How important is relevant research for an undergrad?

I'm a student in electrical engineering, and my interests lie primarily in areas with a large overlap between physics and electrical engineering. I'm currently doing research with a professor of computer engineering, doing computer engineering research, which doesn't exactly line up with my interests, but it is research experience.

Now, when I'm applying for graduate schools, I believe I'll have to write a statement of purpose. How does it affect my chances of getting into graduate schools if I write about how I want to do research in [certain area of EE], but the school sees that all of my actual research experience is in an entirely different branch of electrical engineering?

Or in other words--do graduate admissions committees care about what field I do my undergrad research in, or do they only care that I do research in general?