15-03-2019 | By Rob Coppinger
Thin metal flags of different sizes and shapes with conforming piezoelectric strips and photovoltaic cells attached could power remote sensors or other electronics indefinitely.
With photovoltaic cells attached to the flag, solar power can be harvested if there is no breeze then energy from the wind can be obtained at night, or whenever there is an airstream. The first prototype flag was made last year from very thin stainless steel sheet, just 0.1 millimetres thick. The metal flag is designed to wave from side to side and the larger the deformation as its swings one way and then the other, the more energy is generated by the piezoelectric strips. Potential applications include avionics, land and sea remote systems, and distributed sensors across smart cities.
“In the next two to three years the goal is to be able to build a flag for a particular application depending on the wind conditions of a certain location and its sun exposure. The idea is to build a flag based around that application and then deploy it to a particular area,” said University of Manchester thermal-hydraulics senior lecturer, Andrea Cioncolini. He added that for a given application, a multi-flag system could be used, and each flag could be a different design.
Caption: The metal flag prototype is shown here with its piezoelectric strips and photovoltaic cells attached along its length. Credit: University of Manchester
Cioncolini’s team used fast video-imaging and object tracking with data-analysis to prove their flags worked. A wind tunnel was used to test the flag’s waving and the tunnel could accommodate a rectangular flag up to 10 centimetres long. The flag was tested in wind speeds up to about 26 metres per second along with constant light exposure of 1,800 Lux. During the wind tunnel experiments, with the different wind speeds and constant light source, a total power output of three to four milli-Watts was generated.
The piezoelectric strips and photovoltaic cells used for the prototype were commercial off-the-shelf products, but Cioncolini said that they could be specially designed for the flags; improving the power output. The thickness of the metal could also be adapted to try to maximise that deformation. Cioncolini explained that not all remote sensors necessarily need power all the time. If only a few readings need to be taken on a daily basis, for example, then the energy needs will be far less.
An experimental campaign is now to go ahead to refine the designs so bespoke flags can be produced for different applications. So far, the Manchester researchers have used what they call a “novel computational framework,” for modelling and simulation of the flags. The computational framework was developed at The University of Manchester. The computation is analysing the interaction of the flag’s structure and the fluid dynamics of the air. The use of computers to model fluid-structure interactions are referred to as virtual engineering. This can allow researchers to physically build fewer prototypes because virtual testing eliminates less effective designs.