Analysis of the Locally Resonant Metamaterial Considering Manufacturability and Its Application to Speakerphone

Abstract

As part of our efforts to prevent the spread of COVID-19, teleconferencing is being incorporated into our daily life. The increase in the frequency of teleconferencing is directly related to the growth of the audio equipment market and the increase in demand for audio equipment in the form of reinvestment in audio system development. This study, in collaboration with Danish audio system company Jabra, aims to improve the frequency flatness of the speakerphone using locally resonant metamaterials with improved manufacturability.

A speakerphone is manufactured in a form in which a driver unit and a microphone unit are combined in a structure with a limited size. The shape of the speakerphone in which the two devices are structurally connected makes the two devices affect each other's performance, and the limited size speakerphone enclosure makes it hard to avoid structural-acoustic radiation. These structural characteristics degrade the speakerphone sound output/recognition performance at a certain frequency. To improve the acoustic performance of the speakerphone, it is necessary to reduce the vibration of the structure. In this study, including the process of confirming this phenomenon through finite element analysis and experiments, we propose a locally resonant metamaterial as a method to prevent the vibration of structures.

Locally resonant metamaterials with vibration attenuation properties at a specific frequency band have been studied in recent decades. The locally resonant metamaterial is implemented as a regular arrangement of a unit structure having a resonance structure, and the local resonance of the resonance structure represents a phenomenon in which the vibration energy of a bending wave is dissipated at a specific frequency band. Locally resonant metamaterials are generally lightweight and exhibit excellent vibration reduction properties in low frequency bands. So the attempts to apply them to actual industrial structures are continuously being made. However, locally resonant metamaterials developed for application to existing industrial structures have a complex resonance structure, so they are manufactured using a 3D printer or by assembling parts. This manufacturing method needs improvement as it is not suitable for the mass production of products. In this study, we propose a cup-shaped locally resonant metamaterial with improved manufacturability.

The cup-shaped locally resonant metamaterial to be fabricated together with the structure was analyzed through the analysis model and verified through the finite element model. The relationship between the frequency band gap and structural characteristics was obtained from a locally resonant metamaterial analytic model applicable to a one-dimensional beam. The one-dimensional analytic model was verified through a finite element numerical model and extended to a two-dimensional model. In addition, to check whether the structure can exhibit a vibration reduction effect when applied to a speakerphone enclosure, an electromagnetic structure-acoustic coupled finite element model was built to obtain an acoustic response, and this was verified through experiments. As a result, it was confirmed that the frequency flatness was improved by applying the locally resonant metamaterial to the enclosure of the speakerphone.