Fraunhofer-Institut für Zuverlässigkeit und Mikrointegration IZM

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  • Publication
    Design and modeling of a novel piezoresistive microphone for aero acoustic measurements in laminar boundary layers using FEM and LEM
    ( 2021)
    Erbacher, Kolja
    ;
    Ngo, Ha-Duong
    ;
    Mackowiak, Piotr
    ;
    Wu, Lixiang
    ;
    Julliard, Emmanuel
    ;
    Spehr, Carsten
    In this paper the modeling and simulation results of a piezo-resistive microphone are presented and a possible fabrication process flow and characterization concept of the sensor are described. The main objective in this funded AEROMIC project is to develop a thin and small in size microphone, which can be integrated into a flexible array, that can be mounted onto an airplane hull for flight tests. The microphone array should be no thicker than 2 mm and should contain more than 80 flush mounted single microphones, allowing acoustic measurement without disturbance of the laminar boundary layer. The pitch of the microphone sensors in the array enable high spatial resolution of the pressure fluctuation. The optimization of geometry of single sensor microphone has been done using FEA (Finite Element Analysis). For the optimization of the geometry of the single microphone chip, FEA of the air damped dynamic behavior of the diaphragm is modeled in Ansys Harmonic Response Analyses with Acoustics ACT package. To model the array on system level, a lumped-element model (LEM) is set up to predict spatial resolution and signal to noise ratio. Derived from the FEA results, a sensor chip layout with three membrane sizes is presented.
  • Publication
    Design of dual-frequency piezoelectric MEMS microphones for wind tunnel testing
    ( 2021)
    Wu, Lixiang
    ;
    Chen, Xuyuan
    ;
    Ngo, Ha-Duong
    ;
    Julliard, Emmanuel
    ;
    Spehr, Carsten
    The demand for aeroacoustic measurement microphones is surging in recent years as new rules on noise reduction and environmental compliance are getting tougher. However, the state-of-the-art microphones including classical measurement microphones and micro-electro-mechanical systems (MEMS) microphones cannot fully meet the strict requirements for wind tunnel testing (WTT) in terms of form factor, acoustic performance, and product price. To break through the bottleneck, a new type of piezoelectric MEMS microphones with dual frequency bands was designed as key part of a dedicate WTT solution, which aims to capture the unsteady pressure fluctuations underneath the turbulent boundary layer and predict the cabin noise excitation. The finite element method (FEM) was applied to analyze and optimize the MEMS design at the system level. The feasibility of the new MEMS design has been preliminarily verified by characterizing the mechanical and electrical properties of first batch of dual-frequency piezoelectric MEMS microphones. The acoustic characterization was conducted to evaluate the overall performance and the system-level FEM model was refined based on the measurement results.