lasers in space

Micro cantilevers unrolling when hit with an infrared laser

Micro cantilevers unrolling when hit with an infrared laser

It’s not really lasers in space, but now we have a laser feeding into the vacuum of the electron microscope. This is great for viewing how microelectromechanical (MEMS) structures respond to infrared light (915 nm). The problem with viewing our strain-engineered MEMS structures on the workbench with an optical microscope, is that they move in and out of the focal plane. We can still collect data using optical microscopy but it’s hard to show people what’s going on, since most of the device is blurry. In contrast, scanning electron microscopes have a nearly infinite depth of field, putting the entire device in focus.

3D Plots: MATLAB tutorial

I’m getting questions about MATLAB plots. Maybe it’s project time. Although I am busy learning Python and matplotlib, I won’t hate on MATLAB–here is my tutorial on plotting your data in 3D using 3 kinds of MATLAB plots.

This time of year brings questions on which software is best for all kinds of topics. Common topics for this question are 3D modelling, microcontroller programming, and electromagnetic simulation. If you’re not told what to use in a class or at work, it’s smart to pick software that lets you get moving fast, rather than aim for the software package that’s #1 in the field. Pick something where you don’t get bogged down in setting up your work environment, whether because it’s easy or because you have local support specifically for that software, so you can move on immediately to learn the things that are more universal. The basic concepts of generating the x,y, and z data for your 3D plot are similar from system to system, while the details of your license server are not.

Matplotlib is aiming for the same features as MATLAB plots, so most of what you would learn in a MATLAB class applies to it even though the syntax is a little different. The main advantage of Python/matplotlib over MATLAB is that it’s free (this can be important after you move to a new job), the disadvantage is that the documentation is less consistent. Greater consistency has a price…probably they have more meetings at the MATLAB factory.

Add some fiber to your 3D printer’s diet

We continue to investigate the potential of strings and fibers added to 3D printed, laser-cut and machined parts. The most basic application is soft, flexible links between parts that wouldn’t normally bend. Beyond that, conductive materials and sliding cables are discussed in this slide set from the IDETC conference.

Here is the preprint 

New grant: Combining Soft Materials with Mechanical Parts

The lab has a new grant from the Kentucky Science and Engineering Foundation: “Combining Soft Materials with Mechanical Parts for Robotic and Human Health Applications.” We will install functional fibers in laser-cut and 3D printed parts using a modified sewing machine. Above: video of the current machine installing high strength Kevlar fiber in a plastic sheet, a process that we will develop to work with thicker fibers in the funded work. In related news, I hit the road with the embroidery machine this summer. The video above shows it stitching a design by Steve Ceron in the Organic Robotics Lab, directed by Rob Shepherd at Cornell. Such fibers are often used to control the expansion of robotic actuators, for example wrapping inflatable soft robotic “fingers” to make them bend instead of puff up. With the support from KSEF, we should be able to do more with these stiff fibers and also soft, stretchy and fuzzy materials–including some newly developed threads from the summer that are pushing the limits of the machine we have now.

Below: Kevlar fiber couched to a plastic sheet, in one of Steve’s layouts.

Below: polymer fibers under development; functional fibers spooled up and ready for stitching.

Snap to it

Our lab has a new paper out in collaboration with the Berfield group about a windowpane-shaped microstructure that has two stable shapes. Tom Lucas (who graduated with a Ph.D. from our group in 2014) and Jaz pointed a heat gun at the MEMS devices one day, trying to flatten them by thermal expansion. This led to the discovery that the structure would flip from one to the other by aiming compressed air at it. Thanks to these experiments and Dan Porter’s model, we know that larger devices flip at lower airflow velocities.

The best applications for these bistable microelectromechanical (MEMS) devices are situations where power is limited, because they don’t need power to hold their shape. For this reason, bistable devices are candidates for radiofrequency (RF) switches in mobile phone applications, where it’s important to conserve the battery. The difference between this windowpane device and most other bistable devices is that the windowpane curls out of the plane of the silicon wafer due to residual stress. Usually MEMS makers try to cancel out residual stress, which is the enemy of predictable in-plane motion. Also different: the device in this paper would probably still be bistable if completely removed from the wafer.

The windowpane-shaped device in the paper could be used as a passive marker for peak airflows. Our group has also switched bistable devices using electric currents. With electrical contacts, it could potentially make a low-power electronic switch using significantly less wafer area than a planar device.