Harnett Lab

This semester’s lab-affiliated Capstone team is busy testing the wireless wearable accelerometers they’ve built. Our Capstone course is a semester of senior year and it’s usually the last project students do for course credit. The big picture for Team 9 is a system to measure training intensity, with some great guidance from the Athletics department. For now, however, this means engineering students are running and sometimes leaping down the hall carrying wireless breadboards. Besides circuits, they’re setting up a data server and handling streaming data. Can they identify jumps and count jumps per minute, for 20 athletes at once? Time will tell!

Their task is to build a system that collects raw data from wearable sensors. Here is interleaved data from two students:

This wall of data can be turned into a plot of vertical acceleration, separated out for each student. Can you tell who is skipping vs jogging? Let’s pit one student against another. Well, these two students seemed to take about the same time to get up to speed. Next, they’re working on finding features in the data such as jumping height, number of hops, and hop rate.

And of course Team 9 is looking at ways to conserve battery power. Even though the battery is rechargeable, it needs to last through a practice. A “charger doctor” for checking on USB device performance is an easy way to keep an eye on system power consumption.

 

 

We continue experimenting with patterning different types of fibers. When fine insulated wire is embroidered onto a piece of linen tape and supplied with a current, it interacts with magnets. Two sets of embroidered coils, one on top and one on the underside of the tape in this video, pull the tape to the left along an alternating magnet array when the coils are energized in a sequence. Flat embroidered coils near magnets are already used as speakers which can be thought of as a kind of actuator. The above tape is an example of a linear motor that is normally built from hard materials, except in a conventional linear motor, the magnetic part moves, and the coils stay still. Below, a single magnet hops along the coil, keeping to the center where the magnetic field is strongest. Here the coil switching rate is increased from 2 Hz in the tape video, to 5 Hz, and the magnet is able to keep up.

In an effort to create tiny holes in our molded rubber parts, we made these small salt crystals by adding concentrated saltwater to alcohol, which is a poor solvent for salt. Right away, it starts to snow 25-micron cubes. The cubes are added to liquid rubber, then dissolved out in water, creating voids–an approach that other groups have used successfully with larger particles like sugar, table salt and rock salt. But can you spot something that isn’t a cube? We had some acrylic microspheres show up in this electron microscope sample, the same material that’s used in acrylic manicures. We were checking out this acrylic powder as another type of sacrificial material to make tiny holes. These plastic spheres charge up easily and seem to get everywhere.

The latest batch of ECE 412 (Embedded Systems) projects is now online. Check out the LED sign that now adorns our lab, the duct-tape based CyberHand and the sound-controlled ping pong tubes. The 14 projects also included a sorting hat, plus a different kind of sorting system based on a pressure sensor. While cardboard and tape are fine building materials for this class where we are mainly evaluating microcontroller skills, the laser at FirstBuild added a special touch to a few projects.

In ECE 473 (Electromagnetic Fields & Waves), which is normally a theory-based class, the fall students had an unusual assignment to build an electromagnetic train– and I was happy to see a few students making use of their MATLAB to plot the magnetic field along the coil. Our coils were short segments to get the basic idea, so here’s a much longer one from YouTube for inspiration. The set of videos from AmazingScience gives more details on fabrication and dimensions than most others.

Check out wireless optical stretch sensors in action in this video. We embedded a strain-sensitive elastic optical fiber into a piece of sticky, stretchy athletic tape that can track muscle stretching in real time. There is a single “U-turn” shaped fiber along with a detachable wireless module that can also collect acceleration and orientation data. With the addition of the optical strain sensor, our system can detect whether a muscle is passive or weight-bearing.