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Won S.M.,University of Illinois at Urbana - Champaign | Kim H.-S.,University of Illinois at Urbana - Champaign | Lu N.,University of Illinois at Urbana - Champaign | Kim D.-G.,University of Illinois at Urbana - Champaign | And 4 more authors.
IEEE Transactions on Electron Devices | Year: 2011

This paper describes the fabrication and properties of flexible strain sensors that use thin ribbons of single-crystalline silicon on plastic substrates. The devices exhibit gauge factors of 43, measured by applying uniaxial tensile strain, with good repeatability and agreement with expectation based on finite-element modeling and literature values for the piezoresistivity of silicon. Using Wheatstone bridge configurations integrated with multiplexing diodes, these devices can be integrated into large-area arrays for strain mapping. High sensitivity and good stability suggest promise for the various sensing applications. © 2011 IEEE.


Zhang H.,University of North Texas | Xin H.,University of Arizona | Bortolin R.,NextGen Aeronautics, Inc. | Kudva J.,NextGen Aeronautics, Inc.
Microwave and Optical Technology Letters | Year: 2011

A low-profile, compact and easily integrated antenna for RF/microwave applications is presented in this article. The designed antenna works around 430 MHz and can be easily scaled to other frequencies. Metamaterial-inspired slot loop antennas are used as the radiating elements. To shrink the total size of the antenna, periodical structures are loaded to the original slot loop. It is found that with this modification, the total size of the antenna is reduced and the impedance matching of the antenna is improved. To further improve the performance of the proposed antenna, a floating ground plane and a parasitic slot were added, made possible by the multilayered structure of the antenna. As a result, the bandwidth and gain of proposed antenna are increased. © 2010 Wiley Periodicals, Inc.


Petrich J.,NextGen Aeronautics, Inc. | Subbarao K.,University of Texas at Arlington
AIAA Guidance, Navigation, and Control Conference 2011 | Year: 2011

Motivated by the desire to improve the navigation and guidance performance of small unmanned aerial vehicles (UAVs), we propose simple methods for modeling the local wind flow that affects the vehicle's trajectory. Particularly we present an algorithm applicable to estimating those wind patterns when considering a conventional suite of onboard UAV avionics. In addition, the proposed algorithm can be performed efficiently using small, sparse data sets collected in real-time by the sensor platform. As such this paper deals with the estimation of the 3D wind components and shows that successful wind estimation is possible for any UAV trajetory. The available sensors are the GPS, IMU/Compass for heading and elevation and the Air Data sensors for speed measurement. Monte Carlo simulations are performed to illustrate the efficacy of the proposed algorithms. The estimator is then implemented on data obtained from real flight experiments to further illustrate the algorithm's efficacy. © 2011 by Kamesh Subbarao and Jan Petrich.


Ren K.,CAS Beijing Institute of Nanoenergy and Nanosystems | Bortolin R.S.,NextGen Aeronautics, Inc. | Zhang Q.M.,Pennsylvania State University
Applied Physics Letters | Year: 2016

This paper investigates the thermal response of a hybrid actuator composed of an electroactive polymer (EAP) and a shape memory polymer (SMP). This study introduces the concept of using the large strain from a phase transition (ferroelectric to paraelectric phase) induced by temperature change in a poly(vinylidene fluoride-trifluoroethylene) film to tune the shape of an SMP film above its glass transition temperature (Tg). Based on the material characterization data, it is revealed that the thickness ratio of the EAP/SMP films plays a critical role in the displacement of the actuator. Further, it is also demonstrated that the displacement of the hybrid actuator can be tailored by varying the temperature, and finite element method simulation results fit well with the measurement data. This specially designed hybrid actuator shows great promise for future morphing aircraft applications. © 2016 AIP Publishing LLC.


Hajzargarbashi T.,University of Arizona | Kundu T.,University of Arizona | Bland S.,NextGen Aeronautics, Inc.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The wave speed in an anisotropic plate is dependent on the direction of propagation and therefore the conventional triangulation technique does not work for the prediction of the impact point. A method based on the optimization technique was proposed by Kundu et al. to detect the point of impact in an anisotropic plate. They defined an objective function that uses the time of flight information of the ultrasonic signals to the passive transducers attached to the plate and the wave propagation direction (θ) from the impact point to the receiving sensors. This function is very sensitive to the arrival times. A small variation in any one arrival time results in a significant change in the impact point prediction. This shortcoming is overcome here by modifying the objective function and following a new algorithm. Both old and new objective functions (denoted as functions 1 and 2) are used in the new algorithm. This algorithm uses different sets of transducers and identifies the common predictions from different sets. The proposed algorithm is less sensitive to the arrival time variation and thus is capable of predicting the impact point correctly even when the measured arrival time has some error. The objective function 2 is simpler, so the computer code run time is reduced and it is less likely to converge to the local minima when using the simplex or other optimization techniques. The theoretical predictions are compared with experimental results. © 2010 SPIE.


Lacevic N.M.,NextGen Aeronautics, Inc. | Joshi S.P.,NextGen Aeronautics, Inc.
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2013

Many military and industry applications increasingly require advanced materials that are able to simultaneous carry high load (stiffness) and dissipate energy upon impact (damping). Polymer nanocomposites are potentially excellent candidates for these applications since they offer tunability via advancements in nanoscale processing technology (e.g. layer-by-layer deposition). Understanding mechanisms for the simultaneous increase of stiffness and damping in polymer nanocomposites involves characterization of interactions at surfaces between nanoscale constituents and molecular-scale processes including the role of interphase regions and polymer ordering. This information is exceedingly difficult to obtain experimentally due to the small length and time scales and disorder of the system. Here, we perform molecular dynamics (MD) simulations to understand stress and strain heterogeneity responsible for increases in stiffness and dissipation on the nanoscale in a model polymer nanocomposite. We compute local stress and strain fluctuations at polymer-nanoparticle interfaces and identify polymer chain slippage as one of the mechanisms for energy dissipation. © The Society for Experimental Mechanics, Inc. 2013.


Hajzargerbashi T.,University of Arizona | Kundu T.,University of Arizona | Bland S.,NextGen Aeronautics, Inc.
Ultrasonics | Year: 2011

Conventional triangulation techniques fail to correctly predict the acoustic source location in anisotropic plates due to the direction dependent nature of the elastic wave speeds. To overcome this problem, Kundu et al. [1] proposed an alternative method for acoustic source prediction based on optimizing an objective function. They defined an objective function that uses the time of flight information of the acoustic waves to the passive transducers attached to the plate and the wave propagation direction (θ) from the source point to the receiving sensors. Some weaknesses of the original algorithm proposed in Ref. [1] were later overcome by developing a modified objective function [2]. A new objective function is introduced here to further simplify the optimization procedure and improve the computational efficiency. A new algorithm for source location is also introduced here to increase the source location accuracy. The performance of the objective function and source location algorithm were experimentally verified on a homogeneous anisotropic plate and a non-homogeneous anisotropic plate with a doubler patch. Results from these experiments indicate that the new objective function and source location algorithm have improved performance when compared with those discussed in Refs. [1,2]. © 2010 Elsevier B.V. All rights reserved.


Grant
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 124.34K | Year: 2013

A novel composite material ablative TPS for planetary vehicles that can survive a dual heating exposure is proposed. NextGen's TPS concept is a bi-layer functional composite. The top ablative layer is a two polymer composite layer formed in a conformal shape by infiltrating ablative polymer in a Si based polymeric foam with controlled pore size distribution. This layer is for the aerocapture portion of the mission. Underneath it is a ceramic foam core sandwiched between a top ceramic ply and the bottom structural laminated composite substrate. This layer is for the entry portion of the mission. The Si based polymer foam core is similar to the top layer but is already pyrolyzed and is not infiltrated with ablative polymer. The proposed TPS when subjected to aerodynamic heating at high integrated heat loads the foam polymer structure pyrolyzes to the high temperature structure and the filled phenolic or epoxy resin will be charred and ablated. The TPS will be designed to minimize areal density while meeting bondline temperature and ablation rate requirements. The proposed TPS is easy to fabricate in aerodynamic body conformal shapes by simple manufacturing steps. The basis for the proposed concept is recent successful TPS development work performed by NextGen Aeronautics and the University of Washington under the Air Force program.


Grant
Agency: National Aeronautics and Space Administration | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 99.91K | Year: 2010

NextGen Aeronautics, Inc. is proposing an alternate architecture for inflatable lunar habitats that takes advantage of inflatable beam technologies currently being used in various military, aerospace, and commercial applications. Current technology uses a fiber-reinforced elastomeric composite capable of containing high gas pressure, giving the beams the strength needed to form a robust structure that can withstand being buried by regolith for radiation/micrometeorite protection. NextGen's novel approach is to join multiple beams, forming a continuous cellular arched structures or a series of connected rings to form cylinders. Key advantages of this approach include: ability of structure to maintain strength and stiffness independent of pressure in habitable volume, double wall construction preventing puncture of internal/external wall, ability to isolate leaks in affected elements without compromising habitat pressure or structural integrity, possible use of water or other radiation absorbing material to fill beams, and relative ease of creating a rigid structure by filling the beams with foam. We will achieve TRL of 2 in Phase I and technology transition to TRL of 5 in Phase II. NextGen team's strength lies in related prior work, and with investigators who have an exceptional background in inflatable structures and low-stowed volume designs.


Grant
Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase I | Award Amount: 149.95K | Year: 2013

Hydrogen is an attractive fuel option for transportation because its only byproduct is drinkable water; it can be produced from renewable sources; and fuel cells operate optimally by using it. However, due to its relatively low volumetric energy density when compared with other fuels, technologies that enable increases in pressure per a given volume are critical to its adoption. Nanofibers will be added to the interfaces of conventional allcomposite highpressure (700 bar) hydrogen storage tank designs to confer damageresistant benefits that will allow less expensive manufacturing of the tank without sacrificing performance. The success of this technology will enable the adoption of lightduty fuel cell vehicles over gasoline fueled vehicles. Benefits include reduced greenhouse gas emissions, reduced oil consumption, and the enabling of expanded renewable power usage through the use of hydrogen as a means of energy storage. In collaboration with Precision Nanotechnologies and Lincoln Composites, the NextGen Aeronautics team will produce highpressure hydrogen storage tanks for use in Light Duty Fuel Cell Vehicles. The team will incorporate a lowcost nanoreinforcement into highpressure allcomposite tank designs to further increase pressure and lower costs.

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