Biomimetic trapped fluid microsystems for acoustic sensing

An innovative architecture for acoustic sensing using a trapped fluid as an acoustic transmission medium has been developed. This architecture was inspired by the structure of the mammalian cochlea, the most successful natural acoustic sensor design. Micromachining technology was used to fabricate the sensors in order to preserve the physiological size scale of the mammalian cochlea, and to aid in the integration of sensing elements. Mathematical models for microscale acoustics, including fluid-structure interaction, are developed in support of these designs.; Three microsystems are described. First, a lifesize hydromechanical cochlear model is discussed. This model is used to explore the effects of structure orthotropy and fluid viscosity on the mechanics. It is demonstrated that achievable orthotropy ratios of 8:1 in tension do not result in the sharp filtering observed in animal experiments. It is also demonstrated that high viscosities (20 cSt) must be used to introduce enough damping to avoid nonphysiological standing waves. These results underscore the importance of the active mechanisms present in the cochlea which appear to be critical for sharp filtering.; Second, a design for a single-output-channel acoustic sensor with the trapped fluid architecture and a capacitive sensing scheme is described. This device achieves sensitivities (-170 to -200 dB re 1V/muPa in a 30 kHz band) competitive with commercial piezoelectric hydrophones in a compact MEMS design. The system also demonstrates a novel fabrication process for producing trapped-fluid microsystems with integrated capacitive sensors.; Third, a microscale cochlear analogue transducer (muCAT) is described. This system is the first demonstration of integration of multiple sensing elements into a lifesize cochlear-like mechanical structure to produce a multiple-output-channel acoustic sensor capable of mechanical spectral analysis. Electrical output from the 32 integrated capacitive sensors demonstrates competitive sensitivities (-200 to -186 dB re 1 V/muPa) and bandwidth (100 kHz) for some channels. Laser vibrometry results demonstrate the presence of cochlear-like traveling waves and a frequency position map. Electrical output from the integrated sensors does not follow the vibration pattern measured with laser vibrometry.