With the advances in deployable membrane technologies, the possibility of developing large, lightweight reflectors has greatly improved. However, to achieve the required accuracy, precision surface control is needed. The goal of this research was to investigate the feasibility of applying distributed polyvinylidene fluoride actuators and domain control on a flexible reflector and address some of the technical challenges. An analytical model of the integrated reflector-actuator system was developed. A Kapton reflector with polyvinylidene fluoride actuators was experimentally tested and compared with the model. A new least-squares control law is designed to ensure optimal solutions are derived in a rigorous manner when constraints are applied. The model is exercised using individually controlled polyvinylidene fluoride actuators on a large-scale reflector under thermal load. Although the results are promising with the large number of actuators applied, the major challenge is that it is unrealistic to have the same number of power supplies as actuators in actual applications. To resolve this issue, a new optimization methodology was developed, designated as the en masse elimination algorithm, which finds the global optimal solution that groups the actuators to match the limited number of power supplies and achieve minimum surface error. Nomenclature a = planform diameter, m d xy = piezoelectric constants, m∕V E x = electric field in x direction, V∕m E Y = modulus of elasticity, Pa h p = thickness of patch, m h ref = thickness of reflector, m P = inflation pressure, Pa R = radius of curvature, m r, θ, φ = cylindrical coordinates Tr; θ = temperature profile, K T p = membrane tension, N T 0 = bulk temperature shift, K U = strain energy, J u, v, w = coordinate values, m u 0 , v 0 , w 0 = midsurface displacements, m α CTE = coefficient of thermal expansion, K −1 β Y = rotational angles for Love simplification, rad ΔT = linear temperature gradient, K ε = strain ρ = density, kg∕m 3 σ = stress, Pa υ = Poisson's ratio

Insects are a prime source of inspiration towards the development of small-scale, engineered, flapping wing flight systems. To help interpret the possible energy transformation strategies observed in Diptera as inspiration for mechanical flapping flight systems, we revisit the perspective of the dipteran wing motor as a bistable click mechanism and take a new, and more flexible, outlook to the architectural composition previously considered. Using a representative structural model alongside biological insights and cues from nonlinear dynamics, our analyses and experimental results reveal that a flight mechanism able to adjust motor axial support stiffness and compression characteristics may dramatically modulate the amplitude range and type of wing stroke dynamics achievable. This corresponds to significantly more versatile aerodynamic force generation without otherwise changing flapping frequency or driving force amplitude. Whether monostable or bistable, the axial stiffness is key to enhance compressed motor load bearing ability and aerodynamic efficiency, particularly compared with uncompressed linear motors. These findings provide new foundation to guide future development of bioinspired, flapping wing mechanisms for micro air vehicle applications, and may be used to provide insight to the dipteran muscle-to-wing interface.

Ambient vibration sources in many prime energy harvesting applications are characterized as having stochastic response with spectra concentrated at low frequencies and steadily reduced power density as frequency increases (colored noise). To overcome challenges in designing linear resonant systems for such inputs, nonlinear restoring potential shaping has become a popular means of extending a harvester's bandwidth downward towards the highest concentration of excitation energy available. Due to recent works which have individually probed by analysis, simulation, or experiment the opportunity for harvester restoring potential shaping near the elastic stability limit (buckling transition) to improve power generation in stochastic environments-in most cases focusing on postbuckled designs and in some cases arriving at conflicting conclusionswe seek to provide a consolidated and insightful investigation for energy harvester performance employing designs in this critical regime. Practical aspects drive the study and encourage evaluation of the role of asymmetries in restoring potential forms. New analytical, numerical, and experimental investigations are conducted and compared to rigorously assess the opportunities and reach well-informed conclusions. Weakly bistable systems are shown to potentially provide minor performance benefits but necessitate a priori knowledge of the excitation environment and careful avoidance of asymmetries. It is found that a system designed as close to the elastic stability limit as possible, without passing the buckling transition, may be the wiser solution to energy harvesting in colored noise environments.

No abstract

In many applications, the detection of changing gaseous or liquid concentration within an environment is accomplished by monitoring the shift in resonance frequency of a microelectromechanical system designed to adsorb the target analyte. Recently, mass sensing using the onset and crossing of a dynamic bifurcation has been shown to reduce the mass threshold which may be detected. This approach effectively replaces detection of an analog quantity resolved by hardware capability (phase shift or resonant frequency) with a digital quantity having fundamental resolution restricted by system noise (crossing the bifurcation). While promising, successful sensing with oscillators continually excited near a system bifurcation is practically limited in performance by repeatable characteristics close to the critical crossing frequency and the passive detection ability of the sensors has not yet extended to mass quantization over a period of time. In this research, we explore an alternative method to exploit bifurcation for mass sensing by utilizing a new sensor system composed of a small bistable element within a primary linear host sensor that helps alleviate these concerns. The proposed system design provides adjustable control of the rate at which the bifurcation is crossed, helping to tailor the sensitivities of the system encountered in the transition region, introduces new bifurcations to exploit, and lends the opportunity to utilize the numerous bifurcation phenomena sequentially to denote mass accumulation quantity occurring between consecutive jump events. The conceptual underpinnings of the method are presented in detail and example operational trials are demonstrated by simulation to expound its operation and adjustability. Discussion is provided to evaluate the system in terms of existing bifurcation-based mass sensing approaches and to outline remaining goals.