Theoretical investigation on a microphone using optical reflection on curved surface

Abstract

This paper proposes a microphone using a new principle, involving the optical reflection at the curved end surface of a thin glass rod or a glass fiber. This microphone uses the change in the optical total reflection area by the change in the refractive index by the sound pressure. The change ratio in the reflection area depends on the shape of the curved end. This paper investigates theoretically the effect of the curved end shape on the sensitivity for the spherical end and the parabola type end. The microphone is expected to have possibility of practical use, though the sensitivity is low. The sensitivity may be improved by the invention of curved end shape and the detection method. This microphone is expected to have good high frequency response as it can be made small and involves no mechanical vibration.