Photo-actuation, such as that observed in the reversible sun-tracking movements of heliotropic plants, is produced by a complex, yet elegant series of processes. In the heliotropic leaf movements of the Cornish Mallow, photo-actuation involves the generation, transport and manipulation of chemical signals from a distributed network of sensors in the leaf veins to a specialized osmosis driven actuation region in the leaf stem. It is theorized that such an arrangement is both efficient in terms of materials use and operational energy conversion, as well as being highly robust. We concern ourselves with understanding and mimicking these light driven, chemically controlled actuating systems with the aim of generating intelligent structures which share the properties of efficiency and robustness that are so important to survival in Nature. In this work we present recent progress in mimicking these photo-actuating systems through remote light exposure of a metastable state photoacid and the resulting signal and energy transfer through solution to a pH-responsive hydrogel actuator. Reversible actuation strains of 20% were achieved from this arrangement, with modelling then employed to reveal the critical influence hydrogel pKa has on this result. Although the strong actuation achieved highlights the progress that has been made in replicating the principles of biomimetic photo-actuation, challenges such as photoacid degradation were also revealed. It is anticipated that current work can directly lead to the development of high-performance and low-cost solartrackers for increased photovoltaic energy capture and to the creation of new types of intelligent structures employing chemical control systems.
The loads on wind turbine components are primarily from the blades. It is important to control these blade loads in order
to avoid damaging the wind turbine. Rotor control technology is currently limited to controlling the rotor speed and the
pitch of the blades. As blades increase in length it becomes less desirable to pitch the entire blade as a single rigid body,
but instead there is a requirement to control loads more precisely along the length of the blade. This can be achieved with
aerodynamic control devices such as flaps. Morphing technologies are good candidates for wind turbine flaps because
they have the potential to create structures that have the conflicting abilities of being load carrying, light-weight and
shape adaptive. A morphing flap design with a highly anisotropic cellular structure is presented which is able to undergo
large deflections and high strains without a large actuation penalty. An aeroelastic analysis couples the work done by
aerodynamic loads on the flap, the flap strain energy and the required actuation work to change shape. The morphing
flap is experimentally validated with a manufactured demonstrator and shown to have reduced actuation requirements
compared to a conventional hinged flap.
One approach to morphing aircraft is to use bistable or multistable structures that have two or more stable equilibrium configurations to define a discrete set of shapes for the morphing structure. Moving between these stable states may be achieved using an actuation system or by aerodynamic loads. This paper considers three concepts for morphing aircraft based on multistable structures, namely a variable sweep wing, bistable blended winglets and a variable camber trailing edge. The philosophy behind these concepts is outlined, and simulated and experimental results are given.
The Servocell planar bimorph actuator employs a very simple novel construction which provides a very large movement (up to 3mm) in a compact profile. It provides solid state actuation for high volume, cost sensitive applications e.g. valves, locks and circuit breakers. Thermal variations in the piezoelectric properties usually result in a compromise in performance, particularly at low temperature. This paper presents new data on the effects of thermal variations in piezoelectric properties on actuator performance. These data are used to devise a control regime which takes advantage of thermal variations in piezo activity to provide a wide operating window across the temperature range -40 to +125°C. It is shown how the stroke of the actuator can actually be increased at lower temperatures. The system is very simple and can thus be implemented using a very low cost microcontroller. The use of the system is illustrated by real life applications in optical switching, valves, locks, and trip mechanisms.