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MEMS Package for an Iron-Gallium (Galfenol) Nanowire Acoustic Sensor
Keywords: package, mems, acoustic sensor
Packaging is a key issue for the effective working of an iron-gallium (galfenol) nanowire acoustic sensor for the underwater applications. The nanowire acoustic sensor consists of cilia-like nanowires made of galfenol, a magnetostrictive material, which responds by changing magnetic flux flowing through it due to the incoming acoustic waves. Stress induced change in the magnetic flux density can be detected by a GMR sensor underneath. Unlike other transducers, the nanoacoustic sensor cannot be sealed into a hermetic package that does not permit sound to reach it. The sensor also needs to be enclosed in a cavity for the free movement of the nanowires. In addition, the package must resist the ingression of sea water to prevent the corrosion of sensor components as well as shorting of electrical contacts inside. A novel, bio-inspired MEMS package has been designed analogous to a human-ear cochlea for the nanowire acoustic sensor. It is designed after incorporating all the challenges to ensure reliability of the sensor inside sea water. The acoustic performance inside water affected by different package materials has been investigated by conducting several experiments to compare their impedance and attenuation characteristics, moisture absorption, and salt permeation properties. The package filled with silicone oil and molded with polydimethylsiloxane (PDMS) is observed to outperform packages of other encapsulant materials and fluid medium at all frequencies by minimizing attenuation of the acoustic waves at the interface of the package.
Rupal Jain, Graduate Research Assistant
University of Maryland
College Park, MD

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