I immediately recognized it as the sinc function. It's a function that is extremely important in digital signal processing, and one that I see just about every day I'm in the lab. The sinc function is defined as:
In the case of the picture above, r is equal to:
and therefore, sinc(r) is equal to:
This is the partially obscured equation that you see in the picture. I noticed there was a bit of confusion about this equation in the comment section of IFLS, so I thought I'd clear a few things up.
Many people assumed that the formula written on the front is incorrect. They noticed that plotting a function with x, y, and z variables would require a 4-dimensions. While that is true, it doesn't mean that the function is incorrect as written. The function is still correct as long as the z is defined as a variable that is not connected to the cartesian (x,y,z) coordinate system. In other words, z could be a time dependent variable or even a constant. When z = 0, the plot will look like this:
Which looks like the plot from the picture on IFLS. When we let z vary between 1 and 100 you can get a time dependent plot that looks like this:
This is a good example of why it's important to define your variables. If you don't define your variables they could mean anything. A variable can look familiar and mean something completely different. In this case, z is not the Cartesian coordinate z that you're used to seeing. Remember, a variable means nothing until you've defined it. c does not always mean the speed of light, r does not always mean radius, and so on.
Now to the fun part!
I used matlab to make a printable version of this craft. I suggest you print these pictures out on cardstock or the paper will droop down. Print each of the pictures (in order) and have fun putting them together!
Send me a picture of your finished product and I'll post it for everyone to see.
(If I get at least 5 submitted pictures I'll post pictures of the sad attempt that my 6 year old and I made)