve Guaracao, Jorge Mario and Langa, Sergiu and Wall, Franziska and Melnikov, Anton and Stolz, Michael and Morsk, Andreas and Schuffenhauer, David and Conrad, Holger and Schenk, Harald}, title = {Elektrostatischer Gegentakt NED-Aktor f{\"u}r Im-Ohr-µLautsprecher}, doi = {10.24406/publica-2553}, language = {de} }