New ormia-inspired directional MEMS microphone operating in a low frequency band

Directional MEMS microphones inspired by the parasitoid fly Ormia ochracea have been studied since the discovery that the micro-scale tympana structure of this female fly can amplify and locate narrow band mating calls from its host. This presentation will concentrate on the first piezoelectric Ormia-inspired MEMS microphone that operates in a low range of frequency bands overlapping with human vocal frequencies, and as such is suitable for hearing aid applications. Including two plates performing as Ormia’s two tympana, the entire region in motion in our microphone is about 3.2 mm × 1.42 mm × 10 μm. Compared to other piezoelectric Ormia-inspired designs, our design transfers the working frequency band from over 10 kHz to below 3 kHz due to its asymmetric structure and an S-type rotational cantilever. Furthermore, it provides a unidirectional response around two resonance frequencies below 3 kHz. The open-circuit acoustic response of the device is approximately 3.9 mV/Pa at 464 Hz which is close to human vocal frequencies, with a maximum value of 9.9 mV/Pa at 2275 Hz, which is near the frequency region where the human auditory system is most sensitive. The new microphone, coupled with a custom-built preamplifier, has a noise floor of 10 μV/√Hz at 1 kHz.