The superacute ear of the parasitoid fly Ormia ochracea has inspired the development of a variety of novel miniature
directional microphones for sound source localization, in which the effects of air cavity backing the eardrums are often
neglected without validation. In the original testing on the fly ear, the integrity of the air space is shown not to be the key
to the intertympnal coupling. However, it does not necessarily mean that the tympanum can be treated as in vacuo, and
the effects of the air cavity backing the eardrums have yet to be fully understood. In this article, a normalized version of
our previous model of air-backed circular membranes is derived to study the conditions under which the air cavity can be
indeed neglected. This model is then used to study a fly-ear inspired directional microphone design with two clamped
circular membranes mechanically coupled by a bridge. The performance of the directional microphone with air cavity is
evaluated in comparison to its counterpart in vacuo. This article not only provides more insights into the fly ear
phenomena, but builds a theoretical foundation on whether and how to take the air cavity into account in the design of
pressure sensors and directional microphones in general.
We present an improved microfabricated sound localization sensor for unobtrusive surveillance systems inspired by the
tympanic membranes of the parasitoid fly, Ormia ochracea. The device consists of two silicon diaphragms mechanically
coupled by a suspended beam that amplifies the difference in time response, dependent on the incident angle of the
sound source. Fabrication techniques were modified to reduce residual stresses and improve device uniformity.
Enhanced acoustic cues for devices with central pivoting anchors were measured with laser Doppler vibrometry. Device
responses to weak excitations demonstrated good sensitivity over environmental noise. An order of magnitude in time
difference amplification was measured at 90° incident angles with a directional sensitivity of .39μs/degree. These results
provide a foundation for realizing an accurate bio-inspired MEMS directional microphone.
When using microphone array for sound source localization, the most fundamental step is to estimate the time difference
of arrival (TDOA) between different microphones. Since TDOA is proportional to the microphone separation, the
localization performance degrades with decreasing size relative to the sound wavelength. To address the size constraint
of conventional directional microphones, a new approach is sought by utilizing the mechanical coupling mechanism
found in the superacute ears of the parasitic fly Ormia ochracea. Previously, we have presented a novel bio-inspired
directional microphone consisting of two circular clamped membranes structurally coupled by a center pivoted bridge,
and demonstrated both theoretically and experimentally that the fly ear mechanism is replicable in a man-made structure.
The emphasis of this article is on theoretical analysis of the thermal noise floor of the bio-inspired directional
microphones. Using an equivalent two degrees-of-freedom model, the mechanical-thermal noise limit of the structurally
coupled microphone is estimated and compared with those obtained for a single omni-directional microphone and a
conventional microphone pair. Parametric studies are also conducted to investigate the effects of key normalized
parameters on the noise floor and the signal-to-noise ratio (SNR).
We present a microscale implementation of an acoustic localization device inspired by the auditory organ of the parasitic
fly Ormia Ochracea. The device consists of a pair of circular membranes coupled together with a beam. The coupling
serves to amplify the difference in magnitude and phase between the response of the two membranes as the incident
angle of the sound changes, allowing directional information to be deduced from the coupled device response. The
device was fabricated using MEMS technology and tested with laser Doppler vibrometery. Amplification factors of up to
7 times were observed in the phase difference between the membranes at 90 degree incident sound angles, with
directional sensitivity of up to 0.3μs/degree.
The supersensitive ears of the parasitoid fly Ormia ochracea have inspired researchers to develop bio-inspired
directional microphone for sound localization. Although the fly ear is optimized for localizing the narrow-band calling
song of crickets at 5 kHz, experiments and simulation have shown that it can amplify directional cues for a wide
frequency range. In this article, a theoretical investigation is presented to study the use of fly-ear inspired directional
microphones for gunshot localization. Using an equivalent 2-DOF model of the fly ear, the time responses of the fly ear
structure to a typical shock wave are obtained and the associated time delay is estimated by using cross-correlation. Both
near-field and far-field scenarios are considered. The simulation shows that the fly ear can greatly amplify the time delay
by ~20 times, which indicates that with an interaural distance of only 1.2 mm the fly ear is able to generate a time delay
comparable to that obtained by a conventional microphone pair with a separation as large as 24 mm. Since the
parameters of the fly ear structure can also be tuned for muzzle blast and other impulse stimulus, fly-ear inspired acoustic
sensors offers great potential for developing portable gunshot localization systems.
In this article, the equivalent two-degree-of-freedom (2-DOF) model for the hypersensitive ear of fly Ormia
ocharacea is revisited. It is found that in addition to the mechanical coupling between the ears, the key to
the remarkable directional hearing ability of the fly is the proper contributions of the rocking mode and
bending mode of the ear structure. This can serve as the basis for the development of fly-ear inspired
directional microphones. New insights are also provided to establish the connection between the mechanics
of the fly ear and the prior biological experiments, which reveals that the fly ear is a nature-designed
optimal structure that might have evolved to best perform its localization task at 5 kHz. Based on this
understanding, a new design of the fly-ear inspired directional microphone is presented and a
corresponding normalized continuum mechanics model is derived. Parametric studies are carried out to
study the influence of the identified non-dimensional parameters on the microphone performance.
Directional microphones are developed to verify the understanding and concept. This study provides a
theoretical guidance to develop miniature bio-inspired directional microphones, and can impact many
fronts that require miniature directional microphones.