Hey! I'm Grace He, a rising senior interning at the Columbia Laboratory for Unconventional Electronics (CLUE) under Professor Ioannis Kymissis (who likes to be called John) at Columbia University this summer. This lab mainly specializes in electrical engineering, focusing on thin film and hybrid systems. Additionally, they also work on manufacturing tools in sensing, display, and energy conversion. More specifically, this summer, I will be working on a thermal sensor that takes advantage of thermoreflectance: as an electronic device changes in temperature, its reflectivity will also exhibit a change.
Week 1
On my first day at the lab, I was given a few papers to read to familiarize myself with the topic. This included past thermoreflectance experiments and successful calibration attempts. One common idea among these papers was the non-invasive measuring technique of a thermoreflectance camera as opposed to other methods that may be intrusive to the respective electronic device. Moreover, when compared to infrared thermal imaging, thermoreflectance cameras are inexpensive and don't require any additional optical sources.
Later that day, John gave us two mvBlueFox cameras that were attached to two InfiniStix microscopes. The goal was to take images of certain electronics before and after heating to find the change in reflectivity. While these contraptions cost about $1000 each, the quality of the cameras was less than that of a smartphone. While the resolution of the imaging was about parts per thousand, the small changes in reflectivity were about parts per billion. Our solution was actually very simple and didn't require any significant changes. By taking advantage of the fluctuations caused by noise, we would take thousands of images and develop a much more accurate measurement of the reflectivity.
This week, we also completed the mount to support the camera during imaging. Since this was my first hands-on experience, I had a difficult time at first but learned a lot of new skills. After some brainstorming with my lab partner, we came up with this:
Overall design Intermediate Design
While some of the pieces we could already find, we had to make the intermediate through laser cutting! Through a program called DraftSight, I learned how to design and successfully import the intermediate piece to the laser cutter after a few failed attempts. I also learned the naming system of screws, taps, and drills during this process. Additionally, every microscope comes with a working distance. The two scales that we were working with were 44mm at 1.0x and 18mm at 6.0x and the mounts did not match these distances. Consequently, we made our own stages (not shown). Here's one of the finished mounts:
Week 2
After barely surviving week 1, I was onto week 2!
After downloading a bunch of programs and playing around with the settings, we got the cameras to display on the computer (one of the best achievement tbh). However, even after adjusting saturation, exposure, and other factors, the image on the screen was either in very low resolution or completely black. To resolve this issue we decided to make two illuminators. The setups of the two microscopes were slightly different. One already had periscope attached while the other didn't. We decided to take advantage of the periscope by creating a structure to hold an LED to the periscope. The other design included a ring of LEDs that would be wrapped around the microscope. The LED's would be tilted a little to concentrate the light into one point under the microscope.
Even though we got 3D printers at school, I finally got to use TinkerCad for the first time in addition to 3D printing! I realized that it's actually really easy so don't be scared to ask the bio teachers to use it, especially since they're really nice people. TinkerCad was also extremely easy to use once you get the gist. One problem we definitely faced with these models is that the 3D printer was unable to print out holes that moved in the direction parallel to the table. This was because each layer of plastic had to rest on another layer and thus each hole would get filled in. We tried to make the filling density less so that we could possibly push the plastic through but ultimately we just drilled some holes.
Here's also one of the first images we took with the camera of a credit card (SUPER COOL):
This week we also made significant improvements and adjustment to our code. We coded it so that it would continuously take a photo store the pixel values and then take another photo and also store those pixel values. Afterward, the second set of pixel values would be subtracted from the first set of pixel values yielding the difference. While it sounds simple, there were a lot of complications with regard to data type, negative values, and the loops.
Week 3
Week 3 was definitely one of the more tedious weeks as there were a lot of trial and error experiments.
During week 2, we were given a resistor that would heat up as current was passed through. While we could not find the model online, we were able to find the resistance of it through a multimeter. We hooked up the resistor to a voltage controller and ran about 8 V through and could definitely feel a temperature difference.
So, we tested our code for the first time. We took a photo before it was heated and then waited for the resistor to heat up for about 3 minutes and then took another photo. Our results were definitely confusing. Some values were extremely negative while other were extremely positive. We then did the reverse while we waited for the resistor to cool down, but the results were also the same.
To isolate our problem we removed the heating factor and tried to remove the external noise by making the time interval zero seconds. What we expected was an array of zeros for no change. However, we saw a variety of zeros, ones, extremely positive values and extremely negative numbers. What we soon realized was that the lights installed in the lab flickered at a rate of 120 Hz and caused these fluctuations in the data. Our solution was to create a giant box to block any external light.
This design required a door so that we could still access the setup inside as well as a hole towards the bottom so that the wires could come out while limiting the amount of light coming in. Additionally, we had to make it tall enough so that we could adjust the camera in the z-direction.
Another problem we faced was finding the right material. While all the laser-cutting materials in the lab were plastic, they were also translucent or used up thoroughly. Our other option was this black unknown black material with a rubber backside, which was our final choice. We started to regret our choice when we tried laser cutting this material and the material was fuming excessively. Thankfully, the air vacuums were on so all the toxic fumes were taken care of, but we had to play around with the original settings to limit not only the amount of smoke but also my anxiety while I was watching.
Here's one of the finished black boxes: