The emergence of metasurface technology and its accompanying design principles are enabling the development of optical components with multiple functionalities, e.g., polarization discrimination and focusing. In this report, we highlight our experimental results associated with the characterization of a reflective mid-wave infrared (mid-IR) metasurface designed for both imaging and polarization-specific beam splitting in the 4.2 through 4.8 m region of the electromagnetic (EM) spectrum. A large area metasurface (1 cm diameter), fabricated using nano-lithography, was observed to exhibit a high degree of discrimination between transverse electric (TE) and magnetic (TM) polarized light with near diffraction limited focusing.
Nanoporous silicon, commonly recognized for its photoluminescent properties, has gained attention as a new energetic
material capable of energy density more than twice that of TNT. The addition of an oxidizer solution to inert nanoporous
silicon results in an exothermic reaction when heat, friction, or focused light is supplied to the system. The energetic
material can be integrated alongside microelectronics and micro-electro-mechanical systems (MEMS) for on-chip
applications. This integration capability, along with the potential for large energetic yield, makes nanoporous energetic
silicon a viable material for developing novel MEMS Safing and Arming (S&A) technologies. While ignition of
nanoporous energetic silicon has been demonstrated for the purpose of propagation velocity measurements using a YAG
laser, in this paper we show optical ignition for potential integration of the energetic with a miniaturized S&A device.
Ignition is demonstrated using a 514nm laser at 37.7mW and a power density of 2.7kW/cm<sup>2</sup> at a stand-off distance of
23cm. Raman spectroscopy verifies that significant stress in porous silicon is produced by a laser operating near the
power density observed to ignite porous silicon. Lastly, we integrate the nanoporous energetic silicon with a MEMS
S&A, and demonstrate transfer to a firetrain consisting of one primary and one secondary explosive using a thermal
initiator to ignite the nanoporous energetic silicon.
We have investigated the feasibility of significantly improving the performance of currently favored uncooled
infrared (IR) detectors based on Si or VO<sub>x</sub> microbolometers with a new design employing freestanding suspended
network of single-walled carbon nanotubes (SWCNTs). Such networks have high absorption coefficient, high
temperature coefficient of the resistance (TCR) and extremely low thermal mass. This combination of parameters
translates into an uncooled IR detector with high sensitivity and a very fast temporal response. We show estimates
of key parameters for such a device, demonstrate a method to prepare it using suspended SWCNT networks
achieved by selective removal of a sacrificial oxide layer, thereby forming a cavity under the SWCNT network. We
also present TCR and photothermal bolometric response data of this conceptual structure.
We present an improved microfabricated sound localization sensor for unobtrusive surveillance systems inspired by the
tympanic membranes of the parasitoid fly, <i>Ormia ochracea</i>. The device consists of two silicon diaphragms mechanically
coupled by a suspended beam that amplifies the difference in time response, dependent on the incident angle of the
sound source. Fabrication techniques were modified to reduce residual stresses and improve device uniformity.
Enhanced acoustic cues for devices with central pivoting anchors were measured with laser Doppler vibrometry. Device
responses to weak excitations demonstrated good sensitivity over environmental noise. An order of magnitude in time
difference amplification was measured at 90° incident angles with a directional sensitivity of .39μs/degree. These results
provide a foundation for realizing an accurate bio-inspired MEMS directional microphone.
The supersensitive ears of the parasitoid fly <i>Ormia ochracea</i> have inspired researchers to develop bio-inspired
directional microphone for sound localization. Although the fly ear is optimized for localizing the narrow-band calling
song of crickets at 5 kHz, experiments and simulation have shown that it can amplify directional cues for a wide
frequency range. In this article, a theoretical investigation is presented to study the use of fly-ear inspired directional
microphones for gunshot localization. Using an equivalent 2-DOF model of the fly ear, the time responses of the fly ear
structure to a typical shock wave are obtained and the associated time delay is estimated by using cross-correlation. Both
near-field and far-field scenarios are considered. The simulation shows that the fly ear can greatly amplify the time delay
by ~20 times, which indicates that with an interaural distance of only 1.2 mm the fly ear is able to generate a time delay
comparable to that obtained by a conventional microphone pair with a separation as large as 24 mm. Since the
parameters of the fly ear structure can also be tuned for muzzle blast and other impulse stimulus, fly-ear inspired acoustic
sensors offers great potential for developing portable gunshot localization systems.
We present a microscale implementation of an acoustic localization device inspired by the auditory organ of the parasitic
fly Ormia Ochracea. The device consists of a pair of circular membranes coupled together with a beam. The coupling
serves to amplify the difference in magnitude and phase between the response of the two membranes as the incident
angle of the sound changes, allowing directional information to be deduced from the coupled device response. The
device was fabricated using MEMS technology and tested with laser Doppler vibrometery. Amplification factors of up to
7 times were observed in the phase difference between the membranes at 90 degree incident sound angles, with
directional sensitivity of up to 0.3μs/degree.