Total Harmonic Distortion of a Piezoelectric MEMS Loudspeaker in an IEC 60318-4 Coupler Estimation Using Static Measurements and a Nonlinear State Space Model.

Romain Liechti,Thierry Hilt,Christophe Poulain,Stéphane Durand,Franklin Pavageau,Mikaël Colin,Gwenaël Le Rhun,Fabrice Casset,Hugo Kuentz

doi:10.3390/mi12121437

Romain Liechti, Thierry Hilt + Show 7 more

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We propose a method to evaluate the Total Harmonic Distortion generated by a cantilever-based PZT loudspeaker inside an IEC 60318-4 coupler. The model is validated using experimental data of a commercial loudspeaker. Using the time domain equations of the equivalent electrical circuit of the loudspeaker inside the coupler and a state space formulation, the acoustic pressure response is calculated and compared to the measurement of the manufacturer. Next, the stiffness, transduction and capacitance nonlinear functions are evaluated with a Double-Beam Laser Interferometer (DBLI) and a nanoindenter on test devices and on the commercial loudspeaker. By introducing the nonlinear functions into the model as amplitude-dependent parameters, the THD generated by the loudspeaker is calculated and compared to the value provided by the manufacturer. The good agreement between the measurement and the simulation could allow for a rather quick simulation of the performance of similarly designed loudspeakers at the early stage of the design, by only estimating the static linearity of the main nonlinearity sources.

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The aim of this study is to provide such a model to evaluate the distortion generated by a cantilever-based piezoelectric MEMS loudspeaker using static measurements and a lumped equivalent circuit in order to shorten the linearity optimization step of this type of loudspeakers in the design phase
The model presented in this paper allows one to evaluate the Total Harmonic Distortion (THD) generated by a cantilever-based MEMS loudspeaker, by only measuring the nonlinear relations between the stiffness and the displacement, the capacitance and the electric field, and the force and the electric field
Open-loop correction of loudspeaker nonlinearities is tedious for non-MEMS loudspeakers, due to large manufacturing discrepancies, this technique could be more suited for MEMS design, due to the tightest tolerances of the manufacturing processes

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Received: 27 October 2021Accepted: 20 November 2021Published: 24 November 2021Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Licensee MDPI, Basel, Switzerland.Attribution (CC BY) license (https://creativecommons.org/licenses/by/ 4.0/).Loudspeakers are used to converting an electrical signal into sound waves, as accurately as possible, with a sufficiently high sound pressure level. This is usually achieved with a piston-like membrane, behaving as a first-order oscillating system, actuated by an electromechanical transducer. Driven by the forever growing industry of portable and connected devices, research was carried out in order to make the loudspeaker compatible with microfabrication processes, in order to reduce the manufacturing tolerances, the cost and the thickness of the devices. An interesting performance was demonstrated with Micro

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