Packaging of an Iron-Gallium Nanowire Acoustic Sensor for Under-Water Applications

The nanoacoustic sensor incorporates cilia-like nanowires made of galfenol, a magnetostrictive material, which responds to incoming acoustic waves by changing the magnetic flux flowing through it which is measured by a GMR sensor. A package developed for this sensor should provide a protective environment for these nanowires, while still allowing the sound waves to reach the sensing element with least attenuation. A MEMS package has been designed analogous to the cochlea in a human-ear for the nanowire acoustic sensor. Package materials have been selected for their acoustic performance in water by conducting several experiments to compare their impedance and attenuation characteristics, moisture absorption, and salt permeation properties. The package filled with silicone oil and encapsulated with polydimethylsiloxane (PDMS) is observed to outperform other packages at all frequencies in minimizing attenuation of the acoustic waves at the interface of the package. The process sequence for fabrication of the nanoacoustic sensor is presented along with the preliminary results.