Banahalli Ratna

Photoluminescent and electroluminescent properties of Mn-doped ZnS nanocrystals

ZnS:Mn nanocrystals with sizes between 3 and 4 nm were synthesized via a competitive reaction chemistry method, where the surface capping organic species (p-thiocresol) is used as an inhibitor of the crystal growth. The x-ray diffraction and photoluminescent (PL) properties of ZnS:Mn bulk and nanocrystals were compared. A direct current electroluminescent (EL) device having a hybrid organic/inorganic multilayer structure, indium tin oxide/poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT-PSS)/PVK/ZnS:Mn NC/Al, was tested. In this multilayer EL device structure, the PEDOT-PSS leads to enhanced hole injection, while the poly(N-vinylcarbazole) (PVK) serves as a passivation layer between the PEDOT-PSS and nanocrystal layers. Electron–hole recombination was not confined to the ZnS:Mn nanocrystal layer, but also occurred in the PVK layer. The result was emission from both the blue-emitting PVK and yellow-emitting ZnS:Mn nanocrystals. The EL emission spectrum was dependent upon the voltage, showing ...

Comparing the conductivity of molecular wires with the scanning tunneling microscope

Current-voltage characteristics as measured by scanning tunneling microscopy for several different molecular backbones are presented. It is demonstrated that isolated oligo(phenylene ethynylene) molecules have the same measured conductance as oligo(phenylene ethynylene) molecules in a crystalline self-assembled monolayer. This result suggests that previous studies involving relatively large surface areas of self-assembled monolayers can be applied to molecular electronics devices employing small numbers of molecules. In addition, gap resistance measurements are used to rank the molecular conductance of oligo(phenylene ethynylene), oligo(phenylene vinylene), and dodecanedithiol. The observed trend for isolated molecules agrees with earlier large-scale measurements.

“Smart dust” biosensors powered by biomolecular motors

The concept of a microfabricated biosensor for environmental and biomedical monitoring applications which is composed of environmentally benign components is presented. With a built-in power source (the biological fuel ATP) and driven by biological motors (kinesin), sensing in the microdevice can be remotely activated and the presence of a target molecule or toxin remotely detected. The multifaceted progress towards the realization of such a device is described.

Design of a Biomimetic Controlled-Curvature Robotic Pectoral Fin

This paper describes the design, construction, and testing of a biomimetic pectoral (side) fin with actively controlled curvature for UUV propulsion. First, a 3D unsteady computational fluid dynamics (CFD) analysis tool has been adapted to computationally optimize any fin design, followed by a full parametric study based on our findings. Second, this said fin has been constructed, and our working optimized mechanical design is offered. Lastly, we make an experimental vs. computational result comparison for thrust, lift, and flapping moment data - showing that a UUV with this technology can have dramatic improvements in low-speed propulsion and control over traditional thruster methods.

Fuzzy logic PID based control design and performance for a pectoral fin propelled unmanned underwater vehicle

This paper describes the modeling, simulation, and control of a UUV in six degree-of-freedom (6-DOF) motion using two NRL actively controlled-curvature fins. Computational fluid dynamic (CFD) analysis and experimental results are used in modeling the fin as part of the 6-DOF vehicle model. A fuzzy logic proportional-integral-derivative (PID) based control system has been developed to smoothly transition between preprogrammed sets of fin kinematics in order to create a stable and highly maneuverable UUV. Two different approaches to a fuzzy logic PID controller are analyzed: weighted gait combination (WGC), and modification of mean bulk angle bias (MBAB). Advantages and disadvantages of both methods at the vehicle level are discussed. Simulation results show desirable system performance over a wide range of maneuvers.

Computations of Flapping Flow Propulsion for Unmanned Underwater Vehicle Design

Three-dimensional unsteady computations of the flow past a flapping and deforming fin are performed. The computed unsteady lift and thrust force-time histories are validated with experimental data and are in good agreement. Several fin parametric studies are performed for a notional unmanned underwater vehicle. The parametric studies investigated the force production of the fin as a function of varying the flexibility, the bulk amplitude of fin rotation, the vehicle speed, and the fin stroke bias angle. The results of these simulations are used to evaluate the hydrodynamic performance of the vehicle and to support controller development. Computations are also performed to map out the hydrodynamic characteristics of a new test vehicle, designed and built at Naval Research Laboratory to demonstrate the hovering and low-speed maneuvering performance of a set of actively controlled curvature fins.

Design, Development, and Testing of Flapping Fins with Actively Controlled Curvature for an Unmanned Underwater Vehicle

This paper describes the design, construction, and testing of a biomimetic pectoral (side) fin with actively controlled curvature for UUV propulsion. It also describes the development of a test UUV and the design of a fin control system for vertical plane motion. A 3D unsteady computational fluid dynamics (CFD) analysis has been carried out to computationally optimize the fin design including a full study of the primary design parameters. The fin has been constructed and it can reproduce any specified deformation time-history. The full dynamics of the proposed vehicle have been modeled and the forces produced by the flapping fins computed. Finally, the stability of motion in the vertical plane has been analyzed and a control system has been designed.

Robotic pectoral fin thrust vectoring using weighted gait combinations

A method was devised to vector propulsion of a robotic pectoral fin by means of actively controlling fin surface curvature. Separate flapping fin gaits were designed to maximize thrust for each of three different thrust vectors: forward, reverse, and lift. By using weighted combinations of these three pre-determined main gaits, new intermediate hybrid gaits for any desired propulsion vector can be created with smooth transitioning between these gaits. This weighted gait combination WGC method is applicable to other difficult-to-model actuators. Both 3D unsteady computational fluid dynamics CFD and experimental results are presented.

FOUR-FIN BIO-INSPIRED UUV: MODELING AND CONTROL SOLUTIONS

This paper describes the modeling and control development of a bio-inspired unmanned underwater vehicle (UUV) propelled by four pectoral fins. Based on both computational fluid dynamics (CFD) and experimental fin data, we develop a UUV model that focuses on an accurate representation of the fin-generated forces. Models of these forces span a range of controllable fin parameters, as well as take into account leading-trailing fin interactions and free stream flow speeds. The vehicle model is validated by comparing open-loop simulated responses with experimentally measured responses to identical fin inputs. Closed-loop control algorithms, which command changes in fin kinematics, are tested on the vehicle. Comparison of experimental and simulation results for various maneuvers validates the fin and vehicle models, and demonstrates the precise maneuvering capabilities enabled by the actively controlled curvature pectoral fins.Copyright

Scaling studies for an actively controlled curvature robotic pectoral fin

Scaling studies for an actively controlled curvature robotic pectoral fin are presented in detail. Design, development, and analysis of the fin are conducted using a combination of computational fluid dynamics tools and experimental tests. Results include a Generation 2 (Gen2) fin design with approximately 3x more surface area and a slightly larger aspect ratio compared with our Generation 1 (Gen1) version. The Gen2 fin demonstrates 9x more thrust production than the Gen1 fin, validating the computational studies. Additionally, changes to the structural design of the ribs and actuation of the rib angles leads to a power savings and a more efficient fin.