I have to do a short presentation (~10 min) of an interesting application using multivariable calculus (it's for a multi calc class of course) in my field (electrical engineering or just ece in general, don't think it would matter) just for my TA.

Are there anything in particular to recommend that I can start my research on? I really couldn't find anything online.

 

Try atmospheric model: http://en.wikipedia.org/wiki/Atmospheric_model

 

I would imagine many topics in electromagnetics would involve multivariable calculus.

The thing that may be frustrating your searches is that you aren't going to find the term "multivariable calculus" mentioned very often in the work, just like you don't see other broad and/or common mathematical fields mentioned; they are simply the tools that are used, so unless a particular application represents a very unusual use of a mathematical technique, it goes uncommented on.

So what you need to look for are fields in which a key focus is on how changes in one set of variables affect changes in another set of variables, especially if some variables are in both sets.