Development of an Omnidirectional Microphone With High Gain in Low-Frequency Band Based on a Bidirectional Microphone

Bidirectional microphones work as a microphone as well as a sensor with high gain over a wide frequency range, and they are also highly reliable and reasonable in cost, because they are mass-produced. We present novel multiple functional uses of the bidirectional microphones by converting characteristics from bidirectivity and low gain to omnidirectivity and high gain in low-frequency band. A lumped mass mathematical model for explaining principle of the characteristics conversion was presented. Based on the model, the characteristics of the microphone were investigated, and a novel use for the microphone as a sensor was presented. In this paper as examples, we introduced applications for using the microphone as a security sensor, an environment sensor, and a biosignal sensor. The mathematical model was validated through experiments, and the feasibility of the abovementioned applications was examined through experiments.