This paper discusses the prospects of light-driven actuation particularly for actuating fluids at micro-scale for potential use in a novel retinal prosthesis and other drug delivery applications. The prosthesis is conceived to be comprised of an array of light-driven microfluidic-dispenser units, devices that eject very small amounts of fluids on the order of 1 picoliter per second in response to incident light energy in the range of 0.1-1 mW/cm<sup>2</sup>. A light-driven actuator, whose size will ideally be smaller than about 100 micrometers in diameter, independently powers each dispenser unit. Towards this application, various approaches for transducing light energy for actuation of fluids are explored. These approaches encompass both direct transduction of light energy to mechanical actuation of fluid and indirect transduction through an intermediary form of energy, for instance, light energy to thermal or electrical energy followed by mechanical actuation of fluid. Various existing schemes for such transduction are reviewed comprehensively and discussed from the standpoint of the application requirements. Direct transduction schemes exploiting recent developments in optically sensitive materials that exhibit direct strain upon illumination, particularly the photostrictive PLZT (Lanthanum modified Lead Zirconate Titanate), are studied for the current application, and results of some preliminary experiments involving measurement of photovoltage, photocurrent, and photo-induced strain in the meso-scale samples of the PLZT material are presented.
This paper reports the modeling, design, and dynamic simulation of a piezoelectrically-driven microfabricated valve for high frequency regulation of high pressure fluid flows. The enabling concept of the valve is the ability to convert the small displacement of a piezoelectric element into a large valve cap stroke through the use of a hydraulic fluid, while maintaining high force capability. The paper focuses on the development of a sytematic procedure to arrive at a geometric valve design for given performance requirements. Modeling of the non-linear large deflection behavior of the valve membrane and design of this structure to maintain stresses below critical levels are discussed. Design of the piezoelectric material drive portion of the valve to create a stiffness match with the valve membrane and external hydraulic system is detailed. In addition, this paper presents a dynamic simulation of the active valve, including effects such as valve cap dynamics and fluid damping, that allow for understanding and prediction of valve performance under various loading conditions.
The paper introduces a novel transducer technology, called the solid-state micro-hydraulic transducer, currently under development at MIT. The new technology is enabled through integration of micromachining technology, piezoelectrics, and microhydraulic concepts. These micro-hydraulic transducers are capable of bi-directional electromechanical energy conversion, i.e., they can operate as both an actuator that supplies high mechanical force in response to electrical input and an energy generator that transduces electrical energy from mechanical energy in the environment. These transducers are capable of transducing energy at very high specific power output in the order of 1 kW/kg, and thus, they have the potential to enable many novel applications. The concept, the design, and the potential applications of the transducers are presented. Present efforts towards the development of these transducers, and the challenges involved therein, are also discussed.
Static shape control of adaptive structures is currently an important and active research area in the smart structures field. Numerous actuation schemes using smart materials have been proposed and developed for shape control of structures. While the results of the smart material based technology is promising, it is also, however, showing more serious limitations such as scalability of laboratory-scale prototype models into real-scale models. In addition, the smart material based approach for shape control requires a multitude of actuators distributed throughout the host structure, the hence, complicates the control system. This paper introduces a novel alternative design concept for shape control of flexible adaptive structures using a single actuator which need not necessarily be smart material based. The novelty in this concept is that it employs distributed compliance in design--through compliant mechanisms, a class of mechanisms that transmit motion through inherent flexibility--rather than distributed actuation to accomplish the shape changes. The paper outlines a method for synthesis of such compliant mechanisms. The concept, and the synthesis method are illustrated through an example where a specified shape change in the leading edge of an airfoil structure is accomplished. The new concept has a great potential to not only eliminate the scalability problem, but also reduce the control complexity, the weight, and cost of the entire system as well.