At the University of Louisville J. B. Speed School of Engineering
Here is our analysis of bistable beams on flexible supports, written up. The take-home message is that when the support is flat, the beam has two states, up or down. But when you bend the support too far, the beam is only stable in one of the positions. Connect up a readout system to these beams, and you have a kind of “binary” curvature sensor.
Nanoparticles are boring SQUARE HOLES in our silicon wafers!
The gold nanoplates from the O’Toole group enhance the etch rate in our usual silicon-etching process. Mysterious square pores appear when nanoparticles are present on the silicon. Others have made conical nanopores in a different etch chemistry and with different gold nanoparticles, and used them as channels for studying ion transport. But ours are coming out square. There is a well known process to etch square holes in silicon using potassium hydroxide (KOH) or similar etchants, but you have to define the edges of the holes first. At a much larger scale, it’s possible to make square holes using a drill!
Here is the latest iteration of the macro bistable actuator. We inflated two air pockets to make this 3-D printed plastic beam contort into an S-shape; this shape is an important step on the way to “snap-through” of our small and large bistable beams. The work continues Fidel Tewolde’s earlier project and makes good use of the materials and techniques in this excellent tutorial.
Watching the fins on the beam, you can see where we need to exert compressive stress (fins get farther apart) or tensile stress (fins get closer together) in order to make the beam bend. The visible fins provide some insight into our thermally-driven micro-beams, where it is a little harder to see what’s going on.
Here is a spring steel beam snapping from one stable shape to another in our bending tester as it goes past the critical angle. The beam is about 5 cm long and vibrates at 240 Hz. Thanks to Roger Bradshaw and Bill Hnat for the slow-motion video.
Working with gold nanoplates from our collaborators in the O’Toole group, we are looking at thermal expansion in thin films as a way to bend microscale beams. These nanoparticles can be highly wavelength selective. We found that we could achieve selective heating of surfaces coated with two different nanoparticle “species” using two different wavelengths. Meaning, one day you might be able to make your nanodevice do a complex dance by flashing two or more different lasers at it. No wires needed! Both wavelengths we used are in the biological “water window” of near-infrared that can go through tissue.
Nanoparticles such as these also have applications in strain sensing–potentially very useful for our shape-detection work– and in locally increasing the etch rate through materials. They were originally studied for their fascinating photonic properties, and a major motivation for their development is photothermal cancer therapy.
Both our IR sources came from Dragon Lasers (and safety glasses from noIR)
