Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
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Technology Multiplexed Optical Nanosensors For Military Sensing Applications Detecting chemical and biological agents across the battlespace By Ashwin Sampathkumar, Ph.D. C hemical and biological weapons are common in the present-day threat continuum and continue to pose an enduring global threat. The basic science of threat sensing and recognition requires a fundamental understanding of materials that demonstrate measurable changes when stimulated by energy, molecules, or particles from chemical and biological agents. In addition, advancing technologies to protect life-sustaining resources and to defeat threat agents is of paramount importance. Innovative sensing plays a major role in identifying and defeating these global threats. Nanotechnology is an emerging threat detection field that makes use of the unique characteristics of devices engineered at tiny scales to develop highly sensitive and effective threat sensors. Nanosensors can be easily integrated into existing threat surveillance and reconaissance technology like drones, LIDAR, and wearable sensors for warfighters, and they provide additional information for threat recognition. Nano-electromechanical systems (NEMS) may be one of the most promising types of nanodevices for threat detec- tion and neutralization. With the microelectronics industry pushing the frontier of device fabrication deep into the sub- micron range, NEMS have received a great deal of attention in recent years. NEMS offer the potential for a wide array of applications — from ultrasensitive mass and force sensing to imaging and quantum information computing. The devel- opment of distributed NEMS arrays operating in concert is pivotal for all of these emerging sensing, imaging, and data processing technologies. Addressing Technological Challenges Nanosensors are rapidly being developed for a variety of biological and chemical sensing applications. In most of these endeavors, the operation of a nanosensor involves actuating the device harmonically around its fundamental resonance and detecting the subsequent motion, while the device interacts with its environment. Even though a single sensor is exceptionally sensitive, a typical field application requires the detection of signals from many sensors distrib- uted over the surface of a chip. Therefore, one of the key technological challenges in the field of nanosensors is the development of multiplexed measurement techniques to simultaneously detect the motion of a large number of sen- sors. The important and difficult problem of interfacing with a large number of devices and facilitating the use of such arrays is addressed here. Among the most promising envisioned sensor applications are biological and chemical sensing using nanoresonators. The minuscule active mass of a nanoresonator in the picto- gram to femtogram (10 -12 to 10 -15 g) range and its high qual- ity factor render the resonator extremely sensitive to added mass that directly correlates to molecular-level threats in the environment. The sensors can also be tagged to identify and classify chemical and biological agents in a heterogeneous environment. Theoretical analysis gives an expression for the analyte sensing limits of a nanoresonator as follows: Δδm min ~ M eff ( Δf ) 1/2 10 -(DR/20) (1) where δm min is the minimum detectable mass, M eff is the effective mass of the NEMS resonator, ω 0 is the resonant frequency, Q is the quality factor, Δf is the measurement bandwidth, and DR is the dynamic range of the displacement transducer (dB). Equation 1 reiterates the fact that the mass, quality factor, and resonant frequencies of a NEMS resonator are the primary parameters that come under consideration when designing an analyte detecting sensor. For sensor applications, resonators with high resonant frequency ( ω 0 ) and small effective mass (M eff ) are desired to maintain a high sensitivity to detect changes in mass as a result of the presence of an analyte, which leads to fabrica- tion of devices with a miniscule cross-sectional area. A single Electronic Military & Defense Annual Resource, 4th Edition 26 ω 0 Q