Flapping-wing micro air vehicle (MAV) is an emerging micro-robotic technology, which has several challenges toward its practical implementation. Inspired by insect flight, researchers have adopted bio-mimicking approach to accomplish its engineering model. There are several methods to synthesize such an electromechanical system. A piezoelectric actuator driven flapping mechanism, being voltage controlled, monolithic, and of solid state type exhibits greater potential than any conventional motor driven flapping wing mechanism at small scale. However, the demand for large tip deflection with constrained mass introduces several challenges in the design of such piezoelectric actuators for this application. The mass constraint restricts the geometry, but applying high electric field we can increase the tip deflection in a piezoelectric actuator. Here we have investigated performance of rectangular piezo-actuator at high electric field. The performance measuring attributes such as, the tip deflection, block force, block moment, block load, output strain energy, output energy density, input electrical energy, and energy efficiency are analytically calculated for the actuator at high electric field. The analytical results suggest that the performance of such an actuator can be improved by tailoring the geometry while keeping the mass and capacitance constant. Thereby, a tapered piezoelectric bimorph cantilever actuator can provide better electromechanical performance for out-of-plane deflection, compared to a rectangular piezoelectric bimorph of equal mass and capacitance. The constant capacitance provides facility to keep the electronic signal bandwidth unchanged. We have analytically presented improvement in block force and its corresponding output strain energy, energy density and energy effi- ciency with tapered geometry. We have quantitatively and comparatively shown the per- formance improvement. Then, we have considered a rigid extension of non-piezoelectric material at the tip of the piezo-actuator to increase the tip deflection. We have an- alytically investigated the effect of thick and thin rigid extension of non-piezoelectric material on the performance of this piezo-actuator. The formulation provides scope for multi-objective optimization for the actuator subjected to mechanical and electrical con- straints, and leads to the findings of some useful pareto optimal solutions. Piezoelectric materials are polarized in a certain direction. Driving a piezoelectric actuator by high electric field in a direction opposite to the polarized direction can destroy the piezo- electric property. Therefore, unipolar high electric field is recommended to drive such actuators. We have discussed the drawbacks of existing switching amplifier based piezo- electric drivers for flapping wing MAV application, and have suggested an active filter based voltage driver to operate a piezoelectric actuator in such cases. The active filter is designed to have a low pass bandwidth, and use Chebyshev polynomial to produce unipolar high voltage of low flapping frequency. Adjustment of flapping frequency by this voltage driver is compatible with radio control communication. To accomplish the flapping-wing mechanism, we have addressed a compatible dis- tributed compliant mechanism, which acts like a transmission between the flapping wing of a micro air vehicle and the laminated piezoelectric actuator, discussed above. The mechanism takes translational deflection at its input from the piezoelectric actuator and provides angular deflection at its output, which causes flapping. The feasibility of the mechanism is investigated by using spring-lever (SL) model. A basic design of the com- pliant mechanism is obtained by topology optimization, and the final mechanism is pro- totyped using VeroWhitePlus RGD835 material with an Objet Connex 3D printer. We made a bench-top experimental setup and demonstrated the flapping motion by actuating the distributed compliant mechanism with a piezoelectric bimorph actuator.

Bats are some of the most agile flyers in nature. Their wings are highly articulated which affords them very fine control over shape and form. This thesis investigates the flight of Hipposideros Pratti. The flight pattern studied is nominally level and straight. Measured wing kinematics are used to describe the wing motion. It is shown that Proper Orthogonal Decomposition (POD) can be used to effectively to filter the measured kinematics to eliminate outliers which usually manifest as low energy higher POD modes, but which can impact the stability of aerodynamic simulations. Through aerodynamic simulations it is established that the first two modes from the POD analysis recover 62% of the lift, and reflect a drag force instead of thrust, whereas the first three modes recover 77% of the thrust and even more lift than the native kinematics. This demonstrates that mode 2, which features a combination of spanwise twisting (pitching) and chordwise cambering, is critical for the generation of lift, and more so for thrust. Based on these inferences, it is concluded that the first 7 modes are sufficient to represent the full native kinematics. The aerodynamic simulations are conducted using the immersed boundary method on 128 processors. They utilize a grid of 31 million cells and the bat wing is represented by about 50000 surface elements. The movement of the immersed wing surface is defined by piecewise cubic splines that describe the time evolution of each control point on the wing. The major contribution of this work is the decomposition of the native kinematics into canonical flapping wing physical descriptors comprising of the flapping motion, stroke-plane deviation, pitching motion, chordwise, and spanwise cambering. It is shown that the pitching mode harvests a Leading Edge Vortex (LEV) during the upstroke to produce thrust. It also stabilizes the LEV during downstroke, as a result, larger lift and thrust production is observed. Chordwise cambering mode allows the LEV to glide over and cover a large portion of the wing thus contributing to more lift while the spanwise cambering mode mitigates the intensification of LEV during the upstroke by relative rotation of outer part of the wing ( hand wing ) with respect to the inner part of the wing ( arm wing). While this thesis concerns itself with near straight-level flight, the proposed decomposition can be applied to any complex flight maneuver and provide a basis for unified comparison not only over different bat flight regimes but also across other flying insects and birds. / MS