No abstract

In this paper, we report on the design and characterization of a microelectromechanical systems (MEMS) directional sensor inspired by the tympana configuration of the parasitic fly Ormia ochracea. The sensor is meant to be operated at resonance and act as a natural filter for the undesirable frequency bands. By means of breaking the symmetry of a pair of coupled bridged membranes, two independent bending vibrational modes can be excited. The electronic output, obtained by the transduction of the vibration to differential capacitance and then voltage through charge amplifiers, can be manipulated to tailor the frequency response of the sensor. Four different frequency characteristics were demonstrated. The sensor exhibits, at resonance, mechanical sensitivity around 6 μm/Pa and electrical sensitivity around 13 V/Pa. The noise was thoroughly characterized, and it was found that the sensor die, rather than the fundamental vibration, induces the predominant part of the noise. The computed average signal-to-noise (SNR) ratio in the pass band is about 91 dB. This result, in combination with an accurate dipole-like directional response, indicates that this type of directional sensor can be designed to exhibit high SNR and selectable frequency responses demanded by different applications.

After inscribing an ordinary grating in a multimode fiber, the reflectivity spectrum of this grating is studied when the fiber is subjected to a longitudinal static strain. It is observed that the phase‐matching condition is approximately satisfied by a few modes, causing the appearance of lateral lobes. Variations in magnitude and peak wavelengths of these reflectivity spectrum lobes are observed and analyzed when the fiber is subjected to an applied strain. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 28: 4–8, 2001.

MeMS acoustic sensors have been developed to mimic the highly-accurate sound-locating system of the Ormia ochracea fly, which detects sound wavelengths much larger than its hearing organ. A typical ormia-based MeMS directional sound sensor possesses two coupled wings that vibrate in response to sound according to a superposition of its two main resonant modes, rocking and bending. Vibrations are transduced into electronic signals by interdigitated comb finger capacitors at each wing's end along with a capacitance measuring circuitry. A sensor designed to exhibit resonant modes closely placed in frequency, enhancing their coupling, was operated with a closed cavity behind the wings. Simultaneous and independent measurements of electronic signals generated at each of the single sensor wings were used to determine incident sound direction of arrival (DoA). DoA was found proportional to the phase shift between them and to the difference over the sum of their amplitudes as well. Single sensor phase shift DOA measurement presented a resolution better than 3° for sound pressure levels of 25 mPa or greater. These results indicate that a single sensor operating in closedcavity configuration can provide hemispherical unambiguous direction of arrival of sound waves which wavelength is much larger than the sensor size. For many animal species, perceiving the direction under which a sensorial stimulus occurs is key for survival and reproduction. Considering auditory stimuli, cues used for these tasks rely on small differences in the pressure disturbances detected by physically separated sensory organs, either in amplitude, time of arrival or both. When the animal size is comparable to the sound wavelength in air, the required physical separation capable of making the differences perceivable by the nervous cells, processing or transmitting the detected stimulus, is naturally assured. For species of much smaller dimensions, the physical impediments of having sufficiently separated sound sensors pushed evolution towards using different mechanisms of detecting and processing the sound waves much needed for their basic survival tasks 1. There are many insects that rely on phonotaxis in order to complete their reproductive cycles 2-5. Usually the process involves parasitism of different species' male hosts by the larvae deposited on or near them. Males give off their location by emitting mating calls, directed to the female individuals of their own species, but those are also heard by female individuals of the parasitic species. This happens in low light conditions, in order to avoid visually based predators, therefore, directional sound sensory capabilities are required for both species 3-7. There are a number of studies concerned with one species of fly, Ormia ochracea, which show the ability of finding the chirping host for their larvae with high accuracy, despite its sensory organ being much smaller than the wavelength 5-8. Miles et al. 9,10 found that the mechanical coupling between two tympana mediated by a semi-rigid cuticle...

In this work, microelectromechanical systems (MEMS)-based directional acoustic sensors operating in an underwater environment are explored. The studied sensors consist of a free-standing single wing or two wings pivoted to a substrate. The sensors operate in a narrow frequency band determined by the resonant frequency of the mechanical structure. The electronic readout of the mechanical response is obtained using interdigitated comb finger capacitors attached to the wings. The characteristics of MEMS sensors immersed in silicone oil are simulated using finite element modeling. The performance of the sensors is evaluated both in air and underwater. For underwater testing and operation, the sensors are packaged in a housing containing silicone oil, which was specially developed to present near unity acoustic transmission. The measurements show that the resonant frequency of the sensors obtained in air shifts to a lower frequency when immersed in silicone oil, which is primarily due to the mass loading of the liquid. The peak sensitivity of the MEMS sensors is approximately 6 mV/Pa or −165 dB re 1 V/μPa, and the directional response shows a dipole pattern. The signal-to-noise ratio was found to be about 200 or 23 dB at 1 Pa incident sound pressure. The results show the potential of MEMS sensors to be used in underwater applications for sound source localization.