Packaging of an iron-gallium (Galfenol) nanowire acoustic sensor

Abstract

Packaging is a key issue for the effective working of an iron-gallium (Galfenol) nanowire acoustic sensor for underwater applications. The nanowire acoustic sensor incorporates cilia-like nanowires made of galfenol, a magnetostrictive material, which responds by changing magnetic flux flowing through it due to bending stress induced by the incoming acoustic waves. This stress induced change in the magnetic flux density is detected by a GMR sensor. An effective package should provide a suitably protective environment to these nanowires, while allowing sound waves to reach the nanowires with a minimum level of attenuation. A bio-inspired MEMS package has been designed, analogous to a human-ear cochlea for the nanowire acoustic sensor. In this paper, the process sequence for fabrication of the package is presented. Unlike other microphones, the nanoacoustic sensor has been enclosed in a cavity to allow free movement of the nanowires in a fluid medium. The package also ensures resisting ingression of sea water and salt ions to prevent the corrosion of sensor components. The effect of package material on sensor performance was investigated by conducting experiments on acoustic impedance and attenuation characteristics, and salt water absorption properties. The package filled with silicone oil and molded with polydimethylsiloxane (PDMS) is observed to outperform other packages at all frequencies by minimizing attenuation of the acoustic waves.

Structure, magnetism, and magnetostrictive properties of mechanically alloyed Fe81Ga19

“…Functional magnetic materials systems that demonstrate large magnetostriction play an important role in a wide range of applications, including sonar systems [1], force, displacement and torque sensors [2], [3], microelectromechanical actuators, and vibration energy harvesting and vibration control devices [4]. To this end, it is important to note that one of the most promising magnetostrictive materials hitherto is Galfenol, Fe 1-x Ga x (Galfenol) [5] an inexpensive, corrosion resistant [6], machinable alloy that in single crystal form exhibits high tensile strength (∼500 MPa) [7], and a moderate magnetostriction (3/2 λ 100 ∼ 350 ppm) under a low magnetic field of ∼100 Oe [7].…”

Design, processing and characterization of mechanically alloyed galfenol & lightly rare-earth doped FeGa alloys as smart materials for actuators and transducers

“…Functional materials systems that demonstrate large magnetostriction play an important role in a wide array of commercial applications ranging from acoustic sensors and linear actuators to electromechanical energy harvesters and sonar transducers. [13][14][15][16] One of the most successful magnetostrictive materials hitherto is the rare-earth compound, (Dy 0.7 Tb 0.3 )Fe 2 (also known as Terfenol D). [17] These alloys demonstrate a cubic C15 laves crystal structure and exhibit large room temperature magnetic-fieldinduced strains up to 2000 ppm (parts per million).…”

“…Rising demand from the sonar industry is driving the overall market. The applications of Galfenol magnetostrictive materials mostly fall in these main categories: Sensors [2,3,13,15,20,53,94], Energy harvesting [5,16] and transducers [7,[10][11][12]53] and sonar systems [2,7,20,53].…”

“…FeGa (i.e., Galfenol) alloys, some of the most important functional magnetic materials, have only recently found their way into sonar systems; force, displacement, and torque sensors; and acoustic and tactile sensors [1][2][3]7,13,20,53,94]. In practical applications, sensors or transducers are required to work over a broad range of temperatures (-40 to 120 °C) [81].…”

“…Functional magnetic materials systems that demonstrate large magnetostriction play an important role in a wide range of applications, including sonar systems [13], force, displacement and torque sensors [14,15], microelectromechanical actuators, and vibration energy harvesting and vibration control devices [16]. To this end, it is important to note that one of the most promising magnetostrictive materials hitherto is Galfenol, Fe 1-x Ga x (Galfenol) [22] -an inexpensive, corrosion resistant [82], machinable alloy that in single crystal form exhibits high tensile strength (∼500 MPa) [21], and a moderate magnetostriction (3/2 λ 100 ∼ 350 ppm) under a low magnetic field of ∼100 Oe [21].…”