Zega Valentina

Assistant Professor

Contacts

+39 0223996213
Department of Civil and Environmental Engineering (DICA) - Politecnico di Milano

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Nonlinear Dynamics in MEMS

Multiple sources of nonlinearities can be identified in MEMS when transformations are no-longer infinitesimal: geometric effects refer to the nonlinear evolution and coupling of stress components within a structure; electrostatics forces depend in an intrinsically nonlinear manner on geometrical gaps, just like gas dissipation. Analytical approaches for real MEMS often leads to results that are only qualitatively correct or need careful device dependent calibration. Numerical approaches are starting to emerge as a general solution, since MEMS might have complicated structures and features that can be hardly reduced to simple models. We propose fully predictive Model Order Reduction (MOR) techniques able to describe the nonlinear dynamics of complex MEMS without the need of experimental calibration of parameters.

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MetaMEMS

Metamaterials are artificial materials with extraordinary properties not available in nature. They are usually made by periodic structures and present a variety of applications. Here, metamaterials are employed in MicroElectroMechanical Systems (MEMS) to open the way to a new class of metaMEMS that can strongly improve the performances of actual MEMS devices or even provide a valid alternative to the actual state of the art.

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Design and optimization of metamaterials

The design and the combination of innovative metamaterials are attracting increasing interest in the scientific community because of their unique properties that go beyond the ones of natural materials. In particular, auxetic materials and phononic crystals are widely studied for their negative Poisson’s ratio and their bandgap opening properties, respectively.

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3D-printed and wet metallized sensors

Additive manufacturing and wet metallization process are combined to fabricate prototypes of differential electro-mechanical accelerometers. The smart combination of existing fabrication processes makes the proposed fabrication flow unique in the sensors field. The mechanical design of the proposed devices exploits the three-dimensionality of the 3D-printing technique and the electrostatic differential readout is allowed thanks to the wet-metallization process of the printed structure. Experimental measurements show a very good agreement with theoretical predictions thus proving a good reliability of the proposed design flow and fabrication process. With their relative small footprints (minimum dimension in the order of hundreds of µm), good performances and high customizability, they represent an important step toward novel application fields of inertial sensors.

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MEMS resonators for real-time clocking applications

MicroElectroMechanical Systems (MEMS) resonators are attracting increasing interest because of their smaller size and better integrability as opposed to their quartz counterparts. However, thermal drift of the natural frequency of silicon structures is one of the main issues that has hindered the development of MEMS resonators. Extensive investigations must be addressed to both the fabrication process (e.g., introducing heavy doping of the silicon) and the mechanical design (e.g., exploiting proper orientation of the device, slots, nonlinearities).

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Frequency Modulated (FM) MEMS Gyroscopes

Frequency Modulated (FM) gyroscopes have been proposed as a possible solution toward the measurements stability against environmental fluctuations as temperature. Thanks to their stability, they promise to overcome the need of the calibration, thus reducing the costs and representing an innovative step toward a new class of MEMS gyroscopes. Instead of controlling the motion of one mode (the drive) and measuring the Coriolis-induced displacement amplitude variations along the three sense axes as done in AM solutions, FM gyroscopes rely on controlling the velocities of the three main orthogonal modes of the proof mass and in measuring the resonance frequency variations induced by the external angular rate on the considered axes. Yaw FM gyroscopes were firstly proposed and experimentally tested by the Berkeley Sensors and Actuators Center, while pitch, roll and 3-axis FM gyroscopes were presented for the first time by the authors.

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MEMS resonant accelerometers

For several kinds of MEMS, resonant sensing has recently been proposed as an alternative way to improve the long-term performance. Also in the case of accelerometers, an alternative to capacitive sensing is represented by resonant micro-devices, which measure the external acceleration through the frequency variation of resonating elements. Numerical modelling of the dynamic behaviour of resonant accelerometers in both linear and nonlinear regime has been addressed together with a proper optimization of the mechanical design of such devices.

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Metamaterials as underwater acoustic barriers

During wind farm construction, piles are driven by short, powerful pressure waves created by the enormous hammers strikes. This strongly affects the behavior of nearby marine seals/mammals. In this project, the attention is focused on noise mitigation systems for pile driving in wind farm construction. Acoustic metamaterials are exploited as underwater acoustic barriers, i.e. noise mitigation systems for wind farm constructions. Acoustic metamaterials indeed exhibit extraordinary performances in sound absorption applications and can be easily mounted and removed, i.e. re-used. Moreover, metamaterials allow broad choice of base materials to be used, allowing to employ recycled and recyclable materials in a fully circular economy approach. (PNRR - GREEN)

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Thelma-Double – an innovative MEMS fabrication process

The aim of the project is to design, fabricate and test innovative MEMS devices exploiting the new features of the recently developed STMicroelectronics fabrication process "Thelma-Double". The "Thelma-Double" thanks to its double layer of polysilicon is able to overcome the main limitations of the standard MEMS fabrication processes (i.e. planarity), thus opening the way to a new generation of MEMS devices. The scientific challenge is then twofold: to overcome the intrinsic planarity of MEMS devices exploiting the "Thelma-Double" features and obtain extraordinary performances not achievable so far through standard MEMS fabrication processes.

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