Microphone membranes tthat have theeir frequency response uniiquely tailoreed to specificc applications are typicallyy produced in an unautomated and expensive manuufacturing prrocess. A combination off holographic stroboscopyy, numerical simulation and laser structuriing is appliedd to shift the resonant frequencies of thee membrane too their desired values given an unknown tension across the microphone membrane due to manuufacturing tollerances. Thee uncharacterized microphone membrane is driven thrrough physical contact withh a piezo. Thhe piezo is swept through a range of frequencies and the full surface profile oscillations are recorded using stroboscopic digitaal holographyy techniques. These resonant displacemennt maps will bee used, in combination with finite differeence eigenvaluue simulationss and perturbattion theory, to determine the preloadedd tension profile across the membrane. Given a desired responsee function of the membrane,, a new membrane mass-density profile can be tailoreed to match the current meembrane to thee requirements of the micropphone. A 20 WW ns Q-switchhed laser steerred by galvanometer mirrorrs will be usedd to restructuree the mass density of the membrane to meeet the design requirements of the micropphone.
B. Nelsen, P. Jacobs, C. Taudt, F. Rudek, and P. Hartmann, "Holographic characterization and laser structuring of a microphone membrane," Proc. SPIE 10678, Optical Micro- and Nanometrology VII, 106780F (Presented at SPIE Photonics Europe: April 25, 2018; Published: 24 May 2018); https://doi.org/10.1117/12.2307487.
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