David, I'd suggest to use physics or biology as targets.
I mean, try to build a bridge between your research area and the applications... which ultimately could turn into a technological or daily application.
Differential geometry -> General relativity (gravitation) -> Fine corrections in GPS devices.
Lineal Algebra -> Quantum mechanics -> Transistors -> Computer and cell phones
Chaos theory -> Critical points -> improvement of Weather predictions
Dynamical systems -> (Population modelling ...)
Path integrals -> Financial market
And so on...
Good luck with the seminar... and enjoy it!!!
P.D.: Include graphics, short videos or simulations, cartoons... I'd also suggest you to watch the film Freakonomics, could help you.